CN112247158A

CN112247158A - Method for enriching gold nanoclusters in aqueous phase

Info

Publication number: CN112247158A
Application number: CN202011130165.2A
Authority: CN
Inventors: 秦卫东; 张倩倩
Original assignee: Beijing Normal University
Current assignee: Beijing Normal University
Priority date: 2020-10-21
Filing date: 2020-10-21
Publication date: 2021-01-22
Anticipated expiration: 2040-10-21
Also published as: CN112247158B

Abstract

The invention provides a method for enriching gold nanoclusters in a water phase, and belongs to the technical field of nano materials. The method comprises the following steps: (1) adjusting the pH value of the gold-enriched nanocluster solution prepared by reacting oxidized glutathione with chloroauric acid to 2-8; (2) mixing a gold nanocluster solution to be enriched with an enrichment solution consisting of acetonitrile and a modifier in a proportion of 1: (4-7) mixing and shaking up; (3) centrifuging at the speed of 500-2000 rpm for 5-20 minutes or standing for 2-4 hours to realize phase separation; (4) collecting gold nanocluster enriched phase. The enrichment method reserves the composition, the appearance, the aggregation mode in the aqueous solution and the optical characteristics of the original nano-cluster core, has the recovery rate of more than 99 percent in the enrichment process, is simple and quick to operate, and can realize large-scale nano-cluster enrichment. The nano-cluster enriched by the method can be directly dissolved in water, and the requirements of optical treatment and homogeneous catalysis are met.

Description

Method for enriching gold nanoclusters in aqueous phase

Technical Field

The invention relates to a method for enriching gold nanoclusters in a water phase, and belongs to the technical field of nano materials.

Background

The gold nanoclusters are nanostructures stacked up by a core consisting of several to several tens of gold atoms and a shell consisting of a complex (au (i) -Ligand) formed by monovalent gold-Ligand wrapping the outside thereof. Usually, the core size of the gold nanocluster is less than 2nm, and the gold nanocluster has a size equivalent to the fermi wavelength, so that a discrete molecular electronic structure and unique reaction properties are shown, and the gold nanocluster is widely applied to the fields of optical treatment, catalysis and the like due to the special properties.

However, high concentrations of gold nanoclusters are generally required in the fields of optical therapy, catalysis and the like, and the concentrations of gold nanoclusters obtained by chemical synthesis methods are generally not up to the requirements, so that the synthesized gold nanoclusters need to be enriched. As the enrichment method, ultracentrifugation, ultrafiltration, immunocapture, chromatography, and solvent precipitation have been reported. However, these methods have some disadvantages, such as incomplete enrichment by ultracentrifugation, and low yield, time and cost of ultrafiltration, immunocapture, chromatography and solvent precipitation; in addition, the gold nanoclusters may be denatured by chromatography and solvent precipitation. Therefore, it is a technical problem to be solved urgently to develop an efficient and convenient gold nanocluster enrichment technology.

Disclosure of Invention

The invention aims to provide an efficient and convenient enrichment method of gold nanoclusters in a water phase. The inventor finds that the gold nanocluster solution generated by the reaction of oxidized glutathione and chloroauric acid is mixed with an enrichment solvent (a mixture of acetonitrile and a modifier) in a certain proportion to generate oil-shaped liquid drops, the liquid drops are immiscible with the enrichment solvent and have a density higher than that of the enrichment solvent, and more importantly, the gold nanoclusters in the original water phase solution are almost completely enriched in the oil-shaped liquid drops. In view of the above, the present patent provides a method for enriching gold nanoclusters in an aqueous phase, which is characterized by comprising the following steps:

(1) adjusting the pH value of the gold nanocluster solution to be enriched to 2-8;

the gold nanocluster solution to be enriched is prepared by reacting oxidized glutathione with chloroauric acid, the initial concentration of the chloroauric acid in a reactant is 1-20 mM, and the ratio of the initial molar concentration of the oxidized glutathione to the initial molar concentration of the chloroauric acid is 2: 1-5: 1;

(2) adding the gold nanocluster solution to be enriched into the enriched solution, and shaking up; the enrichment solution consists of acetonitrile and a modifier; the modifier is one or more of chloroform, carbon tetrachloride, tetrahydrofuran, ethyl acetate, cyclohexane and normal hexane;

(3) phase separation;

(4) collecting gold nanocluster enriched phase.

