A colorimetric detection of Hg2+ based on gold nanoparticles synthesized oxidized N-methylpyrrolidone as a reducing agent

A colorimetric detection of Hg2+ based on gold nanoparticles synthesized oxidized N-methylpyrrolidone as a reducing agent | 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 Research Article A colorimetric detection of Hg 2+ based on gold nanoparticles synthesized oxidized N-methylpyrrolidone as a reducing agent Dou Yang, Rentian Guan, Shuhan Jiang, Min Wang, Shuai Zhang, Xiaoyu Fan, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2400759/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 In this study, a gold nanoparticles colorimetric probe (AuNPs) with direct response to mercury ions (Hg 2+ ) were developed using treated N-methylpyrrolidone (NMP) and chloroauric acid (HAuCl 4 ) as precursors. NMP showed good reducibility after high temperature hydrolysis and could be used as reducing and stabilizing agent to synthesize AuNPs. The prepared AuNPs have obvious characteristic absorption peaks and appear wine-red. At the same time, it was found that the presence of Hg 2+ can cause the aggregation of AuNPs, increased the absorbance at 700 nm, and changed the color of the solution into blue-gray. This method is capable of sensitive and specific determination of Hg 2+ ranging from 1 to 30 µM, with the limit of detection (LOD) at 0.3 µM. The method showed good specificity for the determination of Hg 2+ and has the potential to be applied to Hg 2+ detection in sewage samples in the environment. Hg2+ gold nanoparticles N-methylpyrrolidone colorimetry visual mode Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction Heavy metals not only pollute the environment, but also have a negative impact on human health. Mercury (Hg) is a heavy metal element naturally present in air, water and soil. It can be widely distributed in the environment through natural activities and human activities [ 1 – 3 ]. Hg 2+ exists in both inorganic and organic forms, which belong to persistent toxic pollutants and can be enriched in organisms through the action of the food chain [ 4 ]. Causes a range of health problems such as myocardial infarction, minamata disease, and some autisms by damaging the kidneys, central nervous system, and reproductive system [ 5 , 6 ]. Traditional methods for detection of Hg 2+ often require expensive, complex and bulky instruments, and the operation process is complicated, which makes it difficult to meet the needs of routine analysis and field analysis [ 7 – 9 ]. Such as atomic absorption spectrometry, mass spectrometry and high performance liquid chromatography (HPLC) [ 10 – 12 ]. Therefore, there is an urgent need to explore a method for Hg 2+ detection and monitor with high sensitivity, good selectivity, and simple operation. Recently, many sensing probes for Hg 2+ detection based on colorimetric detection and fluorescence turn on sensing are being developed [ 13 – 15 ]. At the same time, the advantages of gold nanoparticles (AuNPs), such as good biocompatibility, easy chemical functionalization, and unique optical properties, have been gradually understood [ 16 – 21 ]. In the Ultraviolet-visible (UV-vis) absorption spectrum, the position of the absorption peak produced by AuNPs is related to its particle size (or aggregated state) and shape, and the intensity of the absorption peak is linearly related to the concentration of AuNPs in the solution [ 22 , 23 ]. Therefore, AuNPs has unique advantages in the development of colorimetric sensors. For example, AuNPs-based colorimetry has been widely used to detect Hg 2+ . Recently, Ma et al. successfully constructed a novel label-free colorimetric sensor, and for the first time proposed Co 2+ as exonuclease III cofactors. Using auxiliary signal amplification and unmodified AuNPs as indicators to achieve Hg 2+ ultrasensitive detection [ 24 ]. Gosavi’s group reported that the successful used of AuNPs /rhodamine B (RB)/hexanedithiol (HDT) nanocomposite system for highly selective detection of Hg 2+ in urine and ground water [ 25 ]. Chen et al. proposed an amalgam formation method using gold, combined with Hg 2+ mediated the growth of AuNPs, which colorimetric sensing assay capable of efficient and rapid detection of Hg 2+ [ 26 ]. However, in these methods, some ligands contain sulfhydryl groups and have a strong sulfide odor, and the detection of Hg 2+ are based on multi-step or complex systems, and the detection process is complicated. Therefore, an environmentally friendly colorimetric probe that can directly respond to Hg 2+ is urgently needed. In this work, using pretreated N-methylpyrrolidone (NMP) as reducing and stabilizing agent, an AuNPs colorimetric probe with direct response to Hg 2+ was developed, avoiding the use of environmentally unfriendly thiol ligand-like ligands. The presence of Hg 2+ can be caused the aggregation of AuNPs, the absorbance at 700 nm increased and the solution color changed from wine-red to blue-gray were observed, which is easy to identified with the naked eye. These results show that the method has good selectivity for the detection of Hg 2+ , which lays a foundation for further detection of Hg 2+ in environmental sewage samples. 2. Experimental Section 2.1. Chemicals NMP was supplied by Tci Development Co., Ltd. (Shanghai, China). Including NaOH, Fe(NO 3 ) 3 , CuCl 2 , HgCl 2 , Zn(CH 3 COO) 2 , Pb(NO 3 ) 2 , MgCl 2 , CoCl 2 , BaCl 2 , CrCl 3 , NaCl, NiSO 4 ·6H 2 O, CdCl 2 , CaCl 2 , HCl, HNO 3 and chloroauric acid (HAuCl 4 ) metal salts were acquired from Aladdin Reagent Co., Ltd. (Shanghai, China). All these chemicals are of analytical grade and used directly. Deionized water provided by the Milli-Q water purification system was used for the entire experiment. 2.2. Apparatus The UV-750 spectrophotometer (PerkinElmer, USA) was used for measurement of UV-vis absorption spectra. The morphology and size of AuNPs were recorded on a Talos F200X transmission electron microscope (TEM, Thermo Scientific Ltd., USA). The TEM used a common copper grid to load the sample and operated at an accelerating voltage of 200 kV. Fourier Transform infrared (FT-IR) spectra were carried on a Nicolet 6700 (Thermo Scientific Ltd., USA), used the KBr method. X-ray photoelectron spectroscopy (XPS) was performed on a K-Alpha spectrometer (Thermo Scientific Ltd., USA). 2.3. Preprocessing of NMP* The method of preprocessing NMP has been modified according to previous literature [ 27 ]. 50 mL of NMP and 50 mg NaOH were put in a 150 mL one-neck flask, and then refluxed at 160°C for 12 h under argon protection. After the reaction was completed, a brown-yellow transparent solution was obtained. Centrifuged at 12000 rpm for 30 minutes, and the supernatant was removed to acquired a pasty precipitation (NMP*). Dissolve the NMP* in 6.5 ml of deionized water and stored at 4°C for use in the next step. 2.4. Preparation of AuNPs The preparation steps of AuNPs refer to the previous literature [ 28 ]. All reactions were performed in glassware thoroughly cleaned using aqua regia. 2400 µL NMP*, 800 µL ultrapure water and 100 µL of HAuCl 4 (24.28 mM) were blended and stirred at 70°C for 45 min. During this period, the color gradually changed from pale-yellow to wine-red, which proved that AuNPs had been formed. The cooled solution was stored at 4°C for later studies. 