Water-soluble powdered noble metal nanomaterials, their preparation methods and applications

Abstract

The present invention discloses a water-soluble powdered noble metal nanomaterial, a preparation method thereof and an application thereof, belonging to the technical field of nanomaterials. The water-soluble powdered noble metal nanomaterial is prepared by dispersing a noble metal nanomaterial colloidal solution in an aqueous solution of C 16 TAB with a concentration ≥ 0.2 M or an aqueous solution of C 18 TAB with a concentration ≥ 0.05 M, and then performing vacuum freeze-drying. The advantages of the present invention are as follows: Without adding traditional antifreezing agents, a water-soluble powdered noble metal nanomaterial suitable for the sensing field is prepared, which not only solves the problem of irreversible aggregation faced in the preparation process of nanoparticle powders, but also avoids the influence of traditional antifreezing agents on the sensing system; An integrated all-powdered nitrite / ascorbic acid detection nanocolorimetric analysis kit can be constructed by using the water-soluble powdered noble metal nanomaterial, solving the problems of easy aggregation, difficult preservation and inaccurate results of colloidal nanoparticles.

Description

Technical Field

[0001] The present invention relates to noble metal nanomaterials and their preparation methods and applications, and particularly to water-soluble powdered noble metal nanomaterials and their preparation methods and their applications in LSPR colorimetric analysis, belonging to the technical field of nanomaterials. Background Art

[0002] LSPR colorimetric analysis (nano-colorimetric analysis) based on noble metal nanomaterials has very wide applications due to its high detection sensitivity and wide color change range, and has realized colorimetric analysis and detection of various substances such as heavy metal ions, anions, and biomacromolecules. At present, in nano-colorimetric analysis, most of the commonly used noble metal nanomaterials are colloidal solutions, and there are mainly the following problems:

[0003] (1) Colloidal nanoparticles have a high specific surface area and surface free energy, so they are very easy to aggregate. To solve this problem, many literatures perform surface modification through physical or chemical adsorption of ligands to improve the colloidal stability of noble metal nanomaterials in solution. However, solvents, the acidity and alkalinity of solutions, reaction temperature, salts, and charged molecules, etc. will all cause irreversible aggregation of noble metal nanomaterials, which has a great impact on distance-induced colorimetric analysis and detection of noble metal nanomaterials, and is prone to the appearance of false positive or false negative results, affecting the accuracy of experiments;

[0004] (2) The chemical and optical properties of noble metal nanomaterial colloidal solutions are unstable, so they have high requirements for storage conditions and a short storage time. In order to extend their storage time as much as possible, they need to be stored refrigerated and away from light;

[0005] (3) Noble metal nanomaterial colloidal solutions are usually stored in glass bottles, and obvious wall sticking phenomenon will occur after long-term storage, affecting the concentration of noble metal nanomaterials and the accuracy of analysis and detection results.

[0006] It can be seen that how to achieve long-term stable storage of noble metal nanomaterial colloidal solutions is an urgent problem to be solved.

[0007] Vacuum freeze-drying technology is usually used in food, pharmaceuticals, etc. and can extend the storage time of substances. The working principle is as follows:

[0008] The product to be dried is frozen to a temperature below its eutectic point, so that the water in it becomes ice, and then under a certain vacuum degree, the solid ice directly sublimes and turns into water vapor, and finally after the treatment of the vacuum system, the corresponding dehydrated sample is obtained.

[0009] The products obtained by using vacuum freeze-drying technology not only have relatively stable properties, but also have good rehydration properties.

[0010] To solve the problems faced by colloidal solutions of noble metal nanomaterials, some studies have attempted to use vacuum freeze-drying technology to convert colloidal solutions of noble metal nanomaterials into corresponding solid powders to improve the stability of noble metal nanomaterials. However, due to the generation of certain pressure during the vacuum freeze-drying process, irreversible aggregation of nanoparticles will occur. To solve this problem, cryoprotectants need to be introduced during the freeze-drying process. These cryoprotectants will vitrify during freezing, forming an amorphous glassy matrix, inhibiting the migration of nanoparticles, and thus inhibiting the aggregation of nanoparticles, realizing the preparation of redispersible nanometer powders.

[0011] Alaaldin M. Alkilany et al. used trehalose and mannitol as cryoprotectants and successfully converted a colloidal solution of citrate-protected gold nanoparticles into the corresponding solid powder using vacuum freeze-drying technology; in addition, Hidetaka Yokota et al. also achieved the preparation of solid powders of rituximab-protected gold nanorods using the same freeze-drying cryoprotectants (with different ratios of trehalose and mannitol). In addition to the above-mentioned cryoprotectants, Majd A. Hamaly et al. used a mixture of sucrose and sucrose monopalmitate as a cryoprotectant for freeze-drying for the preparation of gold nanoparticle powders.

[0012] At present, most of the cryoprotectants used in vacuum freeze-drying technology are sugars and proteins, and the content of cryoprotectants is relatively high. Sometimes, multiple reagents need to be introduced, which has a great impact on colorimetric analysis detection. Summary of the Invention

[0013] To solve the deficiencies of the prior art, the first object of the present invention is to provide a method for preparing water-soluble powder noble metal nanomaterials that can be directly used for colorimetric analysis detection without adding traditional cryoprotectants, and the water-soluble powder noble metal nanomaterials prepared by this method; the second object of the present invention is to provide the application of the aforementioned water-soluble powder noble metal nanomaterials in LSPR colorimetric analysis.

[0014] To achieve the above first goal, the present invention adopts the following technical solutions:

[0015] A method for preparing water-soluble powder noble metal nanomaterials, characterized in that a surfactant pre-crystallization-assisted vacuum freeze-drying of colloidal nanomaterials is used to prepare water-soluble powder noble metal nanomaterials, specifically including the following steps:

[0016] Step1: Prepare a colloidal solution of noble metal nanomaterials;

[0017] Step2: Disperse the colloidal solution of noble metal nanomaterials prepared in Step1 in an aqueous solution of C 16 TAB with a concentration ≥ 0.2M or an aqueous solution of C18 In the TAB aqueous solution, mix evenly to obtain a mixed solution;

[0018] Step 3: Vacuum freeze-dry the mixed solution obtained in Step 2 to obtain a water-soluble powder state noble metal nanomaterial.

[0019] Preferably, in Step 1, the noble metal nanomaterial colloidal solution includes: AuNRs colloidal solutions with aspect ratios of 2 and 3.2, AuNPs colloidal solutions of 13 nm and 30 nm, AuNBPs colloidal solution, AgNPs colloidal solution, SiO2@AgNPs colloidal solution, silver cube colloidal solution, and silver octahedron colloidal solution.

[0020] Preferably, in Step 2, the noble metal nanomaterial colloidal solution and C 16 TAB aqueous solution or C 18 The volume ratio of the TAB aqueous solution is 1:19, and C 16 The concentration of the TAB aqueous solution is 0.3 M, and C 18 The concentration of the TAB aqueous solution is 0.05 M to 0.2 M.

[0021] A water-soluble powder state noble metal nanomaterial, characterized in that it is prepared by the foregoing method.

[0022] In order to achieve the above second objective, the present invention adopts the following technical solutions:

[0023] The application of the foregoing water-soluble powder state noble metal nanomaterial in LSPR colorimetric analysis, characterized in that as a colorimetric sensing material, it is used to construct an integrated all-powdered nano-colorimetric analysis kit.

[0024] Preferably, the integrated all-powdered nano-colorimetric analysis kit is constructed from the foregoing water-soluble powder state noble metal nanomaterial and oxalic acid powder, and is used to detect nitrite.

[0025] Preferably, the integrated all-powdered nano-colorimetric analysis kit is constructed from the foregoing water-soluble powder state noble metal nanomaterial, AgNO3 solid powder, and NaOH-glycine buffer solution solid powder, and is used to detect ascorbic acid.

