Near-infrared ii region emitting ultrasmall gold nanoparticles, method of preparation and use thereof

Abstract

The application relates to the technical field of metal nanoparticles, and particularly discloses near-infrared two-region luminescent ultra-small gold nanoparticles as well as a preparation method and application thereof, the preparation method of the ultra-small gold nanoparticles comprises the following steps: S1, preparing gold nanoparticles with an Au(0) inner core / Au(I)-thiolate shell structure and capable of emitting green visible light; and S2, performing selective etching on the Au(I)-thiolate shell of the gold nanoparticles by using a controllable photochemical irradiation mode, realizing controllable red shift of a luminescence waveband, and obtaining near-infrared two-region luminescent ultra-small gold nanoparticles. The near-infrared two-region luminescent ultra-small gold nanoparticles have the advantages of not needing external etching reagents, a green and mild process, precise and selective regulation of a particle luminescence waveband, stable product structure, and strong optical controllability.

Description

Technical Field

[0001] This invention relates to the field of metal nanoparticle technology, and in particular to an ultrasmall gold nanoparticle that emits near-infrared II emission, its preparation method, and its application. Background Technology

[0002] In the field of modern materials science, luminescent gold nanoparticles, especially ultrasmall particles with a size of less than 3 nanometers, have become a highly promising class of optical materials due to their unique properties. These materials bridge the gap between atomic / molecular emitters and plasmonic nanostructures, exhibiting outstanding characteristics such as tunable emission wavelength, excellent stability, and good biocompatibility, making them promising for applications in numerous fields such as bioimaging, sensing, nanomedicine, and optoelectronics.

[0003] Currently, one of the key challenges and core research directions in this field is to find reliable methods to precisely control the emission wavelength of luminescent gold nanoparticles. This is because the emission wavelength is directly related to its practical application performance. For example, in deep tissue bioimaging and biosensing, long-wavelength light in the near-infrared region has received widespread attention and favor because it can significantly reduce light scattering and autofluorescence background interference.

[0004] Over the past few decades, researchers have actively explored and developed a series of methods to control the electronic structure of ultrasmall gold nanoparticles to achieve emission redshifts, covering aspects such as heteroatom doping, control of metal core size or morphology, surface ligand engineering, and alteration of external environmental conditions. However, existing strategies generally have limitations, typically achieving only limited spectral redshifts, usually confined to the range of tens of nanometers, and difficult to extend to the highly valuable near-infrared II region. While some more aggressive methods, such as chemical etching, can induce significant redshifts, they are accompanied by a series of problems, including harsh reaction conditions, poor process controllability, and the generation of large, non-luminescent byproducts. Therefore, achieving robust, wide-range, and highly controllable redshifts, especially extending emission into the near-infrared II region, remains a major challenge to be solved in this field.

[0005] On the other hand, light, as an external stimulus, has been widely used in many fields such as photocatalysis, phototherapy, photolithography, and information security due to its inherent advantages such as non-invasiveness, non-contact manipulation, and high spatiotemporal resolution. However, in the research of ultrasmall gold nanoparticles, the role of light presents a double-edged sword. Similar to organic dyes, gold nanoparticles often face the problem of photoinduced instability. Irradiation can change their metallic core or surface structure, causing the particles to aggregate into larger, non-luminescent particles, ultimately leading to fluorescence quenching. This undoubtedly hinders their practical application.

[0006] In summary, developing a method that can effectively solve the above problems, achieve robust, wide-range and highly controllable redshift of ultrasmall gold nanoparticles, and overcome photoinduced instability is of great significance for promoting the widespread application of luminescent gold nanoparticles in various related fields. Summary of the Invention

[0007] Based on this, the purpose of the present invention is to provide an ultra-small gold nanoparticle with near-infrared II emission, its preparation method and application, which has the advantages of tunable infrared II emission, excellent optical performance and good stability.

[0008] This invention is achieved through the following detailed technical solutions:

[0009] A method for preparing near-infrared II luminescent ultrasmall gold nanoparticles includes the following steps: S1: Preparation of gold nanoparticles with an Au(0) core / Au(I)-thiol shell structure that can emit visible green light; S2: Selective etching of the Au(I)-thiol salt shell of the gold nanoparticles is performed by a controllable photochemical irradiation method to achieve a controllable redshift of the emission band and obtain ultra-small gold nanoparticles that emit light in the near-infrared II region.

