From Past to Present: Gold Nanoparticles (AuNPs) in Daily LifeSynthesis Mechanisms, Influencing Factors, Characterization, Toxicity, and Emerging Applications in Biomedicine, Nanoelectronics, and Materials Science.

Gold nanoparticles showed potential use in biomedical, but their toxicity can vary depending on the size, shape, surface charge, and functionalization ( Table and Figure ). Smaller particles penetrate easily leading to oxidative stress, inflammation, or genetic damage. Surface modification improves the toxicity of AuNPs. Gold nanoparticles synthesized using melatonin reduced the toxicity and enhanced biocompatibility. Melatonin served as both a reducing agent and stabilizing agent, producing uniform nanoparticles with antioxidant properties. They show minimal cytotoxicity in cell viability assays by interacting safely with biological environments. This approach can reduce the negative impacts of AuNPs, depicting safer use in medical applications like drug delivery and imaging. Another study examines the size and surface chemistry of gold nanoparticles influencing their impact on neurons. The particles also build up in cell structures, disrupting their function. They highlight the importance of nanoparticles for safe use in treatments involving the nervous system. Biosynthesized gold nanoparticles using plant extracts exhibit reduced cytotoxicity due to their natural capping agents. Biocompatibility and eco-friendly synthesis make them suitable for biomedical applications. Tables , , and depicts toxicity of AuNPs tested on various mice models, Zebrafish models and on various cell line. Toxicity mechanism of gold nanoparticle. Reprinted with permission from ref . Copyright Elsevier B.V. Many studies have been carried out to replace these nanoparticles with biobased materials to address toxicity-related issues in various applications. Gold nanoparticles (AuNPs) exhibit unique biomedical potential, yet their toxicity remains a concern, as size, shape, surface chemistry, and concentration significantly influence cellular uptake, oxidative stress, and cytotoxic responses. Table depicts various factors affecting toxicity of AuNPs. Gold nanoparticles (30, 50, 90 nm) exhibited dose- and time-dependent cytotoxicity in HL-60 and HepG2 cells. Cytotoxicity correlated with oxidative stress markers, including increased ROS, GSH depletion, and altered SOD (Superoxide Dismutase) activity. NAC conferred partial protection, particularly with 30 nm particles. Effects varied slightly with nanoparticle size and cell type. Gold nanoparticles (∼20 nm) with citrate or 11-MUA coatings were tested on HepG2 cells. Both showed no cytotoxicity, but citrate-AuNPs induced DNA damage at low concentrations. Internalization was similar for both, highlighting surface coating’s role in AuNPs’ biocompatibility and genotoxic potential despite negligible cytotoxic effects. Surface charge significantly influenced the cytotoxicity of 1.5 nm gold nanoparticles in human keratinocyte (HaCaT) cells. Charged AuNPs induced dose-dependent toxicity, mitochondrial dysfunction, altered gene expression, and apoptosis, while neutral AuNPs caused necrosis, highlighting surface charge as a key factor in AuNP–cell interactions. In HL7702 human liver cells, 8 nm gold nanoparticles (AuNPs) triggered early cytosolic glutathione (GSH) depletion, leading to mitochondrial depolarization and apoptosis. Strong Au–S interactions initiated Bax translocation, H 2 O 2 buildup, and caspase-3 activation, confirming GSH loss as a key apoptotic trigger via the mitochondrial pathway. Gold nanoparticles (AuNPs) exhibited dose-dependent cytotoxic effects on human spermatozoa, significantly reducing motility and viability at higher concentrations. AuNPs were internalized by sperm cells, indicating potential reproductive toxicity and the need for further investigation into their genotoxic effects on germ cells. AuNPs induced oxidative stress and autophagy in MRC-5 human lung fibroblasts. Increased lipid peroxidation, autophagosome formation, and upregulation of MAP-LC3, ATG7, and stress response proteins suggest AuNPs trigger oxidative damage, with autophagy acting as a protective cellular response mechanism. Gold nanoparticles (AuNPs) are often considered less toxic than silver counterparts. Their toxicity is primarily linked to oxidative stress, disruption of cell membranes, and DNA damage. They tend to accumulate in digestive tissues, causing lipid peroxidation and disrupting in antioxidant enzyme functions. At moderate concentrations AuNP depicts low cytotoxicity, increased reactive oxygen species shows long-term threats to the environment. They depict significant environmental toxicity due to their high mobility, reactivity, and accumulation of living organisms. In aquatic systems, they are absorbed by plankton and fish, disrupting vital functions and moving through the food web. In soil, AuNPs impact plant growth and disrupts the microbial activities, altering nutrient availability. Their persistence and capacity to penetrate biological barriers that may lead to oxidative stress and DNA damage in unintended organisms. Proper regulation and eco-safe design are essential to reduce the environmental risks. Gold nanoparticles (AuNPs) are used in various industries and can enter the environment via waste streams or incorrect disposal methods. Due to their small size, they can be easily absorbed by organisms, potentially disrupting biological activities. In aquatic environments, they threaten fish and microbes by causing oxidative stress and bioaccumulation. The lack of comprehensive data on their long-term effects raises concerns, stressing the need for monitoring, product labeling, and implementing proper nanowaste management regulations to limit the environmental damage. Another study shows variable toxicity in aquatic environments, based on factors like size, shape, and surface coating. Functionalized AuNPs developed for medical applications may pose ecological hazards. In studies with microalgae and Daphnia magna , AuNPs induced oxidative stress and DNA damage. Aggregation in water does not necessarily reduce toxicity, they can move through food webs. Gold nanoparticles synthesized using Carica papaya leaf extract demonstrated an eco-friendly and effective approach for photocatalytic degradation of methylene blue, achieving 95% reduction in 90 min and 99% removal of total organic carbon. Characterization confirmed their crystalline structure, morphological, and surface characteristics.

Gold nanoparticles can be synthesized through a variety of methods ( Figure ). Physical methods such as micropatterning, sputtering, , pyrolysis, , laser ablation, − and ball milling, , use mechanical forces or energy-based processes to generate nanoparticles ( Table ). Due to the absence of any chemical moiety or process involved, the nanoparticles are high in purity along with a minimum amount of contamination. However, the imperfect surface structure of the nanoparticles and the high cost of the process, which requires a massive amount of energy to maintain high-pressure and high-temperature conditions, have particular demerits. For instance, in a study by Sylvestre et al., gold nanoparticles were synthesized using femtosecond laser ablation in aqueous solutions, hence leading to partial oxidation and a negatively charged surface. This charge, enhanced by Cl – , OH – , or N-propylamine, prevented the coalescence and controlled the nanoparticle size. Oxidation increased the reactivity, aiding functionalization through covalent and electrostatic interactions allowing for precise control over nanoparticle growth, producing stable, uniformly sized particles (5–8 nm) suitable for various applications in nanotechnology and materials science. In another study by Mafuné et al. AuNPs were synthesized via laser ablation of a gold plate in sodium dodecyl sulfate solution. Their absorption matched chemically prepared nanoparticles. Increased surfactant concentration reduced particle size, stabilizing them above 10 –5 M. Larger nanoparticles (>5 nm) were fragmented into 1–5 nm sizes using a 532 nm laser. Similarly, Resta et al. synthesized AuNPs via pulsed laser deposition (PLD) on amorphous carbon/glass and single-crystalline MgO substrates. Despite similar nucleation rates, nanoparticle shape varied: quasi-spherical on amorphous substrates and faceted on MgO. High-energy ions (≥200 eV) enhanced nucleation, while epitaxial growth on MgO enabled shape control, following the Wulff-Kaichew theorem. Similarly, Donnelly et al. used nanosecond pulsed laser deposition (PLD) on Si and sapphire substrates in a vacuum for the synthesis of AuNPs. Atomic force microscopy confirmed nanoparticle formation below 5 nm thickness, with increasing deposition leading to coalescence. Optical absorption showed surface plasmon resonance, shifting to longer wavelengths as film thickness increased. Jankowsk et al. utilized high-voltage AC arc discharge in distilled water to synthesize AuNPs, with characterization through X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), ultraviolet–visible (UV–vis), and inductively coupled plasma-mass spectrometry (ICP-MS) confirming nanoparticle formation, crystallinity, and stability. The synthesis process showed that increasing the discharge time resulted in larger nanoparticles, with AuNPs-2 having a crystallite size of 8.4 ± 3.2 nm and AuNPs-5 exhibiting a size of 11.6 ± 2.8 nm. This cost-effective and environmentally friendly method provides controlled nanoparticle synthesis without the need for stabilizers, making it a viable alternative to DC methods. Endla and Radhika utilized high-energy ball milling to convert microsized Au powder into nanoparticles over a 20-h process. Particle size decreases from 115 to 22 nm, with increased strain and B values. The energy of vacancy formation and Debye temperature were evaluated, showing significant effects on particle size and strain. Hatakeyama et al. synthesized AuNPs using sputter deposition in the ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate. The size of AuNPs was influenced by target temperature, applied voltage, and capture medium temperature, while sputtering time, working distance, and discharge current, had minimal effects. Lower temperatures and higher voltages produced smaller NPs. In a study by Gromov et al., AuNPs and Au–Cu nanoalloys were synthesized using thermal evaporation, condensation, and heating in a vacuum. Due to size effects, their melting point decreased, influencing phase formation and structural deviations from bulk phase diagrams. TEM analysis revealed nanoparticle migration and fusion, affecting their final composition and stability. On the other hand, chemical-based methods ( Table ) utilize the unique properties of different chemicals to mediate the synthesis of AuNPs. They are synthesized chemically by reducing gold salts like HAuCl 4 using agents such as sodium citrate or NaBH 4 . The reduction leads to nucleation, followed by controlled growth. Stabilizing agents prevent aggregation, thus ensuring desired size and shape formation through surface interactions. Some techniques such as microemulsion, − electrochemical methods, radiation-induced synthesis, , Turkevich synthesis, Brust–Schiffrin synthesis, seeding-growth technique, ascorbic acid mediated synthesis, , and synthesis with NaBH 4 , , have been widely used to synthesize AuNPs. Synthesis method for AuNPs: top-down and bottom-up approach. Apart from the traditional physical and chemical methods of synthesis, green synthesis ( Table ) has gained a lot of attention primarily due to its essence of sustainability and low toxicity. There are several eco-friendly and biocompatible techniques to synthesize AuNPs that utilize plant extracts, bacteria, and microbes. The chemical composition and concentration of reducing agents in organic extracts are significant and can vary, which in turn influences the characteristics of the final product. These variations lead to differences in size and shape, which in turn affect the function and application of the material. Many biomolecules including, phenols, flavonoids, amino acids, proteins, enzymes, amines, aldehydes, ketones, carboxylic acids, and alkaloids act as electron donors, which enable the reduction of cationic gold to form AuNPs. The properties of the resulting nanoparticles are determined by factors such as the plant extract concentration, the type of metal salt used, the pH of the reaction mixture, and the reaction temperature. , For instance, Srinath et al. reported the biosynthesis of biocompatible gold nanoparticles (AuNPs) using Brevibacillus formosus isolated from the Hutti gold mine, India. The bacterial metabolites acted as reducing and stabilizing agents. Synthesized AuNPs (5–12 nm, spherical) were characterized using UV–vis, Fourier transform infrared (FTIR), dynamic light scattering (DLS), and TEM and also exhibited strong antibacterial activity against S. aureus along with biocompatibility with chicken RBCs, highlighting their potential for biomedical applications. In another study by Singh and Kundu, biosynthesis of gold nanoparticles (AuNPs) using Pseudomonas aeruginosa and Rhodopseudomonas capsulata was carried out. The pH significantly influenced size and shape, with spherical 10–20 nm AuNPs at pH 7 and nanoplates at pH 4. Altaf et al. reported the green synthesis of gold nanoparticles (AuNPs) using Iris kashmiriana rhizome extract with spherical AuNPs (∼80 nm). These nanoparticles exhibited strong antibacterial, antibiofilm, and antiadherence properties, particularly against Streptococcus mutans , making them effective for coating orthodontic appliances. Daramola et al. evaluated the bacteria-mediated synthesis of gold nanoparticles (AuNPs) using Bacillus subtilis and P. aeruginosa . The process involved the microbial reduction of gold salts, producing stable, biocompatible nanoparticles of size 118 nm. Abu-Elghait et al. developed optimal conditions for the biosynthesis of gold (AuNPs) using Trichoderma saturnisporum . The ideal conditions for AuNPs were pH 6.94, 33.2 °C, and 1.21 mmol, offering a more efficient alternative to traditional synthesis methods. Another study, Omole et al. explored the microbial synthesis of gold nanoparticles (AuNPs) using Lysinibacillus fusiformis and HAuCl4 solution. The synthesized AuNPs were characterized by UV–vis, SEM, EDX, DLS, TEM, XRD, and FT-IR analyses, revealing spherical particles with a mean size of 121.2 nm. These AuNPs demonstrated significant antibacterial activity against multidrug-resistant bacteria from chronic wounds, indicating their potential for pharmaceutical applications in treating infections caused by Multi-Drug Resistant (MDR) bacteria. Table effectively summarizes all advantages and disadvantages of physical, chemical and various green synthesis methods in synthesis of AuNPs. Comments based on available literature. The biosynthesis of gold nanoparticles (AuNPs) typically follows a straightforward two-step process that does not require extreme temperature or pressure conditions. − Initially, a biological extractsuch as one derived from plants, bacteria, or fungiis combined with a solution of chloroauric acid (HAuCl 4 ). This interaction leads to the reduction of gold ions (Au 3+ ) to elemental gold atoms (Au 0 ). In the second phase, the nucleated gold atoms undergo growth and stabilization, resulting in the formation of AuNPs, as illustrated in Figure . Schematic representation of AuNPs biosynthesis mechanism and mechanism of the formation and stabilization of gold nanoparticles by polyphenolic compounds. Adapted with permission from ref . Copyright 2022, MDPI, Basel, Switzerland. The synthesis is often visually confirmed by a distinct color change in the solution, indicating nanoparticle formation. The chemical reduction of Au 3+ to Au 0 in the presence of water can be represented by the reactions depicted in above Figure . Phytochemicals present in plant extractssuch as amino acids, proteins, carbohydrates, phenolic acids, flavonoids, and terpenoidsplay crucial roles in the green synthesis of metal and metal oxide nanoparticles. These bioactive compounds act as natural reducing and stabilizing agents, enabling nanoparticle formation under mild, eco-friendly conditions without the need for toxic chemicals or harsh physical processes. The literature suggests that the extent of synthesis of AuNPs is directly linked with reduction potential of plant extract. Nevertheless, these plant extracts have varieties of phytomolecules of different classes such as polyphenols, terpenes, etc. It has been seen that there are 3 key factors influencing the efficiency of this biosynthesis process : (1) the degree to which metal ions are reduced by compounds in the extract, (2) the concentration of reducing agents, and (3) the composition of bioactive compounds that stabilize the resulting AuNPs. It is very likely that higher the amount of content of reducing substances, higher would be rate of formation of AuNPs and promotes the creation of smaller nanoparticles, and enhances their stability. − , Amino acids and proteins reduce metal ions and stabilize nanoparticles through electron donation and capping, while carbohydrates (e.g., polysaccharides) contribute to particle size and morphology control due to their hydrophilic and catalytic properties. Phenolic acids and flavonoids facilitate metal ion reduction via hydrogen or electron transfer, often through redox or keto–enol transitions. Huang et al. elaborated in details mechanisms of phenolic acids in biosynthesis of AuNPs ( Scheme ). One of such representative mechanism is illustrated below, which was proposed by Manyuan and Danwanichakul. In concern work, they illustrated synthesis of AuNPs with the help of spent coffee ground extract. Terpenoids, commonly found in essential oils, also assist in nanoparticle synthesis, particularly silver nanoparticles apart from AuNPs, due to their strong reducing capacity. Hossanisaadi et al. reviewed studies