Mesoporous silicon nanocomposite loaded with gold nanoparticles as well as preparation method and application of mesoporous silicon nanocomposite

Abstract

The invention relates to a meso-porous silicon nano-composite loaded with gold nanoparticles and a preparation method and application thereof, the nano-composite comprises meso-porous silicon nanoparticles and gold nanoparticles loaded on the meso-porous silicon nanoparticles, and the surfaces of the gold nanoparticles are modified with cationic polymers. According to the composite system disclosed by the invention, the gold nanoparticles and the mesoporous silicon nanoparticles are combined, so that the problem of quickly removing the gold nanodots in vivo is solved, the circulation time of the gold nanodots is prolonged, and the tumor targeting property and the photo-thermal efficiency of the gold nanodots are remarkably improved. Under the irradiation of near-infrared laser, the composite system can generate local high temperature at a tumor part, so that the efficient killing of tumor cells is promoted, and meanwhile, the damage to surrounding healthy tissues is reduced. The composite system has excellent photothermal conversion performance and low systemic toxicity, provides an efficient and low-toxicity treatment platform for photothermal therapy of tumors, and has a wide clinical application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomedicine, and relates to a mesoporous silica nanocomposite loaded with gold nanoparticles, a preparation method thereof, and an application thereof. Background Art

[0002] Cancer remains a major challenge in the global health field. Due to its high incidence, high mortality, and highly heterogeneous nature of tumors, traditional treatment methods (such as chemotherapy, radiotherapy, and surgery) often fail to achieve a radical cure effect and are accompanied by serious side effects and drug resistance problems. In recent years, with the rapid development of biomedicine and nanotechnology, photothermal therapy (PTT) has gradually become a promising alternative treatment strategy due to its advantages of precise positioning, controllable energy, and minimally invasive. Mild photothermal therapy (usually carried out at 42 - 43 °C) not only helps to improve the enrichment of photothermal agents at the tumor site, but also can achieve efficient killing of tumor cells while minimizing damage to surrounding healthy tissues.

[0003] Photothermal therapy relies on near-infrared laser to activate photothermal conversion agents to generate local high temperature in the tumor area, inducing apoptosis or necrosis of tumor cells. Although gold nanodots are widely used in PTT due to their excellent photothermal conversion efficiency, they are easily cleared rapidly in vivo, resulting in insufficient drug enrichment at the tumor site, thus affecting the treatment effect. How to prolong the circulation time of gold nanodots in vivo, improve their tumor targeting and photothermal efficacy has become a key problem to be solved urgently at present. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a mesoporous silica nanocomposite loaded with gold nanoparticles, a preparation method thereof, and an application thereof.

[0005] To achieve the purpose of this invention, the following technical solutions are adopted by the present invention:

[0006] In the first aspect, the present invention provides a mesoporous silica nanocomposite loaded with gold nanoparticles, wherein the nanocomposite comprises mesoporous silica nanoparticles and gold nanoparticles loaded on the mesoporous silica nanoparticles, and a cationic polymer is modified on the surface of the gold nanoparticles.

[0007] The composite system (MSN@Au) involved in the present invention combines gold nanoparticles (Au) with mesoporous silica nanoparticles (MSNs), solves the problem of rapid clearance of gold nanodots in vivo, extends their circulation time, and significantly improves their tumor targeting and photothermal efficiency. Under near-infrared laser irradiation, the composite system can generate local high temperature at the tumor site, promote the efficient killing of tumor cells, and reduce the damage to surrounding healthy tissues at the same time. The composite system has excellent photothermal conversion performance and low systemic toxicity, providing an efficient and low-toxic treatment platform for tumor photothermal therapy and having broad clinical application prospects.

[0008] Preferably, the mass ratio of the cationic polymer to the gold nanoparticles is (2-6):1, such as 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, etc.

[0009] The mass ratio of the mesoporous silica nanoparticles to the gold nanoparticles is (3-7):1, such as 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, etc.

[0010] Preferably, the particle size of the gold nanoparticles is 7-13nm, such as 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, etc.

