Facile Fabrication of Hollow Ag-Au Alloy Nanostructures Directly on Filter Paper and their Enhanced Catalytic and Antibacterial Applications

Facile Fabrication of Hollow Ag-Au Alloy Nanostructures Directly on Filter Paper and their Enhanced Catalytic and Antibacterial Applications | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Facile Fabrication of Hollow Ag-Au Alloy Nanostructures Directly on Filter Paper and their Enhanced Catalytic and Antibacterial Applications Saima Shafique, Saira Arif, Unsia Batool, Israr Ahmed, Ghazanfar Ali Khan, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4236742/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Hollow noble metal alloy nanostructures have recently attracted great attention owing to their exceptional potential for various applications. These nanostructures are generally synthesized in solution. However, for several applications, their deposition on the substrate is needed. Herein, we present the novel synthesis of hollow Au-Ag alloy nanostructures directly on the filter paper. The synthesis was carried out in two steps. First, Ag nanostructures were directly grown on the filter paper by reducing the pre-deposited Ag ions with ascorbic acid, yielding Ag nanostructure substrate (AgNS-S). These NPs were subsequently etched with HAuCl 4 exploiting the galvanic replacement reaction (GRR), which yielded hollow Au-Ag alloy nanostructure substrate (HANS-S). Owing to the enhanced surface area and the presence of a high concentration of atoms in the low coordination state, these HANS-S showed excellent catalytic and antibacterial properties. In particular, the rate constants of the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), and the degradation of methyl orange (MO) increased by a factor of approximately 3.5 and 3.4, respectively, when employing HANS-S compared to utilizing AgNS-S. Similarly, the filter paper having hollow Au-Ag alloy nanostructures showed markedly superior antibacterial activity. While AgNS-S did not show any zone of inhibition (ZOI) outside the substrate, HANS-S showed notable ZOI for both S. aureus and E. coli , which verifies the antibacterial activity of these nanostructures against both Gram-positive and Gram-negative bacteria. Physical sciences/Engineering/Biomedical engineering Physical sciences/Nanoscience and technology/Nanobiotechnology Physical sciences/Nanoscience and technology/Nanoscale materials Biological sciences/Biotechnology/Nanobiotechnology/Nanofabrication and nanopatterning Biological sciences/Biotechnology/Nanobiotechnology/Nanoparticles Hollow alloy nanoparticles Au-Ag alloy nanoparticles galvanic replacement reaction (GRR) heterogenous catalysis antibacterial properties 4-nitrophenol methyl orange S. aureus E. coli Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Noble metal nanomaterials have attracted great attention driven by their immense potential across diverse fields including heterogeneous catalysis, and antibacterial applications. 1,2 The performance of these nanomaterials strongly depends on their size, shape, surface area, and chemical composition. 3–5 Consequently, a diverse array of colloidal nanostructures has been synthesized. Moreover, to further enhance the performance of these nanostructures, several methodologies have been devised to tailor their shape, such as modifying surface roughness or introducing hollowness to enhance surface area and energy. 6–8 Hollow nanostructures exhibit distinctive and unique properties that deviate significantly from their solid counterparts due to their unique morphology, enhanced surface area, and high reactivity. 9 Metal oxides are widely employed as catalysts to execute several reactions. 10 The catalytic action for these materials depends upon the activation of charge carriers through visible or ultraviolet light electromagnetic waves. 11 Conversely, metal NPs offer a distinct advantage by enabling electron transfer between a reducing agent and pollutants even without electromagnetic excitation, thereby simplifying the catalytic process. 12 The catalytic activity of metal NPs is markedly influenced by their dimensions, morphology, and surface imperfections. 13 Notably, NPs with hollow interiors have shown superior catalytic properties owing to their enhanced surface area and the presence of high concentration of highly active low-coordination atoms. 8,13,14 Another important focus of the metal NPs research is to combat bacterial infections. In this regard, Ag NPs have emerged as potent agents against a wide range of bacterial species. 15,16 They have demonstrated excellent activity against both Gram-positive and Gram-negative bacteria. 17 Their antibacterial activity is mainly attributed to the release of Ag ions, which upon interaction with bacteria cause cell death. 18 Another path of bactericidal activity is the adhesion and/or penetration of NPs to bacteria. 19,20 NPs can physically interact with bacterial cells by adhering to their surfaces through electrostatic forces, and hydrophobic interactions. 21,22 These interactions can lead to cell membrane disruption, compromising the integrity of the bacterial cell and causing cell death. Both adhesions to cells and Ag ion release are expected to improve with the increase in the surface energy of NPs. In this context, hollow or rough NPs due to a large surface area and high surface energy can be highly effective. Therefore, several recipes have been developed to synthesize NPs with hollow interiors. However, most of the synthesis methods are solution-based. The solution-synthesized NPs usually incorporate surfactants, a common practice to avoid their agglomeration within the solution and control particle size and shape. 3,23,24 However, the inclusion of surfactants comes with certain disadvantages. Primarily, the surface coverage of these surfactants around NPs constrains available adsorption sites, thereby compromising their catalytic, surface-enhanced Raman scattering (SERS), and antibacterial properties. 4,25,26 While multiple methods to remove surfactant molecules from NPs surfaces have been proposed, their implementation invariably introduces complexities. 27,28 Consequently, the development of facile techniques that are eco-friendly for the fabrication of surfactant-free catalysts is very important. Of particular intrigue is the innovative fabrication of these NPs directly on substrates, especially on filter paper. NPs on filter paper offer additional advantages, including catalyst recovery and reusability, wound dressing applications, and swab-based trace detection using SERS. 29–31 So far numerous techniques have been employed to directly grow NPs on filter paper which include drop casting, 32 chemical reduction approach, 33 successive ionic layer absorption and reaction 34 , immersion deposition, 35 thermal deposition, 36 and inkjet printing. 37 However, all these methodologies are primarily focused on the growth of solid NPs on the filter paper. We are not aware of any method that reports the direct fabrication of hollow and surfactant-free nanostructures on the substrate. Herein, we aim to bridge this gap by introducing a unique method for the growth of hollow Au-Ag alloy nanostructures directly on filter paper, potentially unlocking new possibilities for various applications. 2. Experimental Methods 2.1 Materials The chemicals used in this study were silver nitrate (Chem-Lab), chloroauric acid (Merck), ascorbic acid (Sigma-Aldrich), Sodium borohydride (Sigma-Aldrich), 4-nitrophenol (Sigma-Aldrich), methyl orange (Sigma-Aldrich), nitric acid (Sigma-Aldrich), and hydrochloric acid (Sigma-Aldrich). Deionized water was used to make all solutions. For the thorough cleansing of all glassware, aqua regia was used. The chosen substrate for the nanostructure fabrication is Whatman 41 ashless filter paper. For the antibacterial experiment, all culture media, glassware, containers, and micro tips were sterilized by autoclaving. 2.2 Synthesis of AgNS-S The Ag NPs were synthesized on filter paper using a wet chemical technique. In a typical experiment, a piece of filter paper measuring 4x4 cm² was immersed in a solution of AgNO 3 (0.2 M, 16 mL) for 1 minute. After this immersion, the filter paper was removed and dried on the hot plate at a temperature of 40°C. The substrate was then immersed in a freshly prepared solution of ascorbic acid (0.1 M, 16 mL), leading to an instantaneous reduction of Ag⁺ ions to Ag⁰. The prompt shift in the color of the filter paper from white to brown was an indication of the formation of Ag NPs on the filter paper. The resulting substrate containing Ag NPs was then thoroughly washed with deionized water three times to eliminate any residual unreacted reagents or loosely bound Ag NPs from the filter paper. The sequential depiction of these procedural steps is shown in schematics, Fig. 1 (a). Finally, the substrate was cut into four 2×2 cm² pieces for further etching experiments. 