assessing the ability of plant extracts to reduce gold ions. The review examined extracts from 27 plant speciesincluding Rosa damascena , Juglans regia , Caccinia macranthera , etc.many of which are traditionally used in Middle Eastern medicine. Extracts were prepared from different plant parts, and the study identified 28 additional plant species with effective gold ion-reducing capabilities. These extracts successfully facilitated gold nanoparticle synthesis. , Additionally, the success of metal nanoparticle (MNP) biosynthesis depends on the electrochemical potential of the specific metal ion involved. Noble metal salts have reduction potentials ranging from 0.35 to 1.0 V, and metal ions can be reduced to nanoparticles if the extract’s reduction potential exceeds +0.16 V. , Table gives an idea about the reducing potentials of various phytochemicals reported for the synthesis of AuNPs. Adapted and modified with permission from ref . Copyright 2023, MDPI. The biosynthesis by these microorganisms can occur via two distinct pathways: extracellular and intracellular , depending on where the nanoparticle formation takes place ( Figure ). In extracellular biosynthesis , metal ions are reduced outside the bacterial cell through enzymatic activity, leading to nanoparticle formation in the surrounding medium. In contrast, intracellular biosynthesis involves the uptake of metal ions into the cell, where enzymatic processes reduce them internally to form nanoparticles , Schematic representation of AuNPs biosynthesis mechanism through microorganisms. Adapted from ref . Copyright 2022, MDPI, Basel, Switzerland. Gholami-Shabani and colleagues developed a cell-free method for synthesis of AuNPs using α-NADPH-dependent sulfite reductase purified from E. coli . An average sized AuNPs of 10 nm, were confirmed from this novel route. In another review, Shedbalkar et al. covered detailed aspects of mechanisms of microbial AuNPs synthesis. Physicochemical parameters like temperature, pH, and substrate concentration influence intracellular AuNP synthesis and morphology, with monodispersity achievable through their optimizationthough comprehensive studies are lacking. Proteins and amino acids such as cysteine, tyrosine, and tryptophan play key roles in AuNP biosynthesis and stabilization. Free amino or cysteine groups bind AuNPs for stabilization, while tyrosine and tryptophan contribute to NP formation and reduction at high pH through specific binding and redox activity. Protein type also affects AuNP capping and stability. Several other review articles have also been published detailing recent advances in microbe assisted AuNP synthesis. , Chaurasia and colleagues beautifully summarized list of various microbial sources known for producing extracellular and intracellular enzymes involved in AuNPs synthesis along with their influence of particle sizes and shapes. ( Table ) Adapted and reproduced with permission from ref Copyright 2022, Elsevier. Table explains various factors affecting synthesis of AuNPs. Well explained in the ref . A wide number of factors such as size, shape, and type of environment are responsible for the interaction of the AuNPs with light. A coordinated oscillation of electron charge, which is in resonance with the frequency of visible light, is generated by the interaction of free electrons with the oscillating electric fields of a light ray traveling near a colloidal nanoparticle. The size or form of the nanoparticles can be changed to modify the surface plasmon resonance, creating particles with customized optical properties for various purposes. The unique interaction with light, surface plasmon resonance, changes depending on particle sizes. The smaller ones appear red, while larger ones reflect bluish or purplish hues. Shape plays a key role in how cells absorb these particles, with triangular and rod-shaped nanoparticles being taken up more efficiently than star-shaped ones. While larger particles tend to circulate longer and serve as better delivery agents, smaller ones can be more toxic. Yue et al. showed that gold nanoparticle size and shape affect siRNA delivery. Larger particles (50 nm spheres, 40 nm stars) had higher cellular uptake and escaped endosomes, unlike smaller 13 nm spheres. This highlights the importance of nanoparticle design in enhancing functionality for effective gene delivery applications. Xie et al. evaluated how shape influences gold nanoparticle uptake in RAW264.7 cells. Star, rod, and triangle-shaped nanoparticles showed varying internalization, with triangles achieving the highest uptake. Different shapes engaged distinct endocytosis pathways, demonstrating that nanoparticle geometry significantly affects cellular uptake and can guide effective drug delivery system design. These characteristics make gold nanoparticles highly adaptable for medical applications such as imaging, therapy, and drug delivery. Figure gives an idea about various kinds of Au nanostructures. Transmission electron microscope (TEM) images for various kinds of Au nanostructures (a) nanospheres, (b) nanodisks, (c) nanorods, and (d) cubic nanocages. Reproduced from ref . Copyright 2021, with permission of Elsevier. The characterization of AuNPs is usually done via modern analytical techniques mentioned in Figure . Various Characterization techniques used for AuNPs. UV visible absorption spectroscopy is usually performed to study the optical properties and band gap of nanoparticles. When a PerkinElmer 2 spectrometer was used for characterization, it showed a peak in range of 300–900 nm via capturing surface plasmon resonance (SPR) feature for gold nanoparticles. It has been observed that AuNPs shows a strong absorption peak around 520 nm due to SPR and it remains the same irrespective of change in particle shape or the surrounding material. Similarly, on application of gold nanoparticle on APS (aminopropylsilane) -treated glass, we can see the SPR peak shifting to a higher wavelength (red shift) followed by the band broadening due to the electromagnetic interactions between nearby particles. , This is one of the most helpful techniques to find the size, concentration, and aggregation level of gold NPs. While operating, spectrum registration may take some time and the extinct spectra of AuNPs can be derived via Mie theory. Furthermore, in one case, an Electrochemiluminescence biosensor based on gold nanoparticles was synthesized and on characterization, it was observed that a 5 nm gold nanoparticle showed a peak at 515 and 20 nm at 535 nm ( Figure A,B). This demonstrated the size dependent optical property because of the localized SPR (LSPR). The 20 nm one was more effective in increasing the electrochemiluminescence signals leading to a better electron transfer. Iqbal et.al, synthesized sodium alginate (SA) coated AuNps for delivering the natural anticancer compound T-res and on characterization, a peak at 526.4 nm indicated the presence of bare gold nanoparticles, whereas SA coated nanoparticles showed a blue shift that is decrease in peak. This was because the SA improved the nanoparticles dispersion and stability and reduced the interparticle interactions or aggregation. Absorption intensity increases with heat due to improved SPR While analyzing AuNPs, a blue shift was observed for a smaller particle and greater pH resulting in increase in the peak, i.e., from 530 to 640 nm. Overall, UV–vis is an efficient method as it does not require any sample preparation and gold nanoparticles can be analyzed straight way after synthesizing. UV–vis absorption spectra of Au NPs (5 nm) (A), Au NPs (20 nm) (B), and sodium tetrachloroaurate and gold nanoparticles (C). Panel (A) and (B) Reproduced from ref . Copyright 2025, with permission of Elsevier; Panel (C) Reproduced from ref . Copyright 2023, with permission of MDPI. This characterization technique identifies the presence of functional group. In the case of gold nanoparticles synthesized from plant extracts, this method showed the functional groups involved in reduction, capping and stabilization of gold nanoparticles. It also confirmed the presence of phytochemicals by showing a common peak at 3389 cm –1 indicating O–H stretch, alcohol, 2919–2844 cm –1 C–H stretch, 1458 cm –1 (N–H bending), 1700 cm –1 (CC stretch). This is a highly sensitive method for nanoparticles. Nowadays FTIR also shows the interaction of gold nanoparticles with the reactive agents in few seconds. Similarly, advanced version is called attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), which is extremely useful for nanoparticles as it helps in understanding the composition and behavior of these materials. Key absorption bands include: 3286 cm –1 , attributed to −OH stretching vibrations of phenolic compounds and other phytochemicals; 2928 and 2875 cm –1 , corresponding to −CH stretching of alkanes; 1636 cm –1 , associated with −NH bending and −CO stretching; 1512 cm –1 , related to −CH vibrations of alkanes and −NO stretching of nitro compounds; 1454 cm –1 , indicative of −OH bending and – CO stretching in phenolics and similar compounds; and 1387 cm –1 , assigned to −CN stretching of aromatic amine groups ( Figure A). (A) ATR-FTIR spectrum and (B) XRD spectrum of the synthesized Au NPs. Reproduced from ref . Copyright 2022, with permission of MDPI. Commonly known as AFM, is a technique used to determine the structural properties of gold nanoparticles via three-dimensional (3D) image showcasing particle’s size, shape and surface feature. This technique is vital for their use in different fields. When this technique was performed on untreated, gold-coated silanized glass plates with scans at 2.0 Hz with 256 pixels per line. AuNPs appeared roughly spherical with an initial average diameter of 100 nm with a height profile approximately 409 nm after extended soaking. Surface roughness for silanized glass without gold was observed to be 0.755 nm which increases with gold deposition showcasing the nanoparticle attachment. Maximum roughness is observed at 2 h. AFM can be performed in various environments including ambient, gas, liquid and requires minimum surface preparation. Its only disadvantage is its limited scanning size. However, it also provides insights about the ligand binding at nanoscale making it one of the most vital methods. Figure revealing individual spherical gold nanoparticles (AuNPs) and their aggregates. The measured average diameter of the AuNPs ranged from approximately 11 to 19 nm. AFM phase images of AuNPs on a bare graphite substrate. The circled regions exhibited gold nanoparticles and their diameter (particles around 11–19 nm). Reproduced from ref . Copyright 2023, with permission of MDPI. This technique is performed to identify the crystal structure, phase and spatial arrangement of an atom. The X-ray is irradiated on the gold nanoparticle, and the intensity of scattering angle of X-ray from gold nanoparticle is measured. For gold nanoparticles it shows a distinct peak which matches the cubic structure of gold ( Figure B). If a broad peak appears then it indicates the smaller particle size because of the quantum confinement. It is an important characterization technique as it helps to find out the nanoparticle size and structural changes via laser energy. XRD for gold nanoparticle entrenched in a silica xerogel matrix showcased the crystalline nature of the gold nanoparticles, displaying peaks at 2θ = 38.21, 44.45, 65.04, and 77.65° which is corresponding to the (111), (200), (220), and (311) planes of face-centered cubic (FCC) gold. These peaks confirmed the formation of metallic and crystalline AuNps. But on XRD of AuNPs coated with SA, we could observe no significant change in the crystal structure. Further to estimate the particle size, Debye–Scherrer equation should be used. Danchova et.al, study showcased the XRD of AuNPs in a nanocomposite of silica, proving crystalline AuNPs at 111 reflections. It also showed weak peaks of Au-thiolate complexes and at high temperature low cristobalite phase was formed. Similar results were obtained when C. limon juice and E. prostrata leaves were used as reducing agents along gold nanoparticles and a constant, strong peak around 534 nm was observed in all such cases. Overall it is a very versatile technique and as per the XRD card (JCPDS no. 65–2870), the prominent peak at 20 = 38.31, 44.47, 64.58 and 77.43°, indexed to the planes of (111), (200), (220), and (311) is for gold nanoparticles. Only disadvantage of this technique is the XRD peaks are too broad for particles with size less than 3 nm and it cannot detect the amorphous materials. Commonly called SEM is a technique used to identify the morphology and size of particles. It generates three types of images - external X-ray maps, backscattered electron images, and secondary electron images. It needs simple sample preparation by putting a drop of solution on silica plane other conductive substrates and then removing the excess solution. In case of gold nanoparticles to confirm its presence, we can observe spherical particles and enlarged size in SEM images due to the laser energy. It can show variety of geometry like square, rectangle, cubic, triangular all nearly at 60 nm diameter.These nanoparticles can be easily analyzed as SEM does not need any intense sample preparation. It also shows the surface texture, structure and composition. When gold nanoparticles were synthesized using knotweed extract in Pulit et.al, study, we could clearly see spherical rod like structures ranging from 20–200 nm in SEM image indicating the presence of AuNPs. Similarly, gold nanoparticles synthesized using Nepenthes khasiana leaf extract, showed cluster with particle sizes between 50–80 nm. Overall, green synthesized gold nanoparticles tend to form spherical shapes, irrespective of any conditions. Only limitation is that it does not give any details on internal structure and is a very labor intensive and expensive technique. Figure displays the obtained images for tetrachloroaurate­(III) dihydrate (NaAuCl 4 ) appears as cubic crystals. At a magnification of 30,000×, two crystals measuring approximately 0.38 and 0.67 μm were observed. SEM images at 2000× and 30,000× magnification of NaAuCl 4 and AuNP samples. Reproduced from ref . Copyright 2023, with permission of MDPI. This spectroscopy is usually used to analyze the surface composition and chemical state of gold nanoparticles (AuNPs) immobilized on silanized glass substrates. Sharp peaks for Au 4f, Au 4d, and Au 4p and Au 4f 7/2 at 84 eV, confirms the presence of gold. It has a superior capacity to ascertain chemical states, extensive applicability, and nondestructive characteristics. XPS applications encompasses the assessment of oxidation states in nanoscale particles. It also offers insights on nanoparticle surfaces and chemistry, majorly in comparison to uncoordinated ligands. In Seit’s study, there was a significant increase in oxygen-containing carbon species on gold-coated samples, which proves the chemical modification due to the presence and attachment of AuNP. In Tendo et.al, study XPS confirmed the chemical state and single layer orientation of flat gold films and AuNPs. It also helps to identify the effective molecular layer thickness by comparing C 1s and Au 4f peak intensities and gives 10 Å (MP) and 19 Å (MBP) confirming the AuNP films. Similarly on narrow scans for AuNPs synthesized via bacteria, peaks were visible with binding energy between 84 to 88 eV corresponding to aryl shell features. Furthermore, for AuNPs made from Ulva linza , Au was clearly observed due to the presence Au 4f 7/2 and Au 4f 5/2 peaks. Carbon, Nitrogen, Sulfur was also detected, which came from the Ulva linza and helped in reduction of gold ions to nanoparticles to prevent surface clumping and interaction. In some studies, where gold nanoparticle was capped with cysteine or glutathione (that is thiol containing compounds) XPS showed S 2p binding energies (161–164 eV), confirming strong Au–S bonding, essential for nanoparticle stabilization. It also detects the surface contamination by detecting elements like Cl, Na, or C. Furthermore, in bimetallic nanoparticles like Au–Ag or Au–Pd, XPS differentiates interaction and elemental distribution by showcasing shell composition or surface enrichment of one metal over the other. Various studies indicate that, AuNPs synthesized in a green manner showcases peaks with higher binding energy due to surface oxidation and interaction. The prominent shift in peaks denotes the partial oxidation or rigid, stubborn, stable capping interaction. TEM is widely used to study the internal structure, surface morphology, shape, particle size distribution and dispersion of gold nanoparticles. Since electrons have much shorter wavelengths than light, TEM is ideal as it gives better resolution for nanoparticles with nano sizes ( Figure ). Its advanced version is the High-resolution TEM (HRTEM) which shows clear images of the gold core and helps to identify whether particles are crystalline or amorphous. To operate, this method requires a sample preparation, which may lead to gold NP aggregation. Surface alterations are undetectable by normal or ordinary TEM techniques and to overcome this issue glycerol spraying/low-angle rotating metal shadowing TEM and cryo-TEM, is necessary. For AuNPs, a 5–100 nm, spherical shapes are observed on TEM images. Usually polydispersity is confirmed at 30–100 nm range and on heating, gold nanoparticles agglomerate making it easy to identify on TEM images. Similarly, TEM analysis of AuNPs synthesized via bacteria, showed spherical and triangular sites and these nanoparticles synthesized at different conditions had different sizes. For example, AuNPs synthesized at 25 °C had a size of approximately 39.0 ± 9.1 nm and for 42 °C, 36.7 ± 7.7 nm. It was noticed that at pH 12.7, the size was decreased. Recently, AuNPs were synthesized from T. farfara flower buds and was charactersied using TEM which revealed particle size 15–20 nm, indicating efficient size control via plant