High-strength photo-thermal conversion microsphere as well as preparation method and application thereof

Abstract

The invention provides a high-strength photo-thermal conversion microsphere as well as a preparation method and application thereof, and relates to the technical field of biomedical optical materials. The high-strength photothermal conversion PCM / SiO2 microsphere provided by the invention is a micron-sized functional material with optical characteristics of photonic crystals and high-efficiency heat conduction capability, can realize optical localization and slow photon effect, enhances photothermal conversion, and can be used as a photothermal conversion agent in near-infrared light treatment of POCD mice to remarkably improve brain temperature in a hippocampus DG region of the mice, so that the high-strength photothermal conversion PCM / SiO2 microsphere can be used for treating the POCD mice. The traditional Chinese medicine composition has a remarkable improvement effect on cognitive behaviors of POCD mice. The PCM / SiO2 microspheres prepared by the method disclosed by the invention have a wide application prospect in a photo-thermal treatment method.

Description

Technical Field

[0001] The present invention relates to the technical field of biomedical optical materials, and in particular to a microsphere with high-intensity photothermal conversion, a preparation method thereof, and an application thereof. Background Art

[0002] Photothermal therapy (PTT) utilizes light of a specific wavelength to irradiate biological tissues. Photothermal converters convert this energy into heat, thereby causing thermal damage to cells or tissues and achieving therapeutic results. PTT offers advantages such as low toxicity, non-invasiveness, and high precision. Compared to conventional NIR-1 photothermal therapy, NIR-2 photothermal therapy has attracted widespread attention due to its lower energy dissipation, deeper tissue penetration, and higher spatial resolution in biological tissues. However, due to the uncontrollable scattering of light in biological tissue, the number of photons reaching the target is significantly reduced. Increasing the irradiation power of NIR light in an attempt to increase the number of photons at the point of impact can easily cause localized thermal damage to the irradiated tissue. Furthermore, the scattering properties of biological tissue make it difficult to control the propagation path and energy distribution of NIR light within the tissue, limiting its effectiveness in medical applications. Therefore, the key to photothermal therapy lies in developing biocompatible materials that can efficiently and stably achieve photothermal conversion.

[0003] To date, various inorganic materials (such as precious metals, two-dimensional nanomaterials, carbon-based nanomaterials, and metal oxides) and organic materials (such as small molecule photosensitizers, conjugated polymers, semiconducting polymers, and fluorescent materials) have been extensively researched and developed as photothermal converters responsive to the near-infrared region II. However, these materials still face challenges such as complex synthesis methods, poor light absorption and photothermal conversion efficiency, and toxicity. Multifunctional nanocomposite photothermal conversion materials integrate monitoring and treatment, potentially reducing the side effects of single therapies while achieving synergistic effects across multiple treatments.

[0004] Silica itself is not a high-efficiency photothermal conversion material in the traditional sense. It is usually combined with other photothermal active substances or through special structural design to achieve the photothermal conversion function. When silica forms a special microstructure, such as a porous structure, a photonic crystal structure, etc., it will produce special scattering, reflection and interference effects on light, thereby increasing the propagation path of light inside the material and the probability of interaction between light and matter, so that light can be more fully absorbed and converted into thermal energy. Although the photothermal conversion efficiency of silica-based photothermal materials can be improved by various composite and structural design methods, compared with some pure photothermal materials with excellent performance (such as certain precious metal nanomaterials), its overall photothermal conversion efficiency still needs to be further improved. In particular, in practical applications, a higher photothermal conversion efficiency is required to achieve effective treatment or energy conversion functions. At present, the compounding of silica with various new photothermal active materials has become a research hotspot in this field. Based on the above research background, the present invention aims to provide a microsphere material with efficient and stable photothermal conversion prepared by silica and photothermal materials. Summary of the Invention

[0005] (1) Technical problems solved

[0006] In view of the shortcomings of the existing technology, the present invention provides a PCM / SiO2 microsphere with high-intensity photothermal conversion and its preparation method and application.

