Silver ion colorimetric sensor based on smart phone platform and preparation method and application thereof

Abstract

The invention belongs to the technical field of analytical chemistry and optical sensing, and particularly relates to a silver ion colorimetric sensor based on a smart phone platform and a preparation method and application thereof. The preparation method comprises the following steps: chemically reducing chloroauric acid by using sodium citrate to prepare a gold nano colloidal solution, adding ammonium thioglycolate and a PBS buffer solution into the gold nano colloidal solution, and uniformly mixing to obtain the silver ion colorimetric sensor. According to the sensor, through the competitive coordination effect of gold nanoparticles (AuNPs) and silver ions (Ag (I)) on ammonium thioglycolate (ATG), a developing detection mode of inhibiting aggregation of the nanoparticles is realized. Through the three-in-one innovation of nanometer material-optical sensing-intelligent terminal, the technical bottlenecks of the traditional Ag (I) detection method in sensitivity, cost, portability and multi-scene applicability are solved, and the method has great industrialization value in the fields of environmental monitoring, food safety and point-of-care testing (POCT).

Description

Technical Field

[0001] The present invention belongs to the technical field of analytical chemistry and optical sensing technology, and particularly relates to a silver ion colorimetric sensor based on a smartphone platform, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, with the rapid development of industry and agriculture, the problem of heavy metal pollution has posed a serious threat to human health and the ecological environment. As a precious metal with excellent optical, electrical properties and antibacterial activity, silver has shown extensive application value in fields such as photographic imaging, energy devices, and biomedicine. Especially in the medical field, soluble silver compounds and silver nanoparticle preparations have been innovatively applied to scenarios such as the treatment of mental diseases, neuromodulation, and anti-infection due to their broad-spectrum antibacterial activity, further expanding their application boundaries. However, the widespread use of silver ions (Ag(I)) has also increased the environmental burden - as a persistent pollutant, it can accumulate in organisms through the food chain, and excessive intake will cause serious health problems such as neurotoxicity and immunosuppression. Based on this, the World Health Organization (WHO) has strictly limited the concentration of silver ions in drinking water to no more than 0.1 mg / L (0.93 μM), which has put forward higher requirements for the sensitivity and timeliness of environmental monitoring technologies.

[0003] Traditional silver ion detection methods mainly rely on large laboratory instruments such as chromatography-mass spectrometry (GC-MS / LC-MS) and atomic spectroscopy techniques (ICP-MS / AAS), supplemented by electrochemical analysis or fluorescence spectroscopy. Although these methods have a detection ability at the ppm level, their high equipment costs, complex operation processes, and professional operation requirements severely limit the application scenarios of on-site rapid detection. In recent years, gold nanoparticle (AuNPs)-based sensors have become a research hotspot due to their unique advantages: their surface plasmon resonance effect can produce a significant color response (redshift phenomenon), combined with a simple synthesis process and a colorimetric signal that can be distinguished by the naked eye, providing the possibility for the development of low-cost and portable detection solutions. Existing research mainly focuses on generating a colorimetric signal through the aggregation of nanoparticles induced by the target substance, and there is still insufficient exploration of the "reverse regulation" strategy of suppressing aggregation through stabilizer design. If this anti-aggregation mechanism can be broken through, the selectivity and stability of the sensor will be significantly improved, which lays a solid theoretical foundation for the construction of a smartphone-mediated point-of-care testing (POCT) system.

[0004] In view of the bottlenecks of the above technologies, there is an urgent need to develop an innovative detection solution integrating nano-sensing and mobile intelligent terminals. This solution needs to meet the following core requirements: 1) Achieve specific recognition and signal amplification of Ag(I) through functional modification; 2) Use the smartphone camera to complete image acquisition and Image J image analysis software; 3) Build a standardized detection process to ensure the simplicity of on-site operation and the reliability of results. This research not only helps to establish an early warning system for environmental silver pollution, but also provides key technical support for ensuring drinking water safety and promoting the clinical transformation of nano-sensing technology. Summary of the Invention

[0005] The present invention aims to solve the defects in the prior art and provides a silver ion colorimetric sensor based on a smartphone platform, a preparation method and an application thereof. The sensor is simple, fast, highly sensitive in operation, and can realize visual quantitative detection of silver ions.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] In the first aspect, the present invention provides a silver ion colorimetric sensor based on a smartphone platform, which uses negatively charged gold nanoparticles modified with sodium citrate as a sensing element, and introduces ammonium thioglycolate as a functional cross-linking agent in a PBS buffer system to promote the aggregation of gold nanoparticles; through the strong coordination effect between the thiol group and the surface of the gold nanoparticles, a stable Au-S covalent bond is formed, so that the ammonium thioglycolate molecules are anchored on the surface of the gold nanoparticles in a monolayer form.