[0010] Compared to existing technologies, the method for preparing near-infrared II luminescent ultrasmall gold nanoparticles described in this invention relies on the Au(0) core / Au(I)-thiol shell structure of gold nanoparticles. It utilizes the active free radical species generated in situ by light irradiation, combined with the difference in oxidation potential between the two, to selectively etch the shell while preserving the Au(0) core. The visible green light emission of the original particles mainly originates from electronic transitions in the Au(I)-thiol shell. As the shell is gradually and selectively etched, the coordination environment on the particle surface and the overall electronic structure are continuously reconstructed. The energy gap between the highest occupied molecular orbital and the lowest empty molecular orbital continuously narrows, reducing the energy required for electronic transitions, ultimately achieving an ordered redshift of the emission band from the visible green region to the longer-wavelength near-infrared II region. This invention eliminates the need for additional chemical etchants and oxidants, avoiding particle agglomeration, structural damage, and biotoxicity issues caused by exogenous reagents. It also breaks the technical bias that light exposure can easily cause photobleaching and luminescence quenching of gold nanoparticles. By etching, the particle size can be controlled while ensuring colloidal stability. The emission wavelength can be stably controlled from the visible green light region to the near-infrared II region. The process conditions are mild, and the product structure and optical performance are highly controllable.

[0011] Furthermore, the preparation method of these near-infrared II luminescent ultrasmall gold nanoparticles includes the following steps: S1: The gold nanoparticles were synthesized using chloroauric acid as the gold source and tetrahydroxymethylphosphoric chloride as the reducing agent under mercapto ligand modification conditions. S2: Take the gold nanoparticle solution obtained in step S1 and adjust its pH value to 7-13. Perform controlled light modification using a UV-Vis light source to obtain the near-infrared II luminescent ultrasmall gold nanoparticles. This method is adaptable to a wide range of acidity and alkalinity environments, has a high process tolerance, and is convenient for large-scale preparation.

[0012] Further, step S1 involves: adding an aqueous solution of the thiol ligand dropwise to a chloroauric acid solution at room temperature, stirring until the system is colorless and homogeneous; adjusting the pH of the system to alkaline, adding tetrahydroxymethylphosphoric acid solution dropwise, and continuously stirring the reaction at room temperature; after the reaction is complete, dialysis is performed to remove impurities, yielding gold nanoparticles emitting visible green light. The room-temperature liquid-phase synthesis system is simple and easy to operate, and can prepare precursor particles with uniform morphology and luminescence properties.

[0013] Furthermore, in step S1, the molar ratio of chloroauric acid to the thiol functional group of the thiol ligand is 1:3. This ratio can construct a well-structured core-shell system, ensuring that the precursor particles possess stable green light emission performance.

[0014] Furthermore, in step S2, the pH value is adjusted to 8-9. A weakly alkaline environment can efficiently promote the generation of holes and reactive oxygen species, improving the efficiency and precision of selective etching of the shell.

[0015] Furthermore, the ultraviolet-visible light source in step S2 can be any one of a xenon lamp, mercury lamp, LED lamp, or solar simulator; when the ultraviolet-visible light source is a xenon lamp, the light intensity of the xenon lamp is 100–250 mW / cm², and the light reaction time is 0.5–10 h. The selection of light source type and light parameters is flexible, allowing for precise control of the etching degree and achieving gradient adjustment of luminescent performance.

[0016] Furthermore, the thiol ligand in step S1 is a water-soluble thiol ligand, selected from one or more of mercaptopropionic acid, mercaptohexanoic acid, mercaptoundecanoic acid, and glutathione. It is compatible with a variety of water-soluble thiol ligands, has strong universality in its preparation method, and can be extended to various similar luminescent nanosystems.

[0017] Furthermore, this invention also applies for protection of an ultrasmall gold nanoparticle that emits light in the near-infrared II region, which is prepared by the above-described method. The resulting nanoparticles are small in size, well-dispersed, and possess tunable near-infrared II emission capability.

[0018] Furthermore, this invention also seeks to protect the application of the aforementioned near-infrared II luminescent ultrasmall gold nanoparticles in the fields of bioimaging, sensing, nanomedicine, optoelectronics, and information storage. The material exhibits excellent overall performance, meeting the application needs of various scenarios across multiple fields, and has a wide range of applications.

[0019] Furthermore, this invention also applies for protection of a rewritable near-infrared optical information storage composite film, wherein the composite film comprises hydroxypropyl cellulose, citric acid, and the aforementioned ultra-small gold nanoparticles that emit light in the near-infrared II region. Utilizing the dual-band emission characteristics of the particles, the film possesses a dual-mode rewritable storage function in both visible light and near-infrared II regions.