Preferably, the pH value of the gold nanocluster solution to be enriched in step (1) is adjusted by 200mM NaOH or 200mM HCl.

Preferably, the volume ratio of the gold nanocluster solution to be enriched in the step (2) to the acetonitrile solution is 1: (4-7), wherein the volume ratio of the modifier to the acetonitrile is (0-1) to 4.

The phase separation in the step (3) is realized by a centrifugal method or a standing method.

When the phase separation is realized by a centrifugal method, the preferred centrifugal speed is 500-2000 r/min, and the preferred centrifugal time is 5-20 min.

When the phase separation is realized by a standing method, the preferable standing time is 2-4 hours.

And (4) the gold nanocluster enriched phase in the step (4) is in a liquid state.

The gold nanocluster enrichment method provided by the application reserves the composition, morphology, aggregation mode and optical characteristics of the original nanocluster kernel, the recovery rate in the enrichment process is more than 99%, and separation can be completed within 20 minutes through a centrifugation mode; large-scale nano-cluster enrichment operation can be realized by a standing mode. Compared with enrichment methods such as an ultracentrifugation method, an ultrafiltration method, an immunocapture method, a chromatography method and the like, the method is simple and rapid to operate and can enrich on a large scale; compared with a solvent precipitation method, the enriched nano-cluster can be directly dissolved in water, and the requirements of light treatment and homogeneous catalysis can be met.

Drawings

FIG. 1 is a MALDI-TOF-MS analysis of gold nanoclusters of example 1 after the aqueous phase is to be enriched (A) and enriched (B).

FIG. 2 is a TEM image of the aqueous phase gold nanoclusters of example 1.

Fig. 3 is a TEM image of gold nanoclusters after concentration with acetonitrile in example 1.

FIG. 4 is a fluorescence emission spectrum (excitation wavelength 430nm) of the nanoclusters to be enriched in example 1.

FIG. 5 is the fluorescence emission spectrum (excitation wavelength 430nm) of gold nanoclusters in oil phase after enrichment in example 1.

FIG. 6 is a gas chromatography-thermal conductivity measurement method for analyzing volatile components in oily liquid drops in example 2. In the figure, peaks corresponding to 1-3 are respectively water, acetonitrile and n-butanol.

FIG. 7 is a capillary electrophoresis analysis chart of oxidized glutathione (A), oily liquid droplets (B) and upper solution (C) in example 2. In the figure, peak 1 is oxidized glutathione, and the concentration of oxidized glutathione in the standard solution is 0.05 mM.

FIG. 8 is a graph showing the effect of the method (1) of the present invention and the acetonitrile precipitation method (2) on the enrichment of nanoclusters in example 6.

FIG. 9 shows the re-dissolution of enriched nanoclusters of the method (1) and acetonitrile precipitation (2) of the present invention in example 6.

Detailed Description

The patent provides an enrichment method of gold nanoclusters in a water phase, which comprises the following steps:

(1) mixing oxidized glutathione and chloroauric acid, wherein the initial concentration of the chloroauric acid is 1-20 mM, and the ratio of the initial molar concentration of the oxidized glutathione to the initial molar concentration of the chloroauric acid is 2: 1-5: 1; obtaining a gold nanocluster solution after reaction, and adjusting the pH value of the gold nanocluster solution to be enriched to 2-8 by using 200mM NaOH or 200mM HCl;

(2) mixing the gold nanocluster solution to be enriched with the enrichment solution in a ratio of 1: (4-7) mixing and shaking up; the enrichment solution consists of acetonitrile and a modifier; the modifier is one or more of chloroform, carbon tetrachloride, tetrahydrofuran, ethyl acetate, cyclohexane and normal hexane; the volume ratio of the modifier to the acetonitrile is (0-1) to 4;

(3) carrying out phase separation by a centrifugal or standing mode; when the phase separation is realized by a centrifugal method, the centrifugal speed is 500-2000 rpm, and the centrifugal time is 5-20 minutes; when the phase separation is realized by a standing method, the preferable standing time is 2-4 hours;

(4) collecting gold nanocluster enriched phase; the gold nanocluster enriched phase is in a liquid state and is immiscible with the enriched solution.