[0008] In the second aspect, the present invention provides a preparation method of the silver ion colorimetric sensor based on the smartphone platform described in the first aspect, including the following steps:

[0009] Step 1: Prepare a gold nanocolloid solution by chemically reducing chloroauric acid with sodium citrate;

[0010] Step 2: Add ammonium thioglycolate and a PBS buffer solution to the gold nanocolloid solution, mix well, and obtain the silver ion colorimetric sensor.

[0011] In an optional embodiment, the specific process of preparing the gold nanocolloid solution by chemically reducing chloroauric acid with sodium citrate in the step 1 is as follows: After stirring and heating the pre-prepared chloroauric acid solution to boiling, quickly add the freshly prepared sodium citrate solution. When observing that the color of the solution changes from light yellow to wine red, continue heating for 0.5 h, then stop heating and continue stirring, and cool naturally to room temperature to obtain the gold nanocolloid solution.

[0012] In an alternative embodiment, the concentration of the chloroauric acid solution is 1 mmol / L and the volume is 100 mL; the concentration of the sodium citrate solution is 38.8 mmol / L and the volume is 10 mL.

[0013] In an alternative embodiment, the volume ratio of the gold nanocolloid solution, ammonium thioglycolate, and PBS buffer solution in step 2 is 90:10:190.

[0014] In an alternative embodiment, the concentration of the gold nanocolloid solution in step 2 is 0.27 - 3.0 nmol / L.

[0015] In an alternative embodiment, the concentration of ammonium thioglycolate in step 2 is 90 - 120 μmol / L.

[0016] In an alternative embodiment, the PBS buffer solution in step 2 is composed of disodium hydrogen phosphate at 10 mmol / L and sodium dihydrogen phosphate at 10 mmol / L, with a concentration of 10 mM and a pH of 8.15.

[0017] In a third aspect, the present invention provides the application of the silver ion colorimetric sensor based on the smartphone platform described in the first aspect in the visual quantitative detection of silver ions.

[0018] During the detection of silver ions (Ag(I)), through the competitive coordination of Ag(I) with gold nanoparticles (AuNPs) and ammonium thioglycolate (ATG), for the first time, a colorimetric detection mode by inhibiting nanoparticle aggregation is realized. Its detection mechanism stems from the competitive coordination of Ag(I) and AuNPs for the mercapto group of ATG molecules: when Ag(I) is present, it preferentially forms an Ag - S bond with ATG, resulting in the reorganization of the coordination layer on the surface of AuNPs. This coordination competition effectively inhibits the aggregation of AuNPs mediated by ATG and maintains the dispersed state of nanoparticles through surface charge modification. This anti - aggregation process induces a significant SPR spectral shift (λ max blue - shifted from 680 nm to 520 nm), accompanied by the color of the solution changing from the aggregated blue to the dispersed red. This reverse colorimetric mechanism is in sharp contrast to traditional aggregation - type sensors and can be directly distinguished by the naked eye.

[0019] In a fourth aspect, the present invention provides a method for visual quantitative detection of silver ions, comprising the following steps:

[0020] Add the silver ion colorimetric sensor described in the first aspect to the sample to be tested, measure the absorbance of the system using a UV-Vis spectrophotometer, collect the microscopic image of the system after the reaction using a smartphone and store it digitally. Extract the pixel intensity values of the red and blue channels through the Image J image analysis software, calculate the optical density ratio, and construct a standard curve of silver ion concentration versus optical density ratio, so as to realize the visual quantitative detection of silver ion concentration in the sample to be tested.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) The reagents and operation process used in the present invention have no toxic or side effects and are environmentally friendly.

[0023] (2) The present invention is deeply integrated with the smartphone platform, and through the built-in algorithm, the intelligent conversion of RGB signals to concentration values is realized, forming an integrated detection system of "nano-sensing - optical acquisition - intelligent analysis". The detection period is shortened to 30 seconds, which is a hundred times faster than traditional instrumental analysis.