[0011] The particle size of the mesoporous silica nanoparticles is 130-180nm, such as 130nm, 140nm, 150nm, 155nm, 160nm, 170nm, 180nm, etc.

[0012] Preferably, the cationic polymer includes polyethyleneimine (PEI).

[0013] Au is prepared into an Au-PEI complex by reacting with polyethyleneimine (PEI). Au-PEI not only retains the high photothermal conversion efficiency of the gold nanoparticles, but also enhances the interaction with the mesoporous silica nanoparticles through surface functionalization.

[0014] Preferably, the number-average molecular weight of the polyethyleneimine is 20000-30000, such as 20000, 22000, 24000, 25000, 28000, 30000, etc.

[0015] In the second aspect, the present invention provides a preparation method of the mesoporous silica nanocomposite loaded with gold nanoparticles according to the first aspect, and the preparation method includes the following steps:

[0016] (1) Mix and incubate gold nanoparticles (Au) with a cationic polymer in a solution to obtain a reaction mixture; subject the reaction mixture to dialysis treatment to obtain modified gold nanoparticles;

[0017] (2) Mix and incubate the modified gold nanoparticles with mesoporous silica nanoparticles (MSN) in a solution to obtain a mesoporous silica nanocomposite loaded with gold nanoparticles (MSN@Au).

[0018] Preferably, the incubation in step (1) is carried out at 15 - 40 °C (such as 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, etc.) for 20 - 60 min (such as 20 min, 25 min, 30 min, 35 min, 40 min, 50 min, 60 min, etc.).

[0019] Preferably, stirring treatment is also carried out during the incubation in step (1).

[0020] Preferably, the incubation in step (2) is carried out at 15 - 40 °C (such as 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, etc.) for 8 - 15 h (such as 8 h, 9 h, 10 h, 12 h, 13 h, 15 h, etc.).

[0021] Preferably, ultrasonic treatment is also carried out during the incubation in step (2).

[0022] The gold nanoparticles in the mesoporous silica nanocomposite loaded with gold nanoparticles involved in the present invention can be prepared by conventional methods in the art. For example, chloroauric acid (HAuCl4) is used as a precursor to reduce and generate gold nanoparticles.

[0023] Preferably, the method for preparing the gold nanoparticles includes the following steps:

[0024] Heat the chloroauric acid aqueous solution at 90 - 100 °C (such as 90 °C, 93 °C, 95 °C, 97 °C, 100 °C, etc.) for 3 - 7 min (such as 3 min, 4 min, 5 min, 6 min, 7 min, etc.), then mix with a reducing agent and heat at 90 - 100 °C (such as 90 °C, 93 °C, 95 °C, 97 °C, 100 °C, etc.) for 15 - 25 min (such as 15 min, 18 min, 20 min, 25 min, etc.) to obtain gold nanoparticles;

[0025] Preferably, the concentration of the chloroauric acid aqueous solution is 0.005 - 0.5%, such as 0.005%, 0.008%, 0.01%, 0.2%, 0.3%, 0.4%, 0.5%, etc.

[0026] Preferably, the reducing agent includes sodium citrate.

[0027] In the mesoporous silica nanoparticle-loaded gold nanoparticles composite involved in the present invention, the mesoporous silica nanoparticles can be prepared by conventional methods in the art. For example, using raw materials such as cetyl bromide glycol (CPB), urea, ultrapure water, cyclohexane, n-butanol, and tetraethoxysilane (TEOS), through a multi-stage temperature-controlled reaction, MSN with uniform pore size and high specific surface area is synthesized. This MSN has good drug-loading capacity and stability, providing an excellent platform for the subsequent loading of gold nanoparticles.

