A biological hybrid magnetic micromotor and its preparation method and application

Abstract

The application relates to the field of biomedical materials, and particularly discloses a biological hybrid magnetic micromotor as well as a preparation method and application thereof. The preparation method of the biological hybrid magnetic micromotor comprises the following steps: reacting Chlorella vulgaris with ferrous sulfate, potassium hydroxide and potassium nitrate, magnetically separating the obtained reaction solution to obtain a solid, reacting the obtained solid with graphene oxide, and magnetically separating the obtained reaction solution to obtain the biological hybrid magnetic micromotor. The micromotor provided by the application can enhance the contact with a methylene blue solution under the action of a magnetic field, thereby showing higher adsorption efficiency in a short time. The micromotor adsorbed with the methylene blue can accurately navigate to a cell surface, and can generate reactive oxygen under the irradiation of a 664 nm laser and generate heat under the irradiation of an 808 nm laser to cooperatively induce cancer cell death. The application skillfully utilizes the adsorption performance and directional motion behavior of the micromotor, thereby providing a new idea for realizing cascade environmental purification and tumor treatment.

Description

Technical Field

[0001] This invention relates to the field of biomedical materials, and more particularly to a biohybrid magnetic micromotor, its preparation method, and its cascade application in removing organic pollutants and simultaneously killing tumor cells. Background Technology

[0002] Chlorella proteoglycans ( Chlorella pyrenoidosa Chlorella is a spherical, single-celled freshwater green alga, belonging to highly efficient photosynthetic autotrophic organisms, and is widely distributed in nature. This algae is uniformly spherical, with a size of 3-8 micrometers, exhibiting good monodispersity and advantages such as low cultivation cost, ease of large-scale propagation, and high biocompatibility. Its surface is mainly composed of cellulose, hemicellulose, and riboproteins, rich in active functional groups such as hydroxyl, carboxyl, and amino groups. These functional groups can serve as natural metal-binding sites, forming strong bonds with metal ions through coordination bonds or hydrogen bonds, promoting the uniform nucleation, growth, and immobilization of target materials on the algal template surface, making Chlorella an ideal biological template for preparing various high-performance micro / nanomaterials.

[0003] In recent years, biohybrid micromotors based on Chlorella have become a research hotspot in the field of micro-nano technology, showing broad application prospects in environmental remediation and biomedicine. However, most reported micromotors currently possess only a single function, with a few achieving dual-function applications, while systems that can simultaneously integrate environmental purification and biomedical functions remain relatively rare. With continuous technological advancements, developing highly integrated micromotors with cascaded functionality has become a clear trend in this field. Against this backdrop, this invention constructs a micromotor system that can efficiently remove organic pollutants from the aquatic environment while simultaneously achieving biomedical functions. This represents an innovative research approach and provides important insights for the future development of multifunctional synergistic motor therapy platforms. Summary of the Invention

[0004] Purpose of the invention: The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a bio-hybrid magnetic micromotor and its preparation method, as well as its cascade application in removing organic pollutants and simultaneously killing tumor cells.

[0005] To solve the above-mentioned technical problems, the present invention discloses the following technical solution:

[0006] In a first aspect, the present invention discloses a bio-hybrid magnetic micromotor and its preparation method.

[0007] The method for preparing the bio-hybrid magnetic micromotor includes:

[0008] (1) Chlorella was reacted with ferrous sulfate, potassium hydroxide and potassium nitrate to obtain a first reaction solution. The first reaction solution was separated by magnetic separation to obtain a brown first solid.

[0009] (2) The first solid obtained is reacted with graphene oxide to obtain a second reaction liquid. The second reaction liquid is magnetically separated to obtain a bio-hybrid magnetic micromotor.

[0010] In step (1), after mixing the Chlorella solution with the ferrous sulfate solution, the mixture is heated in an oil bath and a mixed solution of potassium hydroxide and potassium nitrate is added under stirring conditions to carry out the first reaction.