[0024] (3) The method of the present invention breaks through the dependence on the laboratory environment of the traditional detection mode, can fully realize on-site in-situ detection, is especially suitable for instant detection scenarios such as emergency monitoring and field screening, and demonstrates excellent portability and timeliness.

[0025] (4) Compared with the prior art, the present invention breaks through the traditional "aggregation coloration" mode and adopts a new mechanism of "dispersion coloration", completely avoiding the common precipitation interference problem of aggregated sensors.

[0026] (5) Compared with traditional sensors, the present invention has the characteristics of multi-scene compatibility, low cost and scalability.

[0027] (6) Through the trinity innovation of "nanomaterials - optical sensing - intelligent terminal", the present invention solves the technical bottlenecks of traditional Ag(I) detection methods in terms of sensitivity, cost, portability and multi-scene applicability, and has great industrialization value in the fields of environmental monitoring, food safety and POCT. Description of the Drawings

[0028] Figure 1 Transmission electron microscope images and corresponding solution color photos of 13 nm gold nanoparticles (a), ammonium thioglycolate-functionalized gold nanoparticles (b), and ammonium thioglycolate-functionalized gold nanoparticles dispersed by Ag(I) (c).

[0029] Figure 2 UV-Vis spectra of 13 nm gold nanoparticles, ammonium thioglycolate-functionalized gold nanoparticles, and ammonium thioglycolate-functionalized gold nanoparticles dispersed by Ag(I).

[0030] Figure 3 Dynamic light scattering particle size diagrams of gold nanoparticles (13.5 nm) (a), ammonium thioglycolate-functionalized gold nanoparticles (140.2 nm) (b), and ammonium thioglycolate-functionalized gold nanoparticles dispersed by Ag(I) (31.2 nm) (c).

[0031] Figure 4 It is a comparison diagram of the degree of dispersion of ammonium thioglycolate-functionalized gold nanoparticles induced by each metal ion and a photograph of the corresponding solution color. The abscissa is the type of metal ion, and the ordinate is the R / B value when the final concentration of the metal ion in the ammonium thioglycolate-functionalized gold nanoparticles is 70 μmol / L.

[0032] Figure 5 Photographs of the corresponding solution colors and standard curves when different concentrations of Ag(I) (final concentrations of Ag(I) are 0.1 μmol / L, 1 μmol / L, 2 μmol / L, 3 μmol / L, 4 μmol / L, 5 μmol / L, 6 μmol / L, 7 μmol / L, 8 μmol / L) are present in the mixed solution.

[0033] Figure 6 It is a schematic diagram of the reaction mechanism for detecting Ag(I) by the silver ion colorimetric sensor of the present invention. Detailed implementation manners

[0034] For the convenience of understanding the present invention, the present invention will be described more comprehensively below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0035] Example 1 Preparation of silver ion colorimetric sensor

[0036] (1) Preparation of AuNPs:

[0037] The synthesis of the gold nanocolloid solution adopts the classical process of chemically reducing chloroauric acid with sodium citrate (its transmission electron microscopy image is as shown in Figure 1 (a)). First, soak the used glassware and magnetic stirrer in aqua regia until clean, repeatedly rinse with ultrapure water, place them in an oven, and dry for later use. Take 100 mL of chloroauric acid solution (1 mmol / L) and add it to a three-necked flask equipped with a reflux device. In a magnetic stirrer with a rotation speed of 14 rpm, heat to vigorous boiling, and then quickly inject 10 mL of freshly prepared sodium citrate solution (38.8 mmol / L). When observing that the solution color changes from light yellow to wine red, continue heating for 0.5 h, then continue stirring and stop heating, and naturally cool to room temperature to obtain the gold nanocolloid solution AuNPs. Seal it and store it refrigerated at 2 - 8 °C for later use;

[0038] (2) Preparation of ATG-AuNPs

[0039] Add 90 μL of AuNPs (3 nmol / L), 10 μL of ammonium thioglycolate (90 μmol / L), and 190 μL of PBS buffer solution (composed of 10 mmol / L disodium hydrogen phosphate and 10 mmol / L sodium dihydrogen phosphate, with a concentration of 10 mM and a pH of 8.15) into an EP tube and mix well. On a constant temperature mixer at 25 °C with a rotation speed of 400 rpm, after reacting fully for 5 min, the silver ion colorimetric sensor (ATG-AuNPs) is prepared. Characterization by transmission electron microscopy and ultraviolet-visible spectrophotometer shows that ammonium thioglycolate molecules are immobilized on the surface of gold nanoparticles through Au-S bonds (as shown in Figure 1 (b), Figure 2 , Figure 3 (b)).