[0020] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating the preparation principle of the near-infrared II luminescent ultrasmall gold nanoparticles of the present invention. Figure 2 This is a graph showing the fluorescence spectrum test results of Example 3; Figure 3 Images of MUA–AuNPs after different illumination times under fluorescent light, ultraviolet light, and 808nm laser. Figure 4 Electrophoretic gel imaging results of MUA–AuNPs after different light treatment times under fluorescent lamp, ultraviolet lamp and 808nm laser; Figure 5 This is a schematic diagram showing the particle size variation results in Example 5; where, Figure 5 a-5c are TEM images of samples treated with different light exposure times. Figure 5 d represents the particle size distribution as statistically analyzed by TEM. Figure 5 e represents the hydrated particle size distribution. Figure 5 f represents the zeta surface potential result; Figure 6 This is a schematic diagram of the test results for the control principle in Example 6; where, Figure 6 a-6c are high-resolution XPS spectra of MUA-AuNPs before and after 240 min of illumination; Figure 7 This is a schematic diagram of the test results for the control principle in Example 6; where, Figure 7 a- Figure 7 c is the XPS high-resolution spectrum of the sample after 30 min of illumination; Figure 8 This is a schematic diagram of the test results for the control principle in Experiment Example 6; where, Figure 8 a- Figure 8 d represents the EPR spectrum; Figure 9 This is a schematic diagram of the universality verification test results for the thiol reagent in Example 7; wherein, Figure 9 a represents the NIR-II imaging results of MHA-AuNPs after different illumination times. Figure 9 b and c are TEM images before and after 60 minutes of illumination, respectively; Figure 10 a is a schematic diagram of the information writing and erasing process of the composite film in Example 8; Figure 10 b is a schematic diagram of the imaging results of the composite film in Example 8 under different lighting conditions. Detailed Implementation

[0022] This invention provides ultrasmall gold nanoparticles that emit light in the near-infrared II region, which are prepared by the following method: S1. Raw material mixing and dissolution: Weigh out the gold source material and the mercapto ligand according to the molar ratio of Au to mercapto functional group 1:3. Dissolve the two materials together in deionized water and continue mixing and stirring at room temperature until all solid raw materials are completely dissolved, the system is uniform and stable, and the final solution is colorless or pale yellow.

[0023] S2. pH control of the system: Add 1.0 mol / L NaOH solution slowly dropwise to the homogeneous mixed solution prepared above under continuous stirring at room temperature, monitor the acidity and alkalinity of the system in real time, and accurately adjust the pH value of the solution to 9~10 to obtain a slightly alkaline reaction precursor solution.

[0024] S3. Room temperature reduction reaction: After pH adjustment, slowly and uniformly add an appropriate amount of tetrahydroxymethylphosphoric acid solution (80wt%, molar ratio of THPC to HAuCl4 is 0.5:1~1.2:1) to the precursor solution. After the addition is complete, keep the room temperature constant and continue stirring for 24 hours to fully complete the gold ion reduction, particle coordination and growth process.

[0025] S4. Dialysis purification: After the reaction is completed, the crude reaction system is transferred to a dialysis bag with a molecular weight cutoff of 3500 Da. Deionized water is used as the medium for dialysis to remove impurities, completely removing unreacted raw materials, small molecule impurities and inorganic salt ions from the system. After purification, gold nanoparticles that emit green light are prepared.

[0026] S5. Photochemical Modification and Emission Wavelength Control: The gold nanoparticles prepared above were redispersed in an aqueous solution, and the pH of the system was adjusted to the slightly alkaline range of pH 8-9. The system was subjected to controllable photochemical irradiation using a light source with ultraviolet-visible light components. By precisely controlling the irradiation duration, the emission wavelength of the gold nanoparticles could be controlled to redshift from the initial visible green light region (500-560 nm) to the near-infrared II region (900-1200 nm). Finally, modified gold nanoparticles with excellent near-infrared II luminescence performance were obtained, namely, ultra-small gold nanoparticles with near-infrared II luminescence.

[0027] Preferably, the preparation method of the present invention has broad process adaptability and raw material substitutability. The specific preferred technical solution is as follows: the gold source used in the present invention is preferably tetrachloroauric acid trihydrate, and the selected mercapto ligand is specifically mercaptoundecanoic acid. The ligand can also be replaced by other water-soluble thiol reagents such as mercaptopropionic acid, mercaptohexanoic acid, and glutathione. After replacing the ligand, the molar ratio of Au to thiol functional group remains unchanged at 1:3, and the resulting product has the same performance. The reaction system in step S5 of this invention is not limited to a pH of 8-9; it can react normally within a wide pH range of 7-13 and stably prepare the target product. In the above preparation method, a xenon lamp is preferably used as the excitation source. Alternatively, a mercury lamp, LED lamp, or solar simulator with ultraviolet-visible light components can be used for equivalent excitation. When a xenon lamp is used as the excitation source, the light intensity is set to 100~250mW / cm², and the illumination is continuous for 0.5~10h.

