Colorimetric sensing of silver ions based on glutathione-mediated MnO2 nanosheets

Accepted Manuscript Title: Colorimetric sensing of silver ions based on glutathione-mediated MnO2 nanosheets Authors: Liuying He, Yuexiang Lu, Feiyang Wang, Wenjie Jing, Ying Chen, Yueying Liu PII: DOI: Reference:

S0925-4005(17)31339-4 http://dx.doi.org/doi:10.1016/j.snb.2017.07.131 SNB 22790

To appear in:

Sensors and Actuators B

Received date: Revised date: Accepted date:

18-4-2017 14-7-2017 17-7-2017

Please cite this article as: Liuying He, Yuexiang Lu, Feiyang Wang, Wenjie Jing, Ying Chen, Yueying Liu, Colorimetric sensing of silver ions based on glutathione-mediated MnO2 nanosheets, Sensors and Actuators B: Chemicalhttp://dx.doi.org/10.1016/j.snb.2017.07.131 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Colorimetric sensing of silver ions based on glutathione-mediated MnO2 nanosheets Liuying He,a, Yuexiang Lu,b Feiyang Wang,a Wenjie Jing,a Ying Chen,a Yueying Liua,*

a

Department of Chemistry, Capital Normal University, Xisanhuan North Rd. 105,

Beijing, 100048, P. R. China

b

Institute of Nuclear and New Energy Technology, Collaborative Innovation Center

of Advanced Nuclear Energy Technology, Beijing Key Lab of Radioactive Waste Treatment, Tsinghua University, Beijing, 100084, P. R. China

[*] Dr YueyingLiu. Corresponding author. E-mail: [email protected]

1

Highlights 1.

A simple, rapid colorimetric platform has been proposed for detection of Ag+ by naked eyes.

2.

The glutathione-mediated MnO2 nanosheets were employed as an artificial oxidase, catalyzing colorless TMB into blue oxTMB instantaneously.

3.

The limit of detection is 4.23 nM, which is of sensitivity to existing other methods.

4.

The proposed colorimetric sensor is of high sensitive and selectivity in water and practical samples.

ABSTRACT We described a rapid and highly sensitive colorimetric method for the detection and quantification of silver ions employing glutathione (GSH)-mediated MnO2 nanosheets as an artificial oxidase. In this assay, the absorption intensity of the chromogenic reaction system enabled the quantification of silver ions. Under the optimum conditions, the linear response ranged for Ag+ was from 10 nM to 800 nM with a correlation coefficient of 0.996. Remarkably, limit of detection in aqueous solutions was 4.23 nM, which was well below United States Environmental Protection Agency (USEPA) permissible limit in drinking water (460 nM). This sensing assay had highly specificity because no significant interference occurred with 10-fold concentration of other metal ions. Moreover, the approach also could be employed to the Ag+ detection in real samples. And the recovery of Ag+ spiked in tap water ranged from 99.62% to 2

108.01%. Importantly, the oxidation reaction of TMB to oxTMB by MnO2 nanosheets completed instantaneously even by naked-eye readout. Therefore, the assay based on GSH-mediated MnO2 nanosheets is simple, rapid, highly sensitive and selective for the quantification of Ag+ in water and practical samples.

Keywords:

MnO2 nanosheets Artificial oxidase Colorimetric assay Silver ions detection GSH-mediated system

1. Introduction Silver ions (Ag+) is one of the most hazardous pollutants[1], which is mainly used in electroplating, photography imaging, dental and medical products, and electronic equipment. The excess amount of silver ions would exert severe effects on the environment and pose adverse to human health [2, 3]. As an important bioactive cation, Ag+ can bind with many metabolites, inactivate sulfhydryl enzymes, accumulate in the body and induce various disorders. Therefore, development of a sensitive and selective sensing platform for quantitative detection of Ag+ is of great importance to both human health and environment protection. Traditional techniques for Ag+ detection mainly include inductively coupled plasma-mass spectrometry (ICP-MS) [4, 5], and atomic absorption/emission spectroscopy [6, 7]. In spite of the availability for detection of Ag+ at trace level, these 3