[0007] (2) Technical solution

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0009] The present invention provides a PCM / SiO2 microsphere with high-intensity photothermal conversion, wherein the PCM / SiO2 microsphere is prepared according to the following steps:

[0010] Step 1: Preparation of monodisperse SiO2 colloidal nanoparticles:

[0011] (1) Preheat 160-200 mL of anhydrous ethanol, 25-35 mL of deionized water, and 10-15 mL of seeds in a 65°C oven. The seeds were prepared by heating 55 mL of water, 0.072 g of L-arginine, and 3.6 mL of cyclohexane at 60°C, adding 4.4 mL of tetraethyl orthosilicate, and stirring for 24 h.

[0012] (2) Preheated anhydrous ethanol and deionized water were mixed evenly and stirred continuously. After stirring for 30-40 minutes, 15-20 mL of aqueous ammonia was added. After stirring for 5-10 minutes, seeds were added and the mixture was stirred for 30 minutes to obtain monodisperse SiO2 colloidal nanoparticles. The mass fraction of aqueous ammonia was 25-28%.

[0013] Step 2: Preparation of photothermal material PCM

[0014] (1) 0.45–0.5 g of one-dimensional cellulose nanocrystal (CNCs) powder was dispersed in 60–70 mL of deionized water by homogenization to obtain a stable CNCs dispersion;

[0015] (2) Ti3C2Mxene was synthesized by wet chemical etching using LiF / HCl solution: 40-45 mL of 9 mol / L hydrochloric acid solution and 3.2-3.5 g of LiF powder were mixed to prepare LiF / HCl etching solution; 2-2.5 g of Ti3AlC2 was then slowly added to the prepared LiF / HCl etching solution under stirring; the mixture was then etched in a sealed polytetrafluoroethylene container at below 40 °C for more than 48 h, and the product was then poured into a test tube and 2 mol / L The unreacted LiF was removed with dilute hydrochloric acid; then, the acidic suspension was repeatedly washed with deionized water and centrifuged at 3500 r / min for 1 min, and the cycle was repeated for at least 8 times until the pH value of the supernatant was 6-6.2; a multilayer MXene dispersion was obtained, and the dispersion was filtered, ultrasonicated in an ice bath for more than 2 h, and centrifuged at 3500 r / h for more than 30 min to obtain a single-layer Ti3C2MXene; Ti3C2MXene was prepared into a 5-10 mg / mL dispersion with deionized water for later use;

[0016] (3) 60-70 mL of CNCs dispersion and 30-35 mL of Ti3C2MXene dispersion were mixed and stirred for more than 30 min to obtain CNC-Ti3C2MXene dispersion;

[0017] (4) Then, 0.3-0.4 g of dopamine hydrochloride was added to the CNC-Ti3C2MXene dispersion, and the mixture was stirred at room temperature for more than 30 min. Then, triethanolamine was added to adjust the pH to 8.5, and the mixture was stirred at room temperature under aerobic conditions for more than 10 h to obtain the photothermal material PCM.

[0018] Step (3) Preparation of PCM / SiO2 microspheres

[0019] (1) Monodisperse SiO2 colloidal nanoparticles and photothermal material PCM are prepared into dispersions with a mass fraction of 0.5-2% using deionized water;

[0020] (2) mixing monodisperse SiO2 colloidal nanoparticles and photothermal material PCM dispersion in a volume ratio of 5-7:4 and ultrasonically dispersing for more than 30 minutes to obtain a mixed dispersion;

[0021] (3) The mixed dispersion is sheared into monodisperse droplets in the silicone oil. The droplets are dried in an oven at 65-70°C for more than 18 hours, and then dried in an oven at 90-100°C for more than 2 hours to obtain PCM / SiO2 microspheres with a size of 100±10μm.

[0022] The present invention also provides the use of PCM / SiO2 microspheres prepared by the above method as a photothermal conversion agent in a photothermal therapy method.