2.3 Fabrication of HANS-S A piece of 2×2 cm² AgNPs-S was immersed in a HAuCl 4 (0.06 M, 4 mL) solution for 2 min. Afterward, the substrate was removed from the solution and thoroughly washed three times with DI water. As a consequence of GRR, Au 3+ ions are reduced to Au⁰, while Ag atoms from the nanostructures oxidize to Ag⁺ ions. The GRR of Ag by Au on AgNS-S is schematically illustrated in Fig. 1 (b). Furthermore, the optical photographs of AgNS-S and HANS-S are shown in Fig. 1 (c). For comparative studies, AgNPs-S and HANS-S of the same batch were used. 2.4 Catalysis measurements The catalytic activity of our substrates was assessed for the reduction of 4-NP and MO. The experimental procedure involved the addition of 1 mL and 0.05 M of sodium borohydride to a solution containing 3 mL and 10 − 5 M of either 4-NP or MO. Following thorough mixing of the solution, the catalyst (2×2 cm²) was introduced, and the reaction's progression was monitored at regular intervals using UV-Vis spectroscopy. The UV-Vis spectra were taken after every 3 minutes in the UV-Vis spectral range of 200–600 nm. In order to test the catalytic reusability of our substrates, the substrate was retrieved with the help of a tweezer from the reaction mixture upon completion of the reaction. After recovery, the substrate was washed with deionized water and dried at 40°C on a hot plate. The substrate was then transferred to another reaction medium i.e., mixture of 4-NP and NaBH 4 . The whole process was repeated four times to test the reusability of our substrates up to five different cycles. 2.5 Antibacterial assessment The disk-diffusion method was used to examine the bactericidal effect by using clinical bacterial strains of Gram-negative E.coli and Gram-positive S. aureus . To perform the antibacterial assessment, our substrates were cut into 1x1 cm 2 size pieces. Typically, bacterial suspension was uniformly spread on the surface of nutrient Muller Hinton agar growth plates. The substrates were then carefully placed on top of the agar, while clean filter paper served as a negative control on each plate. The plates were then incubated at a temperature of 37°C for 18 hours. After the incubation period, digital images of the plates were captured and the ZOI surrounding the square samples were measured. The experiment was carried out in duplicate to ensure the reproducibility of the results. 2.6 Characterization The synthesized substrates underwent comprehensive characterization employing various analytical techniques. The diffused reflectance spectroscopy was employed to acquire reflection spectra of the synthesized substrates using UV spectrophotometer Shimadzu 2700. This was achieved by adjusting the spectrophotometer's wavelength range from 200 nm to 800 nm, maintaining a precise step size of 1 nm. To obtain a detailed understanding of the morphological attributes of the synthesized NPs deposited on filter paper, a scanning electron microscope (SEM) was utilized. Specifically, we utilized the FEI Nova NanoSEM 450 instrument for this purpose. The SEM was equipped with an Oxfor INCA XACT energy dispersive X-ray spectroscope (EDX) detector, facilitating the elemental composition analysis of our samples. The EDX was conducted utilizing an electron beam energy of 15 kV with an adjustable spot size of 6 mm. Transmission electron microscopy (TEM) measurements were conducted using Tecnai TEM 200kV. The TEM samples were prepared by sonicating a piece of substrate for 5 min to collect particles in solution. This was followed by the careful transfer of an aqueous droplet onto a carbon-coated TEM grid. Finally, the catalytic activity of our substrates was evaluated using a UV-1280 Shimadzu Spectrophotometer. 3. Result and Discussion Figure 2 (a) depicts the reflectance spectrum of the AgNS-S. The spectrum reveals a pronounced and substantial dip in reflectance, specifically centered at 414 nm, indicative of the plasmon absorbance of Ag NPs. This dip in the reflectance profile verifies that Ag nanostructures have been successfully fabricated onto the filter paper. Figure 2 (b) depicts the diffused reflectance spectrum of HANS-S. In this case, a prominent dip positioned at 526 nm in the reflectance spectrum is observed. It is noteworthy that the surface plasmon resonance (SPR) peak of Ag-Au alloy NPs is typically reported to fall within the range of 400 to 520 nm. 38 However, a distinction becomes apparent in the case of hollow NPs. The presence of a hollow core functions as a resonant cavity, leading to a redshift in the absorption peak or, alternatively, in the dip observed within the reflection spectrum. 38 In our case of HANS-S, the dip centered at 526 nm within the reflection spectrum supports the successful synthesis of HANS-S. The SEM image of the AgNS-S is depicted in Fig. 3 (a), which offers clear evidence of the nearly spherical shape of the Ag nanostructures that have been successfully formed on the surface of the filter paper. The average size of the Ag nanostructures on the AgNS-S is approximately 370 ± 45 nm. The SEM images of HANS-S are depicted in Fig. 3 (b, c). The images clearly show the near-spherical morphology of the nanostructures. The average size of the etched nanostructures is approximately the same as that of Ag nanostructures. A close-up view of these NPs (Fig. 3 (c)) shows that they have openings, which is indicative of the hollow interior. The hollow interior of the NPs can be better viewed in the TEM image depicted in Fig. 3 (d). The fabricated nanostructures clearly consist of a solid shell with a semi-hollow interior. The elemental composition of both AgNS-S and HANS-S was examined through EDX analysis, and the results are depicted in Figs. 2 (e) and 2(f) respectively. In the case of the AgNS-S, a distinctive and pronounced peak situated around 3 keV is observed in the spectrum, verifying the presence of Ag on the substrate. In the case of the EDX spectrum of HANS-S, the characteristic peaks of both Ag and Au are present, which verifies the Ag and Au bimetallic alloy composition of hollow NPs on the filter paper. By atomic percentage analysis, it is established that the composition of the alloy is 78.21% Ag and 21.79% Au. The direct growth of NPs on the substrate depends sensitively on the choice of reducing agents. The reducing agent plays a crucial role in controlling the size and morphology of NPs. Commonly employed reducing agents include NaBH 4 and ascorbic acid. In our previous study, we reported the successful fabrication of Ag nanostructures on filter paper utilizing NaBH 4 . 31 NaBH 4 is known for its strong reducing power which leads to instantaneous reduction of metal ions, yielding a high concentration of relatively smaller NPs, typically a few nanometers in diameter. In contrast, ascorbic acid is a milder reducing agent which provides a more gradual reduction of Ag + ions, allowing for a controlled growth of Ag NPs over time. This may lead to the fabrication of NPs of larger sizes as we have seen in this study. The formation of HANS-S was achieved by the well-known GRR. During this process, Au 3+ ions are reduced onto the surface of Ag NPs, which act as a sacrificial template. The reaction can be represented as follows 7 , Au 3+ + 3Ag 0 → Au 0 + 3Ag + ( 1 ) This reaction results in the reduction of Au ions to form Au atoms on the surface of the Ag NPs. For the addition of each Au atom, three silver atoms are removed from the NPs, which results in the formation of hollow nanostructures. 3.1 Catalysis To test the catalytic capability of our substrates, we employed the commonly used model reaction of the reduction of 4-NP to 4-AP. While the thermodynamics of reducing 4-NP in the presence of a reducing agent like NaBH 4 are inherently favorable, a significant kinetic barrier arises due to the substantial potential difference between the donor and the acceptor species. 