extract. Overall, TEM images prove that the green-synthesized GNPs are usually spherical, but also show hexagonal, pentagonal, and triangular shapes. TEM images of Au NPs (5 nm) (A, B) and Au NPs (20 nm) (C, D). Reproduced from ref . Copyright 2025, with permission of Elsevier. Dynamic Light Scattering is one of the common and widely used technique to identify the size distribution, average particle size and polydispersity index (PDI) of gold nanoparticles dispersed in a colloidal medium. Unlike electron microscopy techniques that provide direct imaging, DLS offers hydrodynamic diameter measurements that include the particle core, surface coating like capping agents and solvent layer. This makes it valuable for tracking size changes during synthesis, bioconjugation, or storage. This method is based on simple principle which analyses the intensity of light scattering when nanoparticles undergo Brownian motion in suspension. Another study reported synthesis of AuNPs using Evolvulus alsinoides extract and on characterization, the DLS revealed sizes ranging from 50–100 nm with a dominant size near 80.29 nm. Similarly, Mapala et al. found that Mimosa pudica flower extract-refereed AuNPs showed an average size of 24 nm with a narrow range (15–62 nm), which was later confirmed by TEM analysis. DLS also monitors the gold nanoparticles stability by measuring the ζ-potential, which reflects surface charge. High absolute ζ-potential values (typically more than or equal to ± 30 mV) indicate strong interparticle repulsion and colloidal stability, while low values suggest potential aggregation making it advantageous. DLS analysis of AuNPs reported by Oliveira et al. is depicted in Figure . But it may overestimate size in polydisperse or aggregated samples and assume spherical shape during analysis, making other techniques like TEM or SEM essential for accurate morphological validation. (a) DLS analysis of particle size distribution and ζ-potential and (b) schematic representation of the double layer that surrounds the nanoparticle in aqueous medium. Reproduced from ref . Copyright 2023, with permission of MDPI. This technique is widely used to detect the elemental composition of gold nanoparticles (AuNPs). It provides qualitative, semiquantitative, and quantitative data by detecting X-rays emitted from the sample during electron beam interaction and is often performed with electron microscopy like SEM or TEM. EDX also helps in plotting the spatial distribution of other elements present, making it easy to identify the presence of gold. It is major disadvantage is precision of chemical analysis and quantification which is often used in conjunction with X-ray diffraction (XRD) for a more complete understanding of nanoparticle composition and crystallinity. Hence, a combination of XRD and EDS is the best for characterization of gold nanoparticle. For gold nanoparticles and ions, EDX shows a signature peak near 2 to 3 keV. Some reports also show an additional peak near 9 keV, depending on the instrumentation and settings. For AuNPs mediated using T. argentiea flower extract, the EDX depicted a strong gold peak at 3 keV, along with minor signals from carbon, oxygen, and the gold content was estimated to be around 52.27%. , ,

Global regulations for nanomaterials differ significantly across regions. Kus-Liśkiewicz et al., in their comprehensive review, have effectively detailed the global regulatory landscape surrounding nanomaterials ( Table ). They highlight the contrasting approaches across regions, noting how stringent guidelines by agencies like the FDA and EMA differ from the more lenient or absent regulations in parts of Asia and South America. The U.S. FDA and Europe’s EMA mandate stringent nanosafety evaluations for nanomaterials, particularly in food and pharmaceuticals, requiring comprehensive physicochemical, toxicological, and ecotoxicological data. In contrast, countries like China, Japan, South Korea, and Brazil often lack specific regulatory frameworks for nanomaterials in cosmetics and food. The U.S. launched the National Nanotechnology Initiative (NNI) in the year 2000 to promote nanoscience research and define “nanopharmaceuticals”. Despite ongoing advancements, major challenges remain in the classification of novel nanomaterials and the development of standardized testing methods essential for ensuring their safe commercial and clinical application. , Regulations for gold nanoparticles are gradually evolving worldwide, aiming to ensure their safe use in medical, food, and consumer products. Standardized protocols and international harmonization are crucial for effective risk assessment and commercialization. Adapted and modified from ref . Copyright 2021, with permission of MDPI.

In conclusion, gold nanoparticles (AuNPs) have emerged as a highly versatile and valuable nanomaterial due to their unique physicochemical properties, such as high surface area, tunable size, and excellent biocompatibility. As a multidisciplinary subdomain, nanobiotechnology epitomizes the amalgamation of sciences and technologies to produce nano-objects with profound applications. Among nanomaterials, nanoparticles particularly gold nanoparticles (AuNPs) have taken center stage due to their remarkable properties and versatility. The fascination with AuNPs stems from their unique characteristics, which span a wide range of shapes and sizes, enabling diverse and impactful applications. The type of synthesis and reaction conditions mediate how the properties of the AuNPs formed vary. The applications of AuNPs span various fields, including healthcare, drug delivery, catalysis, textiles, agriculture, sensing, and electronics, which makes them pivotal in advancing nanotechnology. The ease of functionalization allows for targeted interactions in biological systems, while their optical properties enable sensitive detection methods. In this review, we have delved deep into the role of AuNPs in nanotechnology, from different types of synthesis routes and properties to the factors affecting them, and their versatile range of applications and toxicity. Overall, nanotechnology, particularly gold nanoparticles, continues to drive scientific research and technological innovation, paving the way for transformative applications across various disciplines. Continued research is essential to optimize their synthesis, minimize toxicity, and unlock their full potential across industries.

Even though AuNPs are considered generally safe and biocompatible and also act as promising agents in biomedical fields due to their unique physicochemical properties, factors like shape, size, drug dosage, electrical charge, and purity of the gold formation can play a role in determining the cytotoxicity. The toxicity can depend on the surface chemistry of the nanoparticles, including the type and concentration of capping ligands, which can also influence their interactions with biological systems. The nanoparticles can be penetrative in nature resulting in increased threat to humans, flora and fauna, and the environment. The synthesis methods should incorporate biobased mechanisms using biobased extracts, hence minimizing the toxic effects. Also, surface modifications to the AuNPs and aggregations significantly affect their functionality and reduce their effectiveness. New researchers should aim to find advanced and green methods of synthesis that aim to improve the health and drug delivery effectiveness, improve sensing applications, incorporate models for safe environmentally friendly catalytic applications, and reduce toxicity. , AuNPs have a high potential application in next-generation electrical sensors, biomedical devices, solar energy harvesting, precision gene therapy delivery methods, advanced anticancer diagnostics, and health and sanitation applications. Future research should focus on optimizing the synthesis strategies of gold nanoparticles (AuNPs) to enhance their stability, biocompatibility, and functionality for diverse biomedical applications. − Comparative studies, such as those evaluating sonochemical − and chemical reduction methods, have demonstrated that synthesis techniques directly influence the physicochemical characteristics and antibacterial activity of AuNPs. Building on this, integrating multifunctional nanostructures such as Fe 3 O 4 @Au hybrids holds promise for advanced applications in drug delivery, catalysis, hyperthermia, and imaging. , Recent advancements in gold nanoparticle (AuNP) research highlight green mycosynthesis using mushrooms like Agaricus bisporus and rapid sonochemical techniques as promising routes for eco-friendly and scalable production. These methods yield stable, crystalline AuNPs with diverse morphologies and excellent catalytic and biomedical properties, including CT contrast enhancement and methylene blue degradation. Core@shell Fe 3 O 4 @Au structures synthesized via optimized sonochemical methods show dual-mode MRI/CT imaging potential. Sonochemistry also outperforms laser ablation in purity and colloidal stability. Furthermore, the development of eco-friendly, green synthesis methods using biological extractssuch as plant or mushroom derivativesnot only reduces environmental toxicity but also improves the therapeutic potential of AuNPs in anticancer treatments. Gold nanoparticles (AuNPs) synthesized using fresh fruiting bodies of Enoki and Shiitake mushrooms as green reducing agents exhibited diverse shapes, good stability, and crystallinity, with sizes around 72–74 nm. These mycosynthesized AuNPs showed effective catalytic degradation of Methylene Blue and potential for biomedical applications. Sonochemical methods further enhanced nanoparticle dispersion and enabled Au coating on Fe 3 O 4 via acoustic cavitation. − Ultrasmall AuNPs derived from fruit peels, for example, demonstrate strong photothermal effects and enhanced biocompatibility, offering a sustainable pathway for developing next-generation nanomedicine. Nowadays, Two-dimensional (2D) gold (Au) nanocrystals have been an area of interest for researchers. Gold nanoparticles are also used in antiaging creams or masks having particle size 5–400 nm, which enhances the collagen formation by 20–200 times. Cosmetic companies such as L’Oreal and L’Core Paris have infused gold nanoparticles in their formulations making them more effective. Recent advancements in biosensor and bioelectronics technology have opened new possibilities in biomedical diagnostics, particularly for early cancer detection. Biosensors are being used for detection of cancer with the use of advance techniques. Fox et al. has done a detailed investigation into the optimized synthesis and mechanism of formation for ultrathin, free-standing two-dimensional gold nanosheets (AuNS), which are approximately 0.47 nm thick and shows aspiring results for applications in computing, biosensing, catalysis, and healthcare. The AuNS were synthesized by one-pot, seedless reaction using chloroauric acid (HAuCl 4 ) reduced by sodium citrate in the presence of methyl orange (MO). Spectrophotometric and TEM analyses confirmed that MO is rapidly oxidized to form 4-diazobenzenesulfonic acid (4-DBSA), and this oxidation is crucial to directing two-dimensional growth. However, by using 4-DBSA alone can yield low-quality AuNS, showing that MO’s self-assembly and in situ oxidation synergistically assists nanosheet formation. UV–vis and other kinetic studies showed the MO degradation during the process follows pseudo-first-order kinetics and occurs within 30 s. Optimization such as delaying the addition of reagents by 30 s and slow mixing were observed for higher yields. Also, by lowering the reaction temperature from 20 °C to 4 °C can enhance AuNS yield by 16 times. The synthesis was complete within 8 h, with nanosheets observable after just 1 h. Mild centrifugation (∼1000 g) was essential to isolate the AuNS over 3D structures. The resulting AuNS showed enhanced catalytic activity compared to spherical gold nanoparticles,which makes them highly attractive for use in catalytic, enzymatic, and diagnostic applications due to their large surface area-to-volume ratio. A study conducted by Huang et al. presents a novel yet cost-effective way to develop an electrochemical biosensor for the ultrasensitive detection of hydrogen peroxide (H 2 O 2 ), a cancer biomarker, especially used in identifying colon cancer cells. The sensor utilizes a dual-nanozyme system by combination of ultrathin 2D conductive Cu-HHTP nanosheets with densely deposited ultrafine gold nanoparticles of size 3 nm. The Cu-HHTP nanosheets provide a large surface area and active Cu–O 4 metal sites which enhances catalytic activity, while the embedded AuNPs prevent from aggregation and further amplifying the response. This synergistic nanohybrid structure offers exceptional electrocatalytic efficiency, achieving an exceptionally low detection limit of 5.6 nM and a high sensitivity of 188.1 μA cm –2 mM –1 . This biosensor successfully tracks real-time H 2 O 2 release in human colon cells, by distinguishing cancerous cells from normal epithelial cells. It exhibits strong selectivity, reproducibility, and stability. This is a promising approach for advancing early cancer diagnostics and could inspire further development of nanozyme-based biosensors in biomedical and clinical applications. Another approach is made by Rauf et al. to develop an electrochemical biosensor using laser-scribed graphene modified with gold nanostructures (LSG-AuNS) to address the limitations of bare LSG electrodes in sensitivity and biomolecule immobilization. Gold nanostructures were electrodeposited onto LSG, which enhances the sensitivity and catalytic activity almost by 2-fold compared to unmodified LSG and commercial screen-printed gold electrodes. This 3D-porous LSG-AuNS platform was utilized to fabricate an aptamer-based sensor for detection of the breast cancer biomarker HER2, achieving a detection limit of 0.008 ng/mL and a broad linear detection range of 0.1–200 ng/mL. This sensor effectively detected HER2 in undiluted human serum with high accuracy. Furthermore, the system was integrated into a hand-held electrochemical point-of-care (POC) device, controlled via a custom mobile application. Although minor nonspecific protein adsorption was noted, the platform demonstrated high potential toward biosensing applications. A highly sensitive and multiplex electrochemical biosensor was developed for detecting multiple cancer-related microRNAs (miRNAs) in plasma by utilizing a dual amplification strategy. This approach by Mohammadniaei et al. combines MXene-Ti 3 C 2 T x nanosheets decorated with 5 nm gold nanoparticles (AuNPs) for enhanced signal transduction and duplex-specific nuclease (DSN)-based target recycling for signal amplification. Colorimetric biosensors rely on the visible color change of gold nanoparticles (AuNPs) in response to the presence or absence of a target analyte. This method offers a simple but yet fast approach for cancer detection. AuNPs are widely used in these sensors due to their unique optical properties, allowing for rapid and easily detectable color shifts that provide a quick visual indication of the analyte. A novel and highly sensitive colorimetric biosensor was developed by Xiao et al. using gold nanoparticle-decorated Bi 2 Se 3 (Au/Bi 2 Se 3 ) nanosheets, synthesized through simple sonication of a gold precursor with Bi 2 Se 3 in water. Bi 2 Se 3 nanosheets exhibit excellent electron-donating properties also it synergizes with AuNPs to enhance catalytic performance, particularly in the 4-nitrophenol (4-NP) reduction by NaBH 4 . The sensor works through a smart “on–off” mechanism: its catalytic activity is briefly turned off when it comes into contact with certain cancer-related antibodies, such as anti-CEA. However, this activity switches back on when the matching antigen like CEA is present. This clever response allows the system to precisely detect cancer biomarkers. Impressively, it can identify carcinoembryonic antigen (CEA) at concentrations as low as 160 picograms per milliliter, demonstrating strong potential for use in real-world clinical diagnostics. The biosensor is versatile for detection of other cancer markers like AFP and PSA. The work introduces a promising platform for biosensing, with future potential in diagnostics, biocatalysis, and smart biomaterial systems, Currently, breast cancer detection methods like mammography, MRI, and biopsy are expensive, invasive, and time-consuming, often yielding inconclusive results. To address these limitations, Selwyna et al. developed a sensitive, label-free electrochemical immunosensor that detects breast cancer by targeting the CA 15–3 biomarker in serum. The sensor uses gold nanoparticles coated with CA 15–3 antibodies, which enhance conductivity and provide a larger surface area for biomolecular interaction. In this setup, nanoparticles were anchored onto a screen-printed carbon electrode (SPCE), and the detection of antigen–antibody interactions is carried out with electrochemical impedance spectroscopy (EIS) and a potentiostat. The immunosensor effectively identifies CA 15–3 levels within a concentration range of 5 to 75 U/mL. Ranjan et al. developed a highly sensitive electrochemical immunosensor for detection of the CD44 antigen, a key breast cancer biomarker. The sensor was based on a hybrid nanocomposite comprising graphene oxide (GO), an ionic liquid (BMIM.BF 4 ), and gold nanoparticles (AuNPs), all immobilized on a glassy carbon electrode (GCE). Graphene oxide (GO) provides numerous oxygen-rich functional groups that facilitate effective antibody attachment. At the same time, the ionic liquid and gold nanoparticles (AuNPs) work together to enhance electron conductivity and expand the electrode’s surface area. These properties combination creates a synergistic effect that greatly improves the overall sensitivity and efficiency of the sensor. This sensor showed the detection range of 5.0 fg/mL to 50.0 μg/mL in both phosphate-buffered saline and human serum.