[0026] The beneficial effects of the present invention are as follows:

[0027] (1) By adopting the method of surfactant pre-crystallization-assisted vacuum freeze-drying of colloidal nanoparticles, the present invention prepares a water-soluble powder state noble metal nanomaterial suitable for the sensing field without adding traditional antifreeze agents, which not only solves the irreversible aggregation problem faced in the preparation process of nanoparticle powders but also avoids the influence of traditional antifreeze agents on the sensing system;

[0028] (2) The preparation method provided by the present invention is simple in operation, applicable to the preparation of different nanoparticle solid powders, and can achieve high-yield preparation of water-soluble powdered noble metal nanomaterials;

[0029] (3) Based on the water-soluble powdered noble metal nanomaterials prepared above, the present invention has successfully constructed an integrated all-powdered nitrite detection nano-colorimetric analysis kit and an ascorbic acid detection nano-colorimetric analysis kit, solving the problems of easy aggregation, difficult preservation, inaccurate detection results, etc. existing in colloidal nanoparticles. More importantly, the detection process is extremely simple and the operation is extremely convenient. Description of the Drawings

[0030] Figure 1 It is the ultraviolet absorption spectrum of gold nanorods before and after freeze-drying and after freeze-reconstitution when the AuNRs colloidal solution is dispersed in deionized water;

[0031] Figure 2 It is the TEM images of gold nanorods before and after freeze-drying when the AuNRs colloidal solution is dispersed in deionized water. Among them, (A) is the TEM image of gold nanorods before freeze-drying, and (B) is the TEM image of gold nanorods after freeze-drying;

[0032] Figure 3 It is the ultraviolet absorption spectrum of gold nanorods before and after freeze-drying and after freeze-reconstitution when the AuNRs colloidal solution is dispersed in C 18 TAB aqueous solution (0.2 M);

[0033] Figure 4 It is the ultraviolet absorption spectrum of gold nanorods before and after freeze-drying when the AuNRs colloidal solution is dispersed in C 18 TAB aqueous solution (0.2 M), and the TEM and elemental mapping images of gold nanorods before and after freeze-drying. Among them, (A) is the TEM image of gold nanorods before freeze-drying, (B) is the TEM image of gold nanorods after freeze-drying, and (C) is the elemental mapping image of gold nanorods after freeze-drying;

[0034] Figure 5 It is the physical comparison photo of the crystallization degree corresponding to surfactants with different carbon chain lengths at 4°C;

[0035] Figure 6 It is the ultraviolet absorption spectrum of gold nanorods before and after freeze-drying when the AuNRs colloidal solution is dispersed in surfactants with the same concentration but different carbon chain lengths. Among them, (A) is the ultraviolet absorption spectrum of gold nanorods before freeze-drying, and (B) is the ultraviolet absorption spectrum of gold nanorods after freeze-drying;

[0036] Figure 7are TEM images of the dispersed state of AuNRs solid powder after freeze-drying when the AuNRs colloidal solution is dispersed in surfactants with the same concentration but different carbon chain lengths. Among them, (A) is the one dispersed in C 10 TAB, and it is the TEM image of the dispersed state of AuNRs solid powder after freeze-drying. (B) is the one dispersed in C 12 TAB, and it is the TEM image of the dispersed state of AuNRs solid powder after freeze-drying. (C) is the one dispersed in C 14 TAB, and it is the TEM image of the dispersed state of AuNRs solid powder after freeze-drying. (D) is the one dispersed in C 16 TAB, and it is the TEM image of the dispersed state of AuNRs solid powder after freeze-drying. (E) is the one dispersed in C 16 TAB, and it is the elemental Mapping image of AuNRs solid powder after freeze-drying. (F) is the one dispersed in C 18 TAB, and it is the TEM image of the dispersed state of AuNRs solid powder after freeze-drying. (G) is the one dispersed in C 18 TAB, and it is the elemental Mapping image of AuNRs solid powder after freeze-drying;

[0037] Figure 8 is a comparison chart of the protective ability of surfactants with the same concentration but different carbon chain lengths on AuNRs during vacuum freeze-drying;

[0038] Figure 9 is a comparison chart of the protective ability of surfactants with different concentrations and different carbon chain lengths on AuNRs during vacuum freeze-drying;

[0039] Figure 10 are the UV absorption spectra of various noble metal nanomaterials before and after vacuum freeze-drying and the SEM or TEM images after vacuum freeze-drying. Among them, (A) is the UV absorption spectrum of gold nanomaterials before and after freeze-drying. Curve a is the gold nanomaterial colloidal solution before drying, and curve b is the redispersion of the gold nanomaterial solid powder in water after drying. (B) is the SEM image of the gold nanomaterials after drying (from left to right are 13nm AuNPs, 30nm AuNPs, AuNRs with an aspect ratio of 2, AuNBPs). (C) is the UV absorption spectrum of silver nanomaterials before and after freeze-drying. Curve a is the silver nanomaterial colloidal solution before drying, and curve b is the redispersion of the silver nanomaterial solid powder in water after drying. (D) is the SEM or TEM image of silver nanomaterials (from left to right are AgNPs, SiO2@AgNPs, silver cubes, silver octahedrons);

[0040] Figure 11 is a comparison chart of the effects of noble metal nanomaterials before and after drying as Raman substrates for detecting 4-mercaptopyridine;

[0041] Figure 12 It is the ultraviolet absorption spectrogram obtained when 13nm AuNPs catalyze the reduction of p-nitrophenol by sodium borohydride;

[0042] Figure 13 It is the ultraviolet absorption spectrogram of the AuNRs solid powder before and after the yield amplification;

[0043] Figure 14 They are the TEM and ultraviolet absorption spectrograms of AuNRs corresponding to different concentrations of nitrite solutions. Among them, (A) is the TEM image of AuNRs in a 0 μM nitrite solution, (B) is the TEM image of AuNRs in a 20 μM nitrite solution, (C) is the TEM image of AuNRs in a 50 μM nitrite solution, and (D) is the ultraviolet absorption spectrogram of AuNRs corresponding to different concentrations of nitrite solutions;

[0044] Figure 15 It is the comparison chart of the effects of different solid acids on detecting nitrite;

[0045] Figure 16 It is the result chart of the selectivity exploration for nitrite detection;

[0046] Figure 17 They are the ultraviolet-visible absorption spectra and linear relationship charts of AuNRs colloidal solution and water-soluble powder gold nanorod A in 0-100 μM nitrite solutions. Among them, (A) is the ultraviolet-visible absorption spectrogram of AuNRs colloidal solution in 0-100 μM nitrite solutions, (B) is the corresponding linear relationship chart of (A), (C) is the ultraviolet-visible absorption spectrogram of water-soluble powder gold nanorod A in 0-100 μM nitrite solutions, and (D) is the corresponding linear relationship chart of (C);

[0047] Figure 18 It is the color change chart of water-soluble powder gold nanorod A in the presence of different concentrations of nitrite;

[0048] Figure 19 It is the effect chart of detecting nitrite by the water-soluble powder gold nanorod A system in a high-salt environment;

[0049] Figure 20 They are the ultraviolet-visible absorption spectrum and the corresponding linear curve chart of kit A in 0-100 μM nitrite solutions. Among them, (A) is the ultraviolet-visible absorption spectrogram of kit A in 0-100 μM nitrite solutions, and (B) is the linear curve chart of kit A in nitrite detection;

[0050] Figure 21It is a comparison chart of the effects of Kit A in detecting nitrite in actual samples. Among them, (A) is a comparison chart of the detection effects of various samples, (B) is a detection spectrum and corresponding color change chart of mineral water, (C) is a detection spectrum and corresponding color change chart before and after filtering simulated seawater, (D) is a detection spectrum and corresponding color change chart before and after filtering surface seawater 1, (E) is a detection spectrum and corresponding color change chart before and after filtering surface seawater 2, and (F) is a detection spectrum and corresponding color change chart before and after filtering deep seawater;

[0051] Figure 22 It is a TEM and ultraviolet absorption spectrum chart of AuNRs in different concentrations of ascorbic acid solutions. Among them, (A) is a TEM chart of AuNRs in a 0 μM ascorbic acid solution, (B) is a TEM chart of AuNRs in a 10 μM ascorbic acid solution, (C) is a TEM chart of AuNRs in a 50 μM ascorbic acid solution, and (D) is an ultraviolet absorption spectrum chart of AuNRs in different concentrations of ascorbic acid solutions;

[0052] Figure 23 It is a result chart of the optimization of ascorbic acid detection conditions under the water-soluble powder AuNRs B system. Among them, (A) is a result chart of the optimization of the pH value of the buffer solution, (B) is a result chart of the optimization of the reaction temperature, and (C) is a result chart of the optimization of the reaction time;

[0053] Figure 24 It is a result chart of the selectivity study of ascorbic acid detection under the water-soluble powder AuNRs B system;

[0054] Figure 25 It is an ultraviolet-visible absorption spectrum and linear relationship chart of AuNRs colloidal solution and water-soluble powder AuNRs B in 0-100 μM ascorbic acid solutions. Among them, (A) is an ultraviolet-visible absorption spectrum chart of AuNRs colloidal solution in 0-100 μM ascorbic acid solutions, (B) is a linear relationship chart corresponding to (A), (C) is an ultraviolet-visible absorption spectrum chart of water-soluble powder AuNRs B in 0-100 μM ascorbic acid solutions, and (D) is a linear relationship chart corresponding to (C);

[0055] Figure 26 It is a color change chart of water-soluble powder AuNRs B in the presence of different concentrations of ascorbic acid;

[0056] Figure 27 It is an ultraviolet-visible absorption spectrum and linear curve chart of Kit B in 0-100 μM ascorbic acid solutions. Among them, (A) is an ultraviolet-visible absorption spectrum chart of Kit B in 0-100 μM ascorbic acid solutions, and (B) is a linear curve chart of Kit B in 0-100 μM ascorbic acid solutions;

[0057] Figure 28It is a comparative diagram of the ultraviolet-visible absorption spectrum and the corresponding wavelength change of ascorbic acid in the actual sample detected by Kit B. Among them, (A) is the ultraviolet-visible absorption spectrum of ascorbic acid in the actual sample detected by Kit B, and (B) is the comparative diagram of the corresponding wavelength change of ascorbic acid in the actual sample detected by Kit B. Detailed implementation mode

[0058] The present invention will be specifically introduced below in conjunction with the attached drawings and specific embodiments.