[0011] The Chlorella solution is prepared by culturing Chlorella in an algal culture medium under light to obtain a culture solution; the obtained culture solution is centrifuged to obtain a precipitate, which is washed with water 1-5 times, and the precipitate is dispersed in water to obtain a uniformly dispersed Chlorella solution. Further, the volume ratio of the Chlorella inoculum to the algal culture medium is 1:(1-5), such as 1:3; the culture temperature is 22-28℃, the light intensity is 2000-3000 Lux, the culture time is 4-6 days, such as 5 days; the centrifugation speed is 3000-5000 r / min, and the time is 3-5 min; the concentration of the Chlorella solution is 5-15 mg / mL, preferably 10 mg / mL.

[0012] The concentration of the ferrous sulfate solution is 20-30 mmol / L, preferably 25 mmol / L.

[0013] The oil bath temperature is raised to 85-95℃.

[0014] In the mixed solution, the concentration of potassium hydroxide is 20-30 mmol / L, preferably 25 mmol / L; and the concentration of potassium nitrate is 0.05-0.15 mol / L, preferably 0.1 mol / L.

[0015] The ratio of Chlorella to ferrous sulfate, potassium hydroxide and potassium nitrate is 10-15 mg: 0.05-0.58 mmol: 0.3-0.95 mmol: 1.5-4 mmol, preferably 10-15 mg: 0.25-0.38 mmol: 0.5-0.75 mmol: 2-3 mmol.

[0016] The temperature of the first reaction is 80-100℃, preferably 90℃.

[0017] The time for the first reaction is 30-60 minutes.

[0018] In step (2), the first solid is added to water and sonicated to obtain a brown solution, and the brown solution is reacted with the graphene oxide solution in a second reaction.

[0019] The ultrasound duration is 10-30 min; the concentration of the brown solution is 0.5-2 mg / mL, preferably 1 mg / mL.

[0020] The concentration of the graphene oxide solution is 5-6 mg / mL, preferably 5.5 mg / mL; the graphene oxide solution is an aqueous solution of graphene oxide.

[0021] The pH of the graphene oxide solution is 7-11, preferably 9; the pH of the graphene oxide solution can be adjusted by ammonia water, such as 30 wt% ammonia water.

[0022] The mass ratio of graphene oxide to the first solid is 1:(0.5-2), preferably 1:(0.8-1.3).

[0023] The temperature of the second reaction is 20-30℃.

[0024] The second reaction takes 10-14 hours, such as 12 hours.

[0025] The bio-hybrid magnetic micromotor produced by the above method is also within the scope of protection of this invention.

[0026] Secondly, the present invention discloses the application of the bio-hybrid magnetic micromotor described in the first aspect above in the removal of organic pollutants from water.

[0027] Thirdly, the present invention discloses the application of the biohybrid magnetic micromotor described in the first aspect above in the preparation of antitumor drugs.

[0028] In some embodiments, the biohybrid magnetic micromotor is a biohybrid magnetic micromotor after the removal of organic pollutants; in some embodiments, the biohybrid magnetic micromotor adsorbing methylene blue is used to prepare antitumor drugs.

[0029] The organic pollutants described in this invention include methylene blue.

[0030] In this invention Ch / Fe3O4 / GO indicates a micromotor that has not adsorbed methylene blue.

[0031] In this invention Ch / Fe3O4 / GO / MB represents a micromotor that has adsorbed methylene blue, abbreviated as CFGB.

[0032] The adsorption described in this invention includes both chemical adsorption and physical adsorption. Specifically, the functional groups such as -COOH and -OH on graphene oxide can bind to the -NH2 group of methylene blue through hydrogen bonding. Ch / Fe3O4 / GO is negatively charged, and methylene blue is positively charged; the two can combine with each other electrostatically.

[0033] The anti-tumor agents described in this invention include those for breast cancer.

[0034] Unless otherwise specified, the solvent for the ferrous sulfate solution, potassium hydroxide solution, and potassium nitrate solution described in this invention is water.

[0035] The bio-hybrid magnetic micromotor provided by this invention can perform tasks across multiple fields through cascading: in the field of environmental remediation, it can efficiently adsorb and remove methylene blue organic pollutants from wastewater through magnetic drive; subsequently, the micromotor, after adsorbing pollutants, can be directly applied to the biomedical field without additional treatment, simultaneously generating photothermal and photodynamic effects under light conditions, achieving efficient killing of tumor cells through reactive oxygen species and heat. This invention realizes a cascaded functional application from environmental purification to cell therapy, providing a new approach for the development of novel multifunctional micro / nanomotors.