[0040] Example 2 Application of Silver Ion Colorimetric Sensor

[0041] (1) Selective Detection

[0042] Take 190 μL of ATG-AuNPs solution, and add 10 μL of metal ion solutions with a concentration of 1.4 mmol / L (including Ag(I), Hg(I), Cu(II), Pb(II), Ca(II), Fe(II), Fe(III), Zn(II), Mg(II), Cd(II), Ni(II), Mn(II), Cr(III), Al(III)) respectively. After mixing well, adjust the final concentration of various metal ions in the system to 70 μmol / L. Place the reaction system on a constant temperature mixer at 25 °C and oscillate and react at a rotation speed of 400 rpm for 5 min. Use a smartphone to collect the microscopic images of each system after the reaction and store them digitally. Extract the pixel intensity values of the red channel (Red, R) and the blue channel (Blue, B) through Image J image analysis software, and calculate the optical density ratio (Red / Blue, R / B value), so as to establish a dispersion evaluation model. As shown in Figure 4 , this ratio is positively correlated with the dispersion degree of nanoparticles. The experimental results show that among the 14 metal ions tested, only Ag(I) exhibits a significant induced dispersion effect. Transmission electron microscopy (TEM) imaging ( Figure 1 (c)) visually shows the monodisperse state of gold nanoparticles after the action of Ag(I), while ultraviolet-visible (UV-Vis) spectroscopy ( Figure 2 ) further verifies the dispersion-aggregation behavior transition induced by Ag(I) through the change of characteristic absorption peaks. Finally, through a dynamic light scattering instrument (DLS) ( Figure 3(c)) Measuring the particle size distribution demonstrated that the addition of Ag(I) effectively inhibited the aggregation of gold nanoparticles.

[0043] (2) Detection of Ag(I)

[0044] Standard solutions of Ag(I) were successively added to ATG-AuNPs, and the final concentrations of Ag(I) were controlled to be 0.10 μmol / L, 1.00 μmol / L, 2.00 μmol / L, 3.00 μmol / L, 4.00 μmol / L, 5.00 μmol / L, 6.00 μmol / L, 7.00 μmol / L, and 8.00 μmol / L respectively. Three parallel experiments were set for each concentration. After mixing, the reaction was allowed to proceed fully for 5 min on a constant temperature mixer at 25 °C. Then, the microscopic images of each reaction system were collected using a smartphone and digitally stored. The pixel intensity values of the red channel (Red, R) and the blue channel (Blue, B) were extracted through the Image J image analysis software, and the optical density ratio (Red / Blue, R / B value) was calculated. A standard curve was plotted with the Ag(I) concentration on the abscissa and the R / B ratio on the ordinate, a linear regression equation for Ag(I) was established, and the regression equation and the correlation coefficient ( Figure 5 ) were calculated. Through linear regression analysis, in the range of 0 - 8 μmol / L, the R / B value showed an excellent linear correlation with the Ag(I) concentration, and the composite linear equation was y = 0.0182x + 0.9675, with the correlation coefficient R 2 = 0.9947. The detection limit of this method was as low as 10.4 nmol / L, demonstrating a sensitive detection ability for Ag(I). It can be seen that as the Ag(I) concentration increased, the R / B value showed a monotonically increasing trend, intuitively reflecting that the dispersion degree of the functionalized gold nanoparticles increased significantly with the increase of the Ag(I) concentration. The present invention successfully established a quantitative detection method for Ag(I) based on the R / B ratio, providing a new visualization analysis technology for the field of heavy metal ion detection.

[0045] (3) Recovery experiment in actual water samples

[0046] Prepare Ag(I) standard solutions with a concentration of 80 μmol / L in tap water and lake water respectively, and set up three groups of parallel experiments. Take 190 μL of ATG-AuNPs and add 10 μL of different Ag(I) water samples containing 80 μmol / L (final concentration is 4 μmol / L). After fully reacting for 5 min on a constant temperature mixer at 25 °C, use a smartphone to take pictures to collect the microscopic images of each reaction system and store them digitally. Extract the pixel intensity values of the red channel (Red, R) and the blue channel (Blue, B) through the Image J image analysis software, so as to calculate the R / B optical density ratio of ATG-AuNPs for different water quality types. As shown in Table 1, compared with the PBS buffer system, the Ag(I) recovery rates in tap water and lake water are both maintained in the range of 90-110%. The specific data shows that the recovery rate of the laboratory tap water sample is 102.44%, and the recovery rate of the Wenying Lake water sample in Datong City is 100.15%. The experimental results show that this detection method shows good accuracy and reliability in different water quality matrices, and its detection performance is not significantly interfered by complex water body components. The present invention has successfully expanded the application scope of the optical detection technology based on nanomaterials in the field of environmental water sample analysis.