[0059] I. Preparation of noble metal nanomaterial colloidal solution

[0060] 1. Preparation of gold nanorod colloidal solution

[0061] The gold nanorods (AuNRs) with aspect ratios of 2 and 3.2 are synthesized by the seed growth method. The specific synthesis process is as follows:

[0062] (1) Seed synthesis: Add 50 μL of aqueous chloroauric acid (HAuCl4·4H2O) solution (50 mM) to 7.7 mL of cetyltrimethylammonium bromide (CTAB) solution (0.1 M). Stir slowly at room temperature. The solution changes from colorless to bright yellow. Quickly add 600 μL of ice-cold sodium borohydride (NaBH4) solution (0.01 M) at one time, and stir vigorously for 2 min. The solution changes from bright yellow to light brown. Stop stirring, and let the obtained seed solution stand still at 26 °C in the dark for 2 h for standby;

[0063] (2) Growth of AuNRs: At room temperature, disperse 1.2 mL of aqueous HAuCl4·4H2O solution (50 mM) in 100 mL of CTAB solution (0.1 M). Add 300 μL of silver nitrate (AgNO3) solution (0.01 M) (for synthesizing AuNRs with an aspect ratio of 2) or 600 μL of AgNO3 solution (0.01 M) (for synthesizing AuNRs with an aspect ratio of 3.2). After mixing evenly, add 960 μL of ascorbic acid (AA) solution (0.01 M). The solution changes from yellow to colorless. Add 200 μL of gold seed solution at one time, and stir for 20 min. The solution color changes from colorless to blue (for AuNRs with an aspect ratio of 2), or from colorless to purple (for AuNRs with an aspect ratio of 3.2). Stop stirring, and let it stand still at room temperature in the dark for 20 h for standby.

[0064] The AuNRs are centrifuged at 8000 rpm for 15 min, washed once with water at 6500 rpm, and concentrated for standby.

[0065] 2. Preparation of gold nanoparticle colloidal solution

[0066] The 13-nm AuNPs and 30-nm AuNPs are synthesized by the citrate reduction method. The specific synthesis process is as follows:

[0067] (1) Synthesis of 13 nm AuNPs: 100 mL of aqueous HAuCl4·4H2O solution (1 mM) was placed in an oil bath at 110 °C, heated under reflux, and 10 mL of aqueous sodium citrate solution (38.8 mM) was added. The solution color changed to wine red. Stirring and refluxing were continued for 30 min, then heating was stopped, and the solution was stirred and cooled to room temperature. It was left standing in the dark for 20 h for standby.

[0068] The 13 nm AuNPs were centrifuged at 12000 rpm for 40 min and concentrated for standby.

[0069] (2) Synthesis of 30 nm AuNPs: 30 μL of aqueous HAuCl4·4H2O solution (0.25 M) was dispersed into 200 mL of deionized water, heated under reflux, and 4 mL of sodium citrate solution (mass fraction 1%) was added. Refluxing was continued for 30 min, and the color changed to rose red. Heating was stopped, and the solution was stirred and cooled to room temperature. It was left standing in the dark for 20 h for standby.

[0070] The 30 nm AuNPs were centrifuged at 5500 rpm for 15 min and concentrated for standby.

[0071] 3. Preparation of gold nanobipyramid colloidal solution

[0072] Gold nanobipyramids (AuNBPs) were synthesized by the seed-mediated growth method. The specific synthesis process is as follows:

[0073] (1) Seed synthesis: 250 μL of aqueous HAuCl4·4H2O solution (0.01 M) and 500 μL of sodium citrate solution (0.01 M) were dissolved in 19.25 mL of deionized water. After mixing evenly, 300 μL of ice-cold NaBH4 solution (0.01 M) was added to obtain an orange-red seed solution, which was aged in the dark for 5 h for standby;

[0074] (2) Preparation of AuNBPs: 5 mL of aqueous HAuCl4·4H2O solution (0.01 M), 1 mL of AgNO3 solution (0.01 M), 2 mL of HCl solution (1 M), and 800 μL of AA solution (0.1 M) were successively added to 100 mL of CTAB solution (0.1 M) and mixed evenly. Then 2.5 mL of the seed solution was added, and the solution was stirred for 2 min. The solution color changed from colorless to purple-red, and the obtained solution was left standing in a 30 °C water bath overnight;

[0075] (3) Purification of AuNBPs: 100 mL of AuNBPs solution was centrifuged at 10,000 rpm for 15 min, redispersed in 75 mL of cetyltrimethylammonium chloride (CTAC) solution (0.08 M), 20 mL of AgNO3 solution (0.01 M) and 10 mL of AA solution (0.1 M) were added, and the reaction was carried out in an oil bath at 65 °C for 4 h to generate silver-coated gold nanorods. The silver-coated gold nanorods were centrifuged at 6,000 rpm for 15 min, dispersed in 75 mL of CTAB aqueous solution (0.05 M), allowed to stand for 4 h, the resulting precipitate was redispersed in 50 mL of deionized water, 5 mL of ammonia water (NH3·H2O) solution (25%) and 500 μL of hydrogen peroxide (H2O2) solution (5%) were added, allowed to stand for 4 h, the supernatant was centrifuged at 7,000 rpm for 15 min, and redispersed in 50 mL of CTAB (0.05 M).

[0076] AuNBPs was centrifuged at 7,500 rpm for 15 min, washed once with water at 6,000 rpm, and concentrated for standby.

[0077] 4. Preparation of silver nanoparticle colloidal solution

[0078] Silver nanoparticles (AgNPs) were synthesized by the citrate reduction method. The specific synthesis process is as follows:

[0079] 1 mL of glycerol was dissolved in 250 mL of deionized water, heated to 95 °C, stirred vigorously, AgNO3 powder (45 mg) and 5 mL of sodium citrate solution (10 mg / ml) were added, and heating was continued for 30 min to obtain a brown-green AgNPs solution.

[0080] AgNPs was centrifuged at 3,600 rpm for 15 min and concentrated for standby.

[0081] 5. Preparation of silica-coated silver nanoparticle colloidal solution

[0082] The synthesis method of silica-coated silver nanoparticles (SiO2@AgNPs) is as follows:

[0083] 0.6 mL of NaOH solution (0.5 M) was dissolved in 24 mL of deionized water, 0.05 g of CTAB was added, stirred at 80 °C for 15 min, then 25 mL of AgNPs colloidal solution was added, stirring was continued for 10 min, 535 μL of tetraethyl orthosilicate (TEOS) and 2 mL of ethanol were added, and the reaction was carried out for 1 h and then centrifuged.

[0084] SiO2@AgNPs was centrifuged at 3,600 rpm for 15 min and concentrated for standby.

[0085] 6. Preparation of silver cube and silver octahedron colloidal solution

[0086] Synthesize silver cubes and silver octahedra by the polyol method. The synthesis process is as follows:

[0087] (1) Preparation of precursor solutions: Dissolve 0.50 g of AgNO3 and 0.86 μg of CuCl2 in 12.5 mL of 1,5-pentanediol to obtain precursor solution A. Dissolve 0.25 g of polyvinylpyrrolidone (PVP) in 12.5 mL of 1,5-pentanediol to obtain precursor solution B;

[0088] (2) Synthesis of silver cubes and silver octahedra: Heat 20 mL of 1,5-pentanediol in an oil bath at 180 °C for 10 min, and simultaneously add the above two precursor solutions at different rates: add 500 μL of precursor solution A every 1 min and 250 μL of precursor solution B every 30 s. Stop adding when the solution becomes transparent (about 6 min) to obtain silver cubes. Continuously add the precursor solutions for 120 min to obtain silver octahedra.

