AuNBPs (at) TiO2-based self-cleaning recyclable SERS (Surface Enhanced Raman Scattering) chip as well as preparation method and application thereof

Abstract

The invention discloses a self-cleaning recyclable SERS (Surface Enhanced Raman Scattering) chip based on AuNBPs (at) TiO2 as well as a preparation method and application of the self-cleaning recyclable SERS chip, and belongs to the technical field of functional nano materials and optical sensing. The SERS chip comprises a substrate and an AuNBPs (at) TiO2 core-shell structure composite material loaded on the substrate, wherein the thickness of a TiO2 shell layer in the AuNBPs (at) TiO2 core-shell structure composite material is 10 to 13 nm. According to the invention, the composite SERS substrate based on the AuNBPs-coated TiO2 core-shell structure is constructed by combining gold nano bipyramid (AuNBPs) with titanium dioxide, and is applied to in-situ monitoring of degradation of organic pollutants, so that the integrated function of pollution detection, efficient degradation and substrate circulation is realized, and a brand new technical scheme is provided for in-situ monitoring and green treatment of the organic pollutants.

Description

Technical Field

[0001] This invention belongs to the field of functional nanomaterials and optical sensing technology, specifically relating to a self-cleaning and recyclable SERS chip based on AuNBPs@TiO2, its preparation method, and its application. Background Technology

[0002] Surface-enhanced Raman scattering (SERS) technology, with its ultra-high detection sensitivity, molecular fingerprinting characteristics, and trace analysis capabilities, has become one of the core technologies for the qualitative and quantitative detection of trace substances in fields such as environmental monitoring, food safety testing, and biomedical analysis. However, traditional SERS substrates generally suffer from the limitation of single-use: on the one hand, the preparation cost of precious metal (such as gold and silver) nanomaterials is high, resulting in high detection costs for single use; on the other hand, the target molecules adsorbed on the substrate surface after detection are difficult to remove effectively, and direct disposal can easily cause environmental pollution, which contradicts the development requirements of green detection technology. To solve these problems, researchers have developed SERS substrates with self-cleaning functions. The core principle is to utilize the photocatalytic properties of semiconductor materials (such as TiO2 and MoS2) to degrade the target molecules adsorbed on the substrate surface under light conditions, thereby achieving the recycling of the substrate. Currently reported SERS substrates with self-cleaning functions are mainly divided into two categories: semiconductor SERS substrates and semiconductor / metal composite SERS substrates. However, most pure semiconductor substrates lack the localized surface plasmon resonance (LSPR) effect, resulting in limited signal enhancement for trace target molecules, making it difficult to meet the needs of low-concentration detection. Secondly, after multiple photocatalytic cycles, metal nanoparticles on some semiconductor / metal composite substrates are prone to aggregation or oxidation, leading to a significant decrease in SERS activity and insufficient cycle stability. Therefore, developing a SERS substrate that combines high sensitivity, excellent cycle stability, and efficient self-cleaning capabilities has become a key breakthrough in propelling SERS technology from laboratory research to practical applications.

[0003] To overcome the sensitivity limitations of pure semiconductor substrates, semiconductor / metal composite SERS substrates have become a research hotspot. These substrates achieve synergistic effects by combining semiconductor metal oxides with noble metal nanomaterials. In recent years, research teams both domestically and internationally have conducted extensive research on semiconductor / metal composite self-cleaning SERS substrates. For example, Li et al. prepared a three-dimensional flower-like MoS2 / Ag@rGO nanocomposite material, which they used as a self-cleaning SERS substrate to detect trace amounts of 17β-estradiol in environmental water. This substrate exhibited a high SERS enhancement factor (EF), a low detection limit, and good linearity, with a self-cleaning cycle count of up to 8 times. Kumar et al. developed an Ag-modified Mn2O3 SERS substrate, which showed ultrasensitive properties for the detection of furazolidone, and after 5 photodegradation cycles, the SERS signal retention rate still reached 92.22%, demonstrating its excellent cycling stability. Despite the progress made in the above research, there is still room for improvement in existing semiconductor / metal composite substrates: for example, the metal nanomaterials (such as silver nanoparticles) used in some substrates are easily oxidized, affecting long-term stability; the photocatalytic degradation efficiency of some substrates still needs to be improved to meet the requirements of rapid recycling; in addition, there is still a lack of research on the integration of in-situ monitoring and efficient degradation of specific highly toxic organic pollutants (such as methylene blue (MB), an organic dye that is widely present in industrial wastewater and difficult to degrade). Summary of the Invention

