CN111484083B

CN111484083B - Preparation and application of manganese oxide nanocluster

Info

Publication number: CN111484083B
Application number: CN202010279719.9A
Authority: CN
Inventors: 张倩; 崔大祥
Original assignee: Shanghai Jiaotong University
Current assignee: Shanghai Jiaotong University
Priority date: 2020-04-10
Filing date: 2020-04-10
Publication date: 2022-02-11
Anticipated expiration: 2040-04-10
Also published as: CN111484083A

Abstract

The invention provides a preparation method and application of a manganese oxide nanocluster, and relates to the field of nano biomedicine. According to the invention, a manganese precursor, a hydrophobic ligand and a reaction solvent are mixed, the manganese precursor is rapidly decomposed and rapidly nucleated in a high-temperature environment, and the ultra-small manganese oxide nano-cluster particles with the surfaces coated with the hydrophobic ligand and uniform particle size distribution are obtained. The manganese oxide nano-cluster particles can form a stable colloid by phase inversion dispersion in an aqueous solution, show high-efficiency nano-enzyme activity in a weakly acidic tumor microenvironment, and release ROS to kill tumor cells. Meanwhile, the manganese oxide nano-cluster particles can also be used as T₁Contrast agent for magnetic resonance imaging of liver cancer lesion tissue. Compared with the prior art, the manganese oxide nano cluster prepared by the method has the advantages of high yield, uniform particle size, good dispersibility, good stability, strong nano enzyme activity and higher T₁Relaxation rate and the like.

Description

Preparation and application of manganese oxide nanocluster

Technical Field

The invention relates to the field of nano biomedicine, in particular to a preparation method and application of a manganese oxide nanocluster.

Background

In recent decades, with the advance of modern medicine and the development of nanotechnology, multifunctional nanomaterials have made breakthrough progress in cancer diagnosis and precise treatment research, and various nano preparations have been approved to be on the market, so that a new solution is provided for overcoming the bottleneck of cancer diagnosis and treatment. However, the process for preparing the multifunctional nano-preparation integrating diagnosis and treatment is complex, and needs stronger research backgrounds of materials, chemistry, biomedicine and the like, and how to prepare the composite nano-carrier with good stability and strong functionality for specific delivery to the liver cancer part is still a difficult point of current research.

The application of manganese oxide nano-materials in the nano-biomedical field is increasingly attracting the wide attention of scientists and is inThe ideal performance is achieved in early monitoring and treating the tumor, which is mainly attributed to the unique physicochemical properties including r₁High relaxation rate, good stability, strong activity of the nano-enzyme, high biocompatibility and the like. Manganese oxide nanoparticles as T for magnetic resonance imaging₁The contrast agent can realize the signal enhancement of a tumor part in a short time, achieves the diagnosis effect of tumor lesion tissues, and has a certain application prospect in magnetic resonance imaging. Meanwhile, with the introduction of the nanoenzyme concept, scientists find that manganese oxide has high-efficiency nanoenzyme activity in a faintly acid tumor microenvironment, can react with hydrogen peroxide generated by tumor cell metabolism to generate a large amount of oxygen so as to relieve the hypoxic problem of tumor tissues, can release a large amount of ROS to kill tumor cells, and has no damage to surrounding normal cells, so that the manganese oxide nanomaterial is beneficial to diagnosis and accurate treatment of liver cancer.

Manganese oxide nanoparticles can be obtained by a coprecipitation method or a pyrolysis method in the prior art. The particle size of the prepared product is not uniform, the particles are large, and the product is suitable for the industrial fields of catalysis or battery application and the like; the latter is not beneficial to the large-scale application of the manganese oxide nano material because the high-temperature reaction usually has higher requirements on equipment and devices in the preparation process and the single-batch yield is lower. The manganese oxide nano material prepared at present has low yield, poor stability and r₁The relaxation rate is low, which is mainly shown as: the manganese oxide nanoparticle has the defects of low yield, difficulty in being used in large animal models, nonuniform particle size distribution, poor dispersibility, small specific surface area, weak colloid stability and the like, has large particles, is difficult to metabolize, often has the problems of agglomeration and the like in biological systems such as blood, cell culture solution and the like, brings lots of troubles for subsequent diagnosis and accurate treatment, and is mainly caused by unsatisfactory preparation and modification of the manganese oxide nanoparticles.