[0023] (3) Beneficial effects

[0024] The high-intensity photothermal conversion PCM / SiO2 microspheres provided by the present invention are a micron-sized functional material that combines the optical properties of photonic crystals with efficient heat conduction capabilities. We achieve photon localization and slow photon effect of near-infrared light of a specific frequency by effectively regulating the photonic band gap of the colloidal crystal, thereby enhancing local photothermal efficiency and achieving coordinated regulation of light and heat. The PCM / SiO2 microspheres provided by the present invention have periodically arranged monodisperse silica particles inside, which can achieve light localization and slow photon effect, thereby enhancing photothermal conversion. Compared with coated SiO2, monodisperse SiO2 assembled to form photonic crystals has the advantages of strong photon localization capability, low optical loss, band-edge slow light enhancement, and low production cost. By introducing the photothermal material PCM that efficiently absorbs 808nm near-infrared light, we can make PCM / SiO2 generate heat quickly. The PCM / SiO2 microspheres prepared by the method of the present invention possess excellent optical and thermal properties, including broadband spectrum, low scattering, and efficient heat generation. They enable high-intensity photothermal conversion. As photothermal conversion agents, they significantly elevated brain temperature in the hippocampal DG region of POCD mice treated with near-infrared light, significantly improving cognitive behavior in these mice. The PCM / SiO2 microspheres prepared by the method of the present invention have broad application prospects in photothermal therapy. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The structure of PCM / SiO2 microspheres under scanning electron microscopy; (A) is the SEM image of PCM / SiO2 microspheres; (B) is the SEM image of monodisperse SiO2 colloidal nanoparticles.

[0026] Figure 2 Schematic diagram of the reflection (A) and transmission (B) spectrum measurement of microspheres.

[0027] Figure 3 The reflection (A) and transmission (B) spectra of the microspheres are measured.

[0028] Figure 4 Schematic diagram of the preparation process of agarose thin layer containing PCM / SiO2 microspheres.

[0029] Figure 5 Schematic diagram of the reflection (a) and transmission (b) spectra of PCM / SiO2 microspheres in a thin agarose layer. The microspheres can produce slow photon effect (c) and photon localization (d) for 808nm near-infrared light.

[0030] Figure 6 Figure 3. Thermal effect of PCM / SiO2 microspheres. Thermal imaging of PCM / SiO2 microspheres in air: (A) when the laser is off, (B) 3 minutes after the laser is turned on. (C) Temperature change curve of the DG region of the mouse hippocampus after PCM / SiO2 microspheres were injected into the region.

[0031] Figure 7 A: Schematic diagram of injecting high-intensity photothermal conversion microspheres into the hippocampal DG region; Figure 7 B: Schematic diagram of 808nm NIR irradiation; Figure 7 C: The temperature of the DG region of the mouse hippocampus was measured. The temperature of the NIR+microsphere group increased by 2.50-2.67°C, which was significantly higher than that of the NIR and NIR+PCM groups. Figure 7 D: Barnes maze trajectory results of the three groups of POCD mice undergoing treatment; Figure 7 E: Barnes maze mouse escape time statistics showed that the NIR+microsphere group had the shortest escape time, indicating that the treatment effect on POCD mice was superior to the other two groups. *p<0.05, **p<0.01. DETAILED DESCRIPTION

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0033] Example 1

[0034] Preparation of PCM / SiO2 microspheres with high-intensity photothermal conversion

[0035] Step 1: Preparation of monodisperse SiO2 colloidal nanoparticles:

[0036] (1) Preheat 160 mL of anhydrous ethanol, 25 mL of deionized water, and 10 mL of seeds in a 65°C oven. The seeds were prepared by heating 55 mL of water, 0.072 g of L-arginine, and 3.6 mL of cyclohexane to 60°C, adding 4.4 mL of tetraethyl orthosilicate, and stirring for 24 h.