[0089] Wash the silver cubes and silver octahedra with alcohol multiple times and concentrate for standby.

[0090] II. Preparation and characterization of gold nanorod solid powders

[0091] Disperse 5 μL of the concentrated AuNRs colloidal solution with an aspect ratio of 3.2 in 95 μL of deionized water and cationic surfactant solutions with different carbon chain lengths (0.01 M, 0.05 M, 0.1 M, 0.15 M, 0.2 M) of C 10 TAB, C 12 TAB, C 14 TAB, C 16 TAB and C 18 TAB), perform vacuum freeze-drying. Redisperse the dried Au NRs solid powder in 500 μL of deionized water, observe the solution color, and measure the ultraviolet absorption spectrum.

[0092] Use high-resolution TEM to characterize the gold nanorod solid powders prepared in deionized water and cationic surfactants with different carbon chain lengths.

[0093] (1) Feasibility of preparing gold nanorod solid powders and TEM microscopic characterization

[0094] When dispersing the AuNRs colloidal solution in deionized water: Before freeze-drying, the AuNRs colloidal solution is purple-red and exhibits two sharp characteristic peaks of gold nanorods at about 520 nm and 720 nm ( Figure 1 ), indicating that the gold nanorods are in a monodispersed state in the solution, which is consistent with the TEM characterization data ( Figure 2(A)) Consistent; after freeze-drying, we obtained a black AuNRs solid powder. After adding deionized water continuously, the black powder could no longer be dispersed in water, and the solution showed a black precipitate, and the absorption spectrum no longer showed the characteristic peaks of gold nanorods ( Figure 1 ), indicating that AuNRs had aggregated, which was consistent with the TEM characterization data ( Figure 2 (B)).

[0095] The AuNRs colloidal solution was freeze-dried to obtain a gray-black solid powder, and the characteristic absorption peaks of the redissolved AuNRs solid powder disappeared, indicating that AuNRs had undergone serious irreversible aggregation during the freeze-drying process, and it was impossible to prepare a redispersible water-soluble AuNRs solid powder. The reasons for the aggregation in this process may come from two main aspects:

[0096] (i) During the freeze-drying process, as the ice crystals gradually grew larger and the liquid region gradually became smaller, the mechanical force generated by the ice crystals gradually squeezed the nanoparticles into a narrow area, and the distance between the nanoparticles became smaller;

[0097] (ii) Due to the gradual accumulation of solutes, the chemical properties such as ionic strength, pH value, and surface charge in this region changed, which jointly caused the irreversible aggregation of AuNRs.

[0098] The above results indicate that to obtain water-soluble powdered AuNRs, it may be necessary to add a suitable protective agent, but it is necessary to minimize the addition of external chemicals, or add a protective agent that has no effect on the LSPR sensing system.

[0099] In this invention, a series of quaternary ammonium salt surfactants were studied for powder preparation. Taking octadecyltrimethylammonium bromide (C 18 TAB) as an example, the mechanism of quaternary ammonium salt surfactants in the preparation of water-soluble powdered AuNRs was explored.

[0100] When the AuNRs colloidal solution was dispersed in the cationic surfactant solution: before freeze-drying, the AuNRs colloidal solution was uniformly dispersed in C 18 TAB aqueous solution (0.2 M) at 40 °C. The colloidal solution showed a purple-red color, and the absorption spectrum showed two typical AuNRs characteristic peaks ( Figure 3 ), and the TEM image showed good dispersibility ( Figure 4 (A)); after freeze-drying, the obtained AuNRs solid powder was dense and uniform, maintaining a complete "cake-like" morphology. The obtained solid powder had good rehydration properties. After dissolving in water, a purple-red AuNRs colloidal solution could be obtained again, and it showed almost the same spectral characteristics as the original solution ( Figure 3 ), and almost all the nanoparticles were dispersed, indicating that C 18TAB has a very strong ability to inhibit the aggregation of nanoparticles. As a protective agent in the freeze-drying process of colloidal nanomaterials, it can well solve the common aggregation problem of nanoparticles during freeze-drying.

[0101] To explore the role of C 18 TAB in the powder formation process, the microstructure inside the solid powder was characterized. It was found through characterization that AuNRs are uniformly distributed in the C 18 TAB crystal similar to "watermelon seeds" ( Figure 4 (B) and (C)), indicating that the nanoparticles are physically separated by the surfactant crystals, restricting the aggregation of nanoparticles. In addition, after the AuNRs colloidal solution freezes and thaws, its absorption spectrum ( Figure 3 ) and color hardly change at all, indicating that C 18 TAB can well protect the nanorods and inhibit the aggregation of nanoparticles. This is due to the C 18 TAB's relatively high freezing point (32 °C). Because in the hot solution state (40 °C), C 18 TAB presents a saturated solution state in the aqueous solution and exists as a large number of micelles. Once the temperature drops by 4 °C, C 18 TAB immediately precipitates to form white crystals, and the solution completely becomes a semi-solid-like state. We speculate that for this reason, at 4 °C (before water freezes), a layer of C 18 TAB crystals may grow on the surface of the gold nanorods and further form a network structure with the crystals inside the liquid, completely fixing the nanorods in the middle of the crystals, thus forming a stable physical rigid structure that can well hinder the squeezing effect of water freezing on the nanoparticles and achieve the protection of the nanoparticles. Because this crystallization process is earlier than the water freezing process, we can call this process "pre-crystallization".

[0102] The above experiments proved that with the assistance of the surfactant C 18 TAB, the preparation of water-soluble powder AuNRs with good dispersibility and complete morphology was achieved by using vacuum freeze-drying technology. This method does not rely on traditional antifreeze agents, and this surfactant belongs to the chemical substances that are inherently present or have similar properties during the synthesis of nanoparticles. Therefore, it is more suitable for applications related to chemical sensing of such nanoparticles.

[0103] (2) Explore the influence of the carbon chain length of the surfactant on the preparation of gold nanorod solid powder

[0104] The above research proved that the pre-crystallization property of the surfactant plays a key role in the freeze-drying process. To better explore the mechanism of the role of pre-crystallization, we compared the homologues of C 18 TAB (C 10 TAB, C12 TAB, C 14 TAB, C 16 TAB and C 18 Study on the crystallization of TAB at 4°C to investigate the effect of carbon chain length on the pre-crystallization performance of surfactants.

[0105] As Figure 5 shown, the carbon chain length shows a positive correlation trend with the pre-crystallization properties of quaternary ammonium surfactants. As the carbon chain length increases, the formation of crystals becomes more and more obvious. C 10 TAB and C 12 The TAB solution is almost transparent and almost no crystals are formed. Starting from C 14 TAB, crystals gradually begin to form and become denser. When the carbon chain length increases to C 18 TAB, the surfactant solution has completely turned into a rigid crystal.

[0106] Based on this result, we speculate that the longer the carbon chain length, the better the protection effect may be during the freeze-drying process of colloidal nanoparticles.

[0107] To confirm this conjecture, the AuNRs colloidal solution was dispersed in the above surfactants at the same concentration, vacuum freeze-dried, and the state of the AuNRs solid powder was characterized by TEM and the optical properties of AuNRs before and after dispersion were characterized by UV-Vis.

[0108] As Figure 6 shown, the AuNRs colloidal solution dispersed in surfactants with low carbon chain lengths (C 10 TAB and C 12 TAB) showed severe aggregation after vacuum freeze-drying, and the resulting solid powder could no longer be redispersed, and the characteristic absorption peak of AuNRs almost completely disappeared. Starting from C 14 TAB, as the carbon chain length of the surfactant increases, the aggregation degree of AuNRs decreases in turn, and the protection ability increases in turn. At the same time, TEM and elemental Mapping also further verified this phenomenon from a microscopic perspective ( Figure 7 ).

[0109] To facilitate the comparison of the effects of surfactants in the freeze-drying of nanoparticles, we used the aggregation degree of the nanoparticles after redissolving the AuNRs solid powder in water to represent it.

[0110] Since the aggregation of AuNRs will cause a decrease in the maximum absorption peak / longitudinal LSPR peak (A λmax ), while the relative intensity in the long-wavelength direction (A λ(max+100) ) increases. Therefore, we use this peak ratio A λ(max+100) / A λmaxIt is used to represent the aggregation degree of nanoparticles. The lower this value is, the lower the aggregation degree of nanoparticles, indicating that the redispersibility of the nanopowder is stronger.