2.5. Colorimetric assay for the Hg 2+ The Hg 2+ detection procedure is described as follows: first, various concentrations of Hg 2+ standard stock solutions were prepared by dissolving the metal salt HgCl 2 in deionized water. Then the AuNPs system was mixed with various concentrations of Hg 2+ at a 1:1 volume ratio and incubated for 10 min. The Uv-vis absorption spectra were acquired at 700 nm in the presence and absence of Hg 2+ . The selectivity of AuNPs to Hg 2+ was investigated by performing detection of other relevant metal ions. 2.6. Pretreatment of real samples In order to explore the practicability of the detection method, three environmental water samples were tested. The lake water was obtained from the artificial lake of Liaocheng University, the tap water was obtained from the chemical laboratory of Liaocheng University, and the river water was obtained from the local natural Tuhai River. After the water samples were precipitated for 24 h, the supernatant was appropriately diluted with deionized water. After adding different concentrations of Hg 2+ standard solutions to the samples, the UV-Vis absorption spectra of AuNPs-Hg 2+ at 700 nm were record. 3. Results And Discussion 3.1 Principles of the colorimetric assay for Hg 2+ In this study, developed a colorimetric assay for Hg 2+ detection using AuNPs (Scheme 1 ).The AuNPs were prepared in the experimental section and displayed red color. According to previous literature [ 27 ], NMP can be oxidized and hydrolyzed to formed NMP* with high reducibility under alkaline and high temperature conditions, and can be used as reducing and templating agents to prepared metal nanoclusters. NMP* and HAuCl 4 were used as precursors to prepared AuNPs with sensitive response to Hg 2+ . In the absence of Hg 2+ , a stable wine-red dispersion was observed and displayed a characteristic surface plasmon resonance (SPR) absorption band at 518 nm (Fig. 1 ). This is because AuNPs are anisotropic nanomaterials, and the absorption spectrum of AuNPs in monodisperse state has only a single peak at 518 nm [ 28 ]. The appearance of Hg 2+ could induce the aggregation of AuNPs, so that the absorbance of AuNPs at 700 nm increased continuously, and the color of the mixture became blue-gray. This is due to the polarization and coupling between the electrons of adjacent nanoparticles when the AuNPs are in an aggregated state, resulting in a red-shift of the maximum absorption wavelength of the AuNPs. Correspondingly, the wine-red AuNPs gradually turned to blue-gray [ 29 ]. As shown in Fig. 2 A and B , this aggregation process was also confirmed by TEM, the AuNPs were in a monodisperse state in the absence of Hg 2+ . After the added of Hg 2+ , the AuNPs were clearly aggregated together, resulting in a significant changed in color and providing colorimetric detection of Hg 2+ . 3.2. Characterization of AuNCs TEM, FT-IR and XPS were used to characterize the resulting functionalized AuNPs. The morphology of AuNPs was first investigated used TEM. The results showed that our as-prepared AuNPs were freely dispersed in water with good water solubility (Fig. 2 A). As shown in Fig. 2 C, by calculated, the particle size distribution of AuNPs was between 8–17 nm with an average diameter of 13 ± 2 nm. HR-TEM revealed the lattice fringes of 2.34 Å for AuNPs consistent with metallic gold (Fig. 2 D), which corresponds to the d spacing of the (111) crystal plane of fcc Au [ 30 ]. FT-IR spectroscopy was used to analysis the surface of AuNPs ( Fig. S1A ). The broad band at 3430.86 cm − 1 corresponds to stretching vibrations of inter molecularly bonded O-H group. The typical peak at 1574.32 cm − 1 is other important peak of functional group and assigned to C = O. Absorption bands located at 1414.10 cm − 1 correspond to the C-N stretching vibration bands. These all demonstrated that the NMP* were successfully engrafted to the AuNPs. The chemical valence state of Au element in AuNPs plays an important role in its optical properties. Fig. S1B shown the HR-XPS spectra of AuNPs in the range of 82–90 eV, Au4f 7/2 and Au4f 5/2 are centered at binding energy values of 84.2 and 87.9 eV, respectively [ 31 ]. Au4f 7/2 and Au4f 5/2 could be further deconvoluted into two distinct peaks, respectively. The higher intensity doublets at binding energies at 84.2 (Au4f 7/2 ) and 88.0 eV (Au4f 5/2 ) could be attributed to Au + , while the binding energies of Au 0 are lower at 88.3 (Au4f 7/2 ) and 87.1 eV (Au4f 5/2 ). According to previous literature, the difference between the peaks of Au4f 7/2 and Au4f 5/2 (about 3.7 eV) is caused by the presence of Au 0 , and in AuNCs, Au 0 occurs in the metal cores protected by surface-capped ligands and Au + [ 32 , 33 ]. 3.3. Optimization of AuNPs Synthesis Conditions The optimal synthesis conditions, including the precursor volume ratio and synthesis temperature, were investigated by comparing the UV-Vis absorption spectra of AuNPs. Fig. S2A shows the UV-Vis absorption spectra of AuNPs prepared at volume ratios of NMP* and HAuCl 4 from 3:1 to 8:1. When the ratio was between 6:1 and 8:1, the absorption spectra showed better characteristic absorption peaks. AuNPs prepared at 70 °C showed the most obvious characteristic absorption peaks when the synthesis temperature was varied between 30 °C and 120 °C ( Fig. S2B ). For environmental friendliness and economy, AuNPs were prepared at 70°C with a volume ratio of NMP*:HAuCl 4 were 6:1. 3.4. Optimization of detection conditions In order to realize efficient and sensitive detection of Hg 2+ , the effects of AuNPs detection concentration, pH value and ionic strength on the experimental results were explored. 3.4.1 Effect of AuNPs concentration Different concentration of AuNPs have different sensitivity to Hg 2+ detection, the effect of AuNPs concentration on Hg 2+ detection was first determined. The concentration of freshly prepared AuNPs stock solution was C 0 , and when the concentration of AuNPs fluctuated in the range of C 0 to 1/6C 0, recorded the absorbance change value (ΔA) at 700 nm. As illustrated in Fig. S3A , as can be seen that with the decrease of AuNPs concentration, ΔA first increases and then decreases, reaching a peak at 1/2C 0 . Therefore, 1/2C 0 was chosen as the optimal concentration of AuNPs. 3.4.2 Effect of pH The pH of the system plays a major role in the sensing process. As shown in Fig. S3B , the effect on Hg 2+ detection by AuNPs was studied, when the pH of the system was varied between 2.0 and 11.0. It can be seen that the response of AuNPs to Hg 2+ was relatively stable when the pH value was in the 4.0 to 7.0 range. Therefore, adjusting the pH of AuNPs to 7.0 was the first choice for the detection system. 3.4.3 Effect of ionic strength In addition, the ionic strength may lead to the aggregation of AuNPs, which in turn affects the stability of AuNPs, resulting in false positive signals. Therefore, NaCl was used to adjust the ionic strength of the system, and the effect of ionic strength on the absorbance of AuNPs was studied. Fig. S3C shown that the absorbance (λ = 700 nm) of AuNPs were basically unchanged when the NaCl concentration was between 0 and 20 mM, but it increases continuously as the NaCl concentration continues to increase. This suggests that high ionic strength reduces the stability of AuNPs. Therefore, it can be concluded that by controlling the ionic strength below 20 mM, false positive signals can be avoided. 