[0028] Preferably, the preparation method of the mesoporous silica nanoparticles includes the following steps:

[0029] Mix cetyl bromide glycol, urea, water, cyclohexane, and n-butanol, and then dropwise add tetraethoxysilane to obtain a mixture; react the mixture at 60-80 °C (such as 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, etc.) for 40-80 min (such as 40 min, 50 min, 60 min, 70 min, 80 min, etc.), then react at 0-10 °C (such as 0 °C, 2 °C, 4 °C, 8 °C, 10 °C, etc.) for 90-150 min (such as 90 min, 100 min, 120 min, 130 min, 150 min, etc.), and finally react at 60-80 °C (such as 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, etc.) for 8-15 h (such as 8 h, 10 h, 12 h, 13 h, 14 h, 15 h, etc.), and perform solid-liquid separation to obtain mesoporous silica nanoparticles.

[0030] Preferably, after the solid-liquid separation, the solid product is washed with ethanol to remove impurities.

[0031] In the third aspect, the present invention provides the application of the mesoporous silica nanoparticle-loaded gold nanoparticles composite according to the first aspect in the preparation of tumor photothermal therapy drugs.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The composite (MSN@Au) involved in the present invention can rapidly generate local high temperature under near-infrared laser irradiation, directly induce apoptosis or necrosis of tumor cells, thereby achieving efficient photothermal therapy; the composite significantly improves the photothermal conversion efficiency by effectively prolonging the circulation time of gold nanodots in vivo and enhancing their enrichment at the tumor site, further enhancing the killing effect on tumor cells. At the same time, this platform shows low systemic toxicity during the treatment process, providing a new, efficient and low-toxic nanomedicine strategy for the photothermal therapy of solid tumors. Description of the Drawings

[0034] Figure 1 is the transmission electron microscope image of the MSN prepared in Example 1;

[0035] Figure 2 It is the transmission electron microscope image of the gold nanoparticles prepared in Example 2;

[0036] Figure 3 It is the transmission electron microscope image of MSN@Au prepared in Example 4;

[0037] Figure 4 It is the graph of the zeta potential measurement results of Au and Au-PEI;

[0038] Figure 5 It is the dynamic light scattering (DLS) graph of MSN and MSN@Au;

[0039] Figure 6 It is the graph of the zeta potential measurement results of MSN and MSN@Au;

[0040] Figure 7 It is the graph of the evaluation results of the photothermal performance of MSN@Au;

[0041] Figure 8 It is the graph of the cytotoxicity data results after treating MDA-MB-231 and 4T1 cells with different concentrations of MSN@Au;

[0042] Figure 9 It is the graph of the cytotoxicity data results of 4T1 cells after different treatments;

[0043] Figure 10 It is the fluorescence staining graph of 4T1 cells stained with calcein-AM and PI after different treatments;

[0044] Figure 11 It is the fluorescence staining graph of 4T1 cells stained with DCFH-DA after different treatments. Detailed implementation manners

[0045] The technical solutions of the present invention will be further described below through specific implementation manners. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0046] Example 1

[0047] Preparation of mesoporous silica nanoparticles (MSN):

[0048] Mix 2 g of cetyl bromide diol (CPB), 1.2 g of urea and 30 mL of ultrapure water. Add 30 mL of cyclohexane and 1.1 mL of n-butanol to the above mixture, and under continuous stirring, dropwise add 5 mL of tetraethoxysilane (TEOS). Stir at 25 °C for 30 min, transfer the reaction mixture to an oil bath at 70 °C and react for 1 hour, then place it in an ice-water bath at 10 °C and react for 2 hours, and finally return to the oil bath at 70 °C and react for 12 hours. After the reaction is completed, centrifuge the product and wash it three times with ethanol. The obtained product is mesoporous silica nanoparticles (MSN) dispersed in ethanol.

[0049] Example 2

[0050] Preparation of gold nanoparticles:

[0051] Add 99 mL of ultrapure water to a three-necked round-bottom flask and start the reaction under magnetic stirring (500 rpm). At the same time, slowly add 1 mL of 1% (w / v) chloroauric acid (HAuCl4) solution through the second neck, and connect a reflux condenser. Then heat to 100 °C to make the solution boil, keep gentle boiling for 5 minutes, and quickly inject 10 mL of 1% (w / v) sodium citrate solution through a syringe. Observe that the solution quickly changes from light yellow to wine red, indicating the formation of gold nanoparticles. Continue refluxing for 20 minutes to ensure complete reduction and particle stability. Then turn off the heating and cool naturally to obtain a gold nanoparticle suspension.