7 To facilitate the reaction, metal NPs can play the pivotal role of an electron relay. This electron relay mechanism facilitates the transfer of electrons from the donor species BH 4 − to the acceptor 4-NP, effectively mitigating the kinetic barrier and thus enhancing the overall feasibility of the reaction. The UV-Vis absorption spectra at different times are depicted in Fig. 4 (a, b). A discernible peak is observed at 400 nm, which is due to the conversion of 4-NP to nitrophenolate anions with the addition of NaBH 4 , while a peak at 300 nm arises due to the presence of 4-AP. As time passes, there is a gradual decrease in the intensity of the peak at 400 nm and an increase in the intensity of the peak around 300 nm. These spectral changes, evolving over time, verify the conversion of the reactant 4-NP into the desired product, 4-AP. It can be clearly seen that the reaction is much faster when HANS-S is employed as a catalyst. In the case of AgNS-S, an observed 87% conversion to 4-AP was observed within 60 min. While for HANS-S, a higher conversion rate of 95% to 4-AP was observed in a mere 24 min. The graphs between ln (C t /C 0 ) and time are depicted in Fig. 4 (c). Here, C 0 and C t are the values of absorbance intensities at the start of the reaction and at the later time t , respectively. There is a clear linear correlation between the ln ( C t /C 0 ) and t , which verifies that the reaction follows pseudo-first-order kinetic using the relation. The apparent rate constant, k app , can be determined by the slope, as given by the following equation $$\text{l}\text{n}\left(\frac{{C}_{t}}{{C}_{o}}\right)=-{k}_{app}t$$ The values of the apparent rate constants for AgNS-S and HANS-S are 0.0341 min − 1 and 0.1178 min − 1 , respectively. Therefore, k app increased by about 3.5-fold when HANS-S was employed as a catalyst. In order to test our catalyst for the catalytic reduction of dyes, we have further studied the reduction reaction of MO by NaBH 4 in the presence of catalyst. As depicted in Fig. 5 (a, b), MO has a strong characteristic absorption peak at 464 nm. The peak’s intensity gradually decreased after the catalyst was inserted in the reaction medium. When AgNS-S was employed as catalysts, 90% of the reaction was completed within 50 min. However, for HANS-S, the MO peak completely disappeared within 28 min, indicating the completion of the reaction. Furthermore, given the excess of NaBH 4 concentration relative to the MO, the reaction follows the dynamics of pseudo-first-order kinetics. Similar to the previous case, there is a good linear correlation between the ln ( C t /C 0 ) and t (see Fig. 5 (c)), which verifies pseudo-first-order kinetic in this case as well. The calculated apparent rate constants were found to be 0.0438 min − 1 for the AgNS-S and a notably higher value of 0.1481 min − 1 for the HANS-S. Hence, the utilization of HANS-S for catalysis results in an approximately 3.4-fold increase in the value of k app . The synthesized catalytic substrates exhibit an array of remarkable features that elevate their catalytic performance. As previously mentioned, surfactants, while useful in stabilizing NPs in colloidal suspensions, can hinder catalytic reactions by blocking active sites. 4 Therefore, the surfactant-free nature of both of our substrates ensures a pristine surface, allowing reactant molecules to interact directly with the active sites. However, the key attributes that sets HANS-S apart from AgNS-S are the enhanced surface area and the presence of high concentrations of low-coordination atoms. These factors, combined with the absence of the surfactant, make HANS-S an excellent candidate for catalytic applications. The reusability of substrates plays a pivotal role in determining the viability of catalysts for their widespread adoption in both industrial and commercial applications. Furthermore, the capacity for substrates to withstand multiple cycles of catalytic reactions without significant deterioration is essential, not only for cost-effectiveness but also for minimizing environmental impact by reducing waste. The assessment of HANS-S reusability was conducted using testing the catalyst for five cycles of 4-NP reduction reaction. Figure 5 (d) depicts the comparative log plot of the first and fifth catalytic cycles. It was observed that there is only about a 12% change in catalytic activity. This is due to less NP leaching which can be ascribed to the improved stability of the NPs deposited on the filter paper, ensuring that a higher proportion of them remain bound to the substrate, even after multiple catalytic cycles. The supporting filter paper is enriched with hydroxyl and carboxyl groups, which provide binding sites for NPs, thereby ensuring their robust attachment to the filter paper 31 . 3.2 Antibacterial activity The antibacterial evaluation of both AgNS-S and HANS-S was conducted against E. coli and S. aureus . Figure 6 (a, b) depicts the image of the bacterial growth of E. coli and S. aureus , respectively, in the presence of our substrates. In both cases, there is no bacterial growth under the substrate pieces. However, for AgNS-S, no inhibition of growth was observed beyond the substrates' surface. On the other hand, HANS-S exhibited higher antibacterial activity with ZOI spanning significantly beyond the substrate’s surface, which indicates a more potent inhibitory effect on bacterial growth. The limited antibacterial activity of AgNS-S can be assigned to the bigger size of Ag NPs, which limits the quick release of Ag + ions. The reduced size of Ag NPs enhances the release of Ag + ions, attributed to the increased surface area and higher surface energy. 39 Previous reports have clearly demonstrated that Ag ion release is highest for the smallest size of Ag NPs. 40 When the Ag NPs’ size is larger than 40 nm, both endocytosis and the release of Ag + ions are less effective for antibacterial activity. 41 The higher antibacterial activity of the HANS-S is in accordance with the previous studies in which solution-synthesized hollow Au-Ag alloy NPs have shown better antibacterial activity compared to the solid Ag NPs. 42 The enhanced activity of Au-Ag alloy NPs could be due to several factors. First, the higher electronegativity of Au pulls the electrons away from the Ag atoms present on the alloy surface making their free energy higher which in turn makes them more reactive and prone to oxidation compared to the case where Ag atoms are present on the surface of monometallic Ag NPs. Another impressive feature of HANS-S is its enhanced surface area. This combined with the higher free energy of Ag-Au alloy ensures an elevated release of silver ions from the HANS-S. The released Ag + ions directly interact with the cell membrane, increasing their permeability by creating pores, and perforation in the bacterium membrane. Harada et. al. reported a 3-fold higher release of Ag ions for the solution-synthesized hollow Au-Ag alloy NPs, compared with the solid Ag NPs 43 . The released Ag ions directly interact with the sulfur-containing cell proteins and periplasmic Ag-binding proteins. 44,45 These interactions lead to a change in the permeability of the protein membrane and its subsequent release causing cell death. 42 4. Conclusion We have developed a novel and straightforward method for directly growing hollow Au-Ag alloy NPs onto filter paper. We demonstrated that HAuCl 4 can be employed for GRR-induced etching of Ag NPs directly on the filter paper surface. The etching of Ag NPs provided an impressive enhancement of the catalytic activity. The apparent rate constants increased by 3.5-fold and 3.4-fold for the reduction reactions of 4-NP and MO, respectively. In reusability testing, a mere 12% decrease in conversion efficiency is observed for the HANS-S which verifies excellent binding of the particles to the filter-paper’s surface. The HANS-S has also shown better antibacterial action, compared to the AgNS-S. We attribute this enhanced performance to the increased surface area and electronic effects induced by the presence of Au atoms. These factors contribute to improved Ag + ion release from the nanoparticles' surface, resulting in more effective bacterial inhibition. Consequently, the HANS-S holds great promise for applications in both antibacterial and catalytic domains. Our innovative methodology can be employed for the direct fabrication of surfactant-free porous alloy nanostructures of other noble metals on substrates. This versatility underscores their potential for widespread advancements in various scientific and technological fields. Declarations Author Contribution Saima Shafique: Writing – original draft, Investigation, Formal analysis Saira Arif: Project administration, Supervision, Investigation, Formal analysis. Unsia Batool: Data Curation, Investigation, Formal analysis, Methodology. Israr Ahmed: Data Curation, Investigation, Methodology. Ghazanfar Ali Khan: Visualization, Formal analysis. Rabia Nawaz: Investigation Muhammad Imran: Supervision, Writing – review and editing Haider Butt: Funding acquisition, Resources, Supervision, Project administration Waqqar Ahmed: Conceptualization, Writing – review & editing, Funding acquisition, Supervision, Resources, Supervision Acknowledgement Saima Shafique: Writing – original draft, Investigation, Formal analysis Saira Arif: Project administration, Supervision, Investigation, Formal analysis. Unsia Batool: Data Curation, Investigation, Formal analysis, Methodology. Israr Ahmed: Data Curation, Investigation, Methodology. Ghazanfar Ali Khan: Visualization, Formal analysis. Rabia Nawaz: Investigation Muhammad Imran: Supervision, Writing – review and editing Haider Butt: Funding acquisition, Resources, Supervision, Project administration Waqqar Ahmed: Conceptualization, Writing – review & editing, Funding acquisition, Supervision, Resources, Supervision Data Availability All data generated or analysed during this study are included in this published article. References Sápi, A. et al. Metallic Nanoparticles in Heterogeneous Catalysis. Catalysis letters vol. 151 2153–2175 at https://doi.org/10.1007/s10562-020-03477-5 (2021). Rana, S. & Kalaichelvan, P. T. Antibacterial activities of metal nanoparticles. Antibact. Act. Met. Nanoparticles 11, 21–23 (2011). Suvith, V. S. & Philip, D. Catalytic degradation of methylene blue using biosynthesized gold and silver nanoparticles. 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Fabrication of flexible, cost-effective, and scalable silver substrates for efficient surface enhanced Raman spectroscopy based trace detection. Colloids and surfaces. A, Physicochemical and engineering aspects vol. 619 at https://doi.org/10.1016/j.colsurfa.2021.126542 (2021). Lee, M. et al. Subnanomolar sensitivity of filter paper-based SERS sensor for pesticide detection by hydrophobicity change of paper surface. ACS sensors 3, 151–159 (2018). Batool, A., Khan, G. A. & Ahmed, W. Seed-mediated growth of highly concentrated silver nanoparticles on a flexible substrate forapplications in SERS-based trace detection. Vib. Spectrosc. 123, 103438 (2022). Dubal, D. P. & Holze, R. A successive ionic layer adsorption and reaction (SILAR) method to induce Mn3O4 nanospots on CNTs for supercapacitorsElectronic supplementary information (ESI) available. See DOI: 10.1039/c2nj40862g. vol. 37 43–48 at https://doi.org/10.1039/c2nj40862g (2013). Wang, C., Liu, B. & Dou, X. 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Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4236742","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":291623313,"identity":"f3da19ce-ecbe-4360-a06b-11261024852c","order_by":0,"name":"Saima Shafique","email":"","orcid":"","institution":"COMSATS University","correspondingAuthor":false,"prefix":"","firstName":"Saima","middleName":"","lastName":"Shafique","suffix":""},{"id":291623315,"identity":"cf2e443b-3f6b-4695-8a16-510c4d5e5650","order_by":1,"name":"Saira Arif","email":"","orcid":"","institution":"COMSATS University Islamabad","correspondingAuthor":false,"prefix":"","firstName":"Saira","middleName":"","lastName":"Arif","suffix":""},{"id":291623316,"identity":"1639cb06-75be-4092-9747-b5641117fec3","order_by":2,"name":"Unsia Batool","email":"","orcid":"","institution":"COMSATS University","correspondingAuthor":false,"prefix":"","firstName":"Unsia","middleName":"","lastName":"Batool","suffix":""},{"id":291623318,"identity":"3733a09b-c573-456f-bebb-5e8b37602abd","order_by":3,"name":"Israr Ahmed","email":"","orcid":"","institution":"Khalifa University","correspondingAuthor":false,"prefix":"","firstName":"Israr","middleName":"","lastName":"Ahmed","suffix":""},{"id":291623319,"identity":"9406fe1c-6669-424b-a5f9-4b668b99d334","order_by":4,"name":"Ghazanfar Ali Khan","email":"","orcid":"","institution":"COMSATS University","correspondingAuthor":false,"prefix":"","firstName":"Ghazanfar","middleName":"Ali","lastName":"Khan","suffix":""},{"id":291623320,"identity":"7a093124-1373-4e72-9a6f-7a95c2d45674","order_by":5,"name":"Rabia Nawaz","email":"","orcid":"","institution":"COMSATS University Islamabad","correspondingAuthor":false,"prefix":"","firstName":"Rabia","middleName":"","lastName":"Nawaz","suffix":""},{"id":291623321,"identity":"5c572c8d-3242-414c-b87e-0e057bb7f672","order_by":6,"name":"Muhammad Imran","email":"","orcid":"","institution":"COMSATS University Islamabad","correspondingAuthor":false,"prefix":"","firstName":"Muhammad","middleName":"","lastName":"Imran","suffix":""},{"id":291623322,"identity":"2eca202a-45d6-4872-a174-c6a5096c7a75","order_by":7,"name":"Haider Butt","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA4ElEQVRIiWNgGAWjYBACAwbGBgkgnQDEjA8bSNPCxsxsSKQWBgaYFjZJorSYsx9uvPFxD0Oewf3+Y5Uz2xjk+RuYHz7Ap8WyJ7HZcsYzhmKDY8xsNze2MRjOOMBmbIDXYQcS26R5DjAkbgBpedjGwLiBgcFMAq+W8w/bpP9AtRQCtdhvYGD//gOvlhtAWxigWhiBDkvcwMBjhk8HUMvDZsueAxLFkseSjSVnnJNInnGYp5iAw9If3vhxwCaP7/DBhx97ymxs+9vbN37Aaw0ESCAxmIlQPwpGwSgYBaMAPwAAE65LExEI3z0AAAAASUVORK5CYII=","orcid":"","institution":"Khalifa University","correspondingAuthor":true,"prefix":"","firstName":"Haider","middleName":"","lastName":"Butt","suffix":""},{"id":291623323,"identity":"83062d5f-58ff-40ee-8601-5805876f17e9","order_by":8,"name":"Waqqar Ahmed","email":"","orcid":"","institution":"COMSATS University","correspondingAuthor":false,"prefix":"","firstName":"Waqqar","middleName":"","lastName":"Ahmed","suffix":""}],"badges":[],"createdAt":"2024-04-08 13:17:32","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4236742/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4236742/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":54903278,"identity":"a57ea5d3-511a-4357-b13f-20f098e83c14","added_by":"auto","created_at":"2024-04-18 10:53:17","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":253310,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustration depicting the synthesizing steps of AgNS-S and HANS-S (a); schematic illustration depicting the GRR of Ag atoms by Au ions (b); and photographs of AgNS-S and HANS-S showing a change in color of the filter paper after etching (c).\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4236742/v1/9a0140bc81572a9ac7517c1f.png"},{"id":54903228,"identity":"a2c03500-4d64-4670-b667-a936f81d8ba9","added_by":"auto","created_at":"2024-04-18 10:52:46","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":47247,"visible":true,"origin":"","legend":"\u003cp\u003eDiffused reflectance spectrum of AgNS-S (a) and HANS-S (b).\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4236742/v1/e1a08adbd1284305a12a4933.png"},{"id":54903267,"identity":"8c742910-150f-4315-9428-a975108aaf2e","added_by":"auto","created_at":"2024-04-18 10:52:59","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":484816,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of AgNS-S (a), and HANS-S (b-c); TEM image of hollow Au-Ag alloy nanostructures (d); EDX spectrum of AgNS-S (e) and HANS-S (f). The relative atomic percentages of Ag and Au are mentioned in \u0026nbsp;e and f.\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4236742/v1/dccf74baac15f2ffc88cc1c3.jpeg"},{"id":54903273,"identity":"a91abe1e-2736-4350-99af-630c33b49943","added_by":"auto","created_at":"2024-04-18 10:53:13","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":178265,"visible":true,"origin":"","legend":"\u003cp\u003eUV-Vis absorption spectra of test reaction of 4-NP for AgNS-S (a), and HANS-S (b); comparative log (C\u003csub\u003et\u003c/sub\u003e/C\u003csub\u003eo\u003c/sub\u003e) versus time plot of AgNS-S and HANS-S (c).\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4236742/v1/429487b667c0a9e21612491e.png"},{"id":54903275,"identity":"b62df4be-f160-40fa-b415-db7720ff4d7a","added_by":"auto","created_at":"2024-04-18 10:53:14","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":198285,"visible":true,"origin":"","legend":"\u003cp\u003eUV Vis absorption spectra of test reaction of MO for AgNS-S (a), and HANS-S (b); comparative log (C\u003csub\u003et\u003c/sub\u003e/C\u003csub\u003eo\u003c/sub\u003e) versus time plot of AgNS-S and HANS-S (c); comparative log (C\u003csub\u003et\u003c/sub\u003e/C\u003csub\u003eo\u003c/sub\u003e) versus time plot for 4-NP in the first, and fifth cycle of catalytic reaction for HANS-S (d).\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4236742/v1/1e98fafc2c430e8e2efad69f.png"},{"id":54903272,"identity":"65de0f0b-660c-4951-a256-3a705a3ce34a","added_by":"auto","created_at":"2024-04-18 10:53:13","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":610670,"visible":true,"origin":"","legend":"\u003cp\u003eZOI of AgNS-S and HANS-S assessed after 18 hours of incubation against \u003cem\u003eE. coli\u003c/em\u003e (a); and \u003cem\u003eS. aureus\u003c/em\u003e (b).