[0004] To address the problems existing in the prior art, the purpose of this invention is to provide a self-cleaning and recyclable SERS chip based on AuNBPs@TiO2, its preparation method, and its application. This invention combines gold nanobipyramidal (AuNBPs) with titanium dioxide (TiO2) to construct a composite SERS substrate based on the AuNBPs@TiO2 core-shell structure, and applies it to in-situ monitoring of organic pollutant degradation, realizing an integrated function of "pollution detection - efficient degradation - substrate recycling", providing a brand-new technical solution for in-situ monitoring and green treatment of organic pollutants.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention is to provide a self-cleaning, recyclable SERS chip based on AuNBPs@TiO2, comprising a substrate and an AuNBPs@TiO2 core-shell composite material loaded on the substrate; the AuNBPs@TiO2 core-shell composite material includes AuNBPs at the core and a TiO2 shell layer covering the AuNBPs. Preferably, the thickness of the TiO2 shell layer in the AuNBPs@TiO2 core-shell composite material is 10~13 nm.

[0006] A second aspect of the present invention is to provide a method for fabricating a self-cleaning, recyclable SERS chip based on AuNBPs@TiO2, comprising the following steps: Preparation of gold nanobipyramidal structures; In a process where titanium precursor solution and morphology modifier are added to water at 30-40℃ for hydrolysis, NaHCO3 aqueous solution and gold nanoparticles are added sequentially, followed by low-temperature crystallization at 120-140℃, transforming amorphous TiO2 into anatase phase. The resulting precipitate is then separated, washed, and dispersed in a dispersant to obtain AuNBPs@TiO2 dispersion. Preferably, the titanium precursor solution is a TiCl3 solution; the morphology modifier is a solution containing fluoride ions, specifically sodium fluoride or potassium fluoride solution; the volume ratio of titanium precursor solution to NaHCO3 aqueous solution is 10:45; the concentration of NaHCO3 aqueous solution is 1.0 M; and the dispersant is preferably anhydrous ethanol. Based on the shortcomings of existing technologies, such as low crystallinity, poor structural uniformity, and inability to adapt to large-scale SERS chip fabrication, this invention improves the TiO2 forming process to enhance the crystallinity and structural uniformity of TiO2.

[0007] The substrate is pre-treated to be hydrophilic, then immersed in an aqueous solution of polydiallyldimethylammonium chloride (1-2 mg / mL, containing 0.5 M NaCl) for 15-20 minutes, and finally removed and dried. At this time, the surface of the substrate is positively charged due to the adsorption of PDDA. Specifically, the hydrophilic pretreatment is plasma treatment.

[0008] The AuNBPs@TiO2 dispersion is concentrated and then dropped onto a positively charged substrate surface. The reaction time is 30-60 minutes. The negatively charged AuNBPs@TiO2 nanoparticles adsorb onto the positively charged substrate surface via electrostatic attraction. After drying, a self-cleaning, recyclable SERS chip based on AuNBPs@TiO2 is obtained. Preferably, the AuNBPs@TiO2 dispersion is concentrated 10 times; the substrate is a silicon wafer, glass plate, or quartz plate.

[0009] As a preferred technical solution, the low-temperature crystallization time is 50-70 minutes. More preferably, the low-temperature crystallization time is 60 minutes.

[0010] A third aspect of the invention is to provide a self-cleaning, recyclable SERS chip based on AuNBPs@TiO2 for in-situ monitoring of organic pollutant degradation, as described in the first aspect. Preferably, the organic pollutant is an organic dye such as methylene blue (MB), with a detection linear range of 10 nM–1 mM and a limit of detection as low as 3.3 nM. Furthermore, the recyclable SERS chip exhibits excellent reproducibility and stability (RSD <10%). After 12 self-cleaning cycles, the SERS signal intensity still retains 63% of its initial detection value.