Therefore, there is a need in the art to develop a multifunctional manganese oxide nanocluster which has high yield, strong activity, easy metabolism and stable existence in an aqueous system and can be directly used for tumor diagnosis and treatment.

Disclosure of Invention

In view of the defects in the prior art, the technical problem to be solved by the invention is to provide a preparation method of a manganese oxide nanocluster with good stability and high yield and an application thereof.

In order to achieve the above object, the present invention provides a method for preparing a manganese oxide nanocluster, comprising the steps of:

(1) mixing a manganese precursor, a hydrophobic ligand and a reaction solvent to obtain a solution a;

(2) heating the solution a at a high temperature to obtain the manganese oxide nano-cluster particles coated with the hydrophobic ligand on the surface to form a solution b, wherein the heating temperature can be set to be 200-300 ℃, for example, the temperature can be set to be 200 ℃, 250 ℃, 280 ℃ or 300 ℃;

(3) alternately centrifuging and resuspending the solution b by using ethanol and chloroform to obtain a solution c;

(4) and (3) performing ligand exchange and dialysis purification on the solution c and the hydrophilic ligand solution to obtain the water-soluble manganese oxide nanocluster, wherein the ligand exchange can be performed at 60-80 ℃, such as 60 ℃, 65 ℃, 70 ℃, 78 ℃ or 80 ℃.

The step (1) and the step (2) can be carried out under the protection of nitrogen.

Further, the manganese precursor is any one of potassium permanganate, manganese acetate, manganese chloride or manganese acetylacetonate.

Further, the hydrophobic ligand is selected from one or at least two mixtures of oleic acid, oleylamine, oleyl alcohol or dodecylamine.

Further, the reaction solvent is any one of octadecene, dibenzyl ether, diphenyl ether or oleylamine.

Further, the hydrophilic ligand is any one of polyethylene glycol, dimercaptosuccinic acid, glutathione or poly (styrene-co-maleic anhydride).

Further, the molar ratio of the manganese precursor, the hydrophobic ligand and the reaction solvent in step (1) is 1: 1: 5 to 1: 8: 20, e.g. 1: 1: 5 or 1: 2: 8 or 1: 3: 9 or 1: 5: 15 or 1: 7: 18 or 1: 8: 20.

further, the temperature raising speed in the step (2) is 1 ℃/min to 15 ℃/min, such as 2 ℃/min, or 5 ℃/min, or 10 ℃/min or 15 ℃/min; the reaction time is from 0.5h to 3h, for example 0.5h or 1h or 2h or 3h or 4h or 5 h.

Further, in step (3), the centrifugation and precipitation rotation speed is 1000-.

Further, the molar ratio of the solution c to the hydrophilic ligand in the step (4) is 1: 5-15, for example 1: 5 or 1: 8 or 1: 10 or 1: 12 or 1: 15.

further, the solution c in the step (4) reacts with the hydrophilic ligand for 1h to 3d, such as 1h or 3h or 8h or 12h or 1d or 2d or 3 d.

On the other hand, the invention also provides a high-efficiency nano enzyme preparation, the high-efficiency nano enzyme preparation is prepared by dispersing the manganese oxide nano clusters prepared by the preparation method in an aqueous solution through ligand exchange, namely the manganese oxide nano clusters are dispersed in the aqueous solution through the ligand exchange to form a stable dispersion system, so that the nano enzyme preparation with the nano enzyme activity and the magnetic resonance imaging function is formed, and the nano enzyme preparation can be used for nano enzyme catalysis in a weak acid environment. After entering the lesion part of the liver through blood circulation, the nano enzyme preparation not only reacts with hydrogen peroxide generated by cancer cell metabolism to generate a large amount of oxygen for improving hypoxic of the tumor part, but also can generate a large amount of ROS in a weak acid environment of the tumor, so that the lesion cell is killed.

In yet another aspect, the nanoenzyme preparation may also be used for magnetic resonance imaging. The invention also provides a magnetic resonance T₁Contrast agent, the magnetic resonance T₁The contrast agent is prepared by dispersing the manganese oxide nano-cluster prepared by the preparation method in an aqueous solution through ligand exchange. The T is₁The contrast agent can quickly reach the lesion part of the liver through blood circulation, and then magnetic resonance imaging is carried out on the tumor part of the liver.