A number of applications of AuNPs have been shown in Figure . The growing resistance of pathogenic microorganisms to a wide range of antibiotics, including the latest ones, presents a major challenge in clinical medicine. One potential solution lies in the use of metal nanoparticles, particularly gold nanoparticles (AuNPs). Gold Nanoparticles are widely used for antimicrobial applications ( Table ) due to their small sizes, high surface area, and unique ability to interact with microbial cells. The antimicrobial effectiveness ( Figure ) of AuNPs is influenced by factors such as the synthesis method, particle size, shape, and the concentration of biologically synthesized nanoparticles. One of the crucial and unique properties of AuNPs is its positively charged nature, which enables them to interact with Gram-positive and Gram-negative bacteria. However, due to their thinner cell walls, Gram-negative bacteria are more susceptible to AuNP penetration. In contrast, Gram-positive bacteria possess a thick peptidoglycan layer that acts as a barrier, limiting nanoparticle entry. , Gold nanoparticles supported on clinoptilolite, mordenite, and faujasite zeolites effectively eliminated E. coli and Salmonella typhi . Faujasite-supported AuNPs (5 nm) showed the highest dispersion and efficiency, reducing bacterial colonies by 90–95%. The zeolite support significantly influenced nanoparticle size, roughness, and biocidal activity. Functionalized gold nanoparticles (AuNPs) effectively combat multidrug-resistant (MDR) bacteria, targeting both Gram-negative and Gram-positive uropathogens. Cationic and hydrophobic AuNPs suppressed 11 MDR clinical isolates with minimal toxicity to mammalian cells. Their surface chemistry plays a crucial role in antimicrobial activity, offering a promising long-term strategy against bacterial resistance. Multifield applications of AuNPs. Mechanism of antibacterial action of AuNPs and unreduced gold ions. Reprinted with permission from ref . Copyright 2022 MDPI. A study by Katas et al. showed powerful antioxidant effects toward AuNPs, helping to protect cells from harmful free radicals. This ability can reduce the oxidative stress-related damage. It contributes to aging and diseases like cardiovascular and neurodegenerative treatments. Gold nanoparticles (AuNPs) stabilized with carboxymethylated frankincense resin (CMFR) showed antioxidant activity by neutralizing DPPH free radicals. AuNPs synthesized from CMFR-AuNPs (7–10 nm) displayed dose-dependent antioxidant properties. Due to the large surface area and strong stability free radical scavenging. CMFR-AuNPs showed potential therapeutic advancements. For instance, a study by Faraday et al. examined that gold nanoparticles affect light transmission and color based on their size and dispersion. The study also examined the gold’s stability and reactivity in different conditions, which shows antioxidant behavior. Gold nanoparticles (AuNPs) produced through the electrodeposition were evaluated using the DPPH assay. Suliasih et al. found that smaller AuNPs with greater particle density exhibited higher antioxidant activity. AuNPs synthesized at −1 V depicted the highest inhibition (36.80%) of free radicals. In another study, Ipek et al. synthesized Gold nanoparticles (AuNPs) using Allium cepa L. peel extract. The analysis identified their spherical shape, ranging from 6.08 to 54.20 nm. Antioxidant tests (DPPH, ABTS, and CUPRAC) showed moderate free radical scavenging ability, less effective than BHA and α-tocopherol. AuNPS synthesized from Spirulina platensis depicted strong antioxidant activity. The DPPH assay showed that at 300 μg/mL, achieved 70% inhibition, effectively neutralizing free radicals. The results showed Spirulina -based AuNps as a natural antioxidant with potential benefits in biomedical and pharmaceutical fields. Another study compared the antioxidant properties of chitosan and green-synthesized gold nanoparticles (AuNPs). Chitosan acted as both a reducing and stabilizing agent for AuNPs and was measured using DPPH, ABTS, hydroxyl radical scavenging, and FRAP assays. Low molecular chitosan (47.8 kDa) showed the highest antioxidant effect. Another study by Radadi et al. showed AuNPs synthesized from Annona muricata leaf extract through ABTS assay, with a maximum of 96.4 μg/mL. Characterization of nanoparticles using UV–vis, FTIR, TEM, and XRD exhibited spherical shape and crystalline structure. Their antioxidant properties are linked to polyphenols and flavonoids in the extract, which enhance the free radical scavenging. Gold nanoparticles (AuNPs) synthesized using Vibrio alginolyticus were tested using DPPH and metal chelating assays. Characterization depicted irregular shapes, ranging from 100 to 150 nm. The nanoparticles showed greater antioxidant effectiveness at lower concentrations. It emphasizes the eco-friendly synthesis of AuNPs. For instance, another study of AuNPs synthesized using Alternaria chlamydospore was tested using the DPPH assay, achieving 71.2% inhibition at 500 μL. Nanoparticles confirmed their spherical shape ranging from 12–15 nm with a high surface area-to-volume ratio, enhancing free radical neutralization. The IC 50 value was 224.97 μg/mL, demonstrating strong antioxidant activity. Gold nanoparticles (AuNPs) results suggest that they could be valuable for biomedical applications. Gold NPs have been extensively used for their anti-inflammatory benefits. Synthesis is done by using various methods such as green synthesis with plant extracts, microbial sources, and chemical modifications. For instance, Au-NPs synthesized using Saussurea costus extract exhibited strong anti-inflammatory effects due to the presence of bioactive polyphenols that stabilize and enhance their biological activity. Similarly, Capsicum annum fruit extract-mediated Au-NPs showed notable anti-inflammatory and antiangiogenic properties. Au- NPs derived from Chaetomium globosum extract demonstrated potent inhibition of inflammatory mediators, making them a viable option for anti-inflammatory treatment. Sivakavinesan et al. synthesized Au-NPs via Citrus sinensis fruit peel extract, which exhibits strong antioxidant and anti-inflammatory activities Similar study was conducted by Gao et al. in which gold nanoparticles were synthesized using citrus peel extract with the ultrasound-assisted method and showed enhanced anti-inflammatory activity. Additionally, AuNPs synthesized from papaya peel extract demonstrated antimicrobial, antioxidant, and anti-inflammatory effects, reinforcing their relevance in pharmaceutical and biomedical fields In a study by Elizalde-Mata et al. AuNPs derived from Croton draco extract exhibited strong antioxidant and anti-inflammatory properties, making them promising for therapeutic applications. Similarly, Eltahir et al. reported that phenolic compounds from Glycyrrhiza glabra showed notable anti-inflammatory effects, suggesting their potential in treating inflammation-related disorders. In another study conducted by Nasab et al. conjugated Au-NPs with cortistatin peptides were successfully employed for targeted drug delivery to asthmatic lung tissues, offering a novel approach for respiratory inflammatory diseases. The Saussurea Costus gold nanoextract demonstrated significant antioxidant, antidiabetic, anti-Alzheimer, and anti-inflammatory activities, making it a potential therapeutic agent for managing oxidative stress related diseases. Prasad et al. synthesized gold nanoparticles using an aqueous extract of Commiphora wightii which were potential anti-inflammatory agents. Hongsa et al. developed chitosan-collagen coated gold nanoparticles for targeted drug delivery of 5-fluorouracil (5-FU), a chemotherapy drug that exhibited controlled and sustained drug release, anti-inflammatory activity, and cytotoxicity studies confirmed their anticancer potential Gold nanoparticles (AuNPs) have emerged as a promising tool in skin disease treatment due to their biocompatibility, enhanced skin penetration, and controlled drug release properties. They offer therapeutic benefits for conditions like psoriasis, atopic dermatitis, skin cancer, and microbial infections by reducing inflammation, stabilizing the skin barrier, and enhancing drug delivery. Qui et al. successfully synthesized antibacterial photodynamic gold nanoparticles (AP-AuNPs) for treating skin infections. These nanoparticles, combining antibacterial peptides and photodynamic effects, showed significant antibacterial activity against S. aureus and E. coli , while also promoting wound healing in infected skin tissues. Cuyler et al. explored the potential of gold nanoparticles synthesized using Bulbine Frutescens to treat Eczema. The nanoparticles demonstrated significant wound closure and inhibited histamine production, suggesting their potential to alleviate skin damage associated with atopic dermatitis Gold nanostructures can also be implemented in melanoma therapy. Leu et al. studied the effect of AuNPs combined with antioxidant epigallocatechin gallate and α-lipoic acid on wound healing in mice, demonstrating anti-inflammatory and antioxidative effects Another study conducted by Oliveira et al. utilized AuNPs in combination with photobiomodulation (low-power laser therapy) to treat dermonecrotic lesions, specifically those caused by the venom of the spider Loxosceles simillis . It effectively reduced necrotic tissue and erythema in animal models Poomrattanangoon and Pissuwan evaluated the wound healing ability of gold nanoparticles coated with collagen-I. Collagen-I@AuNPs reduced the levels of inflammatory cytokines and induced the growth factors involved in wound healing. Dong et al. developed mussel-inspired electroactive, antibacterial, and antioxidative composite membranes with gold nanoparticles and antibacterial peptides for enhancing skin wound healing. The composite membranes promoted cell proliferation and migration and exhibited enhanced antibacterial and antioxidant effects Wu et al. developed an injectable, antibacterial hydrogel based on gold nanorods and an N-calamine polymer for bacteria-infected skin wound healing. The hydrogel demonstrated excellent in vitro antibacterial capacity and promoted wound healing Abbas et al. investigated the efficacy of alginate-coated gold nanoparticles against antibiotic-resistant Staphylococcus and Streptococcus strains that cause acne. The results concluded the potential of Gold NPs as a potential antimicrobial agent to combat antibiotic resistance in acne treatment Gold has long symbolized nobility and attracted attention due to its shiny appearance, it has excellent ductility, biocompatibility, and molecular recognition, and gold is widely used in various fields. Gold nanoparticles (AuNPs) exhibit unique physical and chemical properties, enabling biomedical applications. AuNPs easily bind to proteins and antibodies, aiding in disease diagnosis, gene detection, and cancer treatment. They also show cytotoxic effects on cancer cells and possess antioxidant and anti-inflammatory properties. Research highlights their therapeutic potential in treating retinopathy, neurological diseases, cancers, cardiovascular diseases, infections, and metabolic disorders. Delivering drugs through the ocular route holds great potential for treating various eye diseases, including diabetic retinopathy. This condition is primarily driven by inflammation and elevated vascular endothelial growth factor (VEGF) levels, leading to abnormal blood vessel growth (neovascularization). Ocular drug delivery systems aim to effectively target these factors, improving treatment outcomes for such vision-threatening disorders. Ocular drug delivery is an effective method for treating eye diseases like ocular neovascularization in diabetic retinopathy, which is caused by inflammation, retinal ischemia, and the accumulation of advanced glycation end-products. Elevated vascular endothelial growth factor (VEGF), interleukins, and reactive oxygen species (ROS) also contribute to disease progression. Gold nanoparticles (GNPs) possess antioxidant and antiangiogenic properties, making them ideal for ocular drug delivery. They are biocompatible, easy to synthesize, and can be functionalized to improve movement across ocular barriers. Apaolaza et al. conducted a study where low molecular weight hyaluronan (HA) was used to enhance nanoparticle stability, mobility, and targeting via CD44 receptor interaction. HA-GNPs effectively reached deeper retinal layers, inhibiting neovascularization and protecting retinal pigment epithelial cells. Despite a slight reduction in antioxidant activity, longer studies are needed to assess their full potential in delivering antiangiogenic treatments for intraocular vascular diseases. HA-AuNPs showed excellent colloidal stability, with the HA coating preventing aggregation in the trabecular meshwork of ex vivo porcine eyes. Nanoparticles (120 nm) accumulated the most in this region. Advancements in nanotechnology have improved nanoparticle stability, while coatings like poly­(ethylene glycol) (PEG) enhance biocompatibility, reducing toxicity and increasing circulation time. Although AuNPs show significant potential in biomedical applications, further safety studies are required before clinical implementation. Further research is needed to clarify ocular distribution and potential toxicity, as current biocompatibility data remain conflicting. Diabetes mellitus, commonly known as diabetes, occurs due to reduced insulin secretion by the pancreatic islet cells, leading to elevated blood glucose levels (hyperglycemia). It is characterized by symptoms such as unexplained weight loss, excessive urination (polyuria), increased thirst (polydipsia), and an excessive. Diabetes mellitus is classified into Type 1, Type 2, and Gestational diabetes. Type 1 diabetes results from an autoimmune attack on pancreatic β cells, leading to insulin deficiency. For children, the term juvenile diabetes is used. Type 2 diabetes is caused by insulin resistance and reduced insulin secretion due to defective insulin receptor response. Gestational diabetes occurs during pregnancy when hormonal changes reduce insulin sensitivity and increase blood sugar levels. Management includes dietary modifications, exercise, insulin therapy, and oral medications. Recent nanomedicine research focuses on using nanoparticles for effective insulin delivery in Type 1 diabetes treatment. Nanoparticles offer promising advancements in controlled insulin release, improved bioavailability, and fewer side effects, providing a potential breakthrough in diabetes management and treatment strategies for better patient outcomes. Gold nanoparticles (AuNPs) have shown potential as therapeutic agents for diabetes treatment. As they exhibited anti-inflammatory, antioxidant, and antihyperglycemic effects, disrupting key disease pathways. However, their safety, optimal size, and dosage require further detailed study. Proper characterization is essential to ensure safe applications for treating diabetes and related microvascular complications. Daisy et al. prepared an aqueous extract using Cassia fistula stem bark and synthesized gold nanoparticles (AuNPs) to assess their hypoglycaemic effects. Synthesized AuNPs were characterized using spectroscopy and electron microscopy. In streptozotocin-induced diabetic rats, AuNPs significantly lowered blood glucose, improved liver and kidney function, enhanced lipid profiles, and increased body weight more effectively than the aqueous extract. Phytochemically synthesized AuNPs demonstrated excellent antidiabetic properties by stabilizing serum biochemistry and reversing renal dysfunction. This study confirms that Cassia fistula-derived AuNPs are promising therapeutic agents for diabetes mellitus treatment, outperforming conventional plant extracts in improving metabolic health. AuNPs also reduces hyperglycaemia, oxidative stress, inflammation, and the proteolytic pathway. Gold nanoparticles (AuNPs) in conjugation with natural products have demonstrated promising antidiabetic properties, such as reduction in glycated hemoglobin levels and anti-inflammatory effects. Opris et al. conducted a study aimed to evaluate the therapeutic potential of AuNPs functionalized with Sambucus nigra L. (SN) extract in an experimental rat model of diabetes. Diabetes was induced in 18 male Wistar rats using a single streptozotocin injection. The diabetic rats were then treated with SN extract, gold nanoparticles (AuNPs), or saline for 2 weeks via oral gavage. Another 18 nondiabetic rats received the same treatments. After treatment, blood, liver, and muscle samples were analyzed for oxidative stress markers, liver MMP-2/-9 activity, COX-2 and NFKB expression, and histopathological changes. Serum glucose, cholesterol, ALAT, and ASAT levels were also measured to assess the effects of AuNPs and Sambucus nigra L. extract on diabetes-related metabolic and inflammatory changes. The administration of AuNP-SN extract significantly increased the muscle and systemic GSH/GSSG ratio in diabetic rats compared to untreated diabetic ( p < 0.03) and nondiabetic vehicle-treated groups ( p < 0.05). Malondialdehyde (MDA) levels were reduced in the AuNP-treated diabetic group compared to nondiabetic controls ( p < 0.05). Additionally, COX-2 expression ( p < 0.0001) and proMMP-2 activity ( p < 0.05) were decreased, along with a significant reduction in Kupffer cell percentage (<0.001). Histopathological analysis revealed no structural abnormalities in liver tissue. These findings suggest that AuNPs functionalized with Sambucus nigra L. extract possess strong potential as adjuvants in diabetes therapy by enhancing antioxidant defenses, reducing