[0052] Example 3

[0053] Amination of gold nanoparticles:

[0054] Quickly add the gold nanoparticle suspension prepared in Example 2 to a polyethyleneimine (PEI 25000) solution, and react for 30 minutes under continuous stirring at 30 °C. Dialyze the reaction mixture in water for 24 hours using a dialysis membrane with a molecular weight of 100 kDa to obtain the Au-PEI product.

[0055] Example 4

[0056] Preparation of MSN@Au complex:

[0057] Mix the Au-PEI product prepared in Example 3 with the MSN prepared in Example 1 at 30 °C for 12 h to load Au-PEI on the surface of MSN, form the MSN@Au complex, and store it in PBS and keep it at 4 °C for later use.

[0058] Test Example 1

[0059] Morphology characterization:

[0060] The morphology of the products obtained in Example 1, Example 2, and Example 4 was characterized by transmission electron microscopy (TEM), and the results are as follows Figures 1 - 3 shown. The transmission electron microscopy (TEM) analysis results showed that the synthesized MSN had excellent monodispersity and structural uniformity, and the size of the gold nanoparticles was about 10 nm. Subsequently, polyethyleneimine-functionalized gold nanoparticles were immobilized on the MSN surface through electrostatic interaction. TEM characterization revealed the formation of a high-density gold coating on the MSN surface, showing a contrast of closely packed particles.

[0061] Test Example 2

[0062] Particle size and zeta potential characterization:

[0063] The products obtained in Example 1, Example 2, and Example 4 were subjected to dynamic light scattering (DLS) and zeta potential measurements, and the results are as follows Figures 4 - 6 shown, indicating the successful preparation of the products at each stage.

[0064] Test Example 3

[0065] Evaluation of photothermal performance:

[0066] To evaluate the photothermal effect of MSN@Au, we investigated the temperature increase of a 128 μg / mL MSN@Au solution at different power densities. The results are as follows Figure 7 shown. All MSN@Au solutions showed a significant temperature increase after NIR exposure, and the temperature curves showed an obvious time progression. Notably, the photothermal response of MSN@Au showed a significant laser power-dependent correlation. These findings verified that the photothermal performance of MSN@Au can be precisely adjusted by irradiation parameters, providing an adjustable platform for optimizing treatment outcomes in specific-site anti-tumor applications. The power dependence not only enhanced the adaptability of MSN@Au in complex physiological environments but also minimized off-target thermal damage through spatio-temporal control.

[0067] Test Example 4

[0068] Evaluation of in vitro toxicity:

[0069] (1) Cell culture:

[0070] The human breast cancer cell line MDAMB-231 and the 4T1 murine breast cancer cell line were purchased from the Cell Bank of the Chinese Academy of Sciences (Shanghai, China). MDAMB-231 cells were cultured in Dulbecco's Modified Eagle Medium (DMEM) (Wisent Inc.), and 4T1 cells were maintained in RPMI 1640 medium (Wisent Inc.). The cell culture medium was supplemented with 10% fetal bovine serum (FBS) (Gibco) and 100 U / mL penicillin / streptomycin (Invitrogen). The cells were incubated at 37 °C in a humidified atmosphere of 5% CO2.

[0071] (2) Cytotoxicity assay:

[0072] First, the relative cell viability under different concentration conditions was measured using the Cell Counting Kit-8 (CCK-8) assay kit (Dojindo, Japan). The specific experimental steps were as follows: MDAMB-231 and 4T1 cells were seeded in 96-well plates at a density of 5000 cells per well and incubated overnight at 37 °C. Subsequently, cells were treated with MSN@Au nanoparticles at different concentrations. After 24 hours of incubation, the culture medium was discarded, and 100 μL of fresh medium containing 10% CCK-8 reagent was added and incubated for an additional 2 hours at 37 °C. Subsequently, the absorbance was measured at 450 nm using a multimode microplate reader (Infinite200, TECAN), with untreated cells as the 100% cell viability control. All experiments were repeated 3 times, and data analysis was performed using the mean of all measured values.