[0047] Table 1 Recovery rates of Ag(I) in different water samples

[0048] Water sample type Tap water Lake water Source Laboratory Wenyin Lake Recovery rate 102.44％ 100.15％

[0049] The above are only examples for better explaining the present invention, and are not intended to limit it. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall fall within the scope covered by the present invention.

Claims

1. A silver ion colorimetric sensor based on a smartphone platform, characterized in that The silver ion colorimetric sensor uses negatively charged gold nanoparticles modified with sodium citrate as the sensing element. Under a PBS buffer system, ammonium thioglycolate is introduced as a functional cross-linking agent to promote the aggregation of gold nanoparticles. Through the strong coordination effect between the thiol group and the surface of gold nanoparticles, stable Au-S covalent bonds are formed, enabling ammonium thioglycolate molecules to be anchored on the surface of gold nanoparticles in a monolayer form.

2. The preparation method of the silver ion colorimetric sensor based on the smartphone platform according to claim 1, characterized in that, It includes the following steps: Step 1: Prepare a gold nanocolloid solution by chemically reducing chloroauric acid with sodium citrate. Step 2: Add ammonium thioglycolate and PBS buffer solution to the gold nanocolloid solution, and mix well to obtain the silver ion colorimetric sensor.

3. The preparation method of the silver ion colorimetric sensor based on the smartphone platform according to claim 2, wherein The specific process of preparing the gold nanocolloid solution by chemically reducing chloroauric acid with sodium citrate in Step 1 is as follows: After stirring and heating the pre-prepared chloroauric acid solution to boiling, quickly add the freshly prepared sodium citrate solution. When observing that the color of the solution changes from light yellow to wine red, continue heating for 0.5 h, then stop heating and continue stirring, and naturally cool to room temperature to obtain the gold nanocolloid solution.

4. The preparation method of the silver ion colorimetric sensor based on the smart phone platform according to claim 3, characterized in that, The concentration of the chloroauric acid solution is 1 mmol / L, and the volume is 100 mL; the concentration of the sodium citrate solution is 38.8 mmol / L, and the volume is 10 mL.

5. The preparation method of the silver ion colorimetric sensor based on the smartphone platform according to claim 2, wherein, In Step 2, the volume ratio of the gold nanocolloid solution, ammonium thioglycolate, and PBS buffer solution is 90:10:

190.

6. The preparation method of the silver ion colorimetric sensor based on the smartphone platform according to claim 2, wherein In Step 2, the concentration of the gold nanocolloid solution is 0.27 - 3.0 nmol / L.

7. The preparation method of the silver ion colorimetric sensor based on the smart phone platform according to claim 2, characterized in that, In Step 2, the concentration of ammonium thioglycolate is 90 - 120 μmol / L.

8. The preparation method of the silver ion colorimetric sensor based on the smartphone platform according to claim 2, characterized in that, In Step 2, the PBS buffer solution is composed of disodium hydrogen phosphate at 10 mmol / L and sodium dihydrogen phosphate at 10 mmol / L, with a concentration of 10 mM and a pH of 8.

15.

9. Application of the silver ion colorimetric sensor based on the smartphone platform described in Claim 1 in the visual quantitative detection of silver ions.

10. A method for visual quantitative detection of silver ions, characterized in that, It includes the following steps: Add the silver ion colorimetric sensor described in Claim 1 to the sample to be tested. Use an ultraviolet-visible spectrophotometer to measure the absorbance of the system. Use a smartphone to collect the microscopic image of the system after the reaction and digitally store it. Extract the pixel intensity values of the red channel and the blue channel through Image J image analysis software, calculate the optical density ratio, and construct a standard curve of silver ion concentration against the optical density ratio, so as to realize the visual quantitative detection of silver ion concentration in the sample to be tested.

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