MMP activity, and mitigating inflammation in liver tissue. Further research is warranted to explore their clinical applications in diabetes management. Gold nanoparticles (AuNPs) are now being widely used for treating cardiovascular diseases (CVD) due to their ability to increase the drug delivery to a targeted site, reducing side effects, and maximizing bioavailability ( Table ). AuNPs which are in functionalized form are capable of delivering drug molecules to targeted tissues with enhanced specificity, offering controlled release as well as longer action. These nanoparticles are ideal for controlling atherosclerosis, thrombosis, and myocardial infarction and provide a probable pathway for prospective cardiovascular therapies due to their anticoagulant, antioxidant, and anti-inflammatory properties. Second, due to their unique optical, electronic, and biological properties, they also show potential in recovering cardiovascular disease. They can target selectively atherosclerotic plaques, provide controlled drug release, and function as imaging agents for early diagnosis. They can also decrease oxidative stress, regulate inflammatory reactions, and enhance endothelial function, thereby providing cardio protection. Among the diverse theragnostic nanomaterials, gold nanoparticles (AuNPs) are remarkable because of their special optical and physicochemical properties. AuNPs can facilitate the diagnosis of CVDs by computed tomography (CT) and can carry out photothermal therapy to induce plaque ablation. Their therapeutic efficacy with a reduced side effect is increased due to the ability to deliver drugs directly to the infected effects. Nanotechnology here plays a critical role in the improvement of CVD management as these particles increase therapeutic efficiency, minimize side effects, and allow for controlled drug release. On using branched polyethylenimine-coated gold nanoparticles (bPEI-AuNPs) in collagen hydrogels, it greatly improves the drug delivery, mechanical properties, and conductivity. These hydrogels also improve cardiomyocyte function, inducing rhythmic and synchronized beating. In fact, on incorporating gold nanoparticles (AuNPs) into the biosensor architecture, sensitivity and specificity increase due to their conductivity, extensive surface area, and biocompatibility. The performance of the biosensor, such as its low detection limit (LDL) and high specificity, shows its promise for clinical use, offering a reliable means for evaluating cardiovascular risk and individualized treatment plans. The measurements indicated remarkable blood velocity, pressure, and temperature variations, and additionally, the in vivo biodistribution of AuNP-miR-67, administered subcutaneously, indicated the particles were being cleared mainly through the liver and kidneys within 11 days. Ven et . al points to the possibility of the PNP-AuNP-miRNA hydrogel platform in controlled, sustained miRNA delivery with the additional advantage of being minimally invasive. Future advancements can include the inclusion of targeting ligands for cell-specific delivery, and increasing therapeutic efficiency for targeted treatment of cardiovascular disease and other conditions. Gold nanoparticles (AuNPs) have become attractive nanoplatforms for cancer diagnosis and therapy because of their size, shape, and optical tunability ( Table ). Their use in photothermal therapy, drug delivery, and imaging has exhibited increased tumor targeting ( Figure ) with low systemic toxicity. Yet, issues like biodistribution, cytotoxicity, and immunogenicity must be explored before they can be translated to the clinic. Optimizing AuNP formulations to enhance efficacy and safety in cancer treatment will be a task for future studies. These nanoparticles play a vital role as an anticancer due to their size, shape and physiochemical properties they inhibit. Properties like biocompatibility, high surface area to volume ratio and ease on functionalization makes them suitable for delivery of chemotherapeutic agents on tumor sites. They also help in minimizing the damage to healthy cells and reducing systemic toxicity. By offering controlled drug release, targeted delivery, and reduced side effects, gold nanoparticles represent a multifaceted tool in advancing more effective and personalized cancer treatments. Gold nanoparticles are ideal carriers for targeted drug delivery as they passively accumulate in tumor tissues due to leaky vasculature and poor lymphatic drainage. This is due to an effect known as ‘Enhanced Permeability and Retention Effect’. Second, due to their strong optical properties, they are widely used in CT, MRI, and photoacoustic imaging which are all real-time imaging techniques. Some of its applications in different types of cancer are given in the table below. Schematic mechanism of anticancer activity for AuNPs. Reprinted with permission from ref . Copyright 2021 Elsevier. Gold nanoparticles (AuNPs) show excellent stability, biocompatibility, and interesting optical properties, making them suitable as candidates for drug delivery to tumors. Their nanometer dimensions enable preferential tumor site accumulation through the EPR effect, wherein the leaky tumor vasculature traps nanoparticles while minimizing systemic clearance. Targeting ligand conjugation, e.g., antibodies, peptides, or folic acid, increases specificity and cancer cell uptake, enhancing therapeutic efficacy. Additionally, AuNPs act as photothermal agents, enabling targeted tumor ablation using plasmonic heating upon NIR illumination. These characteristics make AuNPs valuable nanomedicine tools for imaging and targeted therapy. Gold nanoparticles possess unique optical properties, particularly surface plasmon resonance (SPR), which make them suitable for imaging applications in biomedical research. Their tenable size, shape, and surface chemistry allows for efficient functionalization with imaging ligands, enabling their use as contrast agents in molecular imaging and nuclear medicine ( Table ). They can easily modify their surface with polymers, drugs, antibodies, and proteins, and they have become widely used as delivery vehicles. Their prolonged circulation time, enabling extended imaging and enhanced targeting efficiency make them suitable for CT imaging. AuNPs offer approximately 2.7 times greater imaging contrast than iodinated agents. Some traditional iodinated agents like iopamidol and iodixanol often cause allergic reactions and are unsuitable for patients with renal issues due to rapid clearance. Gold NPs have gained significant attention for drug delivery due to their unique structural and functional properties. They have been explored fir drug delivery, particularly in cancer treatments and studies are being conducted on structure-efficacy relationships to optimize their design and application. Additionally, hybrid systems combining AuNPs with other therapeutic agents are being developed. A study conducted by Zazo et al. developed a gold nanoparticle-based system to improve the delivery of stavudine, an antiretroviral drug. The AuNPs used were citrate stabilized and 40 nm in size and prepared by incubating in stavudine solution for 24 h at room temperature. The formulation was tested for drug release at different pH levels and cellular uptake in human macrophages. In vivo studies in wistar rats showed that AuNPs increased stavudine accumulation in HIV (Human Immunodeficiency Virus) reservoirs like the liver, spleen, and macrophages. The liver showed a notable increase in MTR (mean residence time) from 1.28 to 5.67 h and partition coefficient was changed from 0.27 to 0.55. This system had enhanced biodistribution, prolonged drug residence and better targeting of latent HIV sites. No major limitations were directly reported, but the study emphasizes the need for further validation and clinical development. Sun et al. developed a thermosensitive nanoplatform combining AuNPs, hexanoyl glycol chitosan (HGC), a chemotherapeutic agent doxorubicin (DOX) and a photothermal; dye indocyanine green (ICG). AuNPs were synthesized via a citrate reduction method and them coated with HGC through electrostatic interaction, encapsulating DOX and ICG within the HGC shell. This assembly allowed drug release to be triggered by heat generated under 808 nm laser irradiation. It effectively targeted tumors and showed strong cytotoxicity in HeLa and SiHa cells and tumor-bearing mice. Advantages included enhanced therapeutic efficacy, targeted release, and minimal side effects. No major limitations were reported. Similarly, in the research conducted by Devi et al. AuNPs were synthesized using citrate and DOXmediated reduction, then functionalized with BP100 which is a cell penetrating peptide or RGD (targeting peptide). BP100@AuNPs-DOX showed high DOX loading (19.2 μM) with 96% encapsulation efficiency and up to 85% drug release at pH 4.5, better than RGD@AuNPs (70% release). BP100 systems showed superior cellular uptake and anticancer efficacy in HeLa cells. In HeLa cell assays, free DOX showed 32.1% killing, while DOX@AuNPs alone caused 27.2% death. Peptide-functionalized versions significantly improved efficacy-BP100@AuNPs-DOX and RGD@AuNPs-DOX killed 51.4 and 37.3% of cells, respectively. Overall, BP100@AuNPs-DOX exhibited the best anticancer activity, though high DOX concentrations reduced nanoparticle stability. In an experiment carried out by Zheng et al., 214 nm alginate-cysteine nanogels were embedded with 20 nm AuNPs. These DOX@ACA nanogels had 89.6% encapsulation efficiency and 3.7% drug loading. DOX release reached from 42.4 to 67.2% under 532 nm laser irradiation. DOX-AuNPs were highly responsive and effective but synthesis complexity and charge repulsion were the only noted limitations. Although gold nanoparticles offer various benefits as drug delivery vehicles, their broader clinical application is primarily limited by concerns over safety. Factors including particle size, morphology, surface ligands, nuclei acid conjugates, dosage levels, and degradability influence their toxicity. To ensure reproducibility and consistent performance of gold nanoparticles (AuNPs) in drug delivery, maintaining uniformity in their size and shape is essential. Additionally, strategies for encapsulation, surface functionalization, and drug release must be specifically designed to match the physicochemical characteristics of the therapeutic agents being delivered. Release mechanism should be precisely controlled. A further challenge is ensuring the biological stability of AuNPs within physiological environments. Variations in temperature, pH, and the presence of ions or other biomolecules should not compromise the nanoparticle’s functionality or cause premature release or degradation of the loaded drug. Although these challenges demand rigorous design and testing, the unique properties of AuNPs continue to present significant opportunities in advancing drug delivery systems. While numerous studies have shown that AuNPs are generally safe, some have reported toxic effects. For example, a study conducted by Feng et al., involving bacteria such as Shewanella oneidensis (Gram-negative) and Bacillus subtilis (Gram-positive), gold nanoparticles coated with cationic or polyelectrolyte substances were found to exhibit higher toxicity compared to those functionalized with anionic ligands like 3-mercaptopropionic acid or the cationic ligand 3-mercaptopropylamine. Another study explored the use of gold nanoparticles embedded in or added to the soaking solution of contact lenses to enhance sustained release of Bimatoprost for glaucoma treatment. The researchers evaluated drug uptake, release duration, lens transparency, oxygen permeability, and protein adherence. However, certain limitations were identified. GNP- Laden contact lenses caused a high initial burst release of bimatoprost which may lead to side effects like eye redness. While drug release lasted up to 72 h, it dropped after 48 h, potentially below therapeutic levels. There is also concern about nanoparticle leakage, and long-term safety studies are still needed. The EPR effect was a pivotal discovery in nano-oncology, enabling passive targeting of nanoparticles to tumors. However, its clinical applicability has fallen short of expectations, as high accumulation of nanoconjugates in tumors via EPR alone is often inconsistent. , Consequently, the need for active targeting strategies remains critical to improve specificity and therapeutic efficacy in cancer drug delivery. , Gold nanoparticles (AuNPs) exhibit promising quorum quenching capabilities by disrupting bacterial quorum sensing (QS) pathways, which control virulence and biofilm formation ( Table ). AuNPs inhibit QS by downregulating genes linked to bacterial communication, thereby reducing pathogenicity. These nanoparticles offer a potential alternative to antibiotics, especially against multidrug-resistant bacteria. Biosynthesized AuNPs, due to their eco-friendly nature and cost-effectiveness, are emerging as effective antimicrobial agents in combating bacterial infections and managing biofilms. These have shown promising potential as quorum quenchers, effectively inhibiting quorum sensing (QS) and virulence factors in Pseudomonas aeruginosa . Biosynthesized using Streptomyces isolate S91, these monodispersed AuNPs disrupted QS-related traits like pyocyanin, protease, and elastase production. The inhibitory effects were confirmed using RT-PCR, highlighting the potential of AuNPs as novel anti-QS agents for managing microbial resistance and chronic infections. Qais et al., showcased gold nanoparticles synthesized using Capsicum annuum extract demonstrated potent quorum-quenching capabilities against Pseudomonas aeruginosa PAO1 and Serratia marcescens MTCC 97. The AuNPs-CA effectively inhibited QS-regulated virulence factors, including pyocyanin, pyoverdin, elastase, and rhamnolipid production, along with biofilm formation. , Khosravi et al., study highlights the potential of green-synthesized AuNPs as biofilm, paving the way for new strategies to combat multidrug-resistant bacterial infections. Lately, Gold nanoparticles (AuNPs) are increasingly being incorporated in cosmeceuticals due to their antioxidant, anti-inflammatory, and antiaging properties. ( Table and Figure ) outlines the various applications of AuNPs in cosmetics. AuNPs enhance skin permeability, deliver active ingredients, and offer resistance to environmental insult. AuNPs also promote collagen synthesis which reduces wrinkles and improves skin elasticity. However, further research is needed to know long-term safety and efficacy in cosmetic formulations. In cosmeceutical (that is cosmetic + pharmaceutical) applications, gold nanoparticles (AuNPs) offer promising potential for skin delivery systems. Curcumin which is a bioactive component of turmeric inhibits antioxidant and anti-inflammatory properties, with low bioavailability and instability. On encapsulating curcumin in chitosan-gold nanoparticles, the stability, absorption, and therapeutic activity are enhanced, and efficiency increases. Using chitosan derived from Oryctes rhinoceros beetle offers a green approach that converts pests into useful resources, gives remarkable stability, mild toxicity, and uniform nanosized particles, which are ideal for future cosmeceutical products. Nowadays, plant extract-mediated green synthesis of gold nanoparticles (AuNPs) is becoming increasingly popular because it is eco-friendly and does not utilize toxic chemicals. Despite limited studies, these are beneficial in antiaging, rejuvenation, and acne treatment creams and products. Due to their size and big surface-to-volume ratio, AuNPs penetrate skin layers with ease, facilitating the delivery of active components more efficient. Nevertheless, incorporating AuNPs in cosmeceuticals necessitates sensitive care of their environmental footprint, with a focus on green synthesis methods and lifecycle studies This approach ensures that the cosmetic industry can harness the unique benefits of AuNPs while prioritizing sustainability and minimizing ecological impact. Recent advancements include stimuli-responsive AuNP-collagen hydrogel nanoparticles (Au-CHPs), which enable controlled delivery of therapeutic proteins like fibroblast growth factor, superoxide dismutase, and epidermal growth factor. These Au-CHPs enhance wound healing, reduce oxidative stress, and promote skin regeneration, highlighting their potential for targeted, on-demand treatments in skincare. Singh et.al, in his research formulated a cosmeceutical peel-off mask by copolymerizing poly­(vinyl alcohol) (PVA) with sodium alginate, hydroxypropyl methylcellulose, or hydroxyethyl cellulose and incorporating silver nanoparticles (AgNPs). This approach was seen to enhance the antibacterial properties of the mask while maintaining its stability and biocompatibility. Similarly, gold nanoparticles (AuNPs) hold potential in cosmeceuticals due to their antioxidant, antiaging, and anti-inflammatory properties, enabling effective skin rejuvenation, wrinkle reduction, and enhanced product stability. Cosmeceutical applications of AuNPs. Gold nanoparticles (AuNPs) are proven to be beneficial in treating brain dysfunctions due to their unique structure and properties, such as the ability to cross the blood-brain barrier (BBB) and deliver therapeutic agents directly to the brain. Some research and studies have shown that AuNPs are responsible for enhanced drug efficacy, reducing oxidative stress, and modulating neuroinflammation, offering neuroprotection in conditions like Alzheimer’s and Parkinson’s disease. However, further research is required to understand their long-term