3.5. Sensitivity In order to explore the response of the colorimetric sensor to Hg 2+ and LOD, the UV-Vis absorption spectra of AuNPs and different concentrations of Hg 2+ were studied under optimal experimental conditions. From Fig. 3 A, it can be found that the absorbance value at 700 nm gradually increased with the increase of the Hg 2+ concentration, which was due to the fact that increase in the number of aggregated AuNPs with the increase of the Hg 2+ content, thereby increasing the absorbance. Meanwhile, Fig. 3 B described the linear response of Hg 2+ concentrations at 1 ~ 30 µM, and the linear regression equation can be expressed as ΔA = 0.00175 + 0.00339 [Hg 2+ ]. The LOD value for 0.3 µM was determined from the formula: LOD = 3.29 S B /m, where S B and m are the standard deviation of the blank and the slope of the calibration curve, respectively. As shown in Fig. 3 C, these changes in the UV-vis spectra correspond to a gradual change in AuNPs color from wine-red to blue-gray, and the estimated visual LOD is 15µM. 3.6. Selectivity To assess the specificity of the proposed colorimetric assay for Hg 2+ determination, the response to several potential coexisting interfering metal ions (20 μM) was investigated without the addition of masking agents. From the UV-Vis absorption spectra in Fig. 4 A, it can be found that only Hg 2+ significantly increases the absorbance of AuNPs at 700 nm. At the same time, Fig. 4 B also shown that the potential interfering substances have minimal impact on the detection of Hg 2+ , and the colorimetric sensor has good specificity for Hg 2+ . From this fact, it can be concluded that among these general metal ions, only Hg 2+ can cause the aggregation of AuNPs, which provides the possibility for the efficient and selective for Hg 2+ detection by colorimetry. Table 1 Determination of Hg 2+ in environmental water samples Sample Present method Added µM Found µM Recovery % RSD% 0.0 0.1 - - Tap water 10.0 9.1 90.5% 1.87% 20.0 21.7 108.2% 0.78% 0.0 -0.3 - - Lake water 10.0 9.4 97.3% 1.81% 20.0 21.4 108.7% 0.80% 0.0 -0.2 - - River water 10.0 9.7 99.3% 1.75% 20.0 20.9 105.7% 1.63% 3.7. Application Hg 2+ is not only an environmental pollutant, but also can accumulate in the human body through the food chain, causing acute toxicity and damaging human health. Therefore, the detection of Hg 2+ is of great importance to the environment and food safety. To test the potential of AuNPs to detect Hg 2+ , three environmental water samples were tested using the standard spiking method. The results are shown in Table 1 . The recoveries of Hg 2+ in the spiked water samples ranged between 90.5% and 108.7%, and the relative standard deviations ranged between 0.78% and 1.87%, indicating that the colorimetric sensor has great potential in determining the Hg 2+ concentrations in relation to the environment. 4. Conclusions In this paper, a colorimetric probe AuNPs with direct response to Hg 2+ was developed using treated NMP as reducing and stabilizing agent. The presence of Hg 2+ can cause the aggregation of AuNPs and increase the absorbance at 700 nm. The absorbance value of AuNPs showed a good linear relationship with Hg 2+ in the concentration range of 0 ~ 30 µM (R 2 = 0.9905), the LOD at 0.3 µM. At the same time, the wine-red AuNPs turned to blue-gray, and the estimated visual LOD at 15 µM. The method has good specificity for Hg 2+ , which provides a firm foundation for the successful quantitative analysis of Hg 2+ in environmental sewage samples. Declarations Data Availability Statement The authors confirm that the data supporting the findings of this study are available within the article and its supplementary materials. Additional information Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Supplementary Information Below is the link to the electronic supplementary material. Electronic Supplementary Information.doc Ethical Approval The study did not involve human and/or animal studies,This statement does not apply. Competing interests Competing interests The authors declare that they have no competing interests. Funding This work was supported fnancially by Natural Science Foundation of China (91543206), Graduate Education Quality Improvement Plan of Shandong Province (SDYJG21198), and research foundation of Liaocheng University (318050022 and 318012116). Author Contributions Statement Dou Yang completed the design of experimental ideas, the synthesis and feasibility verification of AuNPs, processed the data and related experiment, Rentian Guan, Rentian Guan, Shuhan Jiang are responsible for material characterization, Min Wang, Shui Zhang, Xiaoyu Fan improved the experimental scheme and processed the data. All authors reviewed the manuscript. References Q. Wang, D. Kim, D.D. Dionysiou, G.A. Sorial, D. Timberlake, Sources and remediation for mercury contamination in aquatic systems-a literature review, Environ Pollut. 131 (2) (2004) 323-336. P.B. Tchounwou, W.K. Ayensu, N. Ninashvili, D. Sutton, Review: environmental exposure to mercury and its toxicopathologic implications for public health, Environ Toxicol 18 (3) (2003) 149-175. R. Eisler R, Health risks of gold miners: a synoptic review, Environ Geochem Hlth 25 (3) (2003) 325-345. Y.L. Li, Y.M. Leng, Y.J. Zhang, T.H. Li, Z.Y. Shen, A.G. 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Additional Declarations No competing interests reported. Supplementary Files ElectronicSupplementaryInformation.doc Scheme.1.tif Scheme. 1 Schematic illustration for AuNPs synthesis and the detection of Hg 2+ 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-2400759","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":163592271,"identity":"dbc8941c-1652-475b-a49e-29e4453a3ce2","order_by":0,"name":"Dou Yang","email":"","orcid":"","institution":"Liaocheng University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Dou","middleName":"","lastName":"Yang","suffix":""},{"id":163592272,"identity":"a1685e8b-0217-4824-a575-80ec6b56aa40","order_by":1,"name":"Rentian Guan","email":"","orcid":"","institution":"Liaocheng University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Rentian","middleName":"","lastName":"Guan","suffix":""},{"id":163592273,"identity":"46a854ff-9bb8-4ee3-a6da-d6d457fd1d76","order_by":2,"name":"Shuhan Jiang","email":"","orcid":"","institution":"Liaocheng University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Shuhan","middleName":"","lastName":"Jiang","suffix":""},{"id":163592274,"identity":"3a2dff7f-1827-4f68-bf0a-b7a3442acb5d","order_by":3,"name":"Min Wang","email":"","orcid":"","institution":"Liaocheng University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Min","middleName":"","lastName":"Wang","suffix":""},{"id":163592275,"identity":"397e59f0-8cdd-48fe-afb0-b0112150f131","order_by":4,"name":"Shuai Zhang","email":"","orcid":"","institution":"Liaocheng 