[0036] This invention expands the functional applications of existing bio-hybrid magnetic micromotors by ingeniously combining environmental purification with cell therapy.

[0037] Beneficial effects:

[0038] (1) The raw materials for preparing micron motors using Chlorella as a template are readily available and the operation is simple and convenient.

[0039] (2) By adjusting the parameters of the magnetic field, the magnetic micromotor provided by the present invention can achieve rapid and directional movement in a variety of solutions (water, methylene blue and DMEM cell culture medium solution); compared with the stationary micromotor, the dynamic micromotor exhibits higher adsorption efficiency in a short time due to enhanced contact with the methylene blue solution under the action of the magnetic field.

[0040] (3) In this invention, the micromotor adsorbed with methylene blue can precisely navigate to the cell surface and generate reactive oxygen species under 664 nm laser irradiation and heat under 808 nm laser irradiation to synergistically induce MCF-7 cell death. This invention ingeniously utilizes the adsorption performance and directional movement behavior of the micromotor to provide a new, efficient, flexible, and multifunctional approach for achieving cascade environmental purification and tumor treatment. Attached Figure Description

[0041] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0042] Figure 1 The image shows a scanning electron microscope image of a biohybrid micromotor provided in an embodiment of the present invention.

[0043] Figure 2 This is a schematic diagram of the magnetic response behavior of the bio-hybrid micromotor prepared in an embodiment of the present invention under the action of an external magnetic field.

[0044] Figure 3 This is a schematic diagram showing the motion speed and trajectory of the bio-hybrid micromotor prepared in different media according to an embodiment of the present invention.

[0045] Figure 4 This is a schematic diagram illustrating the magnetic separation effect of the bio-hybrid micromotor prepared according to an embodiment of the present invention.

[0046] Figure 5 The bio-hybrid micromotor prepared in this embodiment of the invention adsorbs methylene blue. Ch Photothermal heating curve of / Fe3O4 / GO / MB under near-infrared laser irradiation.

[0047] Figure 6 The graph shows the survival rate of MCF-7 cells under different laser treatment conditions for the biohybrid micromotor prepared in the embodiments of the present invention.

[0048] Figure 7 This is a schematic diagram of the 3D-printed microchannel cascade application of the bio-hybrid micromotor prepared in an embodiment of the present invention. Detailed Implementation

[0049] The present invention can be better understood from the following embodiments. However, those skilled in the art will readily understand that the descriptions in the embodiments are for illustrative purposes only and should not, and will not, limit the invention as detailed in the claims.

[0050] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0051] The high-concentration Chlorella strains described in the following examples were purchased and had a concentration of approximately 2.5 × 10⁻⁶. 7 per mL.

[0052] The main components of the algae culture medium described in the following examples are: sodium nitrate 1500 mg / L, sodium carbonate 210 mg / L, sodium phosphate potassium dihydrogen phosphate 40 mg / L, magnesium sulfate heptahydrate 75 mg / L, calcium chloride dihydrate 36 mg / L, citric acid 6 mg / L, ferric ammonium citrate 6 mg / L, and water as the solvent.

[0053] The graphene oxide stock solution described in the following examples is a commercially available aqueous solution of graphene oxide with a concentration of 5.5 mg / mL.

[0054] Example 1: A method for fabricating a bio-hybrid magnetic micromotor with cascade applications

[0055] 1) Chlorella ( Ch Cultivation and treatment of Chlorella: 1 mL of high-concentration Chlorella inoculum and 3 mL of algal culture medium were added to an algal culture bottle containing tap water (total volume 500 mL). The culture bottle was then placed in a light incubator for cultivation at 25℃ and a light intensity of 3000 Lux. After 5 days of cultivation, the Chlorella was collected into a 10 mL centrifuge tube, centrifuged at 4000 r / min for 3 min, the supernatant was discarded, and the precipitate was washed 3 times with deionized water. The precipitate was then dispersed in deionized water to obtain a uniformly dispersed Chlorella aqueous solution (10 mg / mL).