[0037] (2) Preheated anhydrous ethanol and deionized water were mixed evenly and stirred continuously. After stirring for 30 minutes, 15 mL of aqueous ammonia was added. After stirring for 5 minutes, seeds were added and the mixture was stirred for 30 minutes to obtain monodisperse SiO2 colloidal nanoparticles. The mass fraction of aqueous ammonia was 25-28%.

[0038] Step 2: Preparation of photothermal material PCM

[0039] (1) 0.45 g of one-dimensional cellulose nanocrystal (CNCs) powder was dispersed in 60 mL of deionized water by homogenization to obtain a stable CNCs dispersion;

[0040] (2) Ti3C2Mxene was synthesized by wet chemical etching using LiF / HCl solution: 40 mL of 9 mol / L hydrochloric acid solution and 3.2 g of LiF powder were mixed to prepare LiF / HCl etching solution; 2 g of Ti3AlC2 was then slowly added to the prepared LiF / HCl etching solution under stirring; the mixture was subsequently etched at 40 °C for 48 h in a sealed polytetrafluoroethylene container, and the product was poured into a test tube, and 2 mol / L dilute hydrochloric acid was added to remove the unreacted LiF; the acidic suspension was then repeatedly washed with deionized water and centrifuged at 3500 r / min for 1 min, with a cycle of not less than 8 times, until the pH value of the supernatant was 6-6.2; a multilayer MXene dispersion was obtained, the dispersion was filtered, ultrasonicated in an ice bath for more than 2 h, and centrifuged at 3500 r / h for more than 30 min to obtain a single-layer Ti3C2MXene; Ti3C2Mxene was prepared into a 5 mg / mL dispersion with deionized water for later use;

[0041] (3) 60 mL of CNCs dispersion and 30 mL of Ti3C2MXene dispersion were mixed and stirred for more than 30 min to obtain CNC-Ti3C2MXene dispersion;

[0042] (4) Then, 0.3 g of dopamine hydrochloride was added to the CNC-Ti3C2MXene dispersion, and the mixture was stirred at room temperature for more than 30 min. Then, triethanolamine was added to adjust the pH to 8.5, and the mixture was stirred at room temperature under aerobic conditions for more than 10 h to obtain the photothermal material PCM.

[0043] Step (3) Preparation of PCM / SiO2 microspheres

[0044] (1) Monodisperse SiO2 colloidal nanoparticles and photothermal material PCM are prepared into dispersions with a mass fraction of 0.5-2% using deionized water;

[0045] (2) mixing monodisperse SiO2 colloidal nanoparticles and photothermal material PCM dispersion in a volume ratio of 5-7:4 and ultrasonically dispersing for more than 30 minutes to obtain a mixed dispersion;

[0046] (3) The mixed dispersion is sheared into monodisperse droplets in the silicone oil. The droplets are dried in an oven at 65-70°C for more than 18 hours, and then dried in an oven at 90-100°C for more than 2 hours to obtain PCM / SiO2 microspheres with a size of 100±10μm.

[0047] Example 2

[0048] Structural Characterization of PCM / SiO2 Microspheres

[0049] The structures of PCM / SiO2 microspheres and monodisperse SiO2 colloidal nanoparticles were observed using scanning electron microscopy. Figure 1 A is the SME diagram of monodisperse SiO2 colloidal nanoparticles. Figure 1 B is the SEM image of PCM / SiO2 microspheres. Figure 1 Compared with A, it can be seen that PCM and SiO2 are assembled in an orderly manner, and PCM is evenly encapsulated in the pores of SiO2.

[0050] Example 3

[0051] Characterization of Photothermal Effect of PCM / SiO2 Microspheres

[0052] The PCM / SiO2 microspheres prepared in this paper primarily enhance photothermal efficiency by increasing the interaction time between light and the medium through light localization and the slow photon effect. Therefore, we verified the light localization and slow photon effect by measuring the transmission and reflection of light through the PCM / SiO2 microspheres.