[0011] The present invention has the following beneficial effects: This invention constructs an AuNBPs@TiO2 core-shell composite SERS substrate by combining gold nanopile bipyramidal (AuNBPs) with titanium dioxide (TiO2), and applies it to in-situ monitoring of MB degradation. The core advantage of this design lies in fully leveraging the synergistic properties of the two materials: First, AuNBPs possess a unique sharp bipyramidal morphology, and based on the "lightning rod effect," its LSPR effect is significantly higher than that of traditional noble metal nanomaterials such as gold nanorods and gold nanospheres. The tips of the bipyramidal peaks can form extremely strong local electromagnetic fields, greatly increasing the number and density of "hot spots," thus increasing the probability of target molecules entering the "hot spots," thereby achieving multi-order-of-magnitude transitions in the Raman signal and significantly improving detection sensitivity. Second, TiO2, as a classic n-type semiconductor material, has the characteristics of low cost, non-toxicity, mature preparation process, and excellent photocatalytic activity. Under ultraviolet or visible light excitation, photogenerated electrons (e) in its valence band (VB) can... - It will jump to the conduction band (CB), while leaving a photogenerated hole (h) in the VB. + h + H2O molecules or OH adsorbed on the substrate surface can be removed. - Oxidation into a highly oxidizing hydroxyl radical (·OH), e - It can then react with O2 to generate superoxide anion (·O2). - The invention provides a novel SERS chip that combines pollution detection, degradation, and substrate self-cleaning functions. Firstly, the two active free radicals can completely degrade organic pollutants (such as MB) into CO2 and H2O, achieving self-cleaning of the substrate. Secondly, Au's Fermi level is lower than TiO2's conduction band level, allowing photogenerated electrons from TiO2 to efficiently transfer to the Au surface, forming a Schottky barrier. This barrier effectively inhibits the recombination of photogenerated electron-hole pairs, prolongs carrier lifetime, further enhances the photocatalytic activity of TiO2, and strengthens the substrate's self-cleaning efficiency and cycle stability. Attached Figure Description

[0012] Figure 1This is a flowchart illustrating the fabrication process of a self-cleaning, recyclable SERS chip based on AuNBPs@TiO2.

[0013] Figure 2 This is a schematic diagram illustrating the mechanism of photocatalytic degradation of organic pollutants using SERS chips.

[0014] Figure 3 The characterization results of the AuNBPs@TiO2 core-shell composite material are shown, including (a) TEM image of AuNBPs@TiO2; (b) EDS surface distribution image; (c) extinction spectra of AuNBPs and AuNBPs@TiO2; and (d) EDS elemental energy spectrum of AuNBPs@TiO2.

[0015] Figure 4 Figure (a) shows the extinction spectra of AuNBPs@TiO2 at different reaction times; Figure (b) shows the change of characteristic absorbance at 755 nm with reaction time.

[0016] Figure 5 TEM images of AuNBPs@TiO2 with different NaHCO3 addition amounts. (a) 400 μL; (b) 450 μL; (c) 500 μL; (d) 600 μL.

[0017] Figure 6 Figure (a) shows the detection of AuNBPs@TiO2 synthesized from different volumes of NaHCO3. -3 (a) SERS spectrum of M MB; (b) 1624 cm⁻¹ -1 Comparison of SERS intensity at various locations.

[0018] Figure 7 Figure (a) shows the detection of AuNBPs@TiO2 chips at different concentration factors. -3 (a) SERS spectrum of M MB; (b) Graph at 1624 cm⁻¹ -1 Comparison of SERS intensity at characteristic peaks.

[0019] Figure 8 1.0 M MB (without SERS substrate), 10 -3 Raman spectra of M on MB (AuNBPs and AuNBPs@TiO2 SERS substrate).

[0020] Figure 9 Figure (a) shows a heatmap of SERS signals at 30 random sites on the same SERS chip; Figure (b) shows a heatmap at 1624 cm. -1 With 1401 cm -1 Peak intensity and RSD.

[0021] Figure 10(a) The figure shows the SERS spectra of 18 sites on 6 batches of chips; (b) The figure shows the SERS spectra of 1624 cm⁻¹. -1 SERS intensity histogram at location (n = 3).

[0022] Figure 11 Figure (a) shows the SERS spectra of different concentrations of MB; Figure (b) shows the SERS spectra at 1624 cm⁻¹. -1 Linear fitting plot of peak intensity versus logarithm of MB concentration.