\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4236742/v1/e34c6a38b62d832aa9f0ee0f.jpeg"},{"id":59838357,"identity":"19cc74c4-1152-4d9c-8f62-c2d57a1ad546","added_by":"auto","created_at":"2024-07-08 09:03:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2168462,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4236742/v1/e3706749-9948-46a2-b68c-fa38e9562d4f.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Facile Fabrication of Hollow Ag-Au Alloy Nanostructures Directly on Filter Paper and their Enhanced Catalytic and Antibacterial Applications","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eNoble metal nanomaterials have attracted great attention driven by their immense potential across diverse fields including heterogeneous catalysis, and antibacterial applications.\u003csup\u003e1,2\u003c/sup\u003e The performance of these nanomaterials strongly depends on their size, shape, surface area, and chemical composition.\u003csup\u003e3\u0026ndash;5\u003c/sup\u003e Consequently, a diverse array of colloidal nanostructures has been synthesized. Moreover, to further enhance the performance of these nanostructures, several methodologies have been devised to tailor their shape, such as modifying surface roughness or introducing hollowness to enhance surface area and energy.\u003csup\u003e6\u0026ndash;8\u003c/sup\u003e Hollow nanostructures exhibit distinctive and unique properties that deviate significantly from their solid counterparts due to their unique morphology, enhanced surface area, and high reactivity.\u003csup\u003e9\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eMetal oxides are widely employed as catalysts to execute several reactions.\u003csup\u003e10\u003c/sup\u003e The catalytic action for these materials depends upon the activation of charge carriers through visible or ultraviolet light electromagnetic waves.\u003csup\u003e11\u003c/sup\u003e Conversely, metal NPs offer a distinct advantage by enabling electron transfer between a reducing agent and pollutants even without electromagnetic excitation, thereby simplifying the catalytic process.\u003csup\u003e12\u003c/sup\u003e The catalytic activity of metal NPs is markedly influenced by their dimensions, morphology, and surface imperfections.\u003csup\u003e13\u003c/sup\u003e Notably, NPs with hollow interiors have shown superior catalytic properties owing to their enhanced surface area and the presence of high concentration of highly active low-coordination atoms.\u003csup\u003e8,13,14\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eAnother important focus of the metal NPs research is to combat bacterial infections. In this regard, Ag NPs have emerged as potent agents against a wide range of bacterial species.\u003csup\u003e15,16\u003c/sup\u003e They have demonstrated excellent activity against both Gram-positive and Gram-negative bacteria.\u003csup\u003e17\u003c/sup\u003e Their antibacterial activity is mainly attributed to the release of Ag ions, which upon interaction with bacteria cause cell death.\u003csup\u003e18\u003c/sup\u003e Another path of bactericidal activity is the adhesion and/or penetration of NPs to bacteria.\u003csup\u003e19,20\u003c/sup\u003e NPs can physically interact with bacterial cells by adhering to their surfaces through electrostatic forces, and hydrophobic interactions.\u003csup\u003e21,22\u003c/sup\u003e These interactions can lead to cell membrane disruption, compromising the integrity of the bacterial cell and causing cell death. Both adhesions to cells and Ag ion release are expected to improve with the increase in the surface energy of NPs. In this context, hollow or rough NPs due to a large surface area and high surface energy can be highly effective. Therefore, several recipes have been developed to synthesize NPs with hollow interiors. However, most of the synthesis methods are solution-based. The solution-synthesized NPs usually incorporate surfactants, a common practice to avoid their agglomeration within the solution and control particle size and shape.\u003csup\u003e3,23,24\u003c/sup\u003e However, the inclusion of surfactants comes with certain disadvantages. Primarily, the surface coverage of these surfactants around NPs constrains available adsorption sites, thereby compromising their catalytic, surface-enhanced Raman scattering (SERS), and antibacterial properties.\u003csup\u003e4,25,26\u003c/sup\u003e While multiple methods to remove surfactant molecules from NPs surfaces have been proposed, their implementation invariably introduces complexities.\u003csup\u003e27,28\u003c/sup\u003e Consequently, the development of facile techniques that are eco-friendly for the fabrication of surfactant-free catalysts is very important.\u003c/p\u003e \u003cp\u003eOf particular intrigue is the innovative fabrication of these NPs directly on substrates, especially on filter paper. NPs on filter paper offer additional advantages, including catalyst recovery and reusability, wound dressing applications, and swab-based trace detection using SERS.\u003csup\u003e29\u0026ndash;31\u003c/sup\u003e So far numerous techniques have been employed to directly grow NPs on filter paper which include drop casting,\u003csup\u003e32\u003c/sup\u003e chemical reduction approach,\u003csup\u003e33\u003c/sup\u003e successive ionic layer absorption and reaction\u003csup\u003e34\u003c/sup\u003e, immersion deposition,\u003csup\u003e35\u003c/sup\u003e thermal deposition,\u003csup\u003e36\u003c/sup\u003e and inkjet printing.\u003csup\u003e37\u003c/sup\u003e However, all these methodologies are primarily focused on the growth of solid NPs on the filter paper. We are not aware of any method that reports the direct fabrication of hollow and surfactant-free nanostructures on the substrate. Herein, we aim to bridge this gap by introducing a unique method for the growth of hollow Au-Ag alloy nanostructures directly on filter paper, potentially unlocking new possibilities for various applications.\u003c/p\u003e"},{"header":"2. Experimental Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eThe chemicals used in this study were silver nitrate (Chem-Lab), chloroauric acid (Merck), ascorbic acid (Sigma-Aldrich), Sodium borohydride (Sigma-Aldrich), 4-nitrophenol (Sigma-Aldrich), methyl orange (Sigma-Aldrich), nitric acid (Sigma-Aldrich), and hydrochloric acid (Sigma-Aldrich). Deionized water was used to make all solutions. For the thorough cleansing of all glassware, aqua regia was used. The chosen substrate for the nanostructure fabrication is Whatman 41 ashless filter paper. For the antibacterial experiment, all culture media, glassware, containers, and micro tips were sterilized by autoclaving.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Synthesis of AgNS-S\u003c/h2\u003e \u003cp\u003eThe Ag NPs were synthesized on filter paper using a wet chemical technique. In a typical experiment, a piece of filter paper measuring 4x4 cm\u0026sup2; was immersed in a solution of AgNO\u003csub\u003e3\u003c/sub\u003e (0.2 M, 16 mL) for 1 minute. After this immersion, the filter paper was removed and dried on the hot plate at a temperature of 40\u0026deg;C. The substrate was then immersed in a freshly prepared solution of ascorbic acid (0.1 M, 16 mL), leading to an instantaneous reduction of Ag⁺ ions to Ag⁰. The prompt shift in the color of the filter paper from white to brown was an indication of the formation of Ag NPs on the filter paper. The resulting substrate containing Ag NPs was then thoroughly washed with deionized water three times to eliminate any residual unreacted reagents or loosely bound Ag NPs from the filter paper. The sequential depiction of these procedural steps is shown in schematics, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a). Finally, the substrate was cut into four 2\u0026times;2 cm\u0026sup2; pieces for further etching experiments.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Fabrication of HANS-S\u003c/h2\u003e \u003cp\u003eA piece of 2\u0026times;2 cm\u0026sup2; AgNPs-S was immersed in a HAuCl\u003csub\u003e4\u003c/sub\u003e (0.06 M, 4 mL) solution for 2 min. Afterward, the substrate was removed from the solution and thoroughly washed three times with DI water. As a consequence of GRR, Au\u003csup\u003e3+\u003c/sup\u003e ions are reduced to Au⁰, while Ag atoms from the nanostructures oxidize to Ag⁺ ions. The GRR of Ag by Au on AgNS-S is schematically illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(b). Furthermore, the optical photographs of AgNS-S and HANS-S are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (c). For comparative studies, AgNPs-S and HANS-S of the same batch were used.