[0053] The specific procedure is as follows: a microsphere is placed on a transparent glass slide, which is then placed on the stage of a metallographic microscope. The microsphere's reflection and transmission peaks are measured in both reflection and transmission modes. In transmission mode, the microscope's lower light source penetrates the glass substrate and microsphere to the objective lens. In reflection mode, the microscope's upper light source shines downward from the objective lens onto the microsphere surface, where it is reflected and returned to the objective lens. Both experiments use a spectrally continuous white light source. Reflection and transmission images are captured using a high-resolution color CCD. To record the transmission spectrum of the photonic crystal microsphere, the microscope's lower light source serves as the incident white light source. A single ordinary optical fiber is used through the objective lens to receive light transmitted through the glass slide and microsphere. Reflection spectra are recorded using a Y-shaped optical fiber. External white light propagates through the fiber and, after reflection from the microsphere surface, is collected and entered into a fiber optic spectrometer at the other end. During the measurement, care should be taken to minimize the influence of ambient light. A flat mirror surface should be selected and the focus adjusted. The reflection spectrum at this point should be recorded as a baseline, or the spectrum passing through transparent glass should be recorded as a baseline for the transmission spectrum. The amplitude of the measured reflection or transmission spectrum is then expressed as a relative value. Measurement diagram as shown Figure 2 shown.

[0054] The measurement results are as follows Figure 3 As shown, Figure 3 A shows that the reflection peak of the microsphere is at 740nm, and the microsphere is at the "red edge" near 808nm, indicating that the microsphere has a slow photon effect. Figure 3 B shows that the transmittance of the microspheres decreases near 740nm, which is the photon band gap, indicating that photon localization has been achieved.

[0055] Example 4

[0056] Effect of PCM / SiO2 microspheres on light in medium

[0057] Experimental method: (1) Preparation of agarose wave layer containing PCM / SiO2 microspheres: PCM / SiO2 microspheres were spread flat in a square groove with a thickness of 200 μm surrounded by a cover glass. To ensure the standardization of the test, the microspheres had to cover the entire bottom of the square groove. Then, 3 g of agarose was dissolved in 100 ml of water and heated to 90 °C to completely dissolve, and then cooled to 45-50 °C. Then, the warm agarose was slowly injected into the square groove with microspheres and allowed to cool and solidify (as shown in the figure). Figure 5 ab).

[0058] (2) Macroscopic detection of the optical effect of PCM / SiO2 microspheres in agarose thin layer: The angle-dependent optical properties of the material were tested using the variable angle measurement module of the UV / visible / near-infrared spectrophotometer (Hitachi U-4100). The direction of the reflected light was adjusted by changing the angle of the mirror to generate a Bragg incident angle of 30-80° (the angle between the incident light and the sample surface), and the corresponding reflection or transmission spectra (such as Figure 5 ). Typical measurement methods are as follows:

[0059] (a) Turn on the light source and preheat for 5 minutes. Spread the agar film flat on the sample table and fix it with a clamp.

[0060] Adjust the M4 to the appropriate position according to the measurement mode (reflection or transmission);

[0061] (b) Adjust M2 and M3 to appropriate positions (e.g., 80°), cover the lens to prevent interference from ambient light, select appropriate integration time and scan speed, and record the reflection (or transmission) spectrum in the range of 400-800 nm;

[0062] (c) Change the positions of M2 and M3 and repeat (b) until the reflection and transmission spectra at all angles are measured.

[0063] Experimental results: The results are as follows Figure 5 As shown in cd, Figure 5 c is the reflection spectrum of the microsphere. The microsphere is at the "red edge" near 808nm, thus having a slow photon effect on 808nm NIR. Figure 5 d is the transmission spectrum of the microsphere. The microsphere has a photon bandgap at 808 nm, which can realize photon localization.

[0064] Example 5

[0065] Thermal Effect of PCM / SiO2 Microspheres

[0066] In vitro test: The thermal image of PCM / SiO2 microspheres in air was taken by a thermal imager at 50mW / cm 2 After irradiating the PCM / SiO2 microspheres in the air with 808nm laser, the temperature of the microspheres increased significantly by 3.6℃. Figure 6 As shown in AB.