[0028] The present invention will now be described in detail with reference to specific embodiments.

[0029] Unless otherwise specified, all raw materials, consumables, and experimental equipment used in this invention are commercially available products, and all chemicals are of analytical grade.

[0030] Example 1: Preparation of MUA-AuNPs This embodiment is used to prepare ultrasmall gold nanoparticles with near-infrared II luminescence properties. HAuCl4·3H2O was used as the gold source, mercaptoundecanoic acid (MUA) as the surface ligand, and tetrahydroxymethylphosphoric chloride (THPC) as the reducing agent. The specific preparation steps are as follows: According to the molar ratio of gold (Au) to MUA of 1:3, the corresponding mass of HAuCl4·3H2O was weighed and added to water along with MUA. The mixture was stirred continuously at 25°C until the solid material was completely dissolved, and the system ultimately presented a colorless or pale yellow homogeneous liquid phase. A 1.0 mol / L sodium hydroxide solution was added dropwise to the prepared mixture to adjust the pH to the range of 9 to 10. A tetramethylphosphoric acid solution (80 wt%, THPC to HAuCl4 molar ratio of 0.7:1) was slowly added to the appropriate dosage required for this reduction reaction. After the addition was completed, the mixture was stirred continuously at room temperature for 24 hours. After the reaction was complete, the reaction system was purified by dialysis using a dialysis bag with a molecular weight cutoff of 3500 Da to remove unreacted raw materials and various impurities, ultimately yielding green-emitting gold mercaptoundecanoate nanoparticles (MUA-AuNPs).

[0031] Example 2: Preparation of MUA-LAuNPs The MUA-AuNPs prepared in Example 1 were prepared into a 0.5 mg / mL MUA-AuNPs solution. 10 mL of the solution was placed in a glass reactor, and the pH of the system was adjusted to 8-9. A 300W xenon lamp equipped with a cutoff filter and meeting the condition of λ>420nm was used to conduct irradiation treatment at room temperature with a light intensity of 250 mW / cm² while stirring. Samples were collected at irradiation times of 10 min, 20 min, 30 min, 60 min, 120 min, 240 min, 360 min, and 600 min. Finally, near-infrared II luminescent mercaptoundecanoic acid ultrasmall gold nanoparticles (MUA-LAuNPs) were obtained.

[0032] For preparation principles, please refer to Figure 1 .

[0033] Example 3: Absorption, excitation, and emission fluorescence spectroscopy of MUA-AuNPs and MUA-LAuNPs 1. Test subjects: MUA-AuNPs prepared in Example 1 (illumination time of 0) and MUA-LAuNPs after illumination treatment for 30, 240 and 600 min in Example 2.

[0034] 2. Test methods: The absorption spectra of the two groups of samples were scanned using a UV-Vis-NIR spectrophotometer with a wavelength range of 200-800 nm. Simultaneously, the excitation and emission spectra of the two groups of samples were measured using a fluorescence spectrophotometer. The characteristic emission peaks of each sample were used as the monitoring signals for the excitation spectra, with a scanning wavelength range of 200-800 nm. The emission spectra were excited at their respective optimal excitation wavelengths, with the scanning wavelengths covering the visible and near-infrared regions. All tests were conducted at room temperature.

[0035] 3. Test results: such as Figure 2 As shown.

[0036] Figure 2The fluorescence spectra, from left to right, show the absorption spectrum (solid line), excitation spectrum (dashed line), and emission spectrum (dotted line) of MUA-AuNPs and MUA-LAuNPs, respectively. The black curve represents MUA-AuNPs, and the red curve represents MUA-LAuNPs after phototreatment. The absorption curves of both types show similar trends, with no obvious surface plasmon resonance absorption peak, indicating that the particle size and structure remained stable before and after photochemical modification, and no aggregation occurred throughout the process. The excitation peaks of the samples are all distributed in the ultraviolet-visible light range, and light in this band can effectively excite the samples to generate fluorescence signals. There is a significant difference in the emission performance of the two types of samples. MUA-AuNPs exhibit a green fluorescence emission signal at 537 nm, while the green emission signal of MUA-LAuNPs completely disappears after phototreatment. Furthermore, MUA-LAuNPs form a double-hump near-infrared emission peak at 940 nm and 990 nm. As the illumination duration increased from 30 min to 600 min, the morphology of the near-infrared emission peak remained unchanged, while the luminescence intensity showed a gradual increase. This fully demonstrates that photochemical treatment can stably modulate the luminescence band of gold nanoparticles from the visible light region to the near-infrared II region.