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University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Tao","middleName":"","lastName":"Liu","suffix":""},{"id":163592279,"identity":"e0bd522a-315a-4e1f-9eb5-d468af14d5d7","order_by":8,"name":"Shuhao Wang","email":"","orcid":"","institution":"Liaocheng University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Shuhao","middleName":"","lastName":"Wang","suffix":""},{"id":163592280,"identity":"6fa775e9-8202-4b26-bdca-256606fa65b5","order_by":9,"name":"Qiaoli Yue","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3klEQVRIiWNgGAWjYLCCBAYGGTb25gYQm7GBWC08bDwHSdECBDwMEolEajG4kXzwxoMaGx4+yYeNn3kYbGQ3HGB+9gC/lrRki4RjaTxs0onN0jwMacYbDrCZG+DXkmMmkcB2GKSljZmH4XDihgM8bBL4teR/k0j4B9QieRCk5T8xWnLYJBLbgFokGEFaDhDWInnmmbFFYh/QLzyJzZJzDJKNZx5mM8Orhe948sObP77ZyMm3Hz744U2FnWzf8eZneLUoHGBgQFIACipmfOqBQL4BRcsoGAWjYBSMAiwAALymRQATSZXjAAAAAElFTkSuQmCC","orcid":"","institution":"Liaocheng University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Qiaoli","middleName":"","lastName":"Yue","suffix":""}],"badges":[],"createdAt":"2022-12-21 09:59:35","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2400759/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2400759/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":31116455,"identity":"3d81c891-a787-4fee-8698-8b2cdf42dcd8","added_by":"auto","created_at":"2023-01-04 18:52:40","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":27625,"visible":true,"origin":"","legend":"\u003cp\u003eAbsorption spectrum and photos of the AuNPs in the presence and in the absence of Hg\u003csup\u003e2+\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"Fig1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2400759/v1/dfc71aa6e096305a0c80195d.jpg"},{"id":31114839,"identity":"c6fc1596-b8d0-4ca1-8f70-78c7fae92fda","added_by":"auto","created_at":"2023-01-04 18:44:40","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":615562,"visible":true,"origin":"","legend":"\u003cp\u003eTEM images of AuNCs (A) and AuNCs+Hg\u003csup\u003e2+\u003c/sup\u003e (B), particle size distribution diagram (C) of AuNCs, and HR-TEM images of AuNCs (D)\u003c/p\u003e","description":"","filename":"Fig2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2400759/v1/7ea1291257580319589e0eaf.jpg"},{"id":31116454,"identity":"e851d876-63d2-4261-9d57-d7d70b03d1cd","added_by":"auto","created_at":"2023-01-04 18:52:40","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":368554,"visible":true,"origin":"","legend":"\u003cp\u003eUV-Vis absorption spectra of AuNPs in the presence of Hg\u003csup\u003e2+\u003c/sup\u003e with various concentrations (0, 1, 2.5, 5, 7.5, 10, 12.5, 15, 20, 25, 30, 35, 40 μM) (A), the linear response between absorbance change (DA) and Hg\u003csup\u003e2+\u003c/sup\u003e concentration (B) and photographs of AuNPs in the presence of different concentrations of Hg\u003csup\u003e2+\u003c/sup\u003e (C)\u003c/p\u003e","description":"","filename":"Fig3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2400759/v1/4dcc3d1b980e2eeb5727c824.jpg"},{"id":31118556,"identity":"9237e78d-35b8-4b21-bf21-8121476792e9","added_by":"auto","created_at":"2023-01-04 19:00:40","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":186007,"visible":true,"origin":"","legend":"\u003cp\u003eAuNCs selectivity study for Hg\u003csup\u003e2+\u003c/sup\u003e, UV-Vis absorption spectra (A) Histogram at 700 nm (B)\u003c/p\u003e","description":"","filename":"Fig4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2400759/v1/49aee1c89b2507f27ee3dbdd.jpg"},{"id":31564582,"identity":"60976217-9e5f-4f80-a31b-a2df795e8363","added_by":"auto","created_at":"2023-01-14 01:14:28","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":751105,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2400759/v1/904cfcdb-8ec2-490d-b197-0b8ab4c5d144.pdf"},{"id":31114840,"identity":"c7dd3566-3069-477a-9cb5-017da070ae07","added_by":"auto","created_at":"2023-01-04 18:44:40","extension":"doc","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":584522,"visible":true,"origin":"","legend":"","description":"","filename":"ElectronicSupplementaryInformation.doc","url":"https://assets-eu.researchsquare.com/files/rs-2400759/v1/99c629914c797b013dfd9f41.doc"},{"id":31114834,"identity":"c13820e2-fd3c-4a3f-8175-cfb1395cae7f","added_by":"auto","created_at":"2023-01-04 18:44:40","extension":"tif","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":628174,"visible":true,"origin":"","legend":"\u003cp\u003eScheme. 1 Schematic illustration for AuNPs synthesis and the detection of Hg\u003csup\u003e2+\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"Scheme.1.tif","url":"https://assets-eu.researchsquare.com/files/rs-2400759/v1/adfb9f9f6e12456573b049cb.tif"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eA colorimetric detection of Hg\u003csup\u003e2+\u003c/sup\u003e based on gold nanoparticles synthesized oxidized N-methylpyrrolidone as a reducing agent\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eHeavy metals not only pollute the environment, but also have a negative impact on human health. Mercury (Hg) is a heavy metal element naturally present in air, water and soil. It can be widely distributed in the environment through natural activities and human activities [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Hg\u003csup\u003e2+\u003c/sup\u003e exists in both inorganic and organic forms, which belong to persistent toxic pollutants and can be enriched in organisms through the action of the food chain [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Causes a range of health problems such as myocardial infarction, minamata disease, and some autisms by damaging the kidneys, central nervous system, and reproductive system [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Traditional methods for detection of Hg\u003csup\u003e2+\u003c/sup\u003e often require expensive, complex and bulky instruments, and the operation process is complicated, which makes it difficult to meet the needs of routine analysis and field analysis [\u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Such as atomic absorption spectrometry, mass spectrometry and high performance liquid chromatography (HPLC) [\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Therefore, there is an urgent need to explore a method for Hg\u003csup\u003e2+\u003c/sup\u003e detection and monitor with high sensitivity, good selectivity, and simple operation.