approaches are costly, time-consuming, complicated, and the need of professional operation, which limits their practical applications. In response to the defects of traditional techniques, the colorimetric sensors have many advantages [8], and the exploration based on functionalized gold nanoparticles (AuNPs) have gained popularity for the detection of Ag+ due to their high extinction coefficient and distance-dependent optical properties [9]. Various ligands including small organic molecules [10, 11], peptides [12], and cytosine-(C)-rich oligonucleotides [13], have been reported for the quantification of Ag+. Although the colorimetric methods based on AuNPs aggregation are powerful, there is somewhat difficult for the analytes at the trace levels. Because it is insensitive to distinguish subtle color change induced by the aggregation degree of AuNPs by naked-eye readout. In addition, these strategies still suffer from tedious probe preparation, unsatisfactory selectivity and sensitivity [14, 15]. Therefore, there are great challenges to obtain higher sensitivity and lower detection limit for Ag+ detection. Recently, as one kind of redox active two-dimensional (2D) nanosheets, single-layer MnO2 nanosheets have attracted considerable interest for their unique properties, including high specific surface area, higher chemical stability, and intrinsic oxidase-like activity [16-18]. Single-layer MnO2 nanosheets have three atomic layers, that is one Mn layer sandwiched by two O layers. Each Mn coordinates to six O atoms to form an edge-sharing MnO6 octahedral crystal lattice, which exhibits a broad absorption peak (200-600 nm) and excellent absorption capability (9.6×103 M−1 cm−1 molar extinction coefficient at 380 nm) [19]. The broad absorption is adaptable to use 4

as effective fluorescence quenchers or energy acceptors for the various targets such as H2O2 [20], T4 polynucleotide kinase [21], and ascorbic acid [22], glutathione [23, 24], and Fe2+ [25]. MnO2 nansheets are reported to have intrinsic oxidase-like activity, which can catalyze colorless substrate TMB to blue oxidized product (oxTMB) at 650 nm [26]. The reaction system using dissolved molecular oxygen in the solution, overcoming the requirement for H2O2. The MnO2 nansheets coupled TMB provides an alternative nanomaterial for the development of novel colorimetric analysis [27]. Nevertheless, colorimetric sensor arrays based on MnO2 nansheets as an artificial enzyme are very rare. Accordingly, there have been great demands for the fabrication of colorimetric sensor arrays based on MnO2 nanosheets. In this paper, we propose an operationally simple and rapid colorimetric strategy for Ag+ detection based on GSH-mediated MnO2 nanosheets (Scheme 1). The redox reaction between MnO2 nanosheets and GSH decreases the produce of oxTMB. As a result, the reaction solution still keeps colorless. When Ag+ is added to the solution, the coordination between GSH and Ag+ [28] inhibits the decomposition of MnO2 nanosheets, and the reaction solution changes to blue. There is a linear relationship between Ag+ concentration and blue oxTMB according to the mechanism. Importantly, GSH-mediated MnO2 nanosheets system has been showed to be highly sensitive and selective detection of Ag+ than other metal ions. We also further demonstrated the analytical potential of this colorimetric sensing system for monitoring Ag+ in water samples.

2. Experimental section 5

2.1 Materials Tetramethylammonium hydroxide (TMA·OH) and 3, 3´, 5, 5´-tetramethylbenzidine (TMB) were obtained from Sigma-Aldrich (Saint Louis, USA). Manganese chloride tetrahydrate (MnCl2·4H2O) and methanol were purchased from Xilong Chemical Co., Ltd (Shantou, China). Silver nitrate, Ethylenediaminetetraacetic acid (EDTA) and hydrogen peroxide (H2O2, 30 wt %) were purchased from Beijing Chemical Works (Beijing, China). Acetic acid (HOAc) and sodium acetate (NaOAc) were purchased from Sangon Biotech. Co., Ltd. (Shanghai, China). L- glutathione reduced (GSH) was obtained from Beijing Biodee Biotechnology Co., Ltd (Beijing, China). All of the reagents and chemicals were at least analytical grade and used as received. The ultrapure water used throughout all experiments was purified by a Milli-Q system (Millipore, Bedford, MA, USA). 2.2 Instruments Absorption spectra were recorded on SpectraMaxRM2e MultiMode Microplate Reader (Molecular Devices, California, USA) at room temperature. The 96-well plates were produced from Costar (3590, USA). Transmission electron microscope (TEM) images were obtained on a Hitachi (H-7650, 80 kV) transmission electron microscope. Absorption spectra of MnO2 was measured on UV-Vis spectrophotometer (UV-2550, Shimadzu, Japan). 2.3 Synthesis of single-layer MnO2 nanosheets The single-layer manganese dioxide nanosheets were prepared as previous reports [29]. In brief, 12 mL of TMA·OH (1.0 M) and 2 mL of 30 wt % H2O2 were diluted to 6