For further understanding of the present invention, the method for enriching gold nanoclusters provided by the present invention is described in detail below with reference to the following examples, and the scope of the present invention is not limited by the following examples.

The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials are commercially available, unless otherwise specified.

According to the present invention, a gold nanocluster solution to be enriched, which is synthesized from oxidized glutathione and chloroauric acid as raw materials, may be prepared according to a method disclosed in the prior art, and is referred to as a gold nanocluster solution in this specification.

Example 1

In this example, the composition, morphology and fluorescence properties of the gold nanoclusters before and after enrichment were compared and studied.

1.1 preparation of gold nanoclusters

5mL of 20mM chloroauric acid (HAuCl) freshly prepared at room temperature with vigorous stirring₄) And 5mL of an aqueous solution of 100mM oxidized glutathione (GSSG) was mixed with 90mL of triple distilled water in a round-bottomed flask (HAuCl under this condition)₄And GSSG at initial concentrations of 1mM and 5mM, respectively), after two minutes of standing, the mixture was placed in a water bath at 80 ℃ for 24 hours with gentle stirring (500 rpm). After the solution was naturally cooled to room temperature, the precipitate was removed by centrifugation at 2000 rpm for 15 minutes, and the supernatant was stored in a refrigerator at 4 ℃ for further use.

1.2 enrichment of gold nanoclusters in aqueous phase

Adjusting the pH value of the gold nanocluster solution to be enriched prepared in the step 1.1 to 2 by using 200mM HCl, adding 1mL of the gold nanocluster solution into a centrifuge tube containing 4mL of acetonitrile, shaking up, standing for 5 minutes, centrifuging at 2000 rpm for 5 minutes, and finding light yellow oily liquid drops with the volume of about 25 mu L at the bottom of the centrifuge tube.

1.3 Mass Spectrometry characterization of gold nanoclusters before and after enrichment

The gold nanocluster is a geometric structure which is similar to molecules and takes gold atoms as a main body, and the number of the gold atoms in the structure influences the optical properties and catalysis of the gold nanoclusterAnd (4) performance. And the mass spectrum is an important tool for analyzing the information of the number of atoms in the gold nanocluster. Matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) spectrogram (figure 1) shows that the M/Z of main ion peaks of the gold nanocluster mass spectrometry before and after enrichment is the same, and the intensities of the peaks are similar. The results of mass spectrometry in Table 1 show that GSSG and HAuCl₄The reaction produced a mixture of gold nanoclusters, which was complexed with reduced Glutathione (GSH) and HAuCl₄The reaction synthesis into nanoclusters is similar (CHEMISELECTROCHEM, 2020,7, 1092-1096). Moreover, some of the gold nanoclusters of this patent are the same as those produced by GSH synthesis, e.g., [ Au ]₁₅S₅+4Cl]^-，[Au₁₇S₆+4Cl]^-And [ Au ]₂₂S₇+4Cl]^-And so on (The Journal of Physical Chemistry Letters,2010,1, 2903-2910). The above results show that the composition of the atoms in the gold nanocluster structure does not change before and after enrichment.

TABLE 1 Mass Spectrometry of Charge to Mass ratios and corresponding gold nanoclusters

1.4 Transmission Electron microscopy characterization of gold nanoclusters before and after enrichment

The structure and solid state aggregation state of gold nanoclusters affect their performance, including catalytic and optical properties, among others. Transmission Electron Microscope (TEM) experiments are respectively carried out on the water-phase gold nanoclusters and the enriched gold nanoclusters in the oily liquid drops, and the results show that the enriched gold nanoclusters have no obvious difference from the water-phase gold nanoclusters in terms of size and appearance (fig. 2 and 3). Indicating that the enrichment process did not cause a change in gold nanocluster structure.