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Catalysis measurements\u003c/h2\u003e \u003cp\u003eThe catalytic activity of our substrates was assessed for the reduction of 4-NP and MO. The experimental procedure involved the addition of 1 mL and 0.05 M of sodium borohydride to a solution containing 3 mL and 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e M of either 4-NP or MO. Following thorough mixing of the solution, the catalyst (2\u0026times;2 cm\u0026sup2;) was introduced, and the reaction's progression was monitored at regular intervals using UV-Vis spectroscopy. The UV-Vis spectra were taken after every 3 minutes in the UV-Vis spectral range of 200\u0026ndash;600 nm.\u003c/p\u003e \u003cp\u003eIn order to test the catalytic reusability of our substrates, the substrate was retrieved with the help of a tweezer from the reaction mixture upon completion of the reaction. After recovery, the substrate was washed with deionized water and dried at 40\u0026deg;C on a hot plate. The substrate was then transferred to another reaction medium i.e., mixture of 4-NP and NaBH\u003csub\u003e4\u003c/sub\u003e. The whole process was repeated four times to test the reusability of our substrates up to five different cycles.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Antibacterial assessment\u003c/h2\u003e \u003cp\u003eThe disk-diffusion method was used to examine the bactericidal effect by using clinical bacterial strains of Gram-negative \u003cem\u003eE.coli\u003c/em\u003e and Gram-positive \u003cem\u003eS. aureus\u003c/em\u003e. To perform the antibacterial assessment, our substrates were cut into 1x1 cm\u003csup\u003e2\u003c/sup\u003e size pieces. Typically, bacterial suspension was uniformly spread on the surface of nutrient Muller Hinton agar growth plates. The substrates were then carefully placed on top of the agar, while clean filter paper served as a negative control on each plate. The plates were then incubated at a temperature of 37\u0026deg;C for 18 hours. After the incubation period, digital images of the plates were captured and the ZOI surrounding the square samples were measured. The experiment was carried out in duplicate to ensure the reproducibility of the results.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6 Characterization\u003c/h2\u003e \u003cp\u003eThe synthesized substrates underwent comprehensive characterization employing various analytical techniques. The diffused reflectance spectroscopy was employed to acquire reflection spectra of the synthesized substrates using UV spectrophotometer Shimadzu 2700. This was achieved by adjusting the spectrophotometer's wavelength range from 200 nm to 800 nm, maintaining a precise step size of 1 nm. To obtain a detailed understanding of the morphological attributes of the synthesized NPs deposited on filter paper, a scanning electron microscope (SEM) was utilized. Specifically, we utilized the FEI Nova NanoSEM 450 instrument for this purpose. The SEM was equipped with an Oxfor INCA XACT energy dispersive X-ray spectroscope (EDX) detector, facilitating the elemental composition analysis of our samples. The EDX was conducted utilizing an electron beam energy of 15 kV with an adjustable spot size of 6 mm. Transmission electron microscopy (TEM) measurements were conducted using Tecnai TEM 200kV. The TEM samples were prepared by sonicating a piece of substrate for 5 min to collect particles in solution. This was followed by the careful transfer of an aqueous droplet onto a carbon-coated TEM grid. Finally, the catalytic activity of our substrates was evaluated using a UV-1280 Shimadzu Spectrophotometer.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Result and Discussion","content":"\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a) depicts the reflectance spectrum of the AgNS-S. The spectrum reveals a pronounced and substantial dip in reflectance, specifically centered at 414 nm, indicative of the plasmon absorbance of Ag NPs. This dip in the reflectance profile verifies that Ag nanostructures have been successfully fabricated onto the filter paper.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b) depicts the diffused reflectance spectrum of HANS-S. In this case, a prominent dip positioned at 526 nm in the reflectance spectrum is observed. It is noteworthy that the surface plasmon resonance (SPR) peak of Ag-Au alloy NPs is typically reported to fall within the range of 400 to 520 nm.\u003csup\u003e38\u003c/sup\u003e However, a distinction becomes apparent in the case of hollow NPs. The presence of a hollow core functions as a resonant cavity, leading to a redshift in the absorption peak or, alternatively, in the dip observed within the reflection spectrum.\u003csup\u003e38\u003c/sup\u003e In our case of HANS-S, the dip centered at 526 nm within the reflection spectrum supports the successful synthesis of HANS-S.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe SEM image of the AgNS-S is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a), which offers clear evidence of the nearly spherical shape of the Ag nanostructures that have been successfully formed on the surface of the filter paper. The average size of the Ag nanostructures on the AgNS-S is approximately 370\u0026thinsp;\u0026plusmn;\u0026thinsp;45 nm. The SEM images of HANS-S are depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b, c). The images clearly show the near-spherical morphology of the nanostructures. The average size of the etched nanostructures is approximately the same as that of Ag nanostructures. A close-up view of these NPs (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c)) shows that they have openings, which is indicative of the hollow interior. The hollow interior of the NPs can be better viewed in the TEM image depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(d). The fabricated nanostructures clearly consist of a solid shell with a semi-hollow interior.\u003c/p\u003e \u003cp\u003eThe elemental composition of both AgNS-S and HANS-S was examined through EDX analysis, and the results are depicted in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(e) and 2(f) respectively. In the case of the AgNS-S, a distinctive and pronounced peak situated around 3 keV is observed in the spectrum, verifying the presence of Ag on the substrate. In the case of the EDX spectrum of HANS-S, the characteristic peaks of both Ag and Au are present, which verifies the Ag and Au bimetallic alloy composition of hollow NPs on the filter paper. By atomic percentage analysis, it is established that the composition of the alloy is 78.21% Ag and 21.79% Au.\u003c/p\u003e \u003cp\u003eThe direct growth of NPs on the substrate depends sensitively on the choice of reducing agents. The reducing agent plays a crucial role in controlling the size and morphology of NPs. Commonly employed reducing agents include NaBH\u003csub\u003e4\u003c/sub\u003e and ascorbic acid. In our previous study, we reported the successful fabrication of Ag nanostructures on filter paper utilizing NaBH\u003csub\u003e4\u003c/sub\u003e.\u003csup\u003e31\u003c/sup\u003e NaBH\u003csub\u003e4\u003c/sub\u003e is known for its strong reducing power which leads to instantaneous reduction of metal ions, yielding a high concentration of relatively smaller NPs, typically a few nanometers in diameter. In contrast, ascorbic acid is a milder reducing agent which provides a more gradual reduction of Ag\u003csup\u003e+\u003c/sup\u003e ions, allowing for a controlled growth of Ag NPs over time. This may lead to the fabrication of NPs of larger sizes as we have seen in this study.\u003c/p\u003e \u003cp\u003eThe formation of HANS-S was achieved by the well-known GRR. During this process, Au\u003csup\u003e3+\u003c/sup\u003e ions are reduced onto the surface of Ag NPs, which act as a sacrificial template. The reaction can be represented as follows\u003csup\u003e7\u003c/sup\u003e,\u003c/p\u003e \u003cp\u003eAu\u003csup\u003e3+\u003c/sup\u003e + 3Ag\u003csup\u003e0\u003c/sup\u003e \u0026rarr; Au\u003csup\u003e0\u003c/sup\u003e\u0026thinsp;+\u0026thinsp;3Ag\u003csup\u003e+\u003c/sup\u003e (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eThis reaction results in the reduction of Au ions to form Au atoms on the surface of the Ag NPs. For the addition of each Au atom, three silver atoms are removed from the NPs, which results in the formation of hollow nanostructures.