20 mL mixture, then it was added into 10 mL of 0.3 M MnCl2·4H2O aqueous solution within 15 s. As the two mixtures were mixed, the solution became dark brown immediately. At room temperate, the obtained dark brown solution was stirred vigorously in the open air. The obtained bulk MnO2 was centrifuged and washed three times with distilled water and methanol, then centrifuged at 12,000 rpm for 10 minutes. After that, the precipitate was dried in vacuum oven at 60 °C. To prepare single-layer MnO2 nanosheets, 10 mg bulk MnO2 was added into 20 mL ultrapure water and ultrasonicated for 10 h. Subsequently, the suspension was centrifuged at 2, 000 rpm for 10 min and the supernatant was stored at 4 °C for further use. To calculate the concentration of resulting MnO2 nanosheets, the absorption spectra of the supernatant was measured and the concentration was quantified according to Lambert−Beer’s Law with the molar extinction coefficient of 9.6 × 103 M−1 cm−1 at 380 nm [30]. 2.4 Colorimetric detection of Ag+ Ag+ was prepared by dissolving silver nitrate (AgNO3) in distilled water. First, 75 μL of 200 μM GSH solution was mixed with different concentration of Ag+ (50 μL). Then, 100 μL of MnO2 (final concentration of 20 μM) and 225 μL of HOAc-NaOAc buffer solution (pH=4.00) were added into the mixture, which was incubated with vigorous shaking for 5 min to react completely. Subsequently, 50 μL of TMB solution was added into the centrifuge tubes. Finally, 200 μL of the reaction mixtures were loaded into a 96-well plate by using the pipette (200 μL), respectively. The 96-well plates are produced from Costar (USA). The type of 96-well plates is 3590, and the 7

maximum volume of each well is about 300 μL. The UV-Vis absorption spectra of the work solutions were measured over the wavelength ranging from 500 nm to 800 nm, respectively. 2.5 Selectivity of Ag+ detection To determine the selectivity of the detection method, the Ag+ and other metal ions with 10-fold concentrations were tested in a same way. We prepared other 13 kinds of metal ions, including Hg2+, Fe2+, Cu2+, Fe3+, K+, Zn2+, Na+, Cd2+, Ca2+, Ni2+, Co2+, Pb2+, Mn2+. The concentration of Ag+ was selected as 1.0 μM, and other metal ions were 10 μM. 2.6 Application to real samples To investigate the detection performance of the sensing strategy in practical application, the tap water was collected and centrifuged at 12, 000 rpm for 10 minutes. And then the supernatant was obtained to remove physical impurities. Subsequently, the Ag+ was dissolved in the tap water for further sensing. The assay condition was same as mentioned above for Ag+ sensing.

3. Results and discussion 3.1 Characterization of MnO2 nanosheets In this work, H2O2 was used to synthesize bulk δ-MnO2 by oxidation of Mn2+ in presence of TMA·OH. As previously described, MnO2 nanosheets was prepared by ultrasonic of the bulk δ-MnO2 sample. Transmission electron microscopy (TEM) and UV-Vis absorption spectra were adopted to characterize the obtained MnO2 nanosheets. As shown in Figure 1A, the TEM image of MnO2 nanosheets revealed a 8

typical two-dimensional layer structure, and exhibited multiple folds and crinkles. As can be seen from Figure 1B, the UV-Vis absorption spectra of MnO2 nanosheets dispersion displayed a characteristic peak at 380 nm, which was attributed to the d-d transition of Mn4+ ions. This was consistent with a number of previous studies about the optical characteristic of two-dimensional layer MnO2 nanosheets [31]. The intensity of absorption peak was increased with the increasing concentrations of MnO2 nanosheets. Besides, the XPS analyses were performed with the prepared MnO2. A wide scan XPS spectrum was shown in Figure 1C, the binding energy peaks of Mn 2p, O 1s, N 1s and C 1s were 641.6, 528.6, 401.6 and 284.6 eV, respectively. There were no extra signals attributed to Mn2O3 and KMnO4 were observed in the XPS spectrum, indicating the acquisition of pure MnO2. In Figure 1D, two characteristic peaks located at 641.2 and 652.95 eV were observed, which can be assigned to Mn 2p3/2 and Mn 2p1/2. Therefore, oxidation state of Mn can be determined as +4 in pure MnO2 [32, 33]. The peak at 528.6 eV in Figure 1E is attributed to O 1s binding energy, which are assigned to the lattice oxygen of [MnO6] octahedral. These results demonstrated that two-dimensional layer MnO2 nanosheets were successfully synthesized. 3.2 Principle of colorimetric sensor The UV-Vis absorption spectra and the corresponding photographs were shown in Figure S1. The 3, 3´, 5, 5´-tetramethylbenzidine (TMB) solution was colorless, and there was barely absorption band range from 500 nm to 800 nm. In the presence of MnO2 nanosheets, the reaction solution changed from colorless to blue, confirming 9