1.5 comparison of fluorescence intensities of gold nanoclusters before and after enrichment

The fluorescence property of the gold nanoclusters reflects information of the core gold atom crystal structure of the nanoclusters, the distribution state of the outer Au- (I) -GSSG complex (including the relative content of Au (I) and Au (0) and the rigidity wrapped by the outer Au- (I) -GSSG complex, and the like), and also indirectly reflects the aggregation characteristic of the gold nanoclusters as a whole in a solution.

The oil-like liquid drops of the enriched nano-clusters contain acetonitrile, and the existence of the acetonitrile can influence the fluorescence property of the gold nano-clusters. In view of the above, centrifugal ultrafiltration is used in the experiment to remove small molecules in the liquid. The specific operation is as follows:

and (3) taking 1mL of the gold nanocluster aqueous solution obtained in the step 1.1, putting the gold nanocluster aqueous solution into an ultrafiltration centrifugal tube (with the molecular weight cutoff of 3kDa and Millipore), centrifuging for 15 minutes at 500 revolutions per minute, adding 1mL of three times of distilled water into the ultrafiltration tube, shaking up, centrifuging for 15 minutes at 500 revolutions per minute again, and carefully dissolving the trapped nanoclusters into 2mL of three times of distilled water to be detected.

And (3) dissolving the oily liquid drops obtained in the step 1.2 after enrichment in 1mL of triple distilled water, putting the oily liquid drops into an ultrafiltration centrifugal tube (with the molecular weight of 3kDa at the cut-off, Millipore), centrifuging for 15 minutes at 500 rpm, adding 1mL of triple distilled water into the ultrafiltration tube, shaking up, centrifuging for 15 minutes at 500 rpm again, and carefully dissolving the entrapped nanoclusters in 2mL of triple distilled water to be detected.

The excitation wavelength for fluorescence measurement was 424nm and the fluorescence emission intensity was measured at an emission wavelength of 606 nm. The emission intensity of the aqueous nanoclusters was measured to be 4.7656 × 10⁵(FIG. 4), the fluorescence emission intensity of the oil-like liquid drop after being dispersed in the same volume of tertiary distilled water after removing acetonitrile is 4.8574X 10⁵(FIG. 5). The fluorescence characteristics of the gold nanoclusters before and after enrichment are not obviously changed, which shows that the aggregation behaviors of the two gold nanoclusters in water are similar.

The experimental results show that the aqueous phase gold nanocluster is added into acetonitrile to form a new phase, the phase is deposited at the bottom and is immiscible with the upper acetonitrile/water mixed phase, so that the enrichment of the aqueous phase gold nanocluster can be realized, the gold atom arrangement of the core of the gold nanocluster and the Au (I) -GSSG property wrapped by the outer layer of the gold nanocluster are not changed in the enrichment process, and the aggregation behavior characteristic of the solid phase nanocluster is not changed; moreover, the enriched nanoclusters can be directly dissolved in triple distilled water, and the aggregation characteristics of the gold nanoclusters dissolved in water are similar to those of a nanocluster solution to be enriched.

Example 2

2.1 preparation of gold nanoclusters

Under vigorous stirring at ambient temperature, 40mL of 50mM HAuCl was freshly prepared₄And 40mL of 100mM GSSG aqueous solution was mixed with 20mL of triple distilled water in a round-bottomed flask (HAuCl under these conditions)₄And GSSG at 20mM and 40mM, respectively), after two minutes of standing, the mixture was placed in a water bath at 80 ℃ for 24 hours with gentle stirring (500 rpm). After the solution was naturally cooled to room temperature, the precipitate was removed by centrifugation at 2000 rpm for 15 minutes, and the supernatant was stored in a refrigerator at 4 ℃ for further use.