[0111] As Figure 8 shown, before freeze-drying, A λ(max+100) / A λmax maintained very close values, and both were lower than 0.3, indicating that the colloidal AuNRs had very good dispersibility before freeze-drying. After freeze-drying, as the carbon chain length of the surfactant increased, A λ(max+100) / A λmax gradually decreased, indicating that the longer the carbon chain length of the surfactant, the better the protection ability. When the carbon chain length increased to C 14 TAB, the redispersion effect of the nanopowder was significantly improved, and when the carbon chain length increased to C 16 TAB and C 18 TAB, the effect was further improved. This trend is consistent with the trend of better crystallization with longer carbon chains observed above, and further indicates that pre-crystallization is the key factor for surfactants to inhibit the freeze-aggregation of nanoparticles.

[0112] (3) Explore the effect of surfactant concentration on the preparation of gold nanorod solid powder

[0113] On the basis of the above research, further explore the effect of surfactant concentration on its protection ability.

[0114] As Figure 9 shown, generally speaking, as the surfactant concentration increased, the aggregation degree of AuNRs decreased in turn, that is, the protection ability of the surfactant increased in turn. For AuNRs protected by C 10 TAB and C 12 TAB, even at higher concentrations, the aggregation degree was very serious and the protection effect was poor. Starting from C 14 TAB, as the concentration increased, the aggregation degree of the AuNRs solid powder decreased greatly, and the AuNRs solid powder prepared under the protection of 0.2M C 16 TAB already had good dispersibility. The AuNRs dispersed in C 18 TAB had very good redispersibility at all concentrations except for slight aggregation at 0.01M concentration.

[0115] Based on the above results, we can draw the conclusion that the higher the surfactant concentration and the longer the carbon chain length, the better the protection effect on AuNRs, and the easier it is to obtain soluble nanomaterials.

[0116] III. Prepare and characterize solid powders of other noble metal nanomaterials

[0117] To verify the applicability of this technology, we attempted to apply this method to noble metal nanoparticles with different sizes and surface properties.

[0118] 50 μL of concentrated 13 nm AuNPs, 30 nm AuNPs, AuNRs with an aspect ratio of 2, AuNBPs, AgNPs, SiO2@AgNPs, silver cubes, and silver octahedra, these noble metal nanomaterials were respectively dispersed in 950 μL of 0.2 M C 18 TAB solution, and vacuum freeze-dried to obtain solid powders of noble metal nanomaterials. These solid powders of noble metal nanomaterials were redispersed in 1 mL of deionized water, the solution color was observed, and the ultraviolet absorption spectrum was measured.

[0119] The morphology of the SiO2@AgNPs colloidal solution was characterized using TEM, and the morphology of other noble metal nanomaterial colloidal solutions was characterized using SEM. As Figure 10 shown, under the protection of 0.2 M C 18 TAB, the solid powders of noble metal nanomaterials obtained after vacuum freeze-drying have good redispersibility and stable optical properties.

[0120] Therefore, the technology of surfactant pre-crystallization assisted vacuum freeze-drying of colloidal nanomaterials provided by the present invention has a good scope of application.

[0121] IV. Surface-Enhanced Raman Spectroscopy Test

[0122] The colloidal solutions of concentrated 30 nm AuNPs, silver cubes, and silver octahedra were dispersed in 0.2 M C 18 TAB, and the concentration was adjusted to be the same as that of the solid powder after drying; the nanomaterials before and after drying were washed with water, and 30 nm AuNPs, silver cubes, and silver octahedra before and after freeze-drying were used as Raman substrates to measure 10 -5 M 4-mercaptopyridine.

[0123] By analyzing the Raman spectra ( Figure 11 ), it was found that:

[0124] (1) As common Raman substrates, the above three nanomaterials can all highly sensitively measure 4-mercaptopyridine;

[0125] (2) The solid powders of the nanomaterials after drying can still be used for the detection of 4-mercaptopyridine, and the detection effect is similar to that before drying.

[0126] In summary, the solid powders of the nanomaterials obtained after drying still possess good surface-enhanced Raman performance and can continue to be used as Raman substrates.

[0127] V. Catalytic Performance Test

[0128] In addition to their optical properties, gold nanoparticles are also good catalysts. Therefore, we investigated the effect of freeze-drying on the catalytic properties of 13 nm AuNPs.

[0129] Using the reduction of p-nitrophenol by sodium borohydride catalyzed by a metal as the catalytic reaction model, and 13 nm AuNPs as the catalyst, the reaction of p-nitrophenol with NaBH4 was catalyzed.

[0130] (1) Without a catalyst

[0131] 1 mL of p-nitrophenol solution (10 -4 M) was reacted with 100 μL of NaBH4 solution (0.1 M) at room temperature for 20 min, and the ultraviolet absorption spectrum was measured.

[0132] (2) The 13 nm AuNPs colloidal solution before freeze-drying was used as the catalyst

[0133] 50 μL of 13 nm AuNPs colloidal solution was added to the mixed solution of 1 mL of p-nitrophenol solution (10 -4 M) and 100 μL of NaBH4 solution (0.1 M), and the reaction was carried out at room temperature for 10 min. The ultraviolet absorption spectrum was measured every 1 min.

[0134] (3) The 13 nm AuNPs solid powder after freeze-drying was used as the catalyst

[0135] 50 μL of 13 nm AuNPs colloidal solution and the corresponding concentration of solid powder were respectively added to the mixed solution of 1 mL of p-nitrophenol solution (10 -4 M) and 100 μL of NaBH4 solution (0.1 M), and the reaction was carried out at room temperature for 10 min. The ultraviolet absorption spectrum was measured every 1 min.

[0136] From Figure 12 it can be clearly observed that:

[0137] (1) In the absence of a catalyst, there was no obvious change in the ultraviolet absorption spectrum within 20 min, indicating that almost no p-aminophenol was produced, suggesting that the efficiency of the reduction of p-nitrophenol by sodium borohydride was extremely low;

[0138] (2) After adding the catalyst 13 nm AuNPs, the reaction rate increased significantly. The color of the solution changed from yellow to colorless at 6 min, and the reaction was basically complete. At the same time, through ultraviolet measurement, it was observed that the characteristic absorption peak of p-nitrophenol gradually weakened and disappeared, and a new characteristic absorption peak of p-aminophenol appeared, indicating that 13 nm AuNPs itself has strong catalytic ability;

[0139] (3) By comparing the catalytic ability of 13nm AuNPs before and after drying, it was found that the catalytic effect after drying was similar to that before drying, and it still had good catalytic performance.

[0140] The above two performance exploration experiments proved that the solid powder of noble metal nanomaterials prepared by the surfactant pre-crystallization assisted vacuum freeze-drying technology still had good surface-enhanced Raman and catalytic properties, indicating that this method had a wider application range.

[0141] VI. Scale-up preparation of gold nanorod solid powder

[0142] Scaling up the chemical experiment yield is an important part of promoting the practical application of a technology. As an analytical reagent, in order to ensure the stability of the properties of AuNRs solid powder, we hoped to increase the yield of the same batch to ensure the accuracy and precision of the experiment. For this reason, we studied the influence of scaling up the experimental system on the drying result.

[0143] At relatively high concentrations of C 18 TAB and C 16 TAB, a good effect of preparing dispersible nano-powder could be shown. Since C16TAB was not only the necessary surfactant in the synthesis process of AuNRs, but also participated in most colorimetric analyses and was a chemical reaction reagent among them, in order to ensure the more convenient development of the experiment, the present invention used C 16 TAB as a protective agent to scale up the yield of nano-powder preparation.

[0144] A 100-fold volume expansion was carried out. We expanded the volume of freeze-drying from 100 μL of AuNRs colloidal solution to 10 mL of AuNRs colloidal solution (similar effects for larger multiples). Specifically:

[0145] Disperse 500 μL of concentrated AuNRs colloidal solution in 9.5 mL of C 16 TAB solution (0.3 M), vacuum freeze-dry, then weigh 110 mg of the dried AuNRs solid powder, redisperse it in 500 μL of deionized water, observe the solution color, measure the ultraviolet absorption spectrum, and compare it with the powder obtained from 100 μL (the volume of freeze-drying) of AuNRs colloidal solution.

[0146] As Figure 13 shown, after the yield was scaled up, the obtained AuNRs solid powder still had the same good dispersibility as that in the small-volume experiment, and a large amount of powder nano-materials obtained could be accurately weighed and sub-packed.