safety, biodistribution, and precise therapeutic mechanisms. Gold nanoparticles (AuNPs) also offer promising potential for treating neurological disorders due to their unique physicochemical properties. They can easily penetrate across the blood-brain barrier (BBB), facilitating drugs’ targeted delivery and minimizing off-target effects. In Alzheimer’s disease AuNPs inhibit amyloid-β aggregation, remove oxidative stress, and regulate neuroinflammation. In Parkinson’s disease (PD), they are neuroprotective through the removal of reactive oxygen species and inhibition of dopaminergic neuron loss. Nevertheless, challenges in toxicity, stability, and controlled release must be addressed for clinical use. Further research is necessary to optimize AuNPs for Safe and effective neurological interventions. In a recent study, AuNPs synthesized via microwave radiation and stabilized with dextrin were administered to diabetic rats. Diabetes can be mitigated by this treatment as it reduces oxidative stress, inflammation, and neurotransmitter imbalances. The higher dose (that is 2 mg/kg) was more effective than the lower dose (1 mg/kg), highlighting AuNPs’ potential in neuroprotection and managing diabetic brain dysfunctions. Gold nanoparticles (GNPs) linked with sodium diclofenac and/or soy lecithin were evaluated for safety and therapeutic potential in treating obesity-related inflammation. The 18 nm GNPs, administered intraperitoneally for 14 days, accumulated significantly in tissues without causing hepatic or renal toxicity. In obese mice, GNPs reduced food intake, and alleviated inflammation and oxidative stress, but did not reverse mitochondrial dysfunction. These findings suggest GNPs could be promising therapeutic agents, pending further safety assessments. Gold nanoparticles inserted into gelatin hydrogels demonstrate strong photothermal properties under near-infrared laser light. These hydrogels enhance MC3T3-E1 preosteoblast, supporting bone regeneration. It produces heat in the localized area promoting cell growth and making this system promising in bone tissue engineering. They provide a minimally invasive and efficient way to improve bone healing through controlled thermal stimulation. AuNPs due to their adjustable optical properties and biocompatibility, are effectively used in plasmonic therapy. The radiation emitted from the laser converts light into localized heat, enabling the targeted destruction of cancer cells. Their surface can be modified for targeting tumors and reducing the damage to healthy tissues. Another study by Faid et al. presents hybrid chitosan-coated AuNPs as effective agents in photothermal therapy. They exhibit biocompatibility and stability, efficiently converting near-infrared light into heat to destroy cancer cells. The chitosan shells support in cellular uptake and prolongs circulation time. It shows significant potential in minimally invasive cancer treatment. A study by Frantellizzi et al. presented 99 mTc-labeled keratin-coated gold nanoparticles (Ker-AuNPs) designed for cancer photothermal therapy and imaging. They show biocompatibility and renal-clearance properties, modeled through a nephron-like system, ensuring minimal toxicity. This dual-function nano platform depicts integrated diagnosis and photothermal treatment in oncological applications. Similar study by Darvish et al. highlighted the use of keratin- coated AuNPs for photothermal therapy. The functionalized AuNPs serve as promising agents for cancer therapy and therapeutic effects. The study investigates anisotropic gold nanoparticles stabilized with choline carboxylic acid ionic liquids for photothermal therapy. They show excellent thermal conversion under infrared light, enabling targeted cancer cell ablation. Their unique structure enhances the stability, biocompatibility, and efficiency. They are effective agents in noninvasive cancer treatments through localized heat generation. Green synthesis of gold nanoparticles for photothermal therapy in combination with chemotherapy. They generate heat to kill cancer cells, enhance drug uptake and therapeutic efficiency. The biocompatible approach reduces side effects and improves the cancer treatment. Another study discussed the nanocellulose-based codelivery system that enhances photothermal therapy. Gold nanoparticles (AuNPs) combined with curcumin are integrated with carboxymethylated cellulose nanofibrils, enhancing the stability, solubility, and release rate. The system boosts photothermal effects under near-infrared irradiation, leading to efficient cancer cell destruction. This method offers a biocompatible and synergistic treatment combining thermal and chemotherapeutic effects with minimal side effects. 4-mercaptobenzoic acid (MBA)-functionalized gold nanoparticles (AuNPs) have demonstrated potent antibacterial activity ( Table ), particularly against multidrug-resistant (MDR) S. aureus and S. epidermidis . Similarly, 4,6-diamino-2-pyrimidine-thiol (DAPT) functionalized gold nanoparticles embedded in a silk fibroin (SF) membrane showed good antibacterial activity against drug-resistant and drug-sensitive strains of E. coli . Controlled release of the DAPT-AuNPs was provided by the hydrophilic nature of the SF membrane. In vivo experiments with SD rats revealed quick healing of the wound in 3 μg/cm 2 -treated groups compared with control groups, or groups treated with plain SF membranes or gauze. Besides surface changes, particle shape is also an important determinant of the antibacterial activity of AuNPs. Irregular AuNPsrod, star, peanut, and porous sphereswere found to cause membrane integrity loss of E. coli and P. aeruginosa . Irregular shapes facilitate interaction with bacterial surfaces, enhance the generation of reactive oxygen species (ROS), and enhance antibiofilm efficacy. All these mechanisms contribute to efficient inhibition of bacteria and biofilm formation inhibition. Antiviral drugs and agents are in great demand throughout the world. Each year millions of infections occur due to the attack of these viruses thus causing infections. Metal nanoparticles have the intrinsic property of antiviral activity which provides a potential solution to mitigate these infections. AuNPs can attach to viral particles, thereby preventing their interaction with cellular or viral receptors and inhibiting the initiation of the viral replication cycle. AuNPs adhere to the cell surface and alter the membrane potential, thereby blocking the viruses from entering the cell. This antiviral action of AuNPs ( Table ) has been attributed to several mechanisms, including the prevention of virus attachment and entry into host cells, interference with plasma membrane binding, inactivation of viral particles prior to entry, and interaction with double-stranded DNA. Gold nanoparticles inhibit a broad spectrum of viruses, including HIV, influenza, and herpes simplex virus due to their antiviral properties. In fact, some research showcased the antiviral potential of gold nanoparticles (AuNPs) against SARS-CoV-2, focusing on their ability to disrupt viral envelopes and prevent viral entry. Ayurvedic metal nanoparticles, such as Swarna Bhasma have unique properties like anti-inflammatory, immunomodulatory, and antiviral effects, making them promising agents for COVID-19 treatment. Furthermore, study is required to authenticate their therapeutic potential against SARS-CoV-2 and other viral infections leading to diseases. Glaucium flavum leaf extract was known to produce stable, spherical AuNPs with a mean size of 32 nm and low aggregation. It was synthesized in a green way and characterization techniques like FTIR, and GC-MS confirmed their stability and bioactivity. The potential of functionalized gold nanoparticles (AuNPs) as an effective antiviral agent against herpes simplex virus (HSV) by inhibiting viral entry and replication was observed by Ayipo et al., in his work. These nanoparticles undergo surface modification of AuNPs to enhance their binding affinity to viral proteins, allowing targeted. These findings highlight the potential of AuNPs in developing advanced antiviral therapies. Similarly, sulfonic group-modified gold nanoparticles (MDS_AuNPs) possess broad-spectrum via antiviral properties but lose efficacy in high-protein environments. To address this, sulfonic mixed-charge modified gold nanoparticles (MC_AuNPs) were developed by introducing positively charged ligands. MC_AuNPs retained antiviral activity even in a 10 mg/mL protein solution, unlike MDS_AuNPs, which failed in 1 mg/mL solutions. Chaika et al., in their work showcased that these gold nanoparticles (AuNPs) exhibit potent antiviral activity against adenovirus and H1N1 influenza virus, with 5 nm size indicating stronger virucidal effects compared to 20 nm AuNPs. The smaller nanoparticles were observed to disrupt viral structures within 2 h, while larger ones made shape changes. AuNPs are universal virucidal agents with low cytotoxicity and minimal reactive oxygen species (ROS) generation due to this physical adsorption mechanism. Gold nanoparticles (AuNPs) are now being widely used in biological and chemical sensing due to their unmatched optical and electronic properties, which enable easy detection of analytes ( Table ) Figure . AuNP-based sensors control the electron transport mechanisms and surface plasmon for electrical and optical readouts. Environmental monitoring, medical diagnostic and real-time detection in complex matrices due to its rapid response times, selectivity, and potential for miniaturization. Gold nanoparticles play a crucial role in biosensors due to their unique properties. Surface Plasmon Resonance (SPR) enables them to exhibit collective electron oscillations when exposed to specific wavelengths of light, allowing for the detection of subtle refractive index changes in the surrounding medium. This characteristic is essential for high-sensitivity biosensing. Additionally, their high surface area to volume ratio facilitates the attachment of numerous biomolecules, improving sensor performance. Fungal-mediated synthesis techniques offer precise control over nanoparticle size and shape, further enhancing surface area and making them highly effective for sensing applications. Moreover, Au NPs are biocompatible and nontoxic allowing functionalization with biomolecules like antibodies, DNA, and peptides without affecting their biological compatibility and making them ideal material for medical and environmental sensing. Summary of different types of gold nanoparticle biosensors. Reproduced from ref . Copyright 2018, with permission of Elsevier. Plasmonic solar cells are an advanced type of photovoltaic technology that utilize the unique optical properties of metal nanoparticles (usually gold, silver, or aluminum) to enhance light absorption and increase solar cell efficiency ( Table ). The key concept behind plasmonic solar cells is the Surface plasmon resonance (SPR), which refers to the collective oscillation of conduction electrons at the surface of metal nanoparticles when excited by incident light. Studies have shown that the incorporation of plasmonic nanostructures in solar cells significantly enhances their power conversion efficiency (PCE). The improvement in PCE largely depends on the type of solar cell, the material used, the shape and size of plasmonic nanoparticles, and their position within the device structure. Gold nanoparticles, despite having lower heat-generation capability than silver or copper, are preferred due to their chemical stability and resistance to oxidation. Heat generated through plasmonic effects is transferred from the nanoparticle to the surrounding medium, affecting the local temperature and thus enabling various applications such as photothermal therapy, catalysis, and sensing. Gold nanoparticles have gained attention in recent years for their multifunctional role in nanomedicine, particularly in drug delivery and theranostics. Their unique ability to be tailored in different size and shapes influences their efficiency in imaging, drug encapsulation, and targeted therapeutic applications. One of the notable uses of AuNPs in veterinary medicine is in rapid disease detection. Moongkardi et al. developed an immunochromatographic assay for detecting bacterial infections such as Salmonella enterica serovars Typhimurium and Enteritidis, in poultry. These assays provide a quick and reliable means of identifying pathogens and can help to improve food safety and animal health. Similarly, AuNPs-biosensors have been employed for the detection of haptoglobin in mastitic milk, thus helping in early detection of subclinical mastitis in dairy cows. AuNPs also play a crucial role in antimicrobial applications. Kumar et al. developed gold nanoparticle-based immunogens for the detection of colistin, a critical antibiotic in veterinary medicine in chicken liver samples. Additionally, AuNPs have been investigated for extending the shelf life of chilled minced meat by inhibiting bacterial growth, particularly against E. coli and Salmonella. In therapeutics, AuNPs have been studied for targeted drug delivery and immunomodulation. Loghmani et al. developed betaine-conjugated AuNPs in a murine model of heatstroke, where they significantly reduced inflammation and oxidative stress by modulating cytokine levels and enhancing immune function Moreover, they are also integrated into regenerative medicine strategies, such as stem cell therapy tracking and tissue repair, demonstrating their potential for veterinary application. The role of AuNPs in role regeneration and dental applications has also been explored, with studies investigating their ability to enhance osseointegration of dental implants in rabbit models. Furthermore, AuNP-based hydrogels have been developed for use in regenerative medicine, providing a biocompatible scaffold for tissue engineering applications. Modern healthcare prioritizes increasing patient survival rates and improving quality of life, with a key focus on developing implantable materials that can mimic natural biological functions. Currently a range of materials such as metals, ceramics, carbon nanostructures, and polymers are widely used in orthopedic and oncological surgeries. However, these materials face challenges such as limited strength, poor biointegration, metal ion diffusion, and toxicity from degradation byproducts. To mitigate these complications, researchers are developing bioactive surface treatments that provide antimicrobial protection Several studies of use for titanium and titanium-based alloys are being reported. Noble metals like platinum, palladium, silver, and gold have gained attention due to their exceptional biocompatibility, resistance to corrosion, and antibacterial properties. Coating implant surfaces with ultrathin layers or nanoparticles of these metals has demonstrated benefits in promoting bone integration and reducing inflammation Due to its biocompatibility, and chemical and corrosion resistance in biological environments, metallic gold and its alloys are being used for implants and surgeries. There are two primary forms of gold known for their antibacterial properties. The first is nanoporous gold (NPG), which features a highly porous structure at the nanometre scale. This unique morphology enhances its surface area, enabling effective interaction with bacterial cells. Studies have demonstrated that gold nanoparticles exhibit antimicrobial effects against E. coli and Staphylococcus epidermidis , making it a promising material for medical and biomedical applications. Solanki et al. synthesized AuNPs using Triphala extract which were found to be biocompatible and possess strong antimicrobial properties, making them a potential alternative for oral care products. Researchers evaluated the cytotoxicity of these nanoparticles and an AuNP-based mouthwash using the Artemia salina (brine shrimp) assay. The mouthwash exhibited mild toxicity at higher concentrations (40–50 μL), with a mortality rate of 46.6%. At lower concentrations (20–30 μL), the mouthwash was found to be safe and effective, suggesting its suitability for use in orthodontic patients. Another study suggested that gold nanoparticles (AuNPs) enhance the biocompatibility, proliferation, and antioxidant properties of dental biomaterials, making them suitable for tissue regeneration and restorative applications Biz et al. combined gold nanoparticles with poly­( l -lysine) (AuNP-PLL) and introduced into dental pulp stem cells (DPSC) which resulted in high cellular uptake without compromising cell viability or inducing apoptosis. This highlights AuNPs’ potential for imaging and monitoring stem cells in regenerative endodontics Dharman et al., synthesized gold nanoparticles using curcumin which demonstrated excellent antimicrobial and anti-inflammatory properties and can be used for treating oral infections and mucosal lesion Dalavi et al., synthesized spherical AuNPs (70 nm) using a microwave irradiation method which exhibited strong antioxidant activity and cytocompatibility with IMR-32 cells and thus can be used for cosmeceuticals and pharmaceutical application. Dentures, which serve as artificial, nonshedding surfaces in the oral cavity, are primarily composed of poly­(methyl methacrylate) (PMMA). AuNPs were synthesized via ultrasonic spray pyrolysis and incorporated into PMMA poly­(methyl methacrylate) to improve its physical and mechanical properties, additionally enhancing its antimicrobial properties. The modified material exhibited similar density and microhardness to conventional PMMA but demonstrated a significant reduction in monomicrobial biofilms of Candida albicans , Streptococcus mitis , S. aureus , and E. coli