Compared with the prior art, the invention has the following beneficial effects:

the invention employs a ligandAnd in the presence of a reaction solvent, the manganese precursor is rapidly decomposed and rapidly nucleated in a high-temperature environment, the ultra-small manganese oxide nanoclusters with uniform particle size distribution are obtained for the first time, the average particle size is 1.7 +/-0.52 nm, and compared with the prior art, the material obtained by the technology is smaller in particle size, and the manganese oxide particles with the particle size of 4-5 nm can be obtained at the minimum; the single batch yield is high, and the net weight can reach gram level; has good monodispersity and stability. According to the invention, the manganese oxide nanoclusters are dispersed in an aqueous solution through phase inversion to form a stable colloid, so that high-efficiency nano enzyme activity is presented in a weakly acidic tumor microenvironment, and ROS is released to kill tumor cells. At the same time, can be used as a T₁The contrast agent is used for real-time magnetic resonance imaging of liver cancer pathological change tissues. The manganese oxide nano cluster prepared by the invention has the advantages of high yield, uniform particle size, good dispersibility, strong nano enzyme activity and higher T₁Relaxation rate and the like, and has wide application prospect in diagnosis and accurate treatment of tumor tissues.

The conception, the specific structure and the technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, the features and the effects of the present invention.

Drawings

FIG. 1 is a transmission electron microscope image of manganese oxide nanoclusters prepared by a preferred embodiment of the present invention;

FIG. 2 is a graph of particle size analysis of manganese oxide nanoclusters prepared according to a preferred embodiment of the present invention;

FIG. 3 is a high resolution TEM image of a manganese oxide nanocluster prepared according to a preferred embodiment of the present invention;

FIG. 4 is a photograph of manganese oxide nanoclusters prepared according to a preferred embodiment of the present invention, dispersed in an aqueous phase, at a concentration of about 6 mg/ml;

FIG. 5 is a TMB catalytic activity assay chart of the nano-enzyme preparation prepared in the weak acid environment according to the preferred embodiment of the present invention;

FIG. 6 shows TMB catalytic activity rate values of the nanoenzyme preparations prepared according to a preferred embodiment of the present invention in a weak acid environment;

FIG. 7 shows oxygen of the present inventionManganese chemical nano cluster r₁A relaxation rate measurement;

FIG. 8 is a diagram showing the effect of magnetic resonance imaging before the contrast agent is injected into the liver cancer site;

FIG. 9 is a graph showing the effect of magnetic resonance imaging of the contrast agent of the present invention on the liver cancer site 24 hours after injection;

FIG. 10 is a graph showing the comparison of signal enhancement intensity before the contrast agent is injected into the liver cancer site and after the contrast agent of the present invention is injected for 24 hours.

Detailed Description

The following examples are given for the detailed implementation and specific operation of the present invention, but the scope of the present invention is not limited to the following examples.

Example 1

The preparation method of the manganese oxide nanocluster specifically comprises the following steps:

(1) under the protection of nitrogen, 1g of manganese chloride, 5g of oleic acid and 20ml of diphenyl ether are mixed in a 100ml three-neck round-bottom flask to obtain a solution a;

(2) after vacuum exhausting, heating the solution a to 200 ℃ at a heating rate of 5 ℃/min under the protection of nitrogen, and continuously heating at the temperature for 1h until the reaction is terminated and the temperature is reduced to room temperature, wherein the obtained brown liquid is a solution b;

(3) placing the solution b in a centrifuge tube, adding 30ml of absolute ethyl alcohol, then carrying out centrifugal precipitation (the centrifugal condition is 5000rpm, 10min) and suspending the precipitate in chloroform, repeating the cleaning method twice, and finally dispersing the obtained product in chloroform to obtain a solution c;

(4) mixing 10ml of 1g/ml solution c and 20ml of 1mg/ml polyethylene glycol solution in a 50ml round-bottom flask, heating to 65 ℃, stirring for 12 hours, adjusting the pH value of the aqueous phase solution to 11, and dialyzing and purifying by using a dialysis bag (molecular weight: 10kDa) to remove redundant ligand molecules to obtain the manganese oxide nanoclusters;

(5) and (3) dispersing the manganese oxide nanoclusters obtained in the step (4) in normal saline to form a stable dispersion system, filtering and sterilizing through a 0.22-micron filter membrane to obtain a nano preparation with both nano enzyme activity and magnetic resonance imaging, adjusting the concentration of the nano preparation to be 6mg/ml, and storing in a refrigerated cabinet at 4 ℃ for later use.