[0147] VII. Application of water-soluble powdered noble metal nanomaterials

[0148] Gold nanorods (AuNRs) are a commonly used nanocolorimetric analysis material. The colorimetric analysis methods developed based on them often have a wide color change range and high sensitivity, and have been widely used in environmental monitoring, food safety, and bioanalysis technology and other fields. The sensing principle of AuNRs can be divided into colorimetric analysis detection based on aggregation effect and colorimetric analysis detection based on non-aggregation effect. It is worth mentioning that the nanocolorimetric analysis method based on the morphological change of gold nanorods is a typical representative in non-aggregation type LSPR sensing analysis. Such nanocolorimetric analysis has the advantages of strong anti-interference ability and wide color change. Its principle is to utilize the characteristics that the longitudinal LSPR absorption peak of gold nanorods is sensitive to the aspect ratio and interfacial refractive index of the nanorods. By regulating the strategies of "etching" (changing the aspect ratio) and "growth" (changing the interfacial refractive index) of nanoparticles, a highly sensitive and multi-color change nanometric analysis method can be constructed.

[0149] Next, we will take two typical non-aggregation type LSPR colorimetric analysis methods of "etching" and "growth" of nanoparticles as models, and take water-soluble powder gold nanorods as an example to study an integrated all-powdered nanocolorimetric analysis kit constructed based on water-soluble powder gold nanorods.

[0150] 1. Experimental section

[0151] (1) Preparation of water-soluble powder gold nanorods

[0152] Preparation of water-soluble powder gold nanorods for detecting nitrite: Disperse 500 μL of concentrated AuNRs colloidal solution in 9.5 mL of 0.3 M C 16 TAB solution, mix evenly and then vacuum freeze-dry to obtain water-soluble powder gold nanorods A.

[0153] Preparation of water-soluble powder gold nanorods for detecting ascorbic acid: Disperse 500 μL of concentrated AuNRs colloidal solution in 4.5 mL of 0.3 M C 16 TAB solution, mix evenly and then vacuum freeze-dry to obtain water-soluble powder gold nanorods B.

[0154] (2) Detection of nitrite

[0155] Detect nitrite with water-soluble powder gold nanorods A: Weigh 110 mg of water-soluble powder gold nanorods A and dissolve it in 400 μL of deionized water (absorbance is 0.7), add 100 μL of 1 M oxalic acid solution, shake well, add 5 μL of NaNO2 solution with different concentrations to the above mixed solution, mix evenly, react at room temperature for 15 min, observe the color change of the solution, and measure the ultraviolet-visible absorption spectrum.

[0156] Detection of nitrite using colloidal solution of gold nanorods: Take 100 μL of AuNRs colloidal solution, add it to 300 μL of deionized water, then add 100 μL of 1 M oxalic acid solution, mix evenly. Add 5 μL of NaNO2 solution with a final concentration of 0 - 100 μM to the above mixed solution, shake well, react at room temperature for 15 min, and measure the ultraviolet absorption spectrum at the corresponding concentration.

[0157] (3) Screening and optimization of solid acids

[0158] Optimization of the type of solid acid: Weigh 110 mg of water-soluble powdered gold nanorods A and dissolve it in 400 μL of deionized water. Add 100 μL of 1 M oxalic acid, citric acid, D-malic acid solution, L(+)-tartaric acid, sulfamic acid, and glycine solution respectively, mix evenly, add 5 μL of 10 μM NaNO2 solution, shake well, and react at room temperature for 15 min. The above experiment is repeated three times in parallel.

[0159] Optimization of oxalic acid concentration: Weigh 110 mg of water-soluble powdered gold nanorods A and dissolve it in 400 μL of deionized water. Mix it with 100 μL of oxalic acid solution with different concentrations, add 5 μL of 10 μM NaNO2 solution, shake well, and react at room temperature for 15 min. The above experiment is repeated three times in parallel.

[0160] (4) Detection of nitrite in actual water samples

[0161] Actual water samples: Wahaha bottled water, seawater (Yellow Sea), river water (Guangdang River, Laishan District, Yantai City), groundwater (Tengzhou City).

[0162] The addition standard method is used to detect the nitrite content in actual water samples. Among them, the addition standard concentrations of Wahaha bottled water are 3 μM, 7 μM, and 10 μM, and the addition standard concentrations of seawater, river water, and groundwater are 10 μM, 25 μM, and 50 μM. In addition, seawater, river water, and groundwater are diluted 5 times before being added to the reaction system.

[0163] (5) Detection of ascorbic acid

[0164] Weigh 25 mg of water-soluble powdered gold nanorods B or 25 μL of AuNRs colloidal solution and dissolve it in 75 μL of deionized water (absorbance is 0.3). Add 390 μL of NaOH-glycine buffer solution (0.2 M) with a pH of 9.4. Dropwise add 5 μL of 0.01 M AgNO3 solution to the mixed solution, shake well, react at room temperature for 5 min, add 5 μL of ascorbic acid solution with different concentrations, mix evenly, and react at 50 °C for 15 min. Observe the color change of the solution and measure the ultraviolet absorption spectrum.

[0165] (6) Optimization of the conditions for detecting ascorbic acid using water-soluble powdered gold nanorods B

[0166] Weigh 25 mg of water-soluble powdered gold nanorods B and dissolve them in 75 μL of deionized water. Then add 390 μL of NaOH-glycine buffer solutions with pH values of 8.6, 9.0, 9.2, 9.4, 9.6, 9.8, 10.0, and 10.6 respectively. Next, add 5 μL of AgNO3 solution (0.01 M) to the mixed solution. After shaking well, react at room temperature for 5 min. Then add 5 μL of 5 μM ascorbic acid solution, shake well, and react at 50 °C for 15 min. The above experiments are repeated three times in parallel.

[0167] The optimization steps for the reaction temperature and reaction time are the same as above.

[0168] (7) Detect ascorbic acid in urine samples

[0169] According to the content of common ascorbic acid in urine, add 0.5 mM, 2 mM, and 5 mM ascorbic acid to artificial urine and real urine diluted 400 times.

[0170] 2. Results and discussion

[0171] (1) Nano-colorimetric analysis kit for detecting nitrite based on "etching" all-powder form

[0172] The all-powdered nitrite detection nano-colorimetric analysis kit provided by the present invention is constructed from a certain amount of water-soluble powdered gold nanorods A and solid acid (oxalic acid) powder.

[0173] Detection principle: After adding the test solution containing nitrite to the kit, the water-soluble powdered gold nanorods A and the solid acid (oxalic acid) powder dissolve rapidly. After the solid acid (oxalic acid) powder dissolves, hydrolysis occurs to produce a large amount of H + (to create an acidic environment). In the presence of CTAB, nitrite oxidatively etches AuNRs, causing changes in the morphology of AuNRs. As the concentration of nitrite increases, the etching effect on AuNRs gradually enhances, the aspect ratio of AuNRs gradually decreases, and finally they are completely etched into monovalent gold ions.

[0174] To characterize the etching effect of nitrite on AuNRs, TEM was used to characterize the specific morphology of AuNRs in nitrite solutions with different concentrations. As Figure 14 shown, as the concentration of the nitrite solution increases, the aspect ratio of AuNRs gradually decreases, changing from 3.2:1 to nearly 1:1. AuNRs are etched into spherical-like nanoparticles, and the corresponding solution color is pink. As the concentration of nitrite increases, the longitudinal absorption peak of AuNRs gradually blue-shifts, and in a 50 μM nitrite solution, the longitudinal absorption peak almost coincides with the transverse absorption peak.

[0175] It can be seen that quantitative analysis of nitrite can be achieved according to the change in the wavelength of the longitudinal LSPR absorption peak of AuNRs, and colorimetric detection of nitrite can be achieved according to the change in the color of the nanorods.

[0176] (2) Screening of solid buffer in the water-soluble powder-state gold nanorod A system

[0177] Regarding solid acids, before determining oxalic acid, we compared the effects of six solid acids, namely oxalic acid (EA), sulfamic acid (SA), citric acid (CA), tartaric acid (TA), malic acid (MA), and glycine (Gly), on the detection of nitrite. As Figure 15 shown, generally speaking, except for sulfamic acid (SA), the stronger the acidity of the solid acid, the higher the sensitivity of nitrite detection. Therefore, oxalic acid (EA) was finally selected as the solid acid for this reaction system.

[0178] (3) Selectivity of nitrite detection in the water-soluble powder-state gold nanorod A system

[0179] Different from the previous research systems, in this invention, solid acid is used as the acidic buffer for the first time, so its selectivity needs to be re-evaluated.

[0180] We conducted selectivity experiment tests with 10-fold concentration of interfering ions. As Figure 16 shown, 10 μM nitrite can cause a change of about 40 wavelengths, while 100 μM of interfering ions show a response similar to that of the blank. It can be seen that this detection system has good selectivity.