the oxidation of TMB by MnO2 nanosheets. The oxidation product of TMB exhibited maximum absorption at 650 nm. GSH as an antioxidant could result in the significant reduction of MnO2 nanosheets listed in Eq. (1). MnO2 + 2GSH + 2H+→Mn2+ + GSSG + 2H2O

(1)

The decomposition of the MnO2 nanosheets inhibited the oxidation of TMB to oxTMB, so the reaction solution still remained colorless. Remarkably, silver ions had high binding specificity with GSH, the catalytic activity of MnO2 nanosheets restored and the color of solution changed from the colorless to blue after addition of Ag+, which attributed to highly sensitivity of silver ions. There is a linear relationship between Ag+ concentration and blue oxTMB according to the mechanism. 3.3 Optimization of experiment conditions In order to achieve high sensitivity, some important parameters including pH, the concentration of TMB and reaction time, were systematically investigated to determine the optimum reaction conditions. The colorimetric conversion of TMB to oxidation TMB by MnO2 nanosheets was highly dependent on pH value. As indicated in Figure 2A, the absorption value of MnO2 nanosheets and TMB system gradually decreased with increasing the pH of HOAc-NaOAc buffer solution, which was ascribe to MnO2 nanosheets exhibiting a strong oxidation activity in an acidic condition. The absorption value of reaction system was maximal when HOAc-NaOAc buffer solution was set at pH 4.0. Therefore, HOAc-NaOAc buffer solution was selected at pH 4.0 for further experiments. Subsequently, the absorption value at 650 nm presented parabola shape with increasing the concentration of TMB. The color of solution was 10

yellow-green at low or high concentration of TMB in Figure 2B. Consequently, 200 μM of TMB was chosen for our experiments. Finally, the reaction time for the oxidation of TMB was investigated in the presence of GSH and Ag+. As shown in Figure 2C, the absorption intensity of oxTMB was no significant change with the increasing reaction time. This result showed that the redox reaction of TMB quickly finished by catalytic activity of MnO2 nanosheets. In order to obtain the good reproducibility, the reaction time of 5 min was selected to develop the colorimetric Ag+ detection. Therefore, 200 μM of TMB, HOAc-NaOAc buffer solution at pH 4.0, and the reaction time of 5 min were chosen for further experiments. 3.4 Optimization of GSH concentrations In order to achieve highly sensitive quantification of Ag+, the different concentrations of GSH for the reduction of MnO2 nanosheets were very important parameter and optimized. As shown in Figure 3, the absorption value of reaction system at 650 nm gradually decreased with the increasing the concentration of GSH, corresponding to the color gradually turns blue to colorless, due to the reduction of MnO2 to Mn2+ and reduce the amount of oxTMB produced by MnO2 nanosheets. To realize highly sensitive detection of Ag+, 30 μM of GSH was chosen for this colorimetric sensor. 3.5 Sensitive assay of silver ions In order to evaluate the sensitivity of this sensing platform towards Ag+, various concentration of Ag+ were added into the reaction system under the optimized experimental conditions, and the UV-Vis spectra was collected in Figure 4A. The 11