2.2 enrichment of gold nanoclusters in aqueous phase

And (3) adjusting the pH value of the gold nanocluster solution to be enriched prepared in the step 2.1 to 8 by using 200mM NaOH, adding 2mL of the gold nanocluster solution into a centrifugal tube containing 14mL of acetonitrile, shaking up, and standing. During standing, a light yellow milky substance is found in the upper acetonitrile/water phase, the upper acetonitrile/water phase gradually moves downwards along with the passage of time, the upper acetonitrile/water phase becomes clear after 4 hours, and light yellow oily liquid drops with the volume of 110 mu L are found at the bottom of a centrifuge tube.

2.3 determination of gold nanocluster content and enrichment recovery rate in oily liquid drop

Sample treatment:

the method for treating the gold nanocluster solution to be enriched comprises the following steps: and (3) taking 2mL of the gold nanocluster solution obtained in the step 2.1, adding 2mL of concentrated nitric acid and 2mL of 40% hydrogen peroxide, shaking up, placing in a polytetrafluoroethylene digestion tank for digestion at 120 ℃ for 3 hours, cooling to room temperature, and metering the volume of the solution to 50mL for detection.

② the processing method of enriched nano-cluster: and (3) taking out oily liquid drops obtained in the step 2.2, adding 2mL of concentrated nitric acid and 2mL of 40% hydrogen peroxide, shaking up, placing in a polytetrafluoroethylene digestion tank for digestion at 120 ℃ for 3 hours, cooling to room temperature, and metering the volume of the solution to 50mL for later measurement.

The inductively coupled plasma atomic emission spectrometry is used to measure that the gold content in the test solution is 0.420mM, and the gold content in the test solution is 0.418mM, so that the recovery rate in the enrichment process is 0.418/0.420 × 100%, which is 99.52%, and the enrichment of the gold nanoclusters in the water phase by the method is nearly complete.

2.4 analysis of the Water and acetonitrile content of the oily drops

The method comprises the steps of dissolving oily liquid drops by using n-butanol as a solvent, analyzing volatile components in the oily liquid drops by using a gas chromatography-thermal conductivity detection method, wherein a typical chromatogram is shown in FIG. 6, taking peak areas of water and acetonitrile into a standard curve for calculation, and an analysis result shows that the oily liquid drops contain 20.2% of water and 10.3% of acetonitrile (volume content).

2.5 analysis of residual amounts of oily droplets and GSSG in acetonitrile/water phase

Before analysis, the acetonitrile/water phase at the upper layer is diluted by 30 times by using distilled water for three times, the oily liquid drop phase is diluted by 1000 times, and the content of the oxidized glutathione in the oily liquid drop phase is detected by using a capillary electrophoresis-ultraviolet detection method. Conditions of capillary electrophoresis: the buffer solution is 20mM sodium dihydrogen phosphate and 10mM borax, the separation voltage is 12kV, the detection wavelength is 200nm, the inner diameter of the capillary is 50 μm, the effective length is 45cm, and the total length is 52 cm. A typical capillary electrophoresis pattern is shown in FIG. 7. And (3) bringing the measured peak areas of the oxidized glutathione into a standard curve, and calculating that the contents of the oxidized glutathione in the oily liquid drop and the upper acetonitrile/water phase solution are 683mM and 0.694mM respectively, which indicates that most of the oxidized glutathione in the nano-cluster water solution enters the oily liquid drop in the enrichment process.

2.6 mechanism of formation of oily droplets

In HAuCl₄And disulfide bond-containing compounds (represented by RSSR), HAuCl₄Is an oxidant capable of oxidizing RSSR into RSOSR at normal temperature and further oxidizing RSO at 80 deg.C₃H. We believe that the disulfide bonds in oxidized glutathione (GSSG) can react similarly. Since GSSG is excessive in the reaction for preparing gold nanoclusters, there are surplus GSSG, GSOSG and GSO in addition to nanoclusters and Au (I) -GSSG complexes on the surface thereof in the gold nanocluster solution₃H。

The inventors discovered that the synthesized gold nanocluster solution can form oily liquid drops when added to acetonitrile at a certain volume ratio, and the following experiment explores the main factors for forming oily liquid drops.