\u003c/p\u003e \u003cp\u003eRecently, many sensing probes for Hg\u003csup\u003e2+\u003c/sup\u003e detection based on colorimetric detection and fluorescence turn on sensing are being developed [\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. At the same time, the advantages of gold nanoparticles (AuNPs), such as good biocompatibility, easy chemical functionalization, and unique optical properties, have been gradually understood [\u003cspan additionalcitationids=\"CR17 CR18 CR19 CR20\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. In the Ultraviolet-visible (UV-vis) absorption spectrum, the position of the absorption peak produced by AuNPs is related to its particle size (or aggregated state) and shape, and the intensity of the absorption peak is linearly related to the concentration of AuNPs in the solution [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Therefore, AuNPs has unique advantages in the development of colorimetric sensors. For example, AuNPs-based colorimetry has been widely used to detect Hg\u003csup\u003e2+\u003c/sup\u003e. Recently, Ma et al. successfully constructed a novel label-free colorimetric sensor, and for the first time proposed Co\u003csup\u003e2+\u003c/sup\u003e as exonuclease III cofactors. Using auxiliary signal amplification and unmodified AuNPs as indicators to achieve Hg\u003csup\u003e2+\u003c/sup\u003e ultrasensitive detection [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Gosavi\u0026rsquo;s group reported that the successful used of AuNPs /rhodamine B (RB)/hexanedithiol (HDT) nanocomposite system for highly selective detection of Hg\u003csup\u003e2+\u003c/sup\u003e in urine and ground water [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Chen et al. proposed an amalgam formation method using gold, combined with Hg\u003csup\u003e2+\u003c/sup\u003e mediated the growth of AuNPs, which colorimetric sensing assay capable of efficient and rapid detection of Hg\u003csup\u003e2+\u003c/sup\u003e [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. However, in these methods, some ligands contain sulfhydryl groups and have a strong sulfide odor, and the detection of Hg\u003csup\u003e2+\u003c/sup\u003e are based on multi-step or complex systems, and the detection process is complicated. Therefore, an environmentally friendly colorimetric probe that can directly respond to Hg\u003csup\u003e2+\u003c/sup\u003e is urgently needed.\u003c/p\u003e \u003cp\u003eIn this work, using pretreated N-methylpyrrolidone (NMP) as reducing and stabilizing agent, an AuNPs colorimetric probe with direct response to Hg\u003csup\u003e2+\u003c/sup\u003e was developed, avoiding the use of environmentally unfriendly thiol ligand-like ligands. The presence of Hg\u003csup\u003e2+\u003c/sup\u003e can be caused the aggregation of AuNPs, the absorbance at 700 nm increased and the solution color changed from wine-red to blue-gray were observed, which is easy to identified with the naked eye. These results show that the method has good selectivity for the detection of Hg\u003csup\u003e2+\u003c/sup\u003e, which lays a foundation for further detection of Hg\u003csup\u003e2+\u003c/sup\u003e in environmental sewage samples.\u003c/p\u003e"},{"header":"2. Experimental Section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Chemicals\u003c/h2\u003e \u003cp\u003eNMP was supplied by Tci Development Co., Ltd. (Shanghai, China). Including NaOH, Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e, CuCl\u003csub\u003e2\u003c/sub\u003e, HgCl\u003csub\u003e2\u003c/sub\u003e, Zn(CH\u003csub\u003e3\u003c/sub\u003eCOO)\u003csub\u003e2\u003c/sub\u003e, Pb(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e, MgCl\u003csub\u003e2\u003c/sub\u003e, CoCl\u003csub\u003e2\u003c/sub\u003e, BaCl\u003csub\u003e2\u003c/sub\u003e, CrCl\u003csub\u003e3\u003c/sub\u003e, NaCl, NiSO\u003csub\u003e4\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO, CdCl\u003csub\u003e2\u003c/sub\u003e, CaCl\u003csub\u003e2\u003c/sub\u003e, HCl, HNO\u003csub\u003e3\u003c/sub\u003e and chloroauric acid (HAuCl\u003csub\u003e4\u003c/sub\u003e) metal salts were acquired from Aladdin Reagent Co., Ltd. (Shanghai, China). All these chemicals are of analytical grade and used directly. Deionized water provided by the Milli-Q water purification system was used for the entire experiment.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Apparatus\u003c/h2\u003e \u003cp\u003eThe UV-750 spectrophotometer (PerkinElmer, USA) was used for measurement of UV-vis absorption spectra. The morphology and size of AuNPs were recorded on a Talos F200X transmission electron microscope (TEM, Thermo Scientific Ltd., USA). The TEM used a common copper grid to load the sample and operated at an accelerating voltage of 200 kV. Fourier Transform infrared (FT-IR) spectra were carried on a Nicolet 6700 (Thermo Scientific Ltd., USA), used the KBr method. X-ray photoelectron spectroscopy (XPS) was performed on a K-Alpha spectrometer (Thermo Scientific Ltd., USA).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Preprocessing of NMP*\u003c/h2\u003e \u003cp\u003eThe method of preprocessing NMP has been modified according to previous literature [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. 50 mL of NMP and 50 mg NaOH were put in a 150 mL one-neck flask, and then refluxed at 160\u0026deg;C for 12 h under argon protection. After the reaction was completed, a brown-yellow transparent solution was obtained. Centrifuged at 12000 rpm for 30 minutes, and the supernatant was removed to acquired a pasty precipitation (NMP*). Dissolve the NMP* in 6.5 ml of deionized water and stored at 4\u0026deg;C for use in the next step.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Preparation of AuNPs\u003c/h2\u003e \u003cp\u003eThe preparation steps of AuNPs refer to the previous literature [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. All reactions were performed in glassware thoroughly cleaned using aqua regia. 2400 \u0026micro;L NMP*, 800 \u0026micro;L ultrapure water and 100 \u0026micro;L of HAuCl\u003csub\u003e4\u003c/sub\u003e (24.28 mM) were blended and stirred at 70\u0026deg;C for 45 min. During this period, the color gradually changed from pale-yellow to wine-red, which proved that AuNPs had been formed. The cooled solution was stored at 4\u0026deg;C for later studies.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5. Colorimetric assay for the Hg\u003csup\u003e2+\u003c/sup\u003e\u003c/h2\u003e \u003cp\u003eThe Hg\u003csup\u003e2+\u003c/sup\u003e detection procedure is described as follows: first, various concentrations of Hg\u003csup\u003e2+\u003c/sup\u003e standard stock solutions were prepared by dissolving the metal salt HgCl\u003csub\u003e2\u003c/sub\u003e in deionized water. Then the AuNPs system was mixed with various concentrations of Hg\u003csup\u003e2+\u003c/sup\u003e at a 1:1 volume ratio and incubated for 10 min. The Uv-vis absorption spectra were acquired at 700 nm in the presence and absence of Hg\u003csup\u003e2+\u003c/sup\u003e. The selectivity of AuNPs to Hg\u003csup\u003e2+\u003c/sup\u003e was investigated by performing detection of other relevant metal ions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6. Pretreatment of real samples\u003c/h2\u003e \u003cp\u003eIn order to explore the practicability of the detection method, three environmental water samples were tested. The lake water was obtained from the artificial lake of Liaocheng University, the tap water was obtained from the chemical laboratory of Liaocheng University, and the river water was obtained from the local natural Tuhai River. After the water samples were precipitated for 24 h, the supernatant was appropriately diluted with deionized water. After adding different concentrations of Hg\u003csup\u003e2+\u003c/sup\u003e standard solutions to the samples, the UV-Vis absorption spectra of AuNPs-Hg\u003csup\u003e2+\u003c/sup\u003e at 700 nm were record.