[0181] (4) Comparison of the performance of water-soluble powder-state gold nanorod A and gold nanorod colloidal solution in detecting nitrite

[0182] To verify the colorimetric sensing performance of water-soluble powder-state gold nanorod A, we compared the performance of water-soluble powder-state gold nanorod A and gold nanorod colloidal solution in detecting nitrite.

[0183] As Figure 17 shown:

[0184] (i) As the concentration of nitrite increases, the maximum absorption wavelength gradually blue-shifts. In the range of 0.1 - 55 μM, the difference in the maximum absorption wavelength shows a good linear relationship with the nitrite concentration. The linear expression is Y = 3.51X + 1.98, and the linear correlation coefficient is 0.996. The detection limit is as low as 0.1 μM, indicating that the AuNRs colloid has high sensitivity in the detection of nitrite;

[0185] (ii) The UV absorption spectra of water-soluble powdered gold nanorod A for detecting nitrite at different concentrations are basically the same as those of the AuNRs colloid, showing a good linear relationship in the range of 0.1 - 55 μM. The linear equation is Y = 3.42X + 2.21, the linear correlation coefficient is 0.997, and the detection limit is as low as 0.1 μM.

[0186] It can be seen that the water-soluble powdered gold nanorod A system constructed in this invention has a detection sensitivity comparable to that of its colloidal solution.

[0187] As Figure 18 shown, the colors of water-soluble powdered gold nanorod A are different in the presence of nitrite at different concentrations.

[0188] In summary, in the etching-induced non-aggregated LSPR colorimetric analysis method, water-soluble powdered gold nanorod A has detection performance comparable to that of the AuNRs colloidal solution, indicating that the preparation process of the nanopowder has no effect on its detection performance. This result is attributed to the fact that no other reagents were added during the preparation of the nanopowder.

[0189] (5) Performance of the water-soluble powdered gold nanorod A system for detecting nitrite in a high-salt environment

[0190] To explore the performance of the water-soluble powdered gold nanorod A system for detecting nitrite in a high-salt environment such as seawater, we used 0.5 M sodium chloride solution to simulate a high-salt environment for testing.

[0191] As Figure 19 shown, curves b and d are the detection effects of nitrite in a high-salt environment (0.5 M NaCl), and their detection performance is comparable to that of nitrite in a pure water system (0 M NaCl) (curves a and c). Therefore, we conclude that this experimental system can be well applied to the detection of nitrite in a high-salt environment.

[0192] (6) Detection of nitrite in actual water bodies using a solid acid buffer and a water-soluble powdered gold nanorod A system

[0193] Table 1 Detection effects of actual water samples

[0194]

[0195]

[0196] As shown in Table 1, this detection system can be used for the high-sensitivity detection of nitrite in various water samples (including drinking water, seawater, lake water, and groundwater), and recovery rates between 80% and 107% can be obtained, showing good detection effects.

[0197] (7) Construction of an integrated all-powdered nitrite detection nano-colorimetric analysis kit

[0198] An integrated all-powdered nitrite detection nano-colorimetric analysis kit (hereinafter referred to as Kit A) was constructed using 110 mg of water-soluble powdered gold nanorods A and 126.07 mg of oxalic acid powder.

[0199] Detection process: Add 500 μL of the solution to be tested to Kit A, shake well, wait for 20 min at room temperature, and perform rapid detection of nitrite by color comparison.

[0200] Sensitivity: Add 500 μL of nitrite standard solutions with different concentrations to Kit A. As Figure 20 shown, with the change of nitrite concentration, the color of the solution changes, and the ultraviolet absorption peak undergoes a blue shift. From 0.1 μM to 50 μM, the nitrite concentration and the wavelength change value show a linear relationship. The linear equation is Y = 3.66X + 0.86, and the linear correlation coefficient is as high as 0.999.

[0201] The above research proves that Kit A constructed by the present invention has high sensitivity and distinct color changes, and can be used for colorimetric analysis and detection of nitrite.

[0202] To explore the actual applicability of Kit A, we detected nitrite in mineral water and various seawater samples by the standard addition method (adding 20 μM nitrite to the actual samples). As Figure 21 shown, the color change in mineral water is basically the same as that of the 20 μM nitrite standard sample; for seawater samples, due to the presence of a large amount of calcium ions, it is easy to react with oxalic acid to form calcium oxalate precipitation, which has a certain impact on colorimetric analysis and detection.

[0203] To solve this problem, the method of filtering with a syringe through a membrane was used to filter the turbid reaction system, and colorimetric analysis was performed on the solution obtained after passing through the membrane. By comparing the color changes of the solution before and after passing through the membrane and the corresponding ultraviolet-visible absorption spectra Figure 21 (C)~ Figure 21 (F)), it can be seen that the effect after passing through the membrane is obvious. For seawater samples, the color change can be clearly observed, and the ultraviolet-visible absorption peak at the corresponding wavelength can be obtained.

[0204] According to the linear curve and Figure 21 the obtained ultraviolet absorption spectra, the recovery rates of the above five samples were calculated.

[0205] Table 2 Detection of nitrite in actual samples by Kit A

[0206]

[0207] It can be seen that the kit A can achieve high-sensitivity detection of nitrite in a variety of actual samples including various seawater, and can obtain a good recovery rate of more than 85% to 110%. These experimental results show that the kit A has a good detection effect.

[0208] (8) Nanocolorimetric Ascorbic Acid Detection Kit Based on “Growth” Fully Powdered Ascorbic Acid

[0209] The fully powdered ascorbic acid detection nanocolorimetric analysis kit provided by the present invention is constructed by a certain amount of water-soluble powdered gold nanorods B, AgNO3 solid powder and NaOH-glycine buffer solution solid powder, wherein the AgNO3 solid powder and the NaOH-glycine buffer solution solid powder are both prepared by vacuum freeze-drying.

[0210] Detection principle: After adding the test solution containing ascorbic acid to the kit, the solid powder dissolves quickly. In the NaOH-glycine buffer solution, an excess of AgNO3 solution is added. Ascorbic acid can reduce silver ions to Ag elemental substance and deposit on the surface of AuNRs, thereby causing the refractive index of the AuNRs interface to change, accompanied by changes in the LSPR wavelength and the corresponding solution color. The detection of ascorbic acid can be achieved based on the absorption spectrum and solution color changes.

[0211] In order to characterize the principle of this analysis, TEM was used to characterize the morphological changes of AuNRs caused by different concentrations of ascorbic acid. Figure 22 As shown in the figure, with the increase of ascorbic acid concentration, the Ag layer on the surface of AuNRs becomes thicker and the lateral growth rate of the Ag layer on the AuNRs is greater than its longitudinal growth rate. The corresponding aspect ratio changes from 3.2:1 to 1.3:1, and the AuNRs wrapped in part of the Ag layer become square with an aspect ratio close to 1:1 and an orange-red color. With the increase of ascorbic acid concentration, the longitudinal absorption peak of AuNRs gradually blue-shifts. When the ascorbic acid concentration reaches 50 μM, the longitudinal absorption peak of AuNRs almost coincides with the lateral absorption peak, and a very obvious Ag characteristic peak appears at 300-400 nm.

[0212] In summary, based on the LSPR sensing principle of growth-induced AuNRs morphology change, the construction of a fully powdered nanocolorimetric kit for detecting ascorbic acid can be realized.

[0213] AuNRs were etched into spherical nanoparticles, and the corresponding solution color was pink; as the nitrite concentration increased, the absorption peak gradually blue-shifted, and in a 50 μM nitrite solution, the longitudinal absorption peak almost coincided with the transverse absorption peak.

[0214] It can be seen that quantitative analysis of nitrite can be achieved based on the change in the longitudinal LSPR absorption peak wavelength of AuNRs, and colorimetric detection of nitrite can be realized according to the change in the color of the nanorods.

[0215] (9) Optimize the detection conditions of ascorbic acid in the water-soluble powder state gold nanorod B system

[0216] The pH value, reaction temperature, and reaction time of the reaction solution are important factors affecting the detection performance of ascorbic acid, so they are optimized.

[0217] From Figure 23 (A), it can be seen that as the pH value of the reaction solution increases, the maximum absorption wavelength difference first increases and then decreases. Therefore, pH 9.4 is selected as the optimal pH value in this reaction system.

[0218] From Figure 23 (B), it can be seen that as the reaction temperature increases, the difference in the maximum absorption wavelength increases rapidly and reaches the maximum at 50 °C. Continuing to increase the reaction temperature will affect the stability of the gold nanorods. Therefore, 50 °C is selected as the optimal reaction temperature.