[0067] In vivo test: PCM / SiO2 microspheres were stereotactically injected into the DG region of the mouse hippocampus at 50 mW / cm 2 Under 808nm laser irradiation, the temperature of the mouse hippocampus DG brain region increased by 2.5℃, and the results were as follows: Figure 6 As shown in C.

[0068] The above results indicate that PCM / SiO2 microspheres have good thermal effects both in vivo and in vitro.

[0069] Example 6

[0070] 1 Experimental animals and group treatment

[0071] Fourteen-week-old male C57BL / 6 mice were used to establish a cognitive dysfunction (POCD) model. The specific method was as follows: the mice were anesthetized with 1.8% isoflurane, a 2.0 cm long incision was made along the midline of the neck, the carotid artery tissue was carefully peeled away from the surrounding area to avoid damaging the vagus nerve, and sterile surgical sutures were used to suture the wound to ensure aseptic conditions. The operation was completed within 15 minutes, and the mice were then anesthetized for 2 hours. The animal body temperature was maintained at 36.8±0.2°C.

[0072] On the second day of modeling, the animals were randomly divided into three groups: POCD+NIR group, POCD+NIR+PCM group (400 nL of 25 mg / mL PCM suspension), and POCD+NIR+microsphere group (50 PCM / SiO2 microspheres), with 5 animals in each group. Excitatory neurons and inhibitory neurons were labeled using rAAV-CaMKIIα-GCaMP6m and rAAV-mDLx-GCaMP6m, respectively. PCM and PCM / SiO2 microspheres were injected into the DG region of the hippocampus ( Figure 7 A) By fixing the non-invasive optical fiber ferrule, each group of mice was continuously exposed to 50 mW / cm 2 808nm NIR irradiation for 5min ( Figure 7 B) On the 7th day, the brain temperature of the hippocampal DG region and Barnes maze behavior of mice in each group were tested.

[0073] The Barnes maze was used to test the improvement in learning and memory abilities in mice, confirming that high-intensity photothermal conversion microspheres (PTCMs)-mediated NIR treatment had a beneficial effect on behavioral improvement in POCD mice. PTCMs were injected into the DG region of the hippocampus via a catheter. Seven days later, frozen sectioning was performed to confirm their location in the DG region.

[0074] The temperature of the hippocampal DG region of mice was measured, and the temperature of the NIR+microsphere group increased by 2.50-2.67℃, which was significantly higher than that of the NIR and NIR+PCM groups ( Figure 7 C), which shows that the PCM / SiO2 microspheres provided by the present invention have good photothermal conversion ability in mice.

[0075] The Barnes maze was used to detect the improvement of mice’s learning and memory abilities. Figure 7As shown in Figures DE, the movement trajectories of mice in the POCD group were disorganized, and the travel and escape times were longer, indicating that the POCD model was successfully established. Compared with the POCD group, the movement trajectories of mice in the POCD+NIR+PCM group were significantly improved, with significantly shorter travel and escape times (p<0.05). Compared with the POCD group, the movement trajectories of mice in the POCD+NIR+microsphere group were significantly improved, with regular movement trajectories and significantly shorter travel and escape times (p<0.0001). The escape time of mice in the POCD+NIR+microsphere group was also significantly shorter than that in the POCD+NIR+PCM group.

[0076] The above results indicate that the PCM / SiO2 microspheres provided by the present invention have a significant effect on improving the learning and memory abilities of POCD mice, and the microspheres can be used as an effective photothermal conversion medium for near-infrared light therapy of POCD.