[0056] 2) Ch Preparation of the Ch / Fe3O4 micromotor: 1 mL of Chlorella solution was added to 10 mL of ferrous sulfate solution (25 mM), mixed thoroughly, and then transferred to a 100 mL round-bottom flask. The mixture was heated in an oil bath at 90 °C. Then, under stirring, a prepared mixed solution of potassium hydroxide and potassium nitrate (20 mL of potassium hydroxide solution (25 mM) and 20 mL of potassium nitrate solution (0.1 M) mixed thoroughly) was slowly added. After reacting at 90 °C for 30 min, a brown solution was obtained. This solution was then magnetically separated using a magnet and washed three times with deionized water. The collected solid was dried to obtain brown solid A, i.e., the Ch / Fe3O4 micromotor. 10 mg of brown solid A was weighed and added to a 10 mL centrifuge tube. After adding deionized water, the mixture was sonicated for 5 min to obtain a brown solution (1 mg / mL).

[0057] 3) ChPreparation of / Fe3O4 / GO micromotor: 2 mL of graphene oxide stock solution was measured into a 50 mL centrifuge tube, diluted with deionized water to 20 mL, and sonicated for 10 min. After sonication, 30% ammonia was added to adjust the pH of the resulting graphene oxide solution to 9. Then, 10 mL of a brown solution was added, and the mixture was placed in a shaker and reacted for 12 h. After the reaction, magnetic particles were separated using a magnet. The magnetic particles were washed three times with deionized water, collected, and dried to obtain a bio-hybrid magnetic micromotor with cascade functionality. Ch / Fe3O4 / GO micro motor.

[0058] Example 2: A method for fabricating a bio-hybrid magnetic micromotor with cascade applications

[0059] 1) Add 1 mL of high-concentration Chlorella inoculum and 3 mL of algal culture medium to an algal culture bottle containing tap water (total volume 500 mL), and then place the culture bottle in a light incubator for cultivation. The cultivation temperature is 25℃, and the light intensity is 3000 Lux. After 5 days of cultivation, collect the Chlorella in a 10 mL centrifuge tube, centrifuge at 5000 r / min for 3 min, discard the supernatant, wash the precipitate 3 times with deionized water, and disperse the precipitate in deionized water to obtain a uniformly dispersed Chlorella solution (10 mg / mL).

[0060] 2) Add 1.5 mL of Chlorella solution to 15 mL of ferrous sulfate solution (25 mM), mix well, and transfer to a 100 mL round-bottom flask. Heat in an oil bath at 90 °C. Then, slowly add the prepared mixed solution of potassium hydroxide and potassium nitrate (30 mL of potassium hydroxide solution (25 mM) and 30 mL of potassium nitrate solution (0.1 M) mixed well) while stirring. React at 90 °C for 60 min to obtain a brown solution. Then, use a magnet to separate the solids magnetically and wash three times with deionized water. Collect and dry to obtain brown solid A. Weigh 10 mg of brown solid A, add it to a 10 mL centrifuge tube, add deionized water, and sonicate for 5 min to obtain a brown solution (1 mg / mL).

[0061] 3) Measure 2 mL of the original graphene oxide solution into a 50 mL centrifuge tube, dilute with deionized water to 20 mL, and sonicate for 10 min. After sonication, add 30% ammonia to adjust the pH of the resulting graphene oxide solution to 9. Then add 10 mL of brown solution and react in a shaker for 12 h. After the reaction, separate the particles using a magnet to obtain magnetic particles. Wash the magnetic particles three times with deionized water, collect and dry them to obtain a bio-hybrid magnetic micromotor with cascade functionality.

[0062] Characterization of the magnetic micromotor fabricated in Example 1:

[0063] 1) The morphology of the obtained magnetic micromotor was characterized using scanning electron microscopy, and the results are as follows: Figure 1 As shown, this micromotor has a spherical structure with magnetic microparticles deposited on its surface and coated with a thin film of graphene oxide.

[0064] 2) Magnetic micromotors possess excellent magnetic response performance. For example... Figure 2 As shown, under the action of an external magnet, the micromotor can be effectively attracted and directionally moved by the magnet, indicating that it is suitable for magnetic field driven operation.