calibration curves were established by the absorption value at 650 nm versus the concentration of Ag+, and the curve exhibited a rising trend and finally reached the platform in Figure 4B. The linear range of Ag+ detection was from 10 nM to 800 nM with correlation coefficient R2=0.996 as illustrated in Figure 4C. The limit of detection (LOD) was about 4.23 nM with a signal-to-noise ratio of 3 (3σ/slope, where σ is the standard deviation). In drinkable water the allowed Ag+ concentration limit was stipulated by the United States Environmental Protection Agency (USEPA) to 460 nM [34]. With increasing the concentration of Ag+ (from 10 nM to 10 μM), visual color changes of the solution from colorless to blue were obtained in Figure 4D. Comparing with other approaches in Table 1, our strategy could achieve Ag+ detection at significantly lower concentration. Besides, our novel colorimetric sensor was highly sensitive and rapid for the quantitation of Ag+. 3.6 Selectivity for silver ion detection In addition to sensitivity, the selectivity of the colorimetric sensor was further identified, the various metal ions including Hg2+, Fe2+, Cu2+, Fe3+, K+, Zn2+, Na+, Cd2+, Ca2+, Ni2+, Co2+, Pb2+, Mn2+ were tested. Figure 5A showed the response of colorimetric assay against blank, 1.0 μM of Ag+ and other metal ions (10 μM) with 10-fold concentrations to Ag+. Both Hg2+ and Cu2+ ions exhibited disturbance. As investigated in previous reports, Hg2+ and Cu2+ could interfere the determination of Ag+, EDTA was chose as a masking agent because it could form more stable complexes with Hg2+ and Cu2+. As shown in Figure 5B, this sensing system performed high selectivity toward silver ion assay in the presence of EDTA. In the 12

meanwhile, the absorption value was about 0.3 only in the presence of silver ions in Figure 5C. The blue color of solution was observed with naked eyes only in addition of silver ions in Figure 5D. Although the concentrations of other metal ions were 10-fold to Ag+, these metal ions had no effect on the sensitivity of Ag+ assay. Remarkably, the addition of Ag+ completely coordinates GSH. Therefore, the reaction solution exhibited blue due to the oxidation TMB catalyzed by MnO2 nanosheets. However, other metal ions had not high binding affinity with GSH, the color change of TMB to oxidation TMB was not observed. 3.7 Analysis of practical samples We employed this colorimetric approach to Ag+ detection in practical samples (tap water was collected from our lab). As shown in Table 2, different concentrations of Ag+ spiked in tap water and measured with the sensing assay, the recovery rate of 50 nM, 100 nM, and 500 nM samples were 108.01%, 107.38%, and 99.62%, respectively. Besides, the proposed approach was employed for the Ag+ of pure tap water, the sensing solution was colorless. These results showed that this colorimetric platform could be used for qualitative and quantitative analysis in real samples.

4. Conclusion In summary, a novel colorimetric sensor based on GSH-mediated MnO2 nanosheets was fabricated successfully for the determination trace amounts of silver ions. The presence of GSH resulted in the destruction of MnO2 nanosheets to Mn2+ ion. However, the absorption intensity of blue oxTMB was significantly enhanced by the addition of Ag+ due to the formation of GSH and Ag+ complexes, allowing the 13

catalytic activity of nanoenzyme to detect and quantify the target analyte. By taking advantage of the highly sensitive GSH/MnO2 redox reaction and highly binding specificity of GSH and Ag+, our colorimetric approach showed wider linear range, higher sensitivity, lower detection limit, and rapid analysis or even by naked eyes. More importantly, the proposed method was successfully applied to the detection of Ag+ in real samples. In addition, this mimic oxidase based on MnO2 nanosheets and substrate TMB displayed excellent stability and reproducibility overcoming the requirement of H2O2. Therefore, this simple, rapid, and cost-efficient sensing platform based on MnO2 nanosheets could extend further to determine various targets by simply adjusting other chelators or ligands.

Acknowledgements The authors gratefully acknowledge the National Natural Science Foundation of China (Grant No. 21105066, No. 21405090), Beijing Natural Science Foundation (Grant No. 2162010), and Scientific Research Project of Beijing Educational Committee (Grant No. KM201610028008).

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Biographies

Yueying Liu received her MS degree and Ph.D degree from Beijing Institute of Technology. After two years of postdoctoral research at Tsinghua University with Professor Xinrong Zhang, she began her own independent career in Department of Chemistry, Capital Normal University. Her research interest is sensor array.

Yuexiang Lu received his Ph.D. degree in Analytical Chemistry from Tsinghua University in 2013 under the direction of Professor Xinrong Zhang. He is currently working at institute of Nuclear and New Energy Technology, Tsinghua University. His research interest is nanomaterial.

Liuying He is currently doing her MS work at Department of Chemistry, Capital Normal University. She is currently working toward sensors.