2.6.1 oil droplet formation ability test of dialysate

To explore the mechanism of formation of oily droplets, the inventors first dialyzed out small molecule components including GSSG, GSOSG and GSO from the 100mL gold nanocluster solution synthesized in step 2.1 using a dialysis membrane₃H, these components were present in 1.5L of dialysate (triple distilled water). The dialysate was concentrated to 80mL by rotary evaporation, adjusted to pH 8 with 200mM NaOH, and 2mL of solution was taken and added to a centrifuge tube containing 14mL of acetonitrile, shaken well and allowed to stand. White emulsion is found in the acetonitrile/water mixed solution during standing, and after 5min, the mixture is centrifuged at 3000 rpm for 5min, so that white oily liquid drops with the volume of about 90 mu L can be found at the bottom of the centrifuge tube. However, this oil was relatively viscous and had poor fluidity, and was almost solidified after being left for 1 day in the presence of the upper acetonitrile/water phase. The formed gold nanoclusters and Au (I) -GSSG on the surface of the gold nanoclusters play a certain role in the oil drop forming process, and the drops containing the gold nanoclusters are low in viscosity and stable.

2.6.2 experiment on the ability of GSOSG to form oil droplets

To explore the role of GSOSG in the formation of droplets, the inventors prepared freshly 40mL of 50mM HAuCl₄And 40mL of an aqueous solution of 100mM GSSG was mixed with 20mL of triple distilled water in a round-bottomed flask (HAuCl under these conditions)₄And GSSG starting concentration of 20mM and 40mM, respectively), the mixture was reacted for 2 hours with gentle stirring (500 rpm). The solution was adjusted to pH 8 with 200mM NaOH, 2mL of the solution was taken and added to a centrifuge tube containing 14mL of acetonitrile, shaken well and allowed to stand. The upper acetonitrile/water phase was found to be a white emulsion on standing, but after 2 hours a precipitate formed at the bottom of the centrifuge tube. Due to HAuCl at normal temperature₄GSOSG is generated by reaction with excess GSSG, and the above experiment shows that GSOSG is not an important component for forming oily liquid drops.

Combining the above experiments, it can be concluded that GSO is formed during the reaction₃H is the main driving force for forming oily droplets and is presumed to form weak strength with acetonitrileHydrogen bonds, and the gold simple substance is an electron-deficient element and can have weak interaction with water molecules, and the substances are mixed to form a new phase which is immiscible with acetonitrile/water phase, good in fluidity and high in stability.

Example 3

This example explores the effect of pH of the aqueous solution of nanoclusters to be enriched on the enrichment effect.

Gold nanoclusters were synthesized as in 2.1, with the pH of the nanocluster solution adjusted with 200mM HCl and 200mM NaOH prior to enrichment. 2mL of the gold nanocluster solution was added into a centrifuge tube containing 14mL of acetonitrile, shaken up, and after standing for 4 hours, the volume of the yellowish oily liquid drop at the bottom of the centrifuge tube was measured, as shown in Table 2. The result shows that the volume of the oily liquid drop is 97-115 mu L within the range of the pH value of the aqueous phase 2-8, which indicates that effective enrichment can be realized within a wider range of the pH value of the aqueous phase solution.

It is particularly noted that GSSG molecules are amphiphilic compounds in nature due to their structural presence of both carboxyl and amino groups. Because GSSG is excessive in the reaction for preparing the gold nanoclusters, the gold nanocluster aqueous solution contains GSSG, the solution has certain buffer capacity, and the pH value of the solution is 2.2. Experiments have found that the addition of a gold nanocluster solution without pH adjustment directly to acetonitrile also forms oily droplets.

TABLE 2 Effect of pH value of aqueous solution of nanoclusters to be enriched on enrichment effect

Example 4

This example explores the effect of the ratio of the volume of gold nanocluster in water to the volume of acetonitrile on the ability to form oily droplets.