Another study incorporating gold nps with PMMA resulted in enhanced antifungal activity and improve oral hygiene for denture wearers. These nanocomposites demonstrated significant antifungal activity against Candida albicans at concentrations above 2.0%, with minimal ion release. Shelf life of food is one of the major global concerns for food loss which increases the importance of advanced packaging solutions. Nanotechnology, particularly metal-based nanoparticles, offers a promising approach to extending shelf life while addressing environmental issues. Nanotechnology in the food industry is predominantly used for processing, packaging, and detecting contaminants like toxins, microbes, pesticides, and food adulteration. Nanoparticles aid in enhancing the taste, smell, texture, look, and shelf life of food products, offering improved quality and safety throughout the supply chain. Green synthesis of gold nanoparticles (AuNPs) is gaining attention for its efficiency, reduced biohazards, and enhanced antimicrobial and antioxidant properties which will be beneficial for food packaging ( Table ). These have remarkable antioxidant, antibacterial, antifungal, anticancer, and barrier properties along with being inert, nontoxic, hypoallergenic nature and biocompatible to humans. AuNPs can be incorporated into smart packaging systems to improve food safety, quality monitoring, and shelf life. However, factors such as nanoparticle concentration, food type, polymer composition, and storage conditions influence their effectiveness and migration into food, necessitating careful evaluation for safe application in packaging. One of the unique properties of AuNPs particularly are surface plasmon resonance (SPR), peroxidase-like activity and their influence on sensing performance. SPR-based sensors include aggregation, antiaggregation, etching, and growth-based methods, each with varying sensitivity and selectivity. Peroxidase-based (nanozyme) sensors offer a higher sensitivity but involve complex protocols. Smaller AuNPs (10 nm) improve SPR-based detection. Despite strong potential, colorimetric sensors are less explored than electrochemical ones for inorganic ion detection. AuNP-based colorimetric sensors offer a simple, fast, and cost-effective method for food safety monitoring without any need for complex equipment. However, challenges remain, including interference from food matrices and the need for specific ligand modifications to enhance selectivity and sensitivity. Future advancements should focus on improving analyte extraction, developing highly specific aptamers, and incorporating signal amplification strategies to enhance detection in real-world food safety applications. Biogenic NPs improves the food shelf life and can serve as biosensors for real-time quality assessment. While promising, challenges remain regarding nanoparticle migration into food and potential toxicity, requiring further research to ensure safety in food-related applications. Sreelakshmi et al. explored the use of chitosan, derived from shrimp waste, as a reducing and capping agent in synthesizing gold nanoparticles (AuNPs) for smart packaging applications in the food and pharmaceutical industries. The reduction time for gold atoms varies depending on the chitosan type, ranging from 6 to 15 min. Higher concentrations of chitosan give rise to smaller, more uniform AuNPs. When exposed to freezing conditions (−18 °C ± 1 °C), the ruby red color of AuNPs shifted to bluish or colorless, which indicates the temperature fluctuation. This visible change confirms the potential of chitosan-based AuNPs as indicators for distinguishing between fresh and frozen products. Alghamdi et al. had also done a study which focuses on developing bionanocomposite films by incorporating gold nanoparticles (AuNPs) into a chitosan (CS) and polyacrylamide (PAM) polymer blend by application of solution casting method. AuNPs were synthesized using Chenopodium murale leaf extract. XRD analysis revealed a crystallinity reduction and an increase in amorphousness by addition of AuNPs. TEM images showed nearly spherical AuNPs, while FTIR spectra confirmed strong interactions between the nanoparticles and the polymer matrix, which was indicated by shifts and intensity changes in functional group bands. UV–vis analysis showed a decrease in both direct and indirect bandgap energies, along with an increase in Urbach energy, reflecting enhanced optical properties. TGA results showed improved thermal stability in Au-CS/PAM composites in comparison to the pure blend. Mechanical testing showed enhanced Young’s modulus, tensile strength, and elongation at break. Additionally, Au-CS/PAM nanocomposites exhibited impressive antimicrobial and antioxidant activity, pointing to their usefulness as active food packaging materials and in optoelectronic applications. Choudhary et al. conducted a study, where poly­(vinyl alcohol) (PVA) composite films incorporating gold nanoparticles (AuNPs) and graphene oxide (GO) was developed and cross-linked using glyoxal or glutaraldehyde (GA). FTIR analysis confirmed effective cross-linking through reduced hydroxyl group transmittance. The addition of AuNPs and GO enhanced mechanical and physical attributes such as tensile strength, Young’s modulus, water vapor transmission rate (WVTR), and water solubility. WVTR tests revealed that nanofillers contributed to reduced permeability by forming a complex, tortuous structure. SEM images showed compact pore morphology in cross-linked films in comparison to pure PVA. Antibacterial activity was observed in both AuNPs- and GO-based composites against E. coli , with PVA-glyoxal-AuNPs films showing a major inhibition zone, indicating superior antimicrobial performance. Besides that, this film extended the shelf life of bananas more effectively than others, confirming its potential for food packaging. In conclusion, the PVA-glyoxal-AuNPs composite exhibited promising structural, antimicrobial, and preservative properties for advanced food packaging applications. Mehmood et al. highlighted the potential of gold nanoparticles (AuNPs) conjugated with gallic acid (GA) as an effective strategy to combat reactive oxygen species (ROS), a major factor in packaged food spoilage. Amine-stabilized AuNPs were synthesized and functionalized with GA from Caesalpinia pulcherrima extract, reducing toxicity and improving antioxidant efficiency. GA-AuNPs exhibited a strong free radical scavenging ability, shown by cyclic voltammetry, with a low IC 50 (4 × 10 –9 g/mL) and high antioxidant coefficient. Even though antimicrobial activity was minimal, GA-AuNPs achieved 94.1% DPPH scavenging, outperforming GA and its derivatives. The study confirms GA-AuNPs to be a safe, multifunctional material for extending food shelf life and serving as a nontoxic antioxidant carrier in food packaging applications. Yang et al. developed a novel ratiometric electrochemical sensor for the simultaneous detection of two endocrine-disrupting compounds (EDCs) as 17β-estradiol (E2) and bisphenol S (BPS), using a composite of gold nanoparticles (AuNPs) and MIL-101­(Fe). Traditional electrochemical sensors have been commonly facing challenges in detecting EDCs in food due to poor reproducibility. To tackle this problem, the sensor utilized the Fe signal inherent to MIL-101­(Fe) as a built-in internal reference, replacing the need for external electroactive tags which are commonly used in ratiometric sensing. AuNPs were electrodeposited onto MIL-101­(Fe), which resulted in a composite material with enhanced electrochemical properties. The stability of the Fe reference signal and the oxidation responses of E2 and BPS has remarkably boosted due to synergistic effect between AuNPs and MIL-101­(Fe).The developed sensor has a wide linear detection range from 0.039 to 7.80 μM and achieved low detection limits of 9.8 nM for E2 and 11.2 nM for BPS. Application in milk sample analysis confirmed the sensor’s excellent reproducibility, sensitivity, stability, and practical performance. This work provides a promising direction for constructing ratiometric electrochemical sensors with the use of electroactive MOFs for rapid and accurate EDC detection in food safety monitoring. The synthesis of nanoparticles (NPs) has garnered significant attention due to their distinctive properties, which make them valuable for a wide range of applications, including composite fibers, biosensors, cryogenic superconducting materials, cosmetics, and electronic components. However, in light of climate change and the depletion of natural resources, there is a growing emphasis on sustainable methods for producing gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs). One promising approach involves using plant extracts, particularly agricultural waste, as a green and eco-friendly alternative. This method aligns with sustainable development goals in agro-industrial practices. Given that plants serve as the foundation for this green synthesis, the resulting NPs are not only environmentally friendly but also exhibit low toxicity, making them suitable for various agricultural applicationsfrom soil treatment to food chain integration. , In June 2009, the Food and Agricultural Organization (FAO) and the World Health Organization (WHO) highlighted the potential of nanotechnology in food and agriculture. Their joint initiative identified several key areas for innovation, including nanostructured ingredients, nanosized biofortification, food packaging, nanocoating, and nanofiltration. NPs can boost productivity of specific plant tissues or structures by beneficial genes, delivering nutrients, or organic compounds. This capability positions NPs as advanced nanodelivery systems, specifically for enhancing crop nutrition and agricultural efficiency. In agriculture, AuNPs have been extensively studied for their direct applications, which include improving seed germination, promoting root growth, and understanding plant responses to metal NPs, also cellular oxidative stress and cytotoxicity. Nanofertilizers and nanopesticides are also being developed by direct use of metal Nanoparticles. Indirect applications of nanoparticles (NPs), using their antimicrobial properties, are primarily centered on advancements in food packaging. These advancements have been extensively imparted in the agricultural industry, with AuNP based products typically incorporating particles ranging from 100 to 250 nm in size, this size range enhances their water solubility and overall effectiveness. In short, the embedding of NPs into agriculture and food systems represents a novel and transformative approach, offering solutions that are both innovative and aligned with sustainability principles. Water is a vital part of the ecosystem and its treatment highlights the need. Several techniques have been developed for this purpose. Agriculture accounts for almost 70% of the world’s renewable water resources which makes it important to consider for wastewater treatment of agricultural water. In order to enhance sustainable agricultural practices, it is necessary to assess the impact of agro nanobiotechnology on water conservation and its quality. To enhance sustainability and efficiency Nanotechnology is gaining attention in agriculture. A notable approach is the development of gold nanoparticles through environmentally friendly biogenic synthesis using natural sources like plants, fungi, and bacteria. These nanoparticles have strong antibacterial and antifungal properties, making them useful in safeguarding crops from harmful pathogens. Moreover, they can aid in pesticide detection and water purification, promoting safer and more effective farming methods. By incorporating nanotechnology into agricultural practices, researchers strive to improve crop protection and optimize resource use while maintaining environmental responsibility. Water pollution caused by nitrophenol, a nitrogen-containing pollutant, creates significant environmental concerns. A novel approach using thiourea-treated gold nanoparticles (AuNPs) to create nanoporous films via filtration was explored for efficient catalytic degradation of nitrophenol into the less toxic aminophenol. The study found that AuNP films treated with 20 μg/mL thiourea and 1000 mM NaBH 4 facilitated rapid conversion within 150 s. These films demonstrated remarkable structural stability and retained 90% catalytic efficiency after seven cycles. The stable mesoporous AuNPs film results in a cost-effective and sustainable solution for industrial wastewater treatment, making it a promising strategy for environmental remediation. A study by Francis et al. utilized a rapid microwave-assisted method to synthesize gold and silver nanoparticles using Mussaenda glabrata leaf extract as a reducing and stabilizing agent. Characterization techniques, including UV–vis, FT-IR, XRD, TEM, and AFM, confirmed the nanoparticles’ FCC crystal structure. Both nanoparticles exhibited strong antioxidant activity and antimicrobial properties against pathogens like Pseudomonas aeruginosa and E. coli . They showed effective degradation of pollutants such as rhodamine B, methyl orange, and 4-nitrophenol, making them promising catalysts for wastewater purification. Agriculture plays a vital role worldwide by ensuring food security and economic stability. Traditional ways for boosting crops include the usage of chemical fertilizers, insecticides, and herbicides. However, excessive use of these agrochemicals has led to soil degradation, loss of biodiversity, and environmental concerns. Nanotechnology approaches are used to enhance crop production, improve food security, and develop pest- and drought-resistant crops. Nanoengineered materials improve nutrient absorption, enable rapid disease detection, and function as nanofertilizers and nanopesticides, boosting productivity while minimizing soil and water contamination. These materials also protect against microbial diseases and pests which reduces chemical use and nutrient loss. Additionally, nanotechnology aids in soil quality monitoring, ensuring optimal crop yields. Ongoing research in agricultural nanotechnology is being used to enhance food quality, safety, and efficiency, supporting sustainable agricultural practices for a growing global population. Its applications have been used across multiple areas, such as precision farming, food preservation, and plant protection, due to the distinctive properties of nanomaterials. These materials are known for their controlled-release capabilities, targeted action on specific sites, and large surface area, making them highly efficient in agricultural use. Nanofertilizers, nano herbicides, and nano pesticides enhance plant growth, optimizing nutrient absorption, and provide effective pest and weed control, ultimately leading to higher yields with very less environmental impact. Over the past decade, nanotechnology in agriculture, specifically nanofertilizers and nanopesticides, has gained attention for its potential to transform farming. This analysis has reviewed scientific, regulatory, and commercial progress, highlighting emerging products, differing sector perceptions, and the challenge of risk-benefit assessment. It focuses on the need for improved formulations, clearer definitions, and smarter, sustainable agrochemical development. Nanotechnology has a vital role in expanding textile applications across various fields, such as protection, fashion, sports, healthcare, the military. By modifying textiles at the nanoscale with functional nanomaterials, it is possible to introduce new features while maintaining their comfort and usability. The textile industry has greatly advanced with the introduction of new applications, especially when combined with nanomaterials. Different types of textilessuch as woven, knitted, and nonwoven fabrics, as well as fibers, yarns, threads, nanofibers, scaffolds, and membranesare now used in high-tech and smart applications. Adding gold nanoparticles (AuNPs) to textiles brings exciting new features, including unique colors, improved filtration, antimicrobial properties, conductivity, UV protection, sensory functions, and catalytic abilities, as explored in this section. Chemical reduction is one of the most used methods for production of textile-fictionalized gold nanoparticles (AuNPs), due to its effectiveness and simplicity. However, there is a growing shift toward greener and more cost-effective alternatives. Traditionally, researchers follow a two-step functionalization approach, where AuNPs are first synthesized and then applied to fabrics. Alternatively, some opt for an in situ approach, where synthesis and deposition occur in a single step. In the two-step method, sodium borohydride (NaBH 4 ) and sodium citrate used as common reducing agents. Various deposition techniques have been explored, such as dropwise deposition, exhaustion, padding, impregnation, and printing with AuNP dispersions. For example, Chan et al. (2016) synthesized AuNPs using chloroauric acid (HAuCl 4 ) as the precursor, NaBH 4 as the reducing agent, and sodium citrate as a capping agent. They applied the nanoparticles to cotton, silk, and wool fabrics using the dropwise deposition method. Zheng et al. synthesized Gold nanoparticles (AuNPs) via citrate reduction, were immobilized onto chitosan-treated soybean knitted fabric by use of the exhaustion method. Moderately polydisperse AuNPs had an average size of ∼35 nm. Successful immobilization was confirmed through spectrophotometric reflectance, X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). XPS analysis showed strong AuNP-chitosan binding. The coated fabrics exhibited enhanced thermal stability, ultraviolet