[0219] From Figure 23 (C), it can be seen that the reaction in this reaction system is rapid within 10 min, and then gradually tends to equilibrium and completely reacts around 15 min. In order to further improve the efficiency of the experiment for detecting ascorbic acid, 15 min is selected as the reaction time for subsequent experiments.

[0220] (10) Selectivity of ascorbic acid detection in the water-soluble powder state gold nanorod B system

[0221] To explore the selectivity and anti-interference ability of this detection system, some common cations and anions, as well as common ions and amino acids in urine, etc. are used as interfering substances in this detection system. The concentration of the interfering substances (1 mM) is 200 times that of the ascorbic acid concentration (5 μM).

[0222] As Figure 24 shown: By comparing the difference in the maximum absorption wavelength, it can be found that this detection system only has a good response to 5 μM ascorbic acid, corresponding to an obvious peak shift, while the presence of other interfering substances does not cause obvious interference.

[0223] Therefore, the detection of ascorbic acid in the water-soluble powder state gold nanorod B system has good selectivity and anti-interference ability, laying a foundation for the development of a highly selective colorimetric analysis kit.

[0224] (11) Compare the performance of water-soluble powder state gold nanorod B and gold nanorod colloidal solution in detecting ascorbic acid

[0225] To verify the colorimetric sensing performance of water-soluble powdered gold nanorods B, we compared the performance of water-soluble powdered gold nanorods B and gold nanorod colloidal solutions in detecting ascorbic acid.

[0226] First, we tested the sensitivity of the AuNRs colloidal solution in detecting ascorbic acid.

[0227] As Figure 25 (A) shows, as the concentration of ascorbic acid increases, the maximum absorption wavelength of AuNRs gradually blueshifts, and the characteristic absorption peak of silver appears.

[0228] Using the change value of the maximum absorption wavelength to perform linear fitting for ascorbic acid at different concentrations, the results are as Figure 25 (B) shows: The change value of the maximum absorption wavelength and the concentration correspond to two different linear relationships. The first segment is from 0.1 μM to 7 μM, and the linear equation is Y = 10.09X - 0.76, with a linear correlation coefficient of 0.996. The second segment is from 8 μM to 35 μM, and the linear equation is Y = 2.79X + 51.05, with a linear correlation coefficient of 0.998. The detection limit is as low as 0.1 μM.

[0229] Secondly, we tested the sensitivity of water-soluble powdered gold nanorods B in detecting ascorbic acid.

[0230] As Figure 25 (C) shows, the change trend of the maximum absorption peak of the gold nanorods is consistent with that of the AuNRs colloidal solution.

[0231] Using the difference in the maximum absorption wavelength to perform linear fitting for ascorbic acid at different concentrations, the results are as Figure 25 (D) shows, a linear curve similar to that of the colloidal nanorod solution is obtained: The first segment is from 0.1 μM to 7 μM, and the linear equation is Y = 9.98X - 0.51, with a linear correlation coefficient of 0.996. The second segment is from 8 μM to 35 μM, and the linear equation is Y = 2.76X + 52.62, with a linear correlation coefficient of 0.995. The detection limit is as low as 0.1 μM.

[0232] In addition, upon observation, as Figure 26 shown, the colors of water-soluble powdered gold nanorods B are different in the presence of ascorbic acid at different concentrations.

[0233] In summary, in the growth-induced non-aggregated LSPR colorimetric analysis method, water-soluble powdered gold nanorods B have detection performance comparable to that of the AuNRs colloidal solution. Combining with the color change of water-soluble powdered gold nanorods B in the presence of ascorbic acid at different concentrations ( Figure 26 ), it provides a basis for the construction of a fully powdered nano-colorimetric analysis kit for detecting ascorbic acid.

[0234] (12) Detection of Ascorbic Acid in Urine Samples

[0235] Ascorbic acid is a common test index in routine urine examinations. To explore the actual applicability of the fully powdered kit, artificial urine and real urine were selected for the detection of the actual samples of water-soluble powdered gold nanorods B.

[0236] Table 3 Detection Effect of Ascorbic Acid in Urine Samples under the System of Water-Soluble Powdered Gold Nanorods B

[0237]

[0238] As can be seen from Table 3, even when the actual sample was diluted 400 times, water-soluble powdered gold nanorods B could still be used for the detection of ascorbic acid in urine with high sensitivity and had good recovery rates, which were all between 84% and 108%, providing a highly sensitive and selective colorimetric analysis reagent for medical detection.

[0239] (13) Construction of an Integrated Fully Powdered Ascorbic Acid Detection Nanocolorimetric Analysis Kit

[0240] Place the AgNO3 solution in the lid of a centrifuge tube in the dark, and place the NaOH-glycine buffer solution in the same centrifuge tube (to avoid the formation of silver hydroxide precipitate). Vacuum freeze-dry to obtain AgNO3 solid powder and NaOH-glycine buffer solid powder. Add 25 mg of water-soluble powdered gold nanorods B to the obtained NaOH-glycine buffer solid powder to complete the construction of the fully powdered ascorbic acid detection nanocolorimetric analysis kit, and obtain Kit B.

[0241] Detection process: Add 500 μL of the solution to be tested to Kit B, shake well, and react at 50 °C for 15 min to achieve the rapid detection of ascorbic acid.

[0242] Sensitivity: Add ascorbic acid standard solutions with different concentrations to Kit B to obtain Figure 27 the ultraviolet absorption spectra and the corresponding linear curve graphs shown. As Figure 27 can be seen, Kit B has high sensitivity, the linear range is 0.1 - 100 μM, the linear equation is Y = 90.64lgX - 23.21, and the linear correlation coefficient is 0.990.

[0243] We applied Kit B to the detection of ascorbic acid in mineral water using the standard addition recovery method. As Figure 28As shown in the figure, by comparing the color change and the ultraviolet-visible absorption spectrogram of the mineral water containing 20 μM ascorbic acid after labeling with those of the 20 μM ascorbic acid standard solution, it can be found that the signal intensities of the two are consistent, and the recovery rate of ascorbic acid in the mineral water is as high as 97.05%. That is, the colorimetric analysis and detection of ascorbic acid in actual samples can be realized by using Kit B.

[0244] In summary, the development of the integrated all-powder colorimetric analysis kit greatly simplifies the detection process and provides a new method and idea for the application of colorimetric analysis methods in multiple fields.

[0245] It should be noted that the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to enumerate all the implementation manners here. Any obvious changes or modifications derived from the technical solution of the present invention still fall within the protection scope of the present invention.

Claims

1. A preparation method of a water-soluble powdered noble metal nanomaterial, characterized in that, The water-soluble powdered noble metal nanomaterials are prepared by surfactant-assisted pre-crystallization and vacuum freeze-drying of colloidal nanomaterials, and specifically include the following steps: Step1: Prepare a colloidal solution of noble metal nanomaterials; Step 2: Disperse the noble metal nanomaterial colloidal solution prepared in Step 1 in an aqueous solution of C 18 TAB with a concentration of 0.2 M. The volume ratio of the noble metal nanomaterial colloidal solution to the C 18 TAB aqueous solution is 1:

19. Mix evenly to obtain a mixed solution; Step3: Vacuum freeze-dry the mixed solution obtained in Step2 to obtain water-soluble powdered noble metal nanomaterials.

2. The preparation method of the water-soluble powdered noble metal nanomaterial according to claim 1, characterized in that, In Step1, the colloidal solution of noble metal nanomaterials includes: AuNRs colloidal solutions with aspect ratios of 2 and 3.2, AuNPs colloidal solutions of 13 nm and 30 nm, AuNBPs colloidal solution, AgNPs colloidal solution, SiO2@AgNPs colloidal solution, silver cube colloidal solution, and silver octahedron colloidal solution.

3. The water-soluble powdered noble metal nanomaterials prepared by the method according to claim 1 or 2.

4. Use of the water-soluble powdered noble metal nanomaterial according to claim 3 in LSPR colorimetric analysis, characterized in that, As a colorimetric sensing material, it is used to construct an integrated all-powdered nano-colorimetric analysis kit. The integrated all-powdered nano-colorimetric analysis kit is constructed from the water-soluble powdered noble metal nanomaterials according to claim 3 and oxalic acid powder, and is used to detect nitrite.

5. Use of the water-soluble powder-like noble metal nanomaterial according to claim 3 in LSPR colorimetric analysis, characterized in that, As a colorimetric sensing material, it is used to construct an integrated all-powdered nano-colorimetric analysis kit. The integrated all-powdered nano-colorimetric analysis kit is constructed from the water-soluble powdered noble metal nanomaterials according to claim 3, AgNO3 solid powder, and NaOH-glycine buffer solution solid powder, and is used to detect ascorbic acid.

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