Feiyang Wang is currently doing her MS work at Department of Chemistry, Capital Normal University. She is currently working toward sensor arrays.

Wenjie Jing is currently doing his MS work at Department of Chemistry, Capital Normal University. He is currently working toward sensor arrays based functional nanomaterials.

Ying Chen is currently doing her BS work at Department of Chemistry, Capital Normal University. She is currently working toward biosensors.

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Scheme Captions

Figure 1 (A) TEM image of MnO2 nanosheets; (B) The UV-Vis absorption spectra of MnO2 nanosheets with different concentrations. (C) XPS spectra of MnO2 nanosheets. (D) and (E) are high resolution Mn2p XPS spectra and O1s XPS spectra, respectively.

Figure 2 (A) The absorbance at 650 nm versus the pH of HOAc-NaOAc buffer solution, the solution containing MnO2 nanosheets (20 μM) and TMB (200 μM); (B) The adsorption value at 650 nm arising from the concentration of TMB, MnO2 nanosheets (20 μM), and HOAc-NaOAc buffer solution at pH 4.0; (C) The kinetics curves of GSH-mediated TMB and MnO2 nanosheets system for Ag+ detection. Inset: the corresponding photographs.

Figure 3 (A) The absorption spectra of reaction mixtures containing MnO2 nanosheets (20 μM), TMB (200 μM) and GSH with different concentration; (B) Absorbance plotted as a function of the concentration of GSH. Inset: the corresponding photographs.

Figure 4 Colorimetric detection of Ag+. (A) absorption spectra; (B) absorption values at 650 nm of colorimetric assay against different concentrations of Ag+ (0, 10, 50, 100, 200, 400, 500, 600, 700, 800, 900, 1000, 2000, 4000, 6000, 8000, 10000 nM); (C) linearity of the assay versus the Ag+ concentrations ranging from 10 nM to 800 nM. 21

Error bars indicate the standard deviation of three independent experiments; (D) photo images of solution after adding the different concentrations of Ag+ (increasing from left to right).

Figure 5 Selectivity of this colorimetric assay. (A, B) The absorption value at 650 nm of the solution with different metal ions in the absence (A) and in the presence (1.0 mM) of EDTA (B); (C, D) The corresponding UV-Vis absorption spectra (C) and color changes (D) of the solution in the presence (1.0 mM) of EDTA. Error bars indicate the standard deviation of three independent experiments. In the experiments, the concentration of Ag+ and other metal ions was 1.0 μM and 10 μM, respectively. Scheme 1 Illustration of the colorimetric assay for silver ions detection by using GSH-mediated MnO2 nanosheets

Table 1 Comparison of this work with various reported methods

Table 2 Results of the Ag+ recovery experiments performed in tap water.

22

Figure 1

23

Figure 2

24

Figure 3

25

Figure 4

26

Figure 5

Scheme 1

27

Table 1 Probes

Read out

Analytical Ranges

LOD Selectivity (nM)

Coumarin-based new Schiff base

Absorption

2-160 μM

0.86

Cu2+, Ag+

[10]

Tween 20-AuNPs

Absorption

1-8 μM

10

Hg2+, Ag+

[15]

Tween 20-AuNPs

Absorption

0.4-1 μM

100

Hg2+, Ag+

[35]

DNA-AuNPs

Absorption

0.59-59 nM

0.59

Ag+

[36]

Peptide-AuNPs

Absorption

10-1000 nM

7.4

Ag+

[12]

DNA-AgNCs

Fluorescence

5-500 nM

10

Ag+

[37]

DNA

Fluorescence

1-100 nM

0.05

Ag+

[2]

DNA

Fluorescence

0.5-13 μM

80

Ag+, Cysteine

[38]

Carbon Quantum Dots AIE-AuNCs

Fluorescence

8-200 μM

5093

Ag+

[39]

Fluorescence

0.5-20 μM

0.2

Ag+

[40]

Hydrazine carbothioamide

Fluorescence

0.33-1.67 μM

590

Hg2+, Ag+

[41]

Creatinine

Fluorescence

5-40 μM

1000

Ag+

[9]

GSH-MnO2 nanosheets

Absorption

10-800 nM

4.23

Ag+

This work

Table 2 Sample

Ag+/nM (Added)

Ag+/nM (Detected)

Recovery (%)

RSD (%)

1

50

54

108.01

0.56

2

100

107

107.38

0.13

3

500

498

99.62

1.65

28

Ref