protection (UPF 50+), and antimicrobial properties, effectively reducing S. aureus (99.94%) and E. coli (96.26%) adhesion. The coating also displayed durability, withstanding five washing cycles with minimal AuNP loss with additional benefit of coloration. XPS analysis suggested AuNPs bound to chitosan in a pure metallic state, though potential antimicrobial mechanisms involving oxidized Au species and reactive oxygen species require further study. These multifunctional fabrics show promise for biomedical applications due to their UV shielding, optical properties, and antimicrobial effectiveness. Shanmugasundaram and Ramkumar has utilized keratin with silver and gold nanoparticles to develop antibacterial wound-healing materials. Human hair, a major waste from barbershops, contains keratin (a biocompatible protein) with wound-healing and antibacterial properties. The nanoparticles, synthesized by chemical reduction, were characterized using UV–visible spectroscopy, particle size, and ζ-potential analysis. Silver and gold nanoparticles formed at 420 and 479 nm with average sizes of 71.8 and 14.59 nm, respectively, and negative ζ-potential values of −18.9 and −3.2 mV. FTIR confirmed the presence of keratin and nanoparticles in coated cotton fabrics. SEM images showed uniform, high-density coatings, while EDX confirmed high oxygen and carbon content. The coated fabrics exhibited excellent physical properties, such as air permeability, moisture content, and water absorbency. Additionally, they demonstrated superior antibacterial activity against burn wound bacteria, making them promising for biomedical wound-healing applications. Lin et al. synthesized Nylon fabrics through heat treatment with citrate assistance by in situ technique. The synthesized AuNPs impart bright colors to the fabrics due to their localized surface plasmon resonance (LSPR) properties. The optical characteristics were analyzed using color strength (K/S) curves, while SEM was used to observe surface conditions. The synthesis process was influenced by pH, with acidic conditions favoring AuNP formation. The treated fabrics exhibited excellent color fastness to washing and rubbing. Additionally, the coloration process significantly enhanced the UV-blocking properties of Nylon fabrics. This study provides both aesthetic and functional benefits, offering a promising approach for textile coloration and UV protection at the same time. Radić et al. conducted study that evaluated two ambient air plasma treatments including volume dielectric barrier discharge (DBD) and diffuse coplanar surface barrier discharge (DCSBD) to enhance gold nanoparticle (AuNPs) deposition on polypropylene (PP) nonwovens. Plasma treatments used to improve surface wettability and sorption, increasing AuNP loading from 17 mg/kg (untreated) to up to 62 mg/kg (DBD-treated). DBD enhances the surface roughness, while DCSBD induces notable chemical changes. Antibacterial tests showed effective activity against S. aureus and E. coli , with higher sensitivity observed in S. aureus . Surprisingly, rinsing enhances the antibacterial properties without reducing AuNP content, due to altered nanoparticle clustering. These findings suggest that AuNPs-loaded plasma-treated PP nonwovens are promising for reusable antibacterial materials, with the choice of plasma method influencing surface and functional properties. Ikegami et al. developed a novel filter-type Au/ZrO 2 catalyst using PET nonwoven fabric as a lightweight, flexible support, offering advantages over conventional catalyst forms. ZrO 2 particles were deposited with a silane agent to create a thin, fish-scale-like layer, followed by gold nanoparticle deposition. This catalyst effectively removed 1000 ppm of CO (83% conversion in 20 min) and 140 ppm formaldehyde (90% removal, 68% oxidized to CO 2 in 90 min) at room temperature. Nearly 100% removal of 0.5 ppm formaldehyde was found in tests simulating indoor conditions for up to 136 h, demonstrating strong performance and long-term effectiveness for air purification applications. A flexible and sensitive surface-enhanced Raman spectroscopy (SERS) substrate was developed by depositing uniform Au nanoparticles onto polydopamine-coated cotton fabrics using Ag nanoparticles as catalytic hotspots. The in situ reduction process produced a dense, even layer of AuNPs which was confirmed by SEM, XRD, and XPS analyses. The substrate, CF/Ag/PDA/Au, showed strong and reproducible SERS signals using 4-MBA as a probe, detecting concentrations as low as 10 –9 M. It also successfully detected carbaryl pesticide residues on cucumbers reduced to 10 –6 M, below regulatory limits. This work highlights the potential of CF/Ag/PDA/Au as a flexible, durable, and effective SERS platform for real-world food safety monitoring. Hence Gold Nanoparticles can be seen as a greener and sustainable approach in the textile industry. In this there is integration of gold nanoparticles (AuNPs) into textiles to create antimicrobial fabrics, emphasizing eco-friendly and effective synthesis and deposition methods. Two main electrochemical approaches have been identified: A two-step process involving separate AuNP synthesis and deposition, and a more efficient one-step in situ synthesis directly on textiles. While the in situ method saves time but still relies on chemical agents for gold reduction. Innovative techniques like plasma treatment and thermal activation using silk fibers have shown promise in enhancing nanoparticle adhesion and reducing chemical usage. These electrochemical strategies have the potential for scalable, low-toxicity fabrication of antimicrobial textiles, especially for biomedical and hygiene applications. However, more research is needed to optimize these methods and evaluate long-term safety and effectiveness. Over the past two decades, gold nanomaterials (AuNMs) have gained remarkable attention due to their unique catalytic properties at the nanoscale. Electrodeposition is a highly controllable synthesis method, commonly used to create gold nanoparticles, nanoclusters, and nanowires. Enhancing both activity and stability by designing monodisperse nanoclusters, multimetallic nanoparticles, and tailoring surface-support interactions is an important area in this. AuNMs have illustrated versatility in chemical, photochemical, and electrochemical catalysis. Their biocompatibility also finds usage in biomedical, such as drug delivery and photodynamic cancer therapy. These advancements position AuNMs as highly promising materials for diverse applications across scientific field. A Study by Zhang et al. showed the development of self-healing and conductive elastomer for wearable sensors. The material consists of poly­(dimethylsiloxane) (PDMS) and gold nanoparticles (AuNPs) by utilizing sulfur–gold (S–Au) interactions. When AuNPs are exposed to near-infrared (NIR) light, the material repairs itself by achieving healing efficiency of 92%. The elastomers exhibit electrical conductivity and strain sensitivity, making it suitable for applications such as monitoring human joint movement and muscle activity in health monitoring and soft robotics. Another study depicted a wearable strain sensor based on the ligand-exchanged AuNPs for detecting human motion. It consists of thin layer of 9 nm gold nanoparticles (AuNPs) deposited on a poly­(dimethylsiloxane) (PDMS) substrate, offering high flexibility and sensitivity capturing small movements of fingers and wrist. With the help of the ligand exchange the conductivity is enhanced, making it well suited for biomedical applications. Another study by Khorablou et al. depicts highly sensitive and flexible sensor which detects methadone. It is built using gold nanoparticles (AuNPs) and polythiophene on a carbon cloth platform, improving sensitivity and enhancing electron transfer. It showed successful application in human blood and urine samples which helps to demonstrate real-time drug detection. For instance, another study discusses about the advancement of wearable sensor for detecting cardiovascular disease (CVD). AuNPs enhance the sensors’ conductivity, sensitivity, and biocompatibility allowing to monitor vital signs like pulse waves, heart sounds, and electrocardiogram (ECG) signals. Their integration into flexible, lightweight material supports real-time health tracking and early cardiovascular disease detection. They offer potential applications in continuous, noninvasive diagnostics and personalized healthcare. A study by Chen et al. demonstrates a wearable electrochemical biosensor utilizing gold nanoparticles (AuNPs) for in situ pesticide detection on crops. It is built on a flexible fiber membrane, a three-electrode system modified with acetylcholinesterase (AchE) and reduced graphene oxide (rGO) to enhance performance. It detects methyl parathion with a low detection limit of 0.48 ppb, providing a rapid and nondestructive method for agricultural monitoring. The development of wearable strain sensors using cross-linked gold nanoparticles (AuNPs) via contact printing method. These sensors are integrated into flexible polyimide (PI) and poly­(dimethylsiloxane) (PDMS) substrates. They demonstrate high strain sensitivity, durability over 10,000 usage cycles, and a rapid response making them well-suitable for healthcare applications. Another study depicted implantable sensors using AuNPs present hydrogel-embedded sensors for continuous biomarker monitoring. They utilize plasmon resonance shifts to detect analyte concentrations through the skin. The tests on anesthetized rats successfully detected kanamycin levels, depicting long-term stability and integration into tissue. A study by Chen et al. demonstrated a wearable glucose sensor designed for continuous monitoring through human sweat, incorporating gold nanoparticles (AuNPs) with aminated multiwalled carbon nanotubes (AMWCNTs) and cross-linked with XSBR and PEDOT: PSS. Integrated onto screen-printed electrodes, it shows high sensitivity, flexibility, and stability making it a potential tool for health tracking and diabetes management. The wearable capacitive sensor designed to monitor leaf moisture was created by depositing gold nanoparticles (AuNPs) onto a poly­(ethylene terephthalate) (PET) membrane using magnetron sputtering, ensuring stable conductivity and adaptability to plant surfaces. The change in capacitance provides a noninvasive method for assessing plant hydration. It has promising applications in agriculture and environmental monitoring. For instance, a study by Wang et al. introduced a sweatband sensor capable of real-time sodium ion, incorporating an all-solid-state ion-selective electrode (ISE) and a reference electrode (RE) by ensuring high sensitivity and stability. It is fabricated via electrodeposition on a flexible substrate, allowing continuous monitoring of hydration levels and electrolyte balance, showing potential applications in personalized healthcare, sports science, and medical diagnostics. A similar study by Dau et al. developed a wearable colorimetric sensor for glucose detection in sweat, integrated with an automated microfluidic chip. It features a glass fiber-based electrode enhanced with gold nanoparticles (AuNPs), improving color stability and sensitivity. This device is designed for continuous health track monitoring, diabetes management, and personalized healthcare applications. Gold nanoparticles (AuNPs) are used in biomedicine due to their high stability, biocompatibility, and flexible properties ( Table ). They play an essential role in drug delivery, biosensing, imaging, and photothermal therapy. Their surface modification enables targeted therapeutic applications by reducing its side effects. Advancements in nanotechnology are enhancing their efficiency for clinical use, medicine, and disease treatment. The plasmonic gold nanoparticles (AuNps) focus on the optical properties, method of synthesis and various biomedical uses. Their plasmonic properties enhance diagnostic techniques such as surface-enhanced Raman spectroscopy (SERS). A study by Oladipo et al. discusses about the biosynthesis of gold nanoparticles (AuNPs) using Datura stramonium seed extract. It is characterized via UV–vis, FTIR, SEM, and EDX, and depicted antifungal, antioxidant, anticoagulant, and thrombolytic activities. They are effective in inhibiting fungal growth, neutralizing free radicals, prevented blood coagulation and clot dissolution. It shows potential applications in biomedicine, particularly for antimicrobial and cardiovascular treatments. For instance, study by Clarance et al. depicted the synthesis of gold nanoparticles (AuNPs) using endophytic fungus Fusarium solani . AuNPs were characterized via various techniques and potent anticancer properties against breast cancer (MCF-7) and cervical (HeLa) cells. The biosynthesized AuNPs were found to trigger apoptosis, block cell proliferation, and induce cell cycle arrest. It shows potential chemotherapeutic agents. Another study by Das et al. explores the synthesis of gold nanoparticles (AuNPs) using Amaranthus plant extract. They exhibit various biomedical applications such as drug delivery, bioimaging, and antimicrobial activity. It shows antioxidant and anticancer properties making is well suited for therapeutic use. The research shows potential applications in nanomedicine, enhancing biocompatible nanomaterials for advanced medical treatments. Gold nanoparticles (AuNPs) have significant applications in nanoelectronics due to their excellent conductivity, stability, and customizable optical properties. They are used in sensors, transistors, and memory devices, allowing miniaturization and enhanced performance of electronic components. Functionalized nanoparticles with organic molecules further improve the efficiency of device and their self-assembly properties, making them ideal for nanocircuit fabrication. GNPs contribute to flexible electronics and molecular-scale computing, forwarding next-generation nanoelectronics technologies. A study by Babajani et al. focuses on the controlled stabilization in heterometallic nanogaps. They use various fabrication techniques, surface modifications, and their influence on electrical characteristics. It shows advanced nanoscale electronics, enabling advancements in molecular circuits, sensors, and quantum devices by distinctive optical and electronic characteristics. Another study investigates the electroless deposition (ELD) of silver thin films on SiO 2 /Si surfaces activated by AuNPs. It depicted successful Ag film growth through distinct stages by improving their electrical and optical properties. AuNPs provide a cost-effective, result in rougher films as compared to traditional palladium activation. It improves film quality by using smaller AuNPs to refine surface morphology and conductivity. A similar study by Ruiz et al. demonstrates the use of DNA origami as a template, leveraging the self-assembling properties of DNA developing nanoscale and circular metallic structures. They enable the precise placement of gold nanoparticles, crucial for miniaturized electronic devices. The fabrication process using atomic force microscopy and gel electrophoresis, depicts the potential of DNA origami for future nanoelectronics application.

The current era is observing a widespread use of nanotechnology and nanomaterials. The ever-increasing demand has motivated researchers to explore and develop novel nanomaterials with enhanced properties for diverse applications. , Nanotechnology is highly versatile, with applications spanning multiple fields such as electronics, sensors, optics, mechanics, catalysis, chemistry, cosmetics, pharmaceuticals, medicine, biomedical sciences, food technology, and environmental science. − Metal nanoparticles are extensively utilized across various industries due to their exceptional physicochemical properties, , including a high surface-area-to-volume ratio, enhanced catalytic activity, and tunable optical and electronic characteristics. − Gold nanoparticle chemistry and physics have developed into a significant subdiscipline within the field of nanotechnology and metal nanoparticles. The unique set of optical properties of small gold particles, the size-dependent electrochemical behavior, and their remarkable chemical stability have established them as the preferred model system for investigating a variety of phenomena. − Gold nanoparticles (AuNPs) are tiny gold particles, typically ranging from 1 to 100 nm synthesized through different methods such as physical, chemical, or green synthesis. They have the unique property of plasmon resonance, which enables applications in sensing, catalysis, imaging, and energy conversion. These properties are influenced by quantum effects and advanced physical processes. At the macroscopic level, gold is recognized for its distinct yellow color, chemical stability, and high redox potential. At the nanoscale, the properties of AuNPs ( Figure ) arise from a blend of its electronic structure and additional effects that are associated with its extremely small size. These include a high ratio of surface atoms to bulk atoms, electromagnetic confinement due to localized plasmon resonance when interacting with optical waves, and quantum effects, which, for example, account for the transition from metallic to semiconducting behavior. , Gold nanoparticles (AuNPs) have gained significant attention in theranostic applications for cancer therapy. In the biomedical field, they are used for highly sensitive biomolecular screening, selective destruction of cancer cells via photothermal therapy, targeted protein labeling, and specific cellular drug delivery. Various properties of gold nanoparticles (AuNPs).