Fig. 1 is a transmission electron microscope image of the prepared manganese oxide nanoclusters, fig. 2 is a particle size analysis image of the prepared manganese oxide nanoclusters, and it can be seen that the prepared ultra-small manganese oxide nanoclusters are uniform in particle size distribution, 1.7 +/-0.52 nm in size, and smaller than manganese oxide obtained in the prior art. FIG. 3 is a high resolution TEM image of a single manganese oxide nanocluster, with the particles appearing as uniform, rounded spheres. FIG. 4 is a photograph of the prepared manganese oxide nanoclusters dispersed in an aqueous phase at a concentration of about 6mg/ml and a total solution volume of 180ml, resulting in a total sample weight of more than 1 g.

The nanometer enzyme catalysis performance of the ultra-small manganese oxide nanometer cluster is measured by utilizing the color development principle of 3,3',5,5' -tetramethyl benzidine (TMB). In a weak acid environment, the ultra-small manganese oxide nano-cluster solution and the TMB solution added with hydrogen peroxide are fully mixed, and an absorption value at 650nm is measured by using an ultraviolet-visible light spectrophotometer. Due to the large specific surface area of the manganese oxide nanocluster, surface electrons promote hydrogen peroxide molecules to release hydroxyl radicals (. OH), and the colorless TMB is catalyzed to be blue oxidized TMB. The absorption value at 650nm measured by an ultraviolet-visible light spectrophotometer is positively correlated with the catalytic efficiency. FIG. 5 is a graph of TMB catalytic activity of the nanoenzyme preparation prepared in example 1 in a weak acid environment (pH5.5), in which the catalytic strength increases with time within 9min, and FIG. 6 is a graph of the rate of TMB catalytic activity of the nanoenzyme preparation in a weak acid environment, i.e., the formula K [ s ] determined by the catalytic rate^-1]＝(A-A₀) T determination of the catalytic Rate of manganese oxide clusters, where A₀The initial absorbance at 650nm, A is the absorbance at 650nm after a period of catalysis, and t is the catalytic time. The nano-enzyme preparation prepared in example 1 has a TMB catalysis rate of 1.417 × 10 under a weak acid environment (pH5.5) calculated^-3s^-1The preparation can catalyze hydrogen peroxide to release a large amount of OH in a short time. Therefore, the nanometer enzyme catalysis performance of the ultra-small manganese oxide nanometer cluster is excellent.

The relaxation rate of the ultra-small manganese oxide nanocluster was examined by using a 3T magnetic resonance imager (2002OMJH, Siemens Germany), and FIG. 7 shows the manganese oxide nanocluster r₁Relaxation rate measurement value r₁The manganese oxide nanocluster r prepared by the method is 6.51x +0.25, so that the manganese oxide nanocluster r prepared by the method is clear from the figure₁The relaxation rate is high; fig. 8 and 9 are magnetic resonance imaging contrast graphs of tumor sites of the liver cancer tumor-bearing mice before and 24h after injection, respectively, and fig. 10 is a contrast graph of signal enhancement intensity before and 24h after injection. As clearly seen from 8-10 in the figure, the signal intensity at the tumor site before and after injection was greatly changed, and the tumor site was significantly enhanced.

Example 2

(1) under the protection of nitrogen, 1.2g of potassium permanganate, 5g of oleylamine and 20ml of benzyl ether are mixed in a 100ml three-neck round-bottom flask to obtain a solution a;

(2) after vacuum exhausting, heating the solution a to 250 ℃ at a heating rate of 1 ℃/min under the protection of nitrogen, and continuously heating at the temperature for 2h until the reaction is terminated and the temperature is reduced to room temperature, wherein the obtained brown liquid is a solution b;

(3) placing the solution b in a centrifuge tube, adding 25ml of absolute ethyl alcohol, then carrying out centrifugal precipitation (centrifugal condition: 3000rpm, 15min) and suspending the precipitate in chloroform, repeating the cleaning method twice, and finally dispersing the obtained product in chloroform to obtain a solution c;

(4) mixing 10ml of 1g/ml solution c and 30ml of 1mg/ml polyethylene glycol solution in a 50ml round-bottom flask, heating to 60 ℃, stirring for 8 hours, adjusting the pH value of the aqueous phase solution to 11, and dialyzing and purifying by using a dialysis bag (molecular weight: 10kDa) to remove redundant ligand molecules to obtain the manganese oxide nanoclusters;

(5) and (3) dispersing the manganese oxide nanoclusters obtained in the step (4) in normal saline to form a stable dispersion system, filtering and sterilizing through a 0.2-micron filter membrane to obtain a nano preparation with both nano enzyme activity and magnetic resonance imaging, adjusting the concentration of the nano preparation to be 6mg/ml, and storing in a refrigerated cabinet at 4 ℃ for later use.