[0037] Example 4: Imaging and Electrophoretic Gel Experiments Regulated by Photochemical Processing 1. Test subjects: MUA-AuNPs prepared in Example 1 (illumination time of 0) and MUA-LAuNPs prepared in Example 2 with illumination treatment times of 10, 30, 60, 120, 240 and 360 min.

[0038] 2. Test methods: Take each sample solution and observe the solution color under fluorescent light, perform green fluorescence imaging under 365nm ultraviolet light excitation, and perform near-infrared II emission imaging under 808nm near-infrared light excitation; at the same time, prepare 1.5wt% agarose gel, use 0.5×TAE solution as electrophoresis buffer, load the samples at each time point and electrophores them under constant voltage of 110V for 30min. After completion, image and observe the gel under sunlight, 365nm ultraviolet light and 808nm near-infrared light respectively.

[0039] 3. Test results: such as Figure 3 and Figure 4 As shown.

[0040] Figure 3 Images of MUA–AuNPs after different illumination times under fluorescent light, ultraviolet light, and 808nm laser. Figure 4 Electrophoretic gel imaging results of MUA–AuNPs after different illumination treatment times under fluorescent lamp, ultraviolet lamp and 808nm laser.

[0041] In solution imaging, the color of the sample solution under fluorescent lamps gradually deepened from an initial pale yellow to a dark brown as the illumination time increased. Under 365nm UV excitation, the original MUA-AuNPs sample at 0 min exhibited obvious green fluorescence, which gradually weakened and eventually disappeared as the illumination time increased. Under 808nm excitation, the initial sample showed no obvious near-infrared signal, but the luminescence intensity in the near-infrared II region gradually increased as the illumination time increased, visually demonstrating the transformation of particle luminescence performance from the visible light region to the near-infrared II region.

[0042] The electrophoretic imaging results were consistent with those of solution imaging: with prolonged illumination, the green fluorescence of the bands disappeared, while the signal in the near-infrared II region gradually increased. Specifically, the original MUA-AuNPs bands were relatively wide and migrated slowly; after 30 minutes of illumination, the bands narrowed and migrated faster, indicating that the nanoparticle size decreased and the size distribution became more concentrated; further extended illumination resulted in slower band migration, which may be due to photochemical reconstruction of the ligand shell on the particle surface, causing a synergistic change in surface charge state and hydrated particle size, verifying the synchronous regulatory effect of photochemical modification on particle structure and optical properties.

[0043] Example 5: Changes in MUA-AuNPs particle size with illumination time 1. Test objects: MUA-AuNPs (illumination time of 0) prepared in Example 1 and MUA-LAuNPs samples with illumination treatment time of 30 and 240 min in Example 2 are used to characterize the changes in particle morphology, particle size and surface charge characteristics at different illumination stages.

[0044] 2. Test method: Dilute the samples at each time point and drop them onto a carbon film copper grid. After drying at room temperature, observe the particle morphology using a transmission electron microscope (TEM). Randomly select at least 100 particles in the field of view to count the size and analyze the particle size distribution. At the same time, dilute the samples to a suitable concentration and use a dynamic light scattering instrument (DLS) to measure the hydrated particle size and zeta potential. Each group of samples was tested three times.

[0045] 3. Test results: such as Figure 5 As shown. Figure 5 a-5c are TEM images of samples treated with different light exposure times. Figure 5 d represents the particle size distribution as statistically analyzed by TEM. Figure 5 e represents the hydrated particle size distribution. Figure 5 f represents the zeta surface potential result.

[0046] TEM images showed that the samples irradiated for 0, 30, and 240 minutes were all uniformly dispersed spherical nanoparticles with no obvious aggregation. Particle size statistics showed that the average particle size was 2.25 ± 0.39 nm at 0 min of irradiation; after 30 min of irradiation, the average particle size decreased to 1.93 ± 0.16 nm, with a narrower particle size distribution; after 240 min of irradiation, the average particle size further decreased to 1.71 ± 0.30 nm, showing an overall trend of gradually decreasing particle size with increasing irradiation time.