[0065] 3) The speed and direction of movement of the micrometer motor can be controlled by an external magnetic field. Figure 3 The examples demonstrate the motion speed and trajectory of the micromotor fabricated in different media. Under conditions of a magnetic field strength of 5 mT and a frequency of 8 Hz, the micromotor exhibits fast motion performance in aqueous solution, methylene blue solution, and DMEM cell culture medium, with motion speeds of 8.83, 6.53, and 8.64 μm / s, respectively. By changing the rotation direction of the magnetic field, the motion direction of the micromotor can be precisely controlled, enabling it to move along "S" or "N" shaped paths.

[0066] Application Example 1

[0067] 1) First, a 0.025 mmol / L methylene blue solution was prepared. The micromotor prepared in Example 1 was dissolved in water to obtain a 10 mg / mL aqueous solution of the micromotor. 100 µL of the 10 mg / mL micromotor aqueous solution was added to 2 mL of the 0.025 mmol / L methylene blue solution, and then the solution was placed in a magnetic field (magnetic field strength 5 mT, frequency 0, 4, 8 Hz) for adsorption experiments for 10 minutes. The study showed that the adsorption rate of the micromotor for methylene blue increased with increasing magnetic field frequency. When the magnetic field frequency was 0 Hz, the micromotor was in a static state, and its adsorption rate for methylene blue was 51.82%; while when the frequency increased to 8 Hz, the adsorption rate increased to 81.10% (adsorption capacity 22.48 mg / g), an increase of 29.28% compared to the static state. Under the optimal adsorption conditions (magnetic field strength 5 mT, frequency 8 Hz), the adsorption efficiency and effect of the micromotor on the methylene blue solution are as follows: Figure 4 As shown, the color of the methylene blue solution treated by the micromotor becomes significantly lighter, and the micromotor can achieve magnetic separation under the action of an external magnet, indicating that the micromotor has a significant adsorption capacity for methylene blue.

[0068] 2) The micromotor (adsorption capacity of 22.48 mg / g) adsorbed with methylene blue in step 1) was prepared into an aqueous dispersion with a concentration of 0.5 mg / mL. An 808 nm laser (1.5 W / cm²) was used to analyze the dispersion. 2 Irradiation was performed for 5 minutes, and the solution temperature was monitored in real time using an infrared thermal imager. The results are as follows: Figure 5 As shown, the micron motor dispersion adsorbed with methylene blue ( Ch The temperature of the (Fe3O4 / GO / MB) sensor increased significantly during illumination, rising by approximately 36.3°C within 5 minutes; while under the same experimental conditions, the temperature of pure water remained almost unchanged. These results demonstrate that the micromotor provided by this invention possesses excellent photothermal conversion performance and is suitable for photothermal therapy of tumor cells.

[0069] 3) Anti-tumor effect study:

[0070] PBS group: MCF-7 cells were co-incubated with phosphate buffer solution (pH=7.4) for 24 h, and the survival rate of MCF-7 cells was calculated using CCK-8 solution and microplate reader.

[0071] CFGB group: The micromotor that adsorbed methylene blue in step 1) (adsorption capacity of 22.48 mg / g) was prepared into an aqueous dispersion with a concentration of 10 mg / mL. After co-incubating the above micromotor aqueous dispersion with MCF-7 cells for 24 h, the viability of MCF-7 cells was calculated using CCK-8 solution and an enzyme-linked immunosorbent assay (ELISA) reader.

[0072] CFGB+664 group: Following the experimental method of CFGB group, after co-incubation for 24 h, irradiated with 664 nm laser for 5 min.

[0073] CFGB+808 group: Following the experimental method of CFGB group, after co-incubation for 24 h, irradiate with 808 nm laser for 5 min.

[0074] CFGB+664+808 group: Following the experimental method of CFGB group, after co-incubation for 24 h, the laser was first irradiated with 664 nm laser for 5 min, and after an interval of 10 min, it was irradiated with 808 nm laser for 5 min.

[0075] Experimental results are as follows Figure 6As shown, compared with the PBS group and the CFGB group, the cell survival rates after irradiation with 664 nm and 808 nm lasers alone were 73.6% and 35.4%, respectively, indicating that irradiation with different wavelengths of laser is the main factor causing cell death, and that photothermal therapy is more effective than photodynamic therapy. After combined irradiation with the two lasers, the cell survival rate decreased to 24.4%, indicating that laser superposition irradiation can significantly enhance the killing effect of the micromotor on MCF-7 tumor cells. This result confirms that the micromotor of the present invention exhibits a synergistic and enhanced anti-tumor effect in combined phototherapy.