Synthesis of gold nanoclusters referring to 2.1, the solution was adjusted to pH 5 with 200mM NaOH, and an aqueous solution of gold nanoclusters of V1 volume was added to acetonitrile of V2 volume under the conditions of table 3, shaken well and left for 4 hours to observe whether the bottom of the centrifuge tube (indicated by √) is formed into oily droplets (indicated by x).

Table 3 effect of gold nanocluster aqueous volume (V1) and acetonitrile volume (V2) on formation of oily droplets

From the results, it can be seen that the water phase: the acetonitrile phase may form oily droplets in a volume ratio of between 1:4 and 1: 8.

Example 5

This example examines the effect of adding a modifier to acetonitrile on enrichment.

The modifier is chloroform, carbon tetrachloride, tetrahydrofuran, ethyl acetate, cyclohexane and normal hexane, and the modifiers with different volumes are respectively added into acetonitrile, so that the volume ratio of the acetonitrile to the modifiers is 1: 1-20: 1. Due to different chemical structures of the modifiers, the polarity difference is large, and the miscibility with acetonitrile is different. Experiments have found that cyclohexane and n-hexane are immiscible when the volume ratio of acetonitrile to modifier is between 1:1 and 5:1, as indicated by "n.a." (table 4). And for trichloromethane, carbon tetrachloride, tetrahydrofuran and ethyl acetate, the volume ratio of acetonitrile to the modifier is 1: 1-20: 1.

For synthesis of gold nanoclusters, see 2.1, the solution was adjusted to pH 5 with 200mM NaOH, 2mL of gold nanocluster solution was added to a centrifuge tube containing 10mL of acetonitrile, shaken well and allowed to stand for 4 hours.

TABLE 4 Effect of modifiers on nanocluster enrichment Capacity

After the modifier is added with acetonitrile, the enrichment behavior is changed after other modifiers are added with acetonitrile except that tetrahydrofuran does not cause the enrichment behavior change of the aqueous phase gold nanocluster solution. In the mixed solution (enriched solvent) of acetonitrile/trichloromethane with the volume ratio of 20:1, when the volume ratio of the aqueous phase gold nanocluster solution to the enriched solvent is 1:10, oily liquid drops can be formed, so that the volume range of the phase to be enriched is widened; in the case of acetonitrile/ethyl acetate mixed solution with the volume ratio of 8:1, oily liquid drops can be formed within the range that the volume ratio of the aqueous phase gold nanocluster solution to the enrichment solvent is 1 (3-10); when acetonitrile/cyclohexane and acetonitrile/n-hexane were used as the rich solvent (both the acetonitrile/cyclohexane and acetonitrile/n-hexane volume ratios were 8:1), the time for forming oily droplets was shortened to 1.5 hours.

Example 6

This example investigates the concentration and re-dissolution of gold nanoclusters in contrast to literature reported methods and explores the regeneration of the acetonitrile organic phase for enrichment.

6.1 concentration of gold nanoclusters

The synthesis of the gold nanoclusters is the same as 1.1.

6.1.1 methods of the invention

50mL of the gold nanocluster solution was added to a round-bottomed flask containing 300mL of acetonitrile/ethyl acetate (the volume ratio of acetonitrile to ethyl acetate was 10:1), shaken, and after standing for 2 hours, a yellow liquid was found at the bottom of the flask, which was then aspirated, and the volume of the solution was measured to be 985. mu.L. The oily liquid had good fluidity (see FIG. 8-1).

6.1.2 method of comparative example

The nanoclusters are enriched using a solvent precipitation method reported in the literature (Journal of the American Chemical Society,2016,138, 390-401). Taking 15mL of gold nanocluster solution, adding 5mL of acetonitrile, uniformly mixing for 5 minutes, and centrifuging at the speed of 5000 rpm to obtain a dark yellow precipitate (see figure 8-2).