[0073] The results were as Figure 8 shown, and even at a concentration as high as 100 μg / mL, MSN@Au did not exhibit significant cytotoxicity against MDA-MB-231 and 4T1 breast cancer cells.

[0074] Then, the Cell Counting Kit-8 (CCK-8) assay kit (Dojindo, Japan) was used to measure the cell viability under different treatment conditions. The specific experimental steps were as follows: 4T1 cells were seeded in 96-well plates at a density of 5000 cells per well and incubated overnight at 37 °C. Subsequently, cells were treated with Au (20 μg / mL, equivalent to the Au concentration in MSN@Au), MSN (100 μg / mL, equivalent to the MSN concentration in MSN@Au), and MSN@Au nanoparticles, respectively.

[0075] After 6 hours of incubation, the cells were subjected to photothermal therapy (PTT), that is, using a wavelength of 808 nm and 0.5 W / cm 2Power laser irradiation for 5 minutes. After further incubation for 24 hours, the culture medium was discarded, 100 μL of fresh culture medium containing 10% CCK-8 reagent was added, and incubation was continued for 2 hours at 37°C. Subsequently, the absorbance was measured at 450 nm using a multifunctional microplate reader (Infinite 200, TECAN), and untreated cells were used as 100% cell viability control. All experiments were repeated 3 times, and the data were analyzed as the average of all measured values. In order to exclude the effect of near-infrared light irradiation (NIR) on cells, a control group was set up, that is, the cells were incubated at the same nanomaterial concentration but without NIR irradiation.

[0076] The results are as follows Figure 9 As shown, at 808nm wavelength, 0.5W / cm 2 After 4 minutes of high-power irradiation, the cell survival rates of the Au and MSN@Au groups decreased to a certain extent, while the cell viability in the corresponding non-illuminated control group did not decrease significantly. In the MSN@Au combined with laser irradiation group, the cell survival rate decreased significantly (less than 50%), indicating that MSN@Au can effectively play a photothermal therapy (PTT) role and induce tumor cell death.

[0077] In addition, Calcein-AM and propidium iodide (PI) were used to fluorescently stain 4T1 cells after different treatments, and the green and red fluorescence signals of the cells were observed under an inverted fluorescence microscope (Leica) to further evaluate cell survival. Calcein-AM can be hydrolyzed by intracellular esterases and produce green fluorescence, marking surviving cells; PI can specifically stain dead cells and present red fluorescence.

[0078] The results are as follows Figure 10 The results showed that in the absence of laser irradiation, cells in all experimental groups mainly showed green fluorescence, indicating that MSN, Au or MSN@Au alone did not cause obvious cell death. However, after the MSN@Au group was irradiated with 808nm laser, most cells showed red fluorescence, further confirming that the photothermal effect successfully induced cell death.

[0079] Test Example 5

[0080] Discussion on in vitro photothermal performance:

[0081] The ROS-sensitive probe 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA), which can be oxidized by ROS to highly fluorescent DCF, was selected to detect the generation of ROS in 4T1 cells after treatment with different treatment groups. Green fluorescence will be generated in the presence of ROS. First, 4T1 cells were incubated with different drugs Au (20 μg / mL, equivalent to the Au concentration in MSN@Au), MSN (100 μg / mL, equivalent to the MSN concentration in MSN@Au), and MSN@Au nanoparticles for 6 hours (the Au treatment group was divided into non-irradiated group / irradiated group, and MSN@Au was also divided into non-irradiated group / irradiated group. The irradiation condition was at a wavelength of 808 nm and 0.5 W / cm 2 ) After the treatment, the cells were washed with PBS, and fresh medium containing 20 μM DCFH-DA was added, and incubated in the dark for 20 minutes. Subsequently, the treated cells were observed using a laser confocal microscope, and the intracellular green fluorescence intensity was detected using a flow cytometer.