The particle size of the ultra-small manganese oxide nano-cluster is 1.7 +/-0.52 nm, the particle size is uniform, and the dispersity is good; after phase inversion, the product can be stably dispersed in water phase solution, has high yield and high nano-enzyme activity and gamma₁The relaxation rate can be used for nano-enzyme catalysis and magnetic resonance imaging of liver cancer sites.

Example 3

(1) under the protection of nitrogen, mixing 2g of manganese acetylacetonate, 2g of oleic acid, 2g of oleylamine and 20ml of octadecene in a 100ml three-neck round-bottom flask to obtain a solution a;

(2) after vacuum exhausting, heating the solution a to 300 ℃ at a heating rate of 3 ℃/min under the protection of nitrogen, and continuously heating at the temperature for 3 hours until the reaction is terminated and the temperature is reduced to room temperature, wherein the obtained brown liquid is a solution b;

(3) placing the solution b in a centrifuge tube, adding 40ml of absolute ethyl alcohol, then carrying out centrifugal precipitation (the centrifugal condition is 8000rpm, 10min) and suspending the precipitate in chloroform, repeating the cleaning method twice, and finally dispersing the obtained product in chloroform to obtain a solution c;

(4) mixing 10ml of 1g/ml solution c and 20ml of 1mg/ml dimercaptosuccinic acid solution in a 50ml round-bottom flask, heating to 70 ℃, stirring for 10 hours, adjusting the pH value of the aqueous phase solution to 11, and dialyzing and purifying by using a dialysis bag (molecular weight: 10kDa) to remove redundant ligand molecules to obtain the manganese oxide nanoclusters;

Example 4

(1) under the protection of nitrogen, 1.5g of manganese acetate, 2g of oleic acid and 10ml of oleylamine are mixed in a 100ml three-neck round-bottom flask to obtain a solution a;

(2) after vacuum exhausting, heating the solution a to 275 ℃ at the heating rate of 5.5 ℃/min under the protection of nitrogen, and continuously heating for 5 hours at the temperature until the reaction is terminated and the temperature is reduced to the room temperature, wherein the obtained brown liquid is a solution b;

(3) placing the solution b in a centrifuge tube, adding 50ml of absolute ethyl alcohol, then carrying out centrifugal precipitation (the centrifugal condition is 5000rpm, 10min) and suspending the precipitate in chloroform, repeating the cleaning method twice, and finally dispersing the obtained product in chloroform to obtain a solution c;

(4) mixing 5ml of solution c with the concentration of 1g/ml and 10ml of poly (styrene-co-maleic anhydride) solution with the concentration of 1mg/ml in a 50ml round-bottom flask, heating to 78 ℃, stirring for 12 hours, adjusting the pH value of the aqueous phase solution to 12, dialyzing and purifying by using a dialysis bag (molecular weight: 10kDa) to remove redundant ligand molecules, and obtaining the manganese oxide nanocluster;

Example 5

(1) under the protection of nitrogen, 1.5g of manganese acetylacetonate, 5g of oleylamine and 10ml of octadecene are mixed in a 100ml three-neck round-bottom flask to obtain a solution a;

(2) after vacuum exhausting, heating the solution a to 300 ℃ at a heating rate of 10 ℃/min under the protection of nitrogen, and continuously heating at the temperature for 0.5h until the reaction is terminated and the temperature is reduced to room temperature, wherein the obtained brown liquid is a solution b;

(3) placing the solution b in a centrifuge tube, adding 30ml of absolute ethyl alcohol, then carrying out centrifugal precipitation (centrifugal condition: 5000rpm, 15min) and suspending the precipitate in chloroform, repeating the cleaning method twice, and finally dispersing the obtained product in chloroform to obtain a solution c;