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results And Discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n\u003ch2\u003e3.1 Principles of the colorimetric assay for Hg\u003csup\u003e2+\u003c/sup\u003e\u003c/h2\u003e\n\u003cp\u003eIn this study, developed a colorimetric assay for Hg\u003csup\u003e2+\u003c/sup\u003e detection using AuNPs (Scheme \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).The AuNPs were prepared in the experimental section and displayed red color. According to previous literature [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e], NMP can be oxidized and hydrolyzed to formed NMP* with high reducibility under alkaline and high temperature conditions, and can be used as reducing and templating agents to prepared metal nanoclusters. NMP* and HAuCl\u003csub\u003e4\u003c/sub\u003e were used as precursors to prepared AuNPs with sensitive response to Hg\u003csup\u003e2+\u003c/sup\u003e. In the absence of Hg\u003csup\u003e2+\u003c/sup\u003e, a stable wine-red dispersion was observed and displayed a characteristic surface plasmon resonance (SPR) absorption band at 518 nm (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). This is because AuNPs are anisotropic nanomaterials, and the absorption spectrum of AuNPs in monodisperse state has only a single peak at 518 nm [\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e]. The appearance of Hg\u003csup\u003e2+\u003c/sup\u003e could induce the aggregation of AuNPs, so that the absorbance of AuNPs at 700 nm increased continuously, and the color of the mixture became blue-gray. This is due to the polarization and coupling between the electrons of adjacent nanoparticles when the AuNPs are in an aggregated state, resulting in a red-shift of the maximum absorption wavelength of the AuNPs. Correspondingly, the wine-red AuNPs gradually turned to blue-gray [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e]. As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eA \u003cstrong\u003eand B\u003c/strong\u003e, this aggregation process was also confirmed by TEM, the AuNPs were in a monodisperse state in the absence of Hg\u003csup\u003e2+\u003c/sup\u003e. After the added of Hg\u003csup\u003e2+\u003c/sup\u003e, the AuNPs were clearly aggregated together, resulting in a significant changed in color and providing colorimetric detection of Hg\u003csup\u003e2+\u003c/sup\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n\u003ch2\u003e3.2. Characterization of AuNCs\u003c/h2\u003e\n\u003cp\u003eTEM, FT-IR and XPS were used to characterize the resulting functionalized AuNPs. The morphology of AuNPs was first investigated used TEM. The results showed that our as-prepared AuNPs were freely dispersed in water with good water solubility (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eA). As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eC, by calculated, the particle size distribution of AuNPs was between 8\u0026ndash;17 nm with an average diameter of 13\u0026thinsp;\u0026plusmn;\u0026thinsp;2 nm. HR-TEM revealed the lattice fringes of 2.34 \u0026Aring; for AuNPs consistent with metallic gold (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eD), which corresponds to the d spacing of the (111) crystal plane of fcc Au [\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eFT-IR spectroscopy was used to analysis the surface of AuNPs (\u003cstrong\u003eFig. S1A\u003c/strong\u003e). The broad band at 3430.86 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponds to stretching vibrations of inter molecularly bonded O-H group. The typical peak at 1574.32 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is other important peak of functional group and assigned to C\u0026thinsp;=\u0026thinsp;O. Absorption bands located at 1414.10 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e correspond to the C-N stretching vibration bands. These all demonstrated that the NMP* were successfully engrafted to the AuNPs. The chemical valence state of Au element in AuNPs plays an important role in its optical properties. \u003cstrong\u003eFig. S1B\u003c/strong\u003e shown the HR-XPS spectra of AuNPs in the range of 82\u0026ndash;90 eV, Au4f\u003csub\u003e7/2\u003c/sub\u003e and Au4f\u003csub\u003e5/2\u003c/sub\u003e are centered at binding energy values of 84.2 and 87.9 eV, respectively [\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e]. Au4f\u003csub\u003e7/2\u003c/sub\u003e and Au4f\u003csub\u003e5/2\u003c/sub\u003e could be further deconvoluted into two distinct peaks, respectively. The higher intensity doublets at binding energies at 84.2 (Au4f\u003csub\u003e7/2\u003c/sub\u003e) and 88.0 eV (Au4f\u003csub\u003e5/2\u003c/sub\u003e) could be attributed to Au\u003csup\u003e+\u003c/sup\u003e, while the binding energies of Au\u003csup\u003e0\u003c/sup\u003e are lower at 88.3 (Au4f\u003csub\u003e7/2\u003c/sub\u003e) and 87.1 eV (Au4f\u003csub\u003e5/2\u003c/sub\u003e). According to previous literature, the difference between the peaks of Au4f\u003csub\u003e7/2\u003c/sub\u003e and Au4f\u003csub\u003e5/2\u003c/sub\u003e (about 3.7 eV) is caused by the presence of Au\u003csup\u003e0\u003c/sup\u003e, and in AuNCs, Au\u003csup\u003e0\u003c/sup\u003e occurs in the metal cores protected by surface-capped ligands and Au\u003csup\u003e+\u003c/sup\u003e [\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n\u003ch2\u003e3.3. Optimization of AuNPs Synthesis Conditions\u003c/h2\u003e\n\u003cp\u003eThe optimal synthesis conditions, including the precursor volume ratio and synthesis temperature, were investigated by comparing the UV-Vis absorption spectra of AuNPs. \u003cstrong\u003eFig. S2A\u003c/strong\u003e shows the UV-Vis absorption spectra of AuNPs prepared at volume ratios of NMP* and HAuCl\u003csub\u003e4\u003c/sub\u003e from 3:1 to 8:1. When the ratio was between 6:1 and 8:1, the absorption spectra showed better characteristic absorption peaks. AuNPs prepared at 70 \u0026deg;C showed the most obvious characteristic absorption peaks when the synthesis temperature was varied between 30 \u0026deg;C and 120 \u0026deg;C (\u003cstrong\u003eFig. S2B\u003c/strong\u003e). For environmental friendliness and economy, AuNPs were prepared at 70\u0026deg;C with a volume ratio of NMP*:HAuCl\u003csub\u003e4\u003c/sub\u003e were 6:1.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n\u003ch2\u003e3.4. Optimization of detection conditions\u003c/h2\u003e\n\u003cp\u003eIn order to realize efficient and sensitive detection of Hg\u003csup\u003e2+\u003c/sup\u003e, the effects of AuNPs detection concentration, pH value and ionic strength on the experimental results were explored.\u003c/p\u003e\n\u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\n\u003ch2\u003e3.4.1 Effect of AuNPs concentration\u003c/h2\u003e\n\u003cp\u003eDifferent concentration of AuNPs have different sensitivity to Hg\u003csup\u003e2+\u003c/sup\u003e detection, the effect of AuNPs concentration on Hg\u003csup\u003e2+\u003c/sup\u003e detection was first determined. The concentration of freshly prepared AuNPs stock solution was C\u003csub\u003e0\u003c/sub\u003e, and when the concentration of AuNPs fluctuated in the range of C\u003csub\u003e0\u003c/sub\u003e to 1/6C\u003csub\u003e0,\u003c/sub\u003e recorded the absorbance change value (\u0026Delta;A) at 700 nm. As illustrated in \u003cstrong\u003eFig. S3A\u003c/strong\u003e, as can be seen that with the decrease of AuNPs concentration, \u0026Delta;A first increases and then decreases, reaching a peak at 1/2C\u003csub\u003e0\u003c/sub\u003e. Therefore, 1/2C\u003csub\u003e0\u003c/sub\u003e was chosen as the optimal concentration of AuNPs.