6.2 concentrated nanocluster redissolution

6.2.1 redissolving the enriched nanoclusters of the present invention

The oily liquid was taken out, added to 2mL of triple distilled water, and gently shaken, the oily liquid was dissolved to form a pale yellow transparent liquid (FIG. 9-1).

6.2.2 redissolving of nanoclusters enriched in comparative examples

The supernatant from FIG. 8-2 was decanted to leave a dark yellow precipitate at the bottom of the centrifuge tube, and 2mL of triple distilled water was added to the centrifuge tube and the precipitate was not dissolved by shaking to form a yellow suspension (FIG. 9-2).

The experimental results show that the nanoclusters enriched by the method can be directly dissolved in water, and are suitable for being applied to application scenes such as a light treatment carrier, homogeneous catalysis and the like in the later period; however, the precipitate formed by the existing nano-cluster enriched by the organic solvent method can not be directly dissolved in water, which indicates that the gold nano-cluster is denatured at this time, and the application of the gold nano-cluster is limited.

6.3 regeneration of the enriched solvent

6.1.1, separating the oily solution from the upper liquid phase, and recovering the upper liquid phase by rotary evaporation at 60 ℃ to obtain 287mL of liquid, wherein the volume ratio of acetonitrile, ethyl acetate and water is 1:0.092:0.0079 by gas chromatography analysis. This liquid was applied to an experiment enriching gold nanoclusters in the aqueous phase, and the procedure of 6.1.1 was repeated to obtain an oily liquid with a volume of 1007 μ L, which was very close to the previous 985 μ L.

The above embodiments in this specification illustrate that the product obtained by the gold nanocluster enrichment method provided by the present application retains the original nanocluster core composition, morphology, aggregation mode in an aqueous solution, and optical characteristics, the recovery rate in the enrichment process is greater than 99%, the separation can be completed within 20 minutes by a centrifugation mode, and a large-scale nanocluster enrichment operation can be realized by a standing mode. Compared with enrichment methods such as an ultracentrifugation method, an ultrafiltration method, an immunocapture method, a chromatography method and the like, the method is simple and rapid to operate; compared with a solvent precipitation method, the enriched nanoclusters can be dissolved in water, and the requirements of direct application to optical therapy and homogeneous catalysis can be met.

Claims

1. A method for enriching gold nanoclusters in an aqueous phase is characterized by comprising the following steps:

(2) adding the gold nanocluster solution to be enriched into the enriched solution, and shaking up;

the enrichment solution consists of acetonitrile and a modifier;

the modifier is one or more of chloroform, carbon tetrachloride, tetrahydrofuran, ethyl acetate, cyclohexane and normal hexane;

(3) phase separation;

(4) collecting gold nanocluster enriched phase.

2. The method for enriching gold nanoclusters in an aqueous phase according to claim 1, wherein the pH of the gold nanocluster solution to be enriched in step (1) is adjusted with 200mM NaOH or 200mM HCl.

3. The method for enriching gold nanoclusters in an aqueous phase according to claim 1, wherein the volume ratio of the gold nanocluster solution to be enriched in step (2) to the acetonitrile solution is 1: (4-7).

4. The method for enriching gold nanoclusters in an aqueous phase according to claim 1, wherein the volume ratio of the modifier to acetonitrile in the step (2) is (0-1): 4.

5. The method for enriching gold nanoclusters in an aqueous phase according to claim 1, wherein the phase separation in the step (3) is achieved by a method of centrifugation or standing.

6. The method for enriching gold nanoclusters in an aqueous phase according to claim 5, wherein the centrifugation speed is 500 to 2000 rpm when the phase separation is performed by a centrifugation method.

7. The method for enriching gold nanoclusters in an aqueous phase according to claim 5, wherein the centrifugation time is 5-20 minutes when the phase separation is realized by the centrifugation method.

8. The method for enriching gold nanoclusters in an aqueous phase according to claim 5, wherein the standing time is 2 to 4 hours when phase separation is achieved by a standing method.

9. The method of claim 1, wherein the gold nanocluster-enriched phase in step (4) is in a liquid state.