[0047] The hydrated particle size test results are consistent with the statistical trend of TEM. At 0 min of illumination, the hydrated particle size was 12.0 ± 3.0 nm, decreasing to 3.9 ± 1.1 nm at 30 min, and further decreasing to 3.4 ± 1.2 nm at 240 min, confirming the dynamic change in particle size during illumination. Zeta potential test results showed that the zeta potential of all samples was negative, at -55.5 ± 8.2 mV, -62.9 ± 14.3 mV, and -47.6 ± 8.9 mV at 0, 30, and 240 min of illumination, respectively, with absolute values ​​all greater than 40 mV. This indicates that the samples at different illumination stages all possessed good colloidal stability, and the surface negative charge characteristics did not change significantly, verifying the maintenance of particle colloidal stability during photochemical modification. The continuous decreasing trend of the hydrated particle size is basically consistent with the particle size change law reflected by the band migration behavior in the electrophoresis experiment. It should be noted that the phenomenon of slower band migration speed after further extending the illumination time in the electrophoresis experiment is not due to the increase in particle size, but rather to the photochemical reconstruction of the ligand shell on the particle surface, which causes a synergistic change in surface charge state and hydrated particle size. TEM and measured data of hydrated particle size both confirm that the particle size continues to decrease throughout the illumination process, which supports the rationality of the above attribution.

[0048] Example 6: Testing the principle of MUA-AuNPs illumination processing to control the emission wavelength towards the near-infrared II region 1. Test subjects: MUA-AuNPs prepared in Example 1 (illumination time of 0) and MUA-LAuNPs samples with illumination treatment times of 20, 30 and 240 min in Example 2.

[0049] 2. Testing Method: XPS test: After the sample is dropped onto the surface of a silicon wafer and dried, an X-ray photoelectron spectroscopy instrument is used with AlKα rays as the excitation source to perform high-resolution scanning of the Au4f, S2p, and P2p orbitals. The relative contents of elements with different valence states are calculated by peak fitting. EPR test: Add DMPO (capture) to the sample solution separately. OH and O2 - ), TEMP (capture) 1O2) and TEMPO (captures holes h + As a capture agent, two control groups were set up with light exposure of 0 min and 20 min, and the characteristic signals of reactive oxygen species were detected by electron paramagnetic resonance spectroscopy.

[0050] 3. Test results: such as Figure 6-8 As shown, where, Figure 6 a- Figure 6 c shows the high-resolution XPS spectra of MUA-AuNPs before and after 240 min of illumination. Figure 7-Figure 7 c is a high-resolution XPS spectrum of MUA-AuNPs after 30 minutes of illumination. Figure 8 a- Figure 8 d represents the EPR test result.

[0051] XPS results showed that the Au4f orbitals could be fitted with two valence states: Au(0) and Au(I). Before illumination, the proportion of Au(0) was 29.1% and that of Au(I) was 70.9%. After 30 min of illumination, the proportion of Au(0) increased to 53.0% and that of Au(I) decreased to 47.0%. Further XPS testing of MUA-AuNP after 240 min of illumination revealed that the proportion of Au(0) further increased to 76.3%, indicating that the Au(I)-thiol ligands on the particle surface were oxidized and gradually detached during illumination, while the Au(0) core was selectively retained. The spectral changes of the S2p and P2p orbitals also confirmed the oxidation and removal process of the ligand structure.

[0052] EPR test results showed that, before illumination, TEMPO exhibited a characteristic triplet EPR signal in the presence of MUA AuNPs. Once illumination was applied, due to the oxidation product TEMPO… + The TEMPO exhibits diamagnetic properties, and its EPR signal is significantly weakened, thus confirming the photogenerated hole h. + The formation of reactive oxygen species (ROS) was observed. Samples exposed to light for 0 minutes showed no obvious reactive oxygen species signal; after 20 minutes of light exposure, ·OH and... 1 O2 and ·O2 - Clear characteristic EPR signals were observed in both studies, confirming the generation of various reactive oxygen species during the illumination process. Combining XPS and EPR results, it can be seen that the reactive oxygen species and holes generated by illumination... + The Au(I)-thiol ligands on the surface of MUA-AuNPs can be oxidized, causing them to detach from the particle surface while retaining the Au(0) core. This enables dynamic regulation of the chemical state of the particle surface and provides a mechanistic explanation for the changes in optical properties induced by photochemical modification.

[0053] Example 7: Universality Verification Test of Thiol Reagents 1. Test subjects: mercaptohexanoic acid modified gold nanoparticles (MHA-AuNPs) prepared according to the method in Example 1, and MHA-AuNPs samples after being treated with different light exposure times (0, 10, 30, 60, 120, 240 min).

[0054] 2. Testing Methods: Following the synthesis process described in Example 1, MHA-AuNPs were prepared by replacing the ligand with mercaptohexanoic acid (MHA). The MHA-AuNPs solution was irradiated with a xenon lamp at a power of 250 mW / cm², and samples were collected at time points of 10, 30, 60, 120, and 240 min. Two characterization methods were performed on the samples: first, NIR-II fluorescence imaging, observing the near-infrared II fluorescence signal of the samples at different irradiation times under 808 nm laser excitation; second, transmission electron microscopy (TEM) characterization, taking samples before irradiation and 60 min after irradiation, dropping them onto a carbon film copper mesh, drying them, and observing changes in particle morphology and particle size.