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Catalysis\u003c/h2\u003e \u003cp\u003eTo test the catalytic capability of our substrates, we employed the commonly used model reaction of the reduction of 4-NP to 4-AP. While the thermodynamics of reducing 4-NP in the presence of a reducing agent like NaBH\u003csub\u003e4\u003c/sub\u003e are inherently favorable, a significant kinetic barrier arises due to the substantial potential difference between the donor and the acceptor species.\u003csup\u003e7\u003c/sup\u003e To facilitate the reaction, metal NPs can play the pivotal role of an electron relay. This electron relay mechanism facilitates the transfer of electrons from the donor species BH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e to the acceptor 4-NP, effectively mitigating the kinetic barrier and thus enhancing the overall feasibility of the reaction.\u003c/p\u003e \u003cp\u003eThe UV-Vis absorption spectra at different times are depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a, b). A discernible peak is observed at 400 nm, which is due to the conversion of 4-NP to nitrophenolate anions with the addition of NaBH\u003csub\u003e4\u003c/sub\u003e, while a peak at 300 nm arises due to the presence of 4-AP. As time passes, there is a gradual decrease in the intensity of the peak at 400 nm and an increase in the intensity of the peak around 300 nm. These spectral changes, evolving over time, verify the conversion of the reactant 4-NP into the desired product, 4-AP. It can be clearly seen that the reaction is much faster when HANS-S is employed as a catalyst. In the case of AgNS-S, an observed 87% conversion to 4-AP was observed within 60 min. While for HANS-S, a higher conversion rate of 95% to 4-AP was observed in a mere 24 min. The graphs between \u003cem\u003eln (C\u003c/em\u003e\u003csub\u003e\u003cem\u003et\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e/C\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e)\u003c/em\u003e and time are depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(c). Here, \u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003et\u003c/em\u003e\u003c/sub\u003e are the values of absorbance intensities at the start of the reaction and at the later time \u003cem\u003et\u003c/em\u003e, respectively. There is a clear linear correlation between the \u003cem\u003eln\u003c/em\u003e (\u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003et\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e/C\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e)\u003c/em\u003e and \u003cem\u003et\u003c/em\u003e, which verifies that the reaction follows pseudo-first-order kinetic using the relation. The apparent rate constant, \u003cem\u003ek\u003c/em\u003e\u003csub\u003e\u003cem\u003eapp\u003c/em\u003e\u003c/sub\u003e, can be determined by the slope, as given by the following equation\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\text{l}\\text{n}\\left(\\frac{{C}_{t}}{{C}_{o}}\\right)=-{k}_{app}t$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe values of the apparent rate constants for AgNS-S and HANS-S are 0.0341 min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 0.1178 min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. Therefore, \u003cem\u003ek\u003c/em\u003e\u003csub\u003e\u003cem\u003eapp\u003c/em\u003e\u003c/sub\u003e increased by about 3.5-fold when HANS-S was employed as a catalyst.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn order to test our catalyst for the catalytic reduction of dyes, we have further studied the reduction reaction of MO by NaBH\u003csub\u003e4\u003c/sub\u003e in the presence of catalyst. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a, b), MO has a strong characteristic absorption peak at 464 nm. The peak\u0026rsquo;s intensity gradually decreased after the catalyst was inserted in the reaction medium. When AgNS-S was employed as catalysts, 90% of the reaction was completed within 50 min. However, for HANS-S, the MO peak completely disappeared within 28 min, indicating the completion of the reaction. Furthermore, given the excess of NaBH\u003csub\u003e4\u003c/sub\u003e concentration relative to the MO, the reaction follows the dynamics of pseudo-first-order kinetics. Similar to the previous case, there is a good linear correlation between the \u003cem\u003eln\u003c/em\u003e (\u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003et\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e/C\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e)\u003c/em\u003e and \u003cem\u003et\u003c/em\u003e (see Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(c)), which verifies pseudo-first-order kinetic in this case as well. The calculated apparent rate constants were found to be 0.0438 min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for the AgNS-S and a notably higher value of 0.1481 min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for the HANS-S. Hence, the utilization of HANS-S for catalysis results in an approximately 3.4-fold increase in the value of \u003cem\u003ek\u003c/em\u003e\u003csub\u003e\u003cem\u003eapp\u003c/em\u003e\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe synthesized catalytic substrates exhibit an array of remarkable features that elevate their catalytic performance. As previously mentioned, surfactants, while useful in stabilizing NPs in colloidal suspensions, can hinder catalytic reactions by blocking active sites.\u003csup\u003e4\u003c/sup\u003e Therefore, the surfactant-free nature of both of our substrates ensures a pristine surface, allowing reactant molecules to interact directly with the active sites. However, the key attributes that sets HANS-S apart from AgNS-S are the enhanced surface area and the presence of high concentrations of low-coordination atoms. These factors, combined with the absence of the surfactant, make HANS-S an excellent candidate for catalytic applications.\u003c/p\u003e \u003cp\u003eThe reusability of substrates plays a pivotal role in determining the viability of catalysts for their widespread adoption in both industrial and commercial applications. Furthermore, the capacity for substrates to withstand multiple cycles of catalytic reactions without significant deterioration is essential, not only for cost-effectiveness but also for minimizing environmental impact by reducing waste. The assessment of HANS-S reusability was conducted using testing the catalyst for five cycles of 4-NP reduction reaction. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(d) depicts the comparative log plot of the first and fifth catalytic cycles. It was observed that there is only about a 12% change in catalytic activity. This is due to less NP leaching which can be ascribed to the improved stability of the NPs deposited on the filter paper, ensuring that a higher proportion of them remain bound to the substrate, even after multiple catalytic cycles. The supporting filter paper is enriched with hydroxyl and carboxyl groups, which provide binding sites for NPs, thereby ensuring their robust attachment to the filter paper\u003csup\u003e31\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Antibacterial activity\u003c/h2\u003e \u003cp\u003eThe antibacterial evaluation of both AgNS-S and HANS-S was conducted against \u003cem\u003eE. coli\u003c/em\u003e and \u003cem\u003eS. aureus\u003c/em\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (a, b) depicts the image of the bacterial growth of \u003cem\u003eE. coli\u003c/em\u003e and \u003cem\u003eS. aureus\u003c/em\u003e, respectively, in the presence of our substrates. In both cases, there is no bacterial growth under the substrate pieces. However, for AgNS-S, no inhibition of growth was observed beyond the substrates' surface. On the other hand, HANS-S exhibited higher antibacterial activity with ZOI spanning significantly beyond the substrate\u0026rsquo;s surface, which indicates a more potent inhibitory effect on bacterial growth.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe limited antibacterial activity of AgNS-S can be assigned to the bigger size of Ag NPs, which limits the quick release of Ag\u003csup\u003e+\u003c/sup\u003e ions. The reduced size of Ag NPs enhances the release of Ag\u0026thinsp;+\u0026thinsp;ions, attributed to the increased surface area and higher surface energy.\u003csup\u003e39\u003c/sup\u003e Previous reports have clearly demonstrated that Ag ion release is highest for the smallest size of Ag NPs.