[0077] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A PCM / SiO2 microsphere with high-intensity photothermal conversion, characterized in that: The PCM / SiO2 microspheres were prepared according to the following steps: Step 1: Preparation of monodisperse SiO2 colloidal nanoparticles: (1) Preheat 160-200 mL of anhydrous ethanol, 25-35 mL of deionized water, and 10-15 mL of seeds in a 65°C oven; (2) Preheated anhydrous ethanol and deionized water were mixed evenly and stirred continuously. After stirring for 30-40 minutes, 15-20 mL of ammonia solution was added. After stirring for 5-10 minutes, seeds were added and the mixture was stirred for 30 minutes to obtain monodisperse SiO2 colloidal nanoparticles. Step 2: Preparation of photothermal material PCM (1) 0.45–0.5 g of one-dimensional cellulose nanocrystal (CNCs) powder was dispersed in 60–70 mL of deionized water by homogenization to obtain a stable CNCs dispersion; (2) synthesizing Ti3C2Mxene by wet chemical etching using LiF / HCl solution, and preparing Ti3C2Mxene into a 5-10 mg / mL dispersion with deionized water for later use; (3) 60-70 mL of CNCs dispersion and 30-35 mL of Ti3C2MXene dispersion were mixed and stirred for more than 30 min to obtain CNC-Ti3C2MXene dispersion; (4) Then, 0.3-0.4 g of dopamine hydrochloride was added to the CNC-Ti3C2MXene dispersion, and the mixture was stirred at room temperature for more than 30 min. Then, triethanolamine was added to adjust the pH to 8.5, and the mixture was stirred at room temperature under aerobic conditions for more than 10 h to obtain the photothermal material PCM. Step 3: Preparation of PCM / SiO2 microspheres (1) Monodisperse SiO2 colloidal nanoparticles and photothermal material PCM are prepared into dispersions with a mass fraction of 0.5-2% using deionized water; (2) mixing the monodisperse SiO2 colloidal nanoparticles and the photothermal material PCM dispersion and ultrasonically dispersing them for more than 30 minutes to obtain a mixed dispersion; (3) The mixed dispersion is sheared into monodisperse droplets in the silicone oil. The droplets are dried in an oven at 65-70°C for more than 18 hours, and then dried in an oven at 90-100°C for more than 2 hours to obtain PCM / SiO2 microspheres with a size of 100±10μm.

2. The method for preparing PCM / SiO2 microspheres with high-intensity photothermal conversion according to claim 1, characterized in that: In step 1, the seeds were prepared by heating 55 ml of water + 0.072 g of L-arginine + 3.6 ml of cyclohexane to 60°C, adding 4.4 ml of tetraethyl orthosilicate and stirring for 24 hours.

3. The method for preparing PCM / SiO2 microspheres with high-intensity photothermal conversion according to claim 1, characterized in that: In step 1, the mass fraction of ammonia water is 25-28%.

4. The method for preparing PCM / SiO2 microspheres with high-intensity photothermal conversion according to claim 1, characterized in that: In step 2, the synthesis method of the Ti3C2Mxene is as follows: 40-45mL of 9moL / L hydrochloric acid solution and 3.2-3.5g of LiF powder are mixed to prepare a LiF / HCl etching solution; then 2-2.5g of Ti3AlC2 is slowly added to the prepared LiF / HCl etching solution under stirring; then, the mixture is etched at below 40°C in a sealed polytetrafluoroethylene container for more than 48h, and then the product is poured into a test tube, and 2mol / L dilute hydrochloric acid is added to remove the unreacted LiF; then, the acidic suspension is repeatedly washed with deionized water and centrifuged at a speed of 3500r / min for 1min, and the cycle is repeated for not less than 8 times, and the supernatant is washed until the pH value is 6-6.2; a multilayer MXene dispersion is obtained, the dispersion is filtered, ice-bathed for more than 2h, and centrifuged at 3500r / h for more than 30min to obtain a single-layer Ti3C2MXene.

5. The method for preparing PCM / SiO2 microspheres with high-intensity photothermal conversion according to claim 1, characterized in that: In step 3, monodisperse SiO2 colloidal nanoparticles and photothermal material PCM dispersion are mixed in a volume ratio of 5-7:

4.

6. Use of the PCM / SiO2 microspheres prepared by the method according to claim 1 as a photothermal conversion agent in photothermal therapy.

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