[0082] The results are as Figure 11 shown. When the cells were cultured only with MSN, Au, or MSN@Au, the intracellular ROS levels changed little. In contrast, when the cells were treated with Au or MSN@Au and exposed to 808 nm laser (0.5 W / cm 2 ) for 5 minutes, the fluorescence intensity of DCFH in the cells increased significantly.

[0083] The above results prove that MSN@Au has significant photothermal toxicity and excellent biocompatibility.

[0084] The applicant declares that the present invention uses the above embodiments to illustrate the technical solutions of the present invention, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of the raw materials of the products of the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

[0085] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0086] In addition, it should be noted that in the above specific embodiments, the various specific technical features described can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

Claims

1. A mesoporous silicon nanocomposite loaded with gold nanoparticles, characterized in that: The nanocomposite comprises mesoporous silicon nanoparticles and gold nanoparticles loaded on the mesoporous silicon nanoparticles, wherein the surface of the gold nanoparticles is modified with a cationic polymer.

2. The mesoporous silicon nanocomposite loaded with gold nanoparticles according to claim 1, characterized in that: The mass ratio of the cationic polymer to the gold nanoparticles is (2-6):1; The mass ratio of the mesoporous silicon nanoparticles to the gold nanoparticles is (3-7):

1.

3. The mesoporous silicon nanocomposite loaded with gold nanoparticles according to claim 1, characterized in that: The particle size of the gold nanoparticles is 7-13 nm; The particle size of the mesoporous silicon nanoparticles is 130-180 nm.

4. The mesoporous silicon nanocomposite loaded with gold nanoparticles according to any one of claims 1 to 3, characterized in that: The cationic polymer comprises polyethyleneimine; Preferably, the number average molecular weight of the polyethyleneimine is 20,000-30,000.

5. The method for preparing a mesoporous silicon nanocomposite loaded with gold nanoparticles according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: (1) mixing gold nanoparticles and cationic polymers in a solution and incubating them to obtain a reaction mixture; dialyzing the reaction mixture to obtain modified gold nanoparticles; (2) The modified gold nanoparticles are mixed and incubated with mesoporous silicon nanoparticles in a solution to obtain a mesoporous silicon nanocomposite loaded with gold nanoparticles.

6. The preparation method according to claim 5, characterized in that: The incubation in step (1) is performed at 15-40° C. for 20-60 min; Preferably, stirring is also performed during the incubation process in step (1).

7. The preparation method according to claim 5, characterized in that: The incubation in step (2) is performed at 15-40° C. for 8-15 hours; Preferably, ultrasonic treatment is also performed during the incubation process in step (2).

8. The preparation method according to claim 5, characterized in that: The preparation method of the gold nanoparticles comprises the following steps: The chloroauric acid aqueous solution is heated at 90-100° C. for 3-7 minutes, then mixed with a reducing agent, and heated at 90-100° C. for 15-25 minutes to obtain gold nanoparticles; Preferably, the concentration of the aqueous solution of chloroauric acid is 0.005-0.5%; Preferably, the reducing agent comprises sodium citrate.

9. The preparation method according to claim 5, characterized in that: The method for preparing the mesoporous silicon nanoparticles comprises the following steps: Mix hexadecanediol bromide, urea, water, cyclohexane and n-butanol, and then add tetraethoxysilane dropwise to obtain a mixture; first react the mixture at 60-80° C. for 40-80 minutes, then react at 0-10° C. for 90-150 minutes, and finally react at 60-80° C. for 8-15 hours, separate the solid and the liquid, and obtain mesoporous silicon nanoparticles; Preferably, after the solid-liquid separation, the solid product is washed with ethanol to remove impurities.

10. Use of the mesoporous silicon nanocomposite loaded with gold nanoparticles according to any one of claims 1 to 4 in the preparation of drugs for photothermal therapy of tumors.

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