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\n\u003ch2\u003e3.4.2 Effect of pH\u003c/h2\u003e\n\u003cp\u003eThe pH of the system plays a major role in the sensing process. As shown in \u003cstrong\u003eFig. S3B\u003c/strong\u003e, the effect on Hg\u003csup\u003e2+\u003c/sup\u003e detection by AuNPs was studied, when the pH of the system was varied between 2.0 and 11.0. It can be seen that the response of AuNPs to Hg\u003csup\u003e2+\u003c/sup\u003e was relatively stable when the pH value was in the 4.0 to 7.0 range. Therefore, adjusting the pH of AuNPs to 7.0 was the first choice for the detection system.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section3\"\u003e\n\u003ch2\u003e3.4.3 Effect of ionic strength\u003c/h2\u003e\n\u003cp\u003eIn addition, the ionic strength may lead to the aggregation of AuNPs, which in turn affects the stability of AuNPs, resulting in false positive signals. Therefore, NaCl was used to adjust the ionic strength of the system, and the effect of ionic strength on the absorbance of AuNPs was studied. \u003cstrong\u003eFig. S3C\u003c/strong\u003e shown that the absorbance (\u0026lambda;\u0026thinsp;=\u0026thinsp;700 nm) of AuNPs were basically unchanged when the NaCl concentration was between 0 and 20 mM, but it increases continuously as the NaCl concentration continues to increase. This suggests that high ionic strength reduces the stability of AuNPs. Therefore, it can be concluded that by controlling the ionic strength below 20 mM, false positive signals can be avoided.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\n\u003ch2\u003e3.5. Sensitivity\u003c/h2\u003e\n\u003cp\u003eIn order to explore the response of the colorimetric sensor to Hg\u003csup\u003e2+\u003c/sup\u003e and LOD, the UV-Vis absorption spectra of AuNPs and different concentrations of Hg\u003csup\u003e2+\u003c/sup\u003e were studied under optimal experimental conditions. From Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eA, it can be found that the absorbance value at 700 nm gradually increased with the increase of the Hg\u003csup\u003e2+\u003c/sup\u003e concentration, which was due to the fact that increase in the number of aggregated AuNPs with the increase of the Hg\u003csup\u003e2+\u003c/sup\u003e content, thereby increasing the absorbance. Meanwhile, Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eB described the linear response of Hg\u003csup\u003e2+\u003c/sup\u003e concentrations at 1\u0026thinsp;~\u0026thinsp;30 \u0026micro;M, and the linear regression equation can be expressed as \u0026Delta;A\u0026thinsp;=\u0026thinsp;0.00175\u0026thinsp;+\u0026thinsp;0.00339 [Hg\u003csup\u003e2+\u003c/sup\u003e]. The LOD value for 0.3 \u0026micro;M was determined from the formula: LOD\u0026thinsp;=\u0026thinsp;3.29 S\u003csub\u003eB\u003c/sub\u003e/m, where S\u003csub\u003eB\u003c/sub\u003e and m are the standard deviation of the blank and the slope of the calibration curve, respectively. As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eC, these changes in the UV-vis spectra correspond to a gradual change in AuNPs color from wine-red to blue-gray, and the estimated visual LOD is 15\u0026micro;M.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\n\u003ch2\u003e3.6. Selectivity\u003c/h2\u003e\n\u003cp\u003eTo assess the specificity of the proposed colorimetric assay for Hg\u003csup\u003e2+\u003c/sup\u003e determination, the response to several potential coexisting interfering metal ions (20 \u0026mu;M) was investigated without the addition of masking agents. From the UV-Vis absorption spectra in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eA, it can be found that only Hg\u003csup\u003e2+\u003c/sup\u003e significantly increases the absorbance of AuNPs at 700 nm. At the same time, Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eB also shown that the potential interfering substances have minimal impact on the detection of Hg\u003csup\u003e2+\u003c/sup\u003e, and the colorimetric sensor has good specificity for Hg\u003csup\u003e2+\u003c/sup\u003e. From this fact, it can be concluded that among these general metal ions, only Hg\u003csup\u003e2+\u003c/sup\u003e can cause the aggregation of AuNPs, which provides the possibility for the efficient and selective for Hg\u003csup\u003e2+\u003c/sup\u003e detection by colorimetry.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eDetermination of Hg\u003csup\u003e2+\u003c/sup\u003e in environmental water samples\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eSample\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"4\" align=\"left\"\u003e\n\u003cp\u003ePresent method\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAdded \u0026micro;M\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eFound \u0026micro;M\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eRecovery %\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eRSD%\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTap water\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e9.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e90.5%\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.87%\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e20.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e21.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e108.2%\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.78%\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-0.3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eLake water\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e9.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e97.3%\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.81%\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e20.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e21.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e108.7%\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.80%\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-0.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eRiver water\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e9.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e99.3%\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.75%\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e20.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e20.9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e105.7%\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.63%\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003e3.7. Application\u003c/h2\u003e\n\u003cp\u003eHg\u003csup\u003e2+\u003c/sup\u003e is not only an environmental pollutant, but also can accumulate in the human body through the food chain, causing acute toxicity and damaging human health. Therefore, the detection of Hg\u003csup\u003e2+\u003c/sup\u003e is of great importance to the environment and food safety. To test the potential of AuNPs to detect Hg\u003csup\u003e2+\u003c/sup\u003e, three environmental water samples were tested using the standard spiking method. The results are shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The recoveries of Hg\u003csup\u003e2+\u003c/sup\u003e in the spiked water samples ranged between 90.5% and 108.7%, and the relative standard deviations ranged between 0.78% and 1.87%, indicating that the colorimetric sensor has great potential in determining the Hg\u003csup\u003e2+\u003c/sup\u003e concentrations in relation to the environment.