[0055] 3. Test results: such as Figure 9 As shown, Figure 9 a represents the NIR-II imaging results of MHA-AuNPs after different illumination times. Figure 9 b and c are TEM images before and after 60 minutes of illumination, respectively.

[0056] MHA-AuNPs initially appear pale red and show no obvious fluorescence signal at room temperature, emitting bright red fluorescence only after being frozen in liquid nitrogen. After phototreatment, NIR-II imaging shows no near-infrared II fluorescence signal at 0 min of illumination. With prolonged illumination, the NIR-II fluorescence signal gradually increases, and clear, bright NIR-II fluorescence is observed after 60 min of illumination, indicating that phototreatment successfully induces near-infrared II luminescence in MHA-AuNPs. TEM characterization results show that the MHA-AuNPs particles are uniformly distributed before illumination, and the particle size significantly decreases after 60 min of illumination, confirming that photolithography leads to a reduction in particle size. These results demonstrate that, similar to MHA-AuNPs, the emission wavelength of MHA-AuNPs can also be modulated towards the near-infrared II region after photochemical treatment according to this invention, proving the good universality of this photo-induced strategy.

[0057] Example 8: Application of MUA-AuNPs in HPC-CA composite films 1. Test object: HPC-CA composite film loaded with MUA-AuNPs. The preparation method of the composite film is as follows: Take 1 mL of the MUA-AuNPs solution prepared in Example 1, add 50 mg / mL hydroxypropyl cellulose (HPC, 30 mL) solution and 45 mg / mL citric acid (CA, 5 mL) solution, stir evenly and pour into a petri dish, and dry in a drying oven at 40℃ for 12 h to obtain a transparent composite film.

[0058] 2. Testing Method: During the information writing stage, a photomask containing "rose" and "panda" patterns was placed on the thin film surface and irradiated with a xenon lamp for 2 hours. During the information erasure stage, the thin film was further irradiated with full-width light without a mask for 2 hours. The information display effect of the thin film was observed under fluorescent light, 365nm ultraviolet light, and 808nm laser excitation.

[0059] 3. Test results: such as Figure 10 As shown, Figure 10 a is a schematic diagram of the information writing and erasing process for the composite film. Figure 10 b shows the thin film imaging results under different lighting conditions.

[0060] Initially, the film is transparent under fluorescent light, exhibits uniform green fluorescence under 365nm UV excitation, and shows no obvious signal under 808nm laser. After mask-based writing, the film shows no significant change under fluorescent light, but red fluorescent "Rose" and "Panda" patterns can be observed under 365nm UV light, and a clear near-infrared II emission pattern is observed under 808nm laser. After full-width illumination erasure, the pattern completely disappears, the film emits uniform light under 808nm laser, and the green fluorescent background under 365nm UV light also changes. These results demonstrate that the MUA-AuNPs-based composite film can achieve dual-mode information writing in both visible and near-infrared II regions through illumination, and supports full-width illumination erasure, showcasing its application potential in the field of erasable and rewritable information storage.

[0061] Compared to existing technologies, this invention breaks through the long-standing technical bias in the field of luminescent gold nanoparticles, transforming ultraviolet / visible light irradiation, which has always been considered a harmful side effect, into a novel and controllable tool for controlling the emission wavelength. Existing technologies generally consider photochemical reactions to only cause photo-aggregation, photobleaching, or luminescence quenching of gold nanoparticles. Therefore, existing photochemical reactions are generally only used for the degradation and removal of targets such as organic pollutants and dyes. This invention, however, takes the opposite approach, applying photochemical etching for the first time to the control of the luminescence performance of ultra-small gold nanoparticles. Without any external etchant or reducing agent, it achieves a super-wide redshift of the emission wavelength from the visible light region to the near-infrared II region simply by controlling the light intensity and time. This solves the technical problem of traditional chemical etching methods being unable to achieve mild, precise, and wide-range luminescence control.

[0062] The regulatory mechanism of this invention is based on the structural characteristics of gold nanoparticles themselves, eliminating the need for the introduction of external selective reagents and offering significant advantages in terms of green efficiency. It utilizes the inherent structural difference between the "Au(0) core / Au(I)-thiol shell" of MUA-AuNPs, and based on the oxidation potential difference between Au(I)-thiol and Au(0), photogenerated free radical species preferentially oxidize the Au(I)-thiol shell with the lower oxidation potential, while completely preserving the Au(0) core. This achieves precise control over the chemical state of the particle surface, without introducing additional impurities or damaging the basic crystal structure of the particles.