[0023] Figure 12 Figure (a) is 10 -5 (a) Real-time SERS spectrum of MMB solution degradation over 90 min; (b) SERS spectrum of MMB solution degradation over 90 min; -1 Bar chart showing the 90-minute change in signal intensity at the location; Figure 13 Middle (a) 10 -4 M MB solution and (b) 10 -6 (c) Real-time SERS spectrum of MB solution on the chip within 90 min; (d) Degradation rate curves of MB at different concentrations and blank samples.

[0024] Figure 14 (a) is the SERS spectrum after 12 cycles; (b) is the spectrum at 1624 cm⁻¹. -1 The graph shows the change in SERS peak intensity with the number of cycles. Detailed Implementation

[0025] The present invention will be further described below with reference to embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0026] In addition, unless otherwise specified, the preparation processes in the following embodiments are all conventional methods in the prior art, and therefore will not be described in detail; all raw materials of the present invention are commercially available products.

[0027] Example A method for fabricating a self-cleaning, recyclable SERS chip based on AuNBPs@TiO2, the fabrication flowchart is shown below. Figure 1 This includes the following steps: 1. Synthesis of gold nanobipyramidal (AuNBPs) Preparation of gold seed solution: 50.0 mM CTAC and 5.0 mM SC were heated and stirred in 27.0 mL of deionized water, then 3.0 mL of HAuCl4·4H2O (2.5 mM) and 0.75 mL of NaBH4 (25.0 mM) were added. The solution was allowed to stand in an oil bath at 80℃ for 90 min; the color of the solution changed from brown to red within a short time.

[0028] Preparation of AuNBPs: The solution was stirred and heated at 55℃ until completely dissolved. Then, 2 mL of HAuCl4 (10 mM), 1 mL of AgNO3 (10 mM), and 2 mL of HCl (1.0 M) were added sequentially to the CTAB solution and mixed thoroughly. 0.8 mL of ascorbic acid (0.1 M) was quickly added, and the solution instantly changed from orange-yellow to transparent. Finally, 2.5 mL of gold seed solution was added, and the solution gradually turned pale purple. After stirring slowly for 5 min, the rotor was removed, and the solution was heated in a water bath at 30℃ overnight to obtain a solution containing AuNBPs. The solution was centrifuged at 6500 rpm for 8 min, the supernatant was discarded, and the precipitate was resuspended in 0.08 M CTAC solution. This centrifugation purification was repeated twice to etch the residual Ag layer on the surface of the AuNBPs. Finally, the purified AuNBPs were stored in 10 mL of CTAC (0.08 M) in the dark. The morphology of the AuNBPs was characterized by TEM, and their extinction spectra were measured using UV-Vis. 2. Synthesis of AuNBPs@TiO2 core-shell composite material Compared to previously reported methods that employ a one-step hydrolysis deposition method, TiO2 prepared by room-temperature hydrolysis is predominantly amorphous, limiting its catalytic activity. While high-temperature annealing can improve crystallinity, it damages the tip structure of AuNBPs, leading to a decline in the LSPR effect. Therefore, TiO2 suffers from drawbacks such as low crystallinity, poor structural uniformity, and inability to be adapted for large-scale SERS chip fabrication. This invention employs a two-step low-temperature hydrothermal-crystallization method: First, low-temperature deposition occurs at 30°C. 100 μL of titanium precursor solution TiCl3 is added to 4 mL of deionized water (18.25 Ω) at 800 rpm. 0.1 mol / L sodium fluoride is added as a morphology modifier to inhibit TiO2 aggregation. The mixture is stirred in the dark for 10 min to promote complete hydrolysis, resulting in a pale purple solution. Under magnetic stirring at 800 rpm, different volumes of 1.0 M NaHCO3 aqueous solution (350 μL, 400 μL, 450 μL, 500 μL, 600 μL) were slowly added dropwise. The solution color gradually deepened to a deep blue. Then, 1 mL of AuNBPs solution (absorbance 5) was quickly added. Next, low-temperature crystallization was performed. The composite material was transferred to a hydrothermal reactor and reacted at 120℃ for 60 min, during which amorphous TiO2 was converted into the anatase phase. After the reaction, the mixed solution was centrifuged at 6500 rpm for 8 min and washed three times. After each centrifugation, the precipitate was resuspended in anhydrous ethanol to remove unreacted TiCl3 and NaHCO3. Finally, the AuNBPs@TiO2 core-shell composite material was stored in 5 mL of anhydrous ethanol in the dark to obtain an AuNBPs@TiO2 dispersion with a concentration of 10 nM. The core-shell structure morphology of the prepared AuNBPs@TiO2 was characterized by TEM, and the absorption spectrum was obtained by UV-Vis spectrophotometry. The core-shell structure morphology of AuNBPs@TiO2 was observed by TEM, the elemental composition and distribution were analyzed by EDS, and its extinction spectrum was measured by UV-Vis.