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn this paper, a colorimetric probe AuNPs with direct response to Hg\u003csup\u003e2+\u003c/sup\u003e was developed using treated NMP as reducing and stabilizing agent. The presence of Hg\u003csup\u003e2+\u003c/sup\u003e can cause the aggregation of AuNPs and increase the absorbance at 700 nm. The absorbance value of AuNPs showed a good linear relationship with Hg\u003csup\u003e2+\u003c/sup\u003e in the concentration range of 0\u0026thinsp;~\u0026thinsp;30 \u0026micro;M (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.9905), the LOD at 0.3 \u0026micro;M. At the same time, the wine-red AuNPs turned to blue-gray, and the estimated visual LOD at 15 \u0026micro;M. The method has good specificity for Hg\u003csup\u003e2+\u003c/sup\u003e, which provides a firm foundation for the successful quantitative analysis of Hg\u003csup\u003e2+\u003c/sup\u003e in environmental sewage samples.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors confirm that the data supporting the findings of this study are available within the article and its supplementary materials.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePublisher\u0026apos;s Note\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary Information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBelow is the link to the electronic supplementary material.\u003c/p\u003e\n\u003cp\u003eElectronic Supplementary Information.doc\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study did not involve human and/or animal studies,This statement does not apply.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCompeting interests The authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported fnancially by Natural Science Foundation of China (91543206), Graduate Education Quality Improvement Plan of Shandong Province (SDYJG21198), and research foundation of Liaocheng University (318050022 and 318012116).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDou Yang completed the design of experimental ideas, the synthesis and feasibility verification of AuNPs, processed the data and related experiment, Rentian Guan, Rentian Guan, Shuhan Jiang are responsible for material characterization, Min Wang, Shui Zhang, Xiaoyu Fan improved the experimental scheme and processed the data. All authors reviewed the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eQ. Wang, D. Kim, D.D. Dionysiou, G.A. Sorial, D. Timberlake, Sources and remediation for mercury contamination in aquatic systems-a literature review, Environ Pollut. 131 (2) (2004) 323-336.\u003c/li\u003e\n \u003cli\u003eP.B. Tchounwou, W.K. Ayensu, N. Ninashvili, D. Sutton, Review: environmental exposure to mercury and its toxicopathologic implications for public health, Environ Toxicol 18 (3) (2003) 149-175.\u003c/li\u003e\n \u003cli\u003eR. Eisler R, Health risks of gold miners: a synoptic review, Environ Geochem Hlth 25 (3) (2003) 325-345.\u003c/li\u003e\n \u003cli\u003eY.L. Li, Y.M. Leng, Y.J. Zhang, T.H. Li, Z.Y. Shen, A.G. 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Liu, B.A. Du, Selective determination of cysteine by resonance light scattering technique based on self-assembly of gold nanoparticles, Anal biochem 351 (1) (2006) 18-25.\u003c/li\u003e\n \u003cli\u003eC.C. Huang, Z. Yang, K.H. Lee, H.T. Chang, Synthesis of highly fluorescent gold nanoparticles for sensing Mercury(II), Angew Chem 119 (36) (2007) 6948-6952.\u003c/li\u003e\n \u003cli\u003eH. Zhang, H. Wu, X. Qin, Y. Shen, X. Wei, G. Liu, Metalloporphyrin and gold nanoparticles modified hollow zeolite imidazole Framework-8 with excellent peroxidase like activity for quick colorimetric determination of choline in infant formula milk powder, Food Chem 384 (2022) 132552.\u003c/li\u003e\n \u003cli\u003eD. Bain, S. Maity, B. Paramanik, A. Patra, Core-size dependent fluorescent gold nanoclusters and ultrasensitive detection of Pb\u003csup\u003e2+\u003c/sup\u003e ion, ACS Sustain Chem \u0026amp; Eng 6 (2) (2018) 2334-2343.\u003c/li\u003e\n \u003cli\u003eA. Morfin-Gutierrez, J.L. S\u0026aacute;nchez-Orozco, L.A. Garc\u0026iacute;a-Cerda, B. Puente-Urbina, H.I. Mel\u0026eacute;ndez-Ortiz, Synthesis and characterization of poly(N-vinycaprolactam)-grafted gold nanoparticles by free radical polymerization for using as chemotherapeutic delivery system，Mater Chem Phys 266（2021）124535.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Scheme 1","content":"\u003cp\u003eScheme 1 is available in the Supplemental Files section.\u003c/p\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":"Hg2+, gold nanoparticles, N-methylpyrrolidone, colorimetry, visual mode","lastPublishedDoi":"10.21203/rs.3.rs-2400759/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2400759/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this study, a gold nanoparticles colorimetric probe (AuNPs) with direct response to mercury ions (Hg\u003csup\u003e2+\u003c/sup\u003e) were developed using treated N-methylpyrrolidone (NMP) and chloroauric acid (HAuCl\u003csub\u003e4\u003c/sub\u003e) as precursors. NMP showed good reducibility after high temperature hydrolysis and could be used as reducing and stabilizing agent to synthesize AuNPs. The prepared AuNPs have obvious characteristic absorption peaks and appear wine-red. At the same time, it was found that the presence of Hg\u003csup\u003e2+\u003c/sup\u003e can cause the aggregation of AuNPs, increased the absorbance at 700 nm, and changed the color of the solution into blue-gray. This method is capable of sensitive and specific determination of Hg\u003csup\u003e2+\u003c/sup\u003e ranging from 1 to 30 \u0026micro;M, with the limit of detection (LOD) at 0.3 \u0026micro;M. The method showed good specificity for the determination of Hg\u003csup\u003e2+\u003c/sup\u003e and has the potential to be applied to Hg\u003csup\u003e2+\u003c/sup\u003e detection in sewage samples in the environment.\u003c/p\u003e","manuscriptTitle":"A colorimetric detection of Hg2+ based on gold nanoparticles synthesized oxidized N-methylpyrrolidone as a reducing agent","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-01-04 18:44:34","doi":"10.21203/rs.3.rs-2400759/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":"e5e3d6fc-041b-4f2d-a7c1-dc262578deec","owner":[],"postedDate":"January 4th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2023-03-06T09:14:36+00:00","versionOfRecord":[],"versionCreatedAt":"2023-01-04 18:44:34","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-2400759","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2400759","identity":"rs-2400759","version":["v1"]},"buildId":"cBFmMYwuxLRRLfASyISRj","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}