[0063] This invention discloses and utilizes a novel photochemical etching mechanism for the first time, achieving precise control over particle size. Unlike conventional chemical etching, which leads to a continuous decrease in particle size until complete dissolution, this invention, through precise control of illumination conditions, enables a unique selective layer-by-layer etching pattern in particle size. The photolithography process effectively removes the Au(I)-thiol shell responsible for green light emission, while precise termination of the etching reaction effectively prevents excessive particle dissolution, ensuring the colloidal stability and luminescent properties of the product. This phenomenon has never been reported in traditional chemical etching systems. The photochemical modification process of this invention is simple to operate, low in cost, and highly versatile. It requires only a conventional UV-Vis light source and can be completed in a room-temperature aqueous solution system, facilitating large-scale production. Furthermore, this control strategy is not strictly limited by the type of ligand, and is applicable not only to gold nanoparticles modified with mercaptoundecanoic acid but also to various water-soluble mercapto ligand-modified gold nanoparticle systems, exhibiting broad process adaptability.

[0064] The near-infrared II luminescent gold nanoparticles prepared by this invention possess excellent properties such as uniform size, good colloidal stability, and high luminescence intensity, and can be directly applied to multiple fields such as bioimaging, optical sensing, and information storage. The erasable and rewritable information storage film prepared based on this material can achieve dual-mode information writing and erasing in both visible light and near-infrared II regions, providing a novel material basis and technical approach for next-generation optical information storage technology.

[0065] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the 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 the present invention also intends to include these modifications and variations.

Claims

1. A method for preparing near-infrared II luminescent ultrasmall gold nanoparticles, characterized in that, Includes the following steps: S1: Preparation of gold nanoparticles with an Au(0) core / Au(I)-thiol shell structure that can emit visible green light; S2: Selective etching of the Au(I)-thiol salt shell of the gold nanoparticles is performed by a controllable photochemical irradiation method to achieve a controllable redshift of the emission band and obtain ultra-small gold nanoparticles that emit light in the near-infrared II region.

2. The method for preparing near-infrared II luminescent ultrasmall gold nanoparticles according to claim 1, characterized in that, Includes the following steps: S1: The gold nanoparticles were synthesized using chloroauric acid as the gold source and tetrahydroxymethylphosphoric chloride as the reducing agent under mercapto ligand modification conditions. S2: Take the gold nanoparticle solution obtained in step S1 and adjust its pH value to 7-13. Use a UV-Vis light source for controlled light modification to obtain the near-infrared II luminescent ultra-small gold nanoparticles.

3. The method for preparing near-infrared II luminescent ultrasmall gold nanoparticles according to claim 2, characterized in that, The S1 step is as follows: at room temperature, the aqueous solution of thiol ligand is added dropwise to the chloroauric acid solution and stirred until the system is colorless and uniform; the pH of the system is adjusted to alkaline, and tetrahydroxymethyl phosphorus chloride solution is added dropwise. The reaction is continuously stirred at room temperature. After the reaction is completed, the impurities are removed by dialysis to obtain gold nanoparticles that emit visible green light.

4. The method for preparing near-infrared II luminescent ultrasmall gold nanoparticles according to claim 3, characterized in that: In step S1, the molar ratio of chloroauric acid to the thiol functional group of the thiol ligand is 1:

3.

5. The method for preparing near-infrared II luminescent ultrasmall gold nanoparticles according to claim 2, characterized in that: In step S2, the pH value is adjusted to 8-9.

6. The method for preparing near-infrared II luminescent ultrasmall gold nanoparticles according to claim 2, characterized in that: The ultraviolet-visible light source in step S2 is any one of a xenon lamp, a mercury lamp, an LED lamp, or a solar simulator; when the ultraviolet-visible light source is a xenon lamp, the light intensity of the xenon lamp is 100-250 mW / cm², and the light reaction time is 0.5-10 h.

7. The method for preparing near-infrared II luminescent ultrasmall gold nanoparticles according to claim 2, characterized in that: The thiol ligand in step S1 is a water-soluble thiol ligand selected from one or more of mercaptopropionic acid, mercaptohexanoic acid, mercaptoundecanoic acid, and glutathione.

8. A type of near-infrared II luminescent ultrasmall gold nanoparticle, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the near-infrared II luminescent ultrasmall gold nanoparticles as described in claim 8 in the fields of bioimaging, sensing, nanomedicine, optoelectronics, and information storage.

10. A rewritable near-infrared optical information storage composite film, characterized in that: The composite film comprises hydroxypropyl cellulose, citric acid, and the near-infrared II luminescent ultrasmall gold nanoparticles as described in claim 8.

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