(4) mixing 5ml of solution c with the concentration of 2g/ml and 10ml of glutathione solution with the concentration of 2mg/ml in a 50ml round-bottom flask, heating to 80 ℃, stirring for 14 hours, adjusting the pH value of the aqueous phase solution to 12, and dialyzing and purifying by using a dialysis bag (molecular weight: 10kDa) to remove redundant ligand molecules to obtain the manganese oxide nanoclusters;

Example 6

(1) under the protection of nitrogen, 2g of potassium permanganate, 5g of oleylamine and 10ml of diphenyl ether are mixed in a 100ml three-neck round-bottom flask to obtain a solution a;

(2) after vacuum exhausting, heating the solution a to 250 ℃ at a heating rate of 15 ℃/min under the protection of nitrogen, and continuously heating at the temperature for 3 hours until the reaction is terminated and the temperature is reduced to room temperature, wherein the obtained brown liquid is a solution b;

(4) mixing 15ml of solution c with the concentration of 2g/ml and 15ml of glutathione solution with the concentration of 3mg/ml in a 50ml round-bottom flask, heating to 70 ℃, stirring for 16 hours, adjusting the pH value of the aqueous phase solution to 12, and dialyzing and purifying by using a dialysis bag (molecular weight: 10kDa) to remove redundant ligand molecules to obtain the manganese oxide nanoclusters;

The average particle size of the ultra-small manganese oxide nanocluster is 1.7 +/-0.52 nm, the particle size is uniform, and the dispersity is good; after phase inversion, the product can be stably dispersed in water phase solution, has high yield and high nano-enzyme activity and gamma₁The relaxation rate can be used for nano-enzyme catalysis and magnetic resonance imaging of liver cancer sites.

The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.

Claims

1. A preparation method of manganese oxide nanoclusters is characterized by comprising the following steps:

(1) mixing 1g of manganese chloride, 5g of oleic acid and 20mL of diphenyl ether to obtain a solution a;

(2) heating the solution a to 200 ℃ at a heating rate of 5 ℃/min and continuously heating at 200 ℃ for 1h to obtain the manganese oxide nano-cluster particles coated with hydrophobic ligands on the surfaces to form a solution b;

(4) and carrying out ligand exchange and dialysis purification on the solution c and the polyethylene glycol solution to obtain the water-soluble manganese oxide nano cluster.

2. A preparation method of manganese oxide nanoclusters is characterized by comprising the following steps:

(1) mixing 1.2g of potassium permanganate, 5g of oleylamine and 20mL of benzyl ether to obtain a solution a;

(2) heating the solution a to 250 ℃ at a heating rate of 1 ℃/min and continuously heating the solution a at 250 ℃ for 2h to obtain the manganese oxide nano-cluster particles coated with hydrophobic ligands on the surfaces to form a solution b;

3. A preparation method of manganese oxide nanoclusters is characterized by comprising the following steps:

(1) mixing 2g of manganese acetylacetonate, 2g of oleic acid, 2g of oleylamine and 20mL of octadecene to obtain a solution a;

(2) heating the solution a to 300 ℃ at a heating rate of 3 ℃/min and continuously heating the solution a at 300 ℃ for 3h to obtain the manganese oxide nano-cluster particles coated with hydrophobic ligands on the surfaces to form a solution b;

(4) and carrying out ligand exchange, dialysis and purification on the solution c and the dimercaptosuccinic acid solution to obtain the water-soluble manganese oxide nano cluster.

4. A preparation method of manganese oxide nanoclusters is characterized by comprising the following steps:

(1) mixing 1.5g of manganese acetylacetonate, 5g of oleylamine and 10mL of octadecene to obtain a solution a;

(2) heating the solution a to 300 ℃ at a heating rate of 10 ℃/min and continuously heating at 300 ℃ for 0.5h to obtain the manganese oxide nano-cluster particles coated with hydrophobic ligands on the surfaces to form a solution b;

(4) and performing ligand exchange, dialysis and purification on the solution c and the glutathione solution to obtain the water-soluble manganese oxide nanocluster.

5. A preparation method of manganese oxide nanoclusters is characterized by comprising the following steps:

(1) mixing 2g of potassium permanganate, 5g of oleylamine and 10mL of diphenyl ether to obtain a solution a;

(2) heating the solution a to 250 ℃ at a heating rate of 15 ℃/min and continuously heating the solution a at 250 ℃ for 3h to obtain the manganese oxide nano-cluster particles coated with hydrophobic ligands on the surfaces, thereby forming a solution b;