[0076] 4) The cascaded application of micromotors was verified using a 3D-printed microfluidic channel. The channel is divided into three regions: a left region containing magnetic micromotors, a middle region containing methylene blue solution, and a right region containing MCF-7 tumor cells. First, a rotating magnetic field was applied to the left side to induce the micromotors to self-assemble into ordered clusters and migrate directionally to the middle region; then, magnetic field navigation was used to efficiently adsorb methylene blue; finally, the dye-loaded motors were guided to the cellular region, and the cells were subjected to 664 nm and 808 nm laser light (1.5 W / cm²). 2 The synergistic therapeutic effect was evaluated under irradiation. The experiment used a smartphone to record motor movement and the adsorption process, and an infrared thermal imager to monitor photothermal heating. The experimental model and results are as follows: Figure 7 As shown, the solution in the middle region changes from blue to light, indicating that the micromotor can efficiently adsorb methylene blue; in the right region, after the motor and cells are co-incubated, the local temperature rises rapidly to 60ºC, leading to cell death (the cells turn red), proving that the methylene blue-loaded micromotor has the ability to synergistically kill tumor cells under laser irradiation.

[0077] In summary, compared with single-function micromotors, the biohybrid magnetic micromotor prepared by Chlorella as a biological template in this invention has cascade functional characteristics. After adsorbing the organic pollutant methylene blue, it can be further used to synergistically kill tumor cells, combining the ability to efficiently remove environmental pollutants and synergistically treat tumor cells, showing higher application efficiency and operational flexibility.

[0078] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. The application of a biohybrid magnetic micromotor that adsorbs methylene blue in the preparation of antitumor drugs, characterized in that, The biohybrid magnetic micromotor adsorbing methylene blue simultaneously generates photothermal and photodynamic effects under illumination, achieving highly efficient killing of tumor cells through reactive oxygen species and heat; the anti-tumor effect includes anti-breast cancer. The method for preparing the bio-hybrid magnetic micromotor includes: (1) Chlorella is reacted with ferrous sulfate, potassium hydroxide and potassium nitrate to obtain a first reaction solution. The first reaction solution is then separated by magnetic separation to obtain a first solid. (2) The first solid obtained is reacted with graphene oxide to obtain a second reaction liquid. The second reaction liquid is magnetically separated to obtain a bio-hybrid magnetic micromotor.

2. The application according to claim 1, characterized in that, In step (1), the ratio of Chlorella to ferrous sulfate, potassium hydroxide, and potassium nitrate is 10-15 mg: 0.05-0.58 mmol: 0.3-0.95 mmol: 1.5-4 mmol; After mixing the Chlorella solution with the ferrous sulfate solution, a mixed solution of potassium hydroxide and potassium nitrate is added to carry out the first reaction; the temperature of the first reaction is 80-100℃.

3. The application according to claim 2, characterized in that, The Chlorella solution is prepared by culturing Chlorella in a culture medium to obtain a culture solution; the obtained culture solution is centrifuged to obtain a precipitate, and the precipitate is dispersed in water to obtain the Chlorella solution; the concentration of the Chlorella solution is 5-15 mg / mL.

4. The application according to claim 2, characterized in that, The concentration of the ferrous sulfate solution is 20-30 mmol / L; the concentration of potassium hydroxide in the mixed solution is 20-30 mmol / L; and the concentration of potassium nitrate in the mixed solution is 0.05-0.15 mol / L.

5. The application according to claim 1, characterized in that, In step (2), the first solid is added to water and sonicated to obtain a brown solution. The brown solution is then reacted with the graphene oxide solution in a second reaction. The temperature of the second reaction is 20-30℃.

6. The application according to claim 5, characterized in that, The concentration of the brown solution is 0.5-2 mg / mL; the concentration of the graphene oxide solution is 5-6 mg / mL; the pH of the graphene oxide solution is 7-11; and the mass ratio of graphene oxide to the first solid is 1:(0.5-2).

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