\u003csup\u003e40\u003c/sup\u003e When the Ag NPs\u0026rsquo; size is larger than 40 nm, both endocytosis and the release of Ag\u003csup\u003e+\u003c/sup\u003e ions are less effective for antibacterial activity.\u003csup\u003e41\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThe higher antibacterial activity of the HANS-S is in accordance with the previous studies in which solution-synthesized hollow Au-Ag alloy NPs have shown better antibacterial activity compared to the solid Ag NPs.\u003csup\u003e42\u003c/sup\u003e The enhanced activity of Au-Ag alloy NPs could be due to several factors. First, the higher electronegativity of Au pulls the electrons away from the Ag atoms present on the alloy surface making their free energy higher which in turn makes them more reactive and prone to oxidation compared to the case where Ag atoms are present on the surface of monometallic Ag NPs. Another impressive feature of HANS-S is its enhanced surface area. This combined with the higher free energy of Ag-Au alloy ensures an elevated release of silver ions from the HANS-S. The released Ag\u003csup\u003e+\u003c/sup\u003e ions directly interact with the cell membrane, increasing their permeability by creating pores, and perforation in the bacterium membrane. Harada et. al. reported a 3-fold higher release of Ag ions for the solution-synthesized hollow Au-Ag alloy NPs, compared with the solid Ag NPs\u003csup\u003e43\u003c/sup\u003e. The released Ag ions directly interact with the sulfur-containing cell proteins and periplasmic Ag-binding proteins.\u003csup\u003e44,45\u003c/sup\u003e These interactions lead to a change in the permeability of the protein membrane and its subsequent release causing cell death.\u003csup\u003e42\u003c/sup\u003e\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eWe have developed a novel and straightforward method for directly growing hollow Au-Ag alloy NPs onto filter paper. We demonstrated that HAuCl\u003csub\u003e4\u003c/sub\u003e can be employed for GRR-induced etching of Ag NPs directly on the filter paper surface. The etching of Ag NPs provided an impressive enhancement of the catalytic activity. The apparent rate constants increased by 3.5-fold and 3.4-fold for the reduction reactions of 4-NP and MO, respectively. In reusability testing, a mere 12% decrease in conversion efficiency is observed for the HANS-S which verifies excellent binding of the particles to the filter-paper\u0026rsquo;s surface. The HANS-S has also shown better antibacterial action, compared to the AgNS-S. We attribute this enhanced performance to the increased surface area and electronic effects induced by the presence of Au atoms. These factors contribute to improved Ag\u0026thinsp;+\u0026thinsp;ion release from the nanoparticles' surface, resulting in more effective bacterial inhibition. Consequently, the HANS-S holds great promise for applications in both antibacterial and catalytic domains. Our innovative methodology can be employed for the direct fabrication of surfactant-free porous alloy nanostructures of other noble metals on substrates. This versatility underscores their potential for widespread advancements in various scientific and technological fields.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eSaima Shafique: Writing \u0026ndash; original draft, Investigation, Formal analysis Saira Arif: Project administration, Supervision, Investigation, Formal analysis. Unsia Batool: Data Curation, Investigation, Formal analysis, Methodology. Israr Ahmed: Data Curation, Investigation, Methodology. Ghazanfar Ali Khan: Visualization, Formal analysis. Rabia Nawaz: Investigation Muhammad Imran: Supervision, Writing \u0026ndash; review and editing Haider Butt: Funding acquisition, Resources, Supervision, Project administration Waqqar Ahmed: Conceptualization, Writing \u0026ndash; review \u0026amp; editing, Funding acquisition, Supervision, Resources, Supervision\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eSaima Shafique: Writing \u0026ndash; original draft, Investigation, Formal analysis Saira Arif: Project administration, Supervision, Investigation, Formal analysis. Unsia Batool: Data Curation, Investigation, Formal analysis, Methodology. Israr Ahmed: Data Curation, Investigation, Methodology. Ghazanfar Ali Khan: Visualization, Formal analysis. Rabia Nawaz: Investigation Muhammad Imran: Supervision, Writing \u0026ndash; review and editing Haider Butt: Funding acquisition, Resources, Supervision, Project administration Waqqar Ahmed: Conceptualization, Writing \u0026ndash; review \u0026amp; editing, Funding acquisition, Supervision, Resources, Supervision\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eAll data generated or analysed during this study are included in this published article.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eS\u0026aacute;pi, A. \u003cem\u003eet al.\u003c/em\u003e Metallic Nanoparticles in Heterogeneous Catalysis. \u003cem\u003eCatalysis letters\u003c/em\u003e vol. 151 2153\u0026ndash;2175 at \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s10562-020-03477-5\u003c/span\u003e\u003cspan address=\"10.1007/s10562-020-03477-5\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRana, S. \u0026amp; Kalaichelvan, P. 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J. 19, 1754\u0026ndash;1761 (2013).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Hollow alloy nanoparticles, Au-Ag alloy nanoparticles, galvanic replacement reaction (GRR), heterogenous catalysis, antibacterial properties, 4-nitrophenol, methyl orange, S. aureus, E. coli","lastPublishedDoi":"10.21203/rs.3.rs-4236742/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4236742/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHollow noble metal alloy nanostructures have recently attracted great attention owing to their exceptional potential for various applications. These nanostructures are generally synthesized in solution. However, for several applications, their deposition on the substrate is needed. Herein, we present the novel synthesis of hollow Au-Ag alloy nanostructures directly on the filter paper. The synthesis was carried out in two steps. First, Ag nanostructures were directly grown on the filter paper by reducing the pre-deposited Ag ions with ascorbic acid, yielding Ag nanostructure substrate (AgNS-S). These NPs were subsequently etched with HAuCl\u003csub\u003e4\u003c/sub\u003e exploiting the galvanic replacement reaction (GRR), which yielded hollow Au-Ag alloy nanostructure substrate (HANS-S). Owing to the enhanced surface area and the presence of a high concentration of atoms in the low coordination state, these HANS-S showed excellent catalytic and antibacterial properties. In particular, the rate constants of the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), and the degradation of methyl orange (MO) increased by a factor of approximately 3.5 and 3.4, respectively, when employing HANS-S compared to utilizing AgNS-S. Similarly, the filter paper having hollow Au-Ag alloy nanostructures showed markedly superior antibacterial activity. While AgNS-S did not show any zone of inhibition (ZOI) outside the substrate, HANS-S showed notable ZOI for both \u003cem\u003eS. aureus\u003c/em\u003e and \u003cem\u003eE. coli\u003c/em\u003e, which verifies the antibacterial activity of these nanostructures against both Gram-positive and Gram-negative bacteria.\u003c/p\u003e","manuscriptTitle":"Facile Fabrication of Hollow Ag-Au Alloy Nanostructures Directly on Filter Paper and their Enhanced Catalytic and Antibacterial Applications","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-18 10:51:52","doi":"10.21203/rs.3.rs-4236742/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"9071f9a8-4a08-4b10-9bc7-900bb03f6a3a","owner":[],"postedDate":"April 18th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":30720284,"name":"Physical sciences/Engineering/Biomedical engineering"},{"id":30720285,"name":"Physical sciences/Nanoscience and technology/Nanobiotechnology"},{"id":30720286,"name":"Physical sciences/Nanoscience and technology/Nanoscale materials"},{"id":30720287,"name":"Biological sciences/Biotechnology/Nanobiotechnology/Nanofabrication and nanopatterning"},{"id":30720288,"name":"Biological sciences/Biotechnology/Nanobiotechnology/Nanoparticles"}],"tags":[],"updatedAt":"2024-07-08T08:55:29+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-18 10:51:52","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4236742","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4236742","identity":"rs-4236742","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}