[0029] 3. Fabrication and performance evaluation of SERS chips Existing technologies produce AuNBPs@TiO2 as dispersed nanoparticles, which require additional coating onto a chip substrate (such as silicon wafers or glass). This coating is prone to detachment, leading to unstable SERS signals. This patent employs a layer-by-layer self-assembly method to fabricate a highly stable SERS chip. First, a 1 cm × 1 cm single-crystal silicon wafer is selected and ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and ultrapure water for 10 min each to remove surface oil and impurities. The wafer is then stored in anhydrous ethanol for later use. Next, the silicon wafer is placed in the reaction chamber of a plasma cleaner, with a power setting of 30 W and a treatment time of 3 minutes. During the treatment, the high-energy oxygen free radicals generated by the plasma oxidize and remove organic matter from the silicon wafer surface, while simultaneously generating a hydrophilic oxide layer and hydroxyl groups on the silicon wafer surface, completing the hydrophilic pretreatment. Then, the wafer is immersed in a polydiallyldimethylammonium chloride (PDDA) aqueous solution (2 mg / mL, containing 0.5 M NaCl) for 20 minutes, removed, rinsed, and dried. At this point, the silicon wafer surface is positively charged due to the adsorption of PDDA. The prepared AuNBPs@TiO2 was concentrated at certain factors (14, 12, 10, 8, 6, 4, and 2 times), and 20 μL of concentrated AuNBPs@TiO2 was added dropwise to the pretreated silicon wafer surface and reacted for 60 minutes. The negatively charged AuNBPs@TiO2 nanoparticles were adsorbed onto the positively charged silicon wafer surface through electrostatic attraction. After rinsing and drying, the "detachment problem" of dispersed particle coating was solved, and the stability of the SERS chip was improved.

[0030] 5 μL of MB solutions of different concentrations were dropped onto the chip surface. After drying at room temperature, the SERS signal was detected using a portable Raman spectrometer. The excitation wavelength was 785 nm, the laser power was 65 mV, the integration time was 2000 ms, and the detection range was 2000–2000 cm⁻¹. -1 For each sample, at least three sites are randomly selected for detection, and the average value is taken as the final signal intensity.

[0031] Application examples Photodegradation monitoring: 20 μL of a 10-fold concentrated AuNBPs@TiO2 dispersion was dropped onto the silicon wafer surface. After drying, 10 μL of 10-fold concentrated AuNBPs@TiO2 dispersion was added. -5 MMB solution was dried, and the detection points were marked and fixed. The SERS spectrum at time t0 was measured. The chip was placed directly below the xenon lamp source (15 cm away, 22.3 mA current), and the SERS spectrum was measured at the same detection point every 15 min until 90 min. The same procedure was used to monitor the blank sample, i.e., only 10 μL of 10... -4 M, 10 -5 M or 10 -6 M MB solution).

[0032] Cyclic monitoring: Add 10 μL of 10 to the SERS substrate. -5The MB solution of M was degraded in 90 min, constituting one cycle. The values ​​of t0 (freshly added MB) and t were recorded after each cycle. 90 The SERS signal intensity (after degradation) was measured, and the cycle was repeated 12 times to examine the self-cleaning cycle performance of the chip.

[0033] Results and Analysis Experimental Principle A combined strategy of "seed growth method for preparing AuNBPs core and hydrolysis method for coating TiO2 shell" was used to synthesize AuNBPs@TiO2 nanocore-shell composite materials. A schematic diagram of the photocatalytic degradation mechanism of organic pollutants in this invention is provided below. Figure 2 The specific reaction mechanism is as follows: (1) Semiconductors generate electron-hole pairs when excited by light: ; (2) Photogenerated electrons are transferred to the metal surface: ; (3) Photogenerated holes are oxidized to generate hydroxyl radicals: ; (4) Degradation of MB by hydroxyl radicals: ; (5) Photogenerated holes directly degrade MB: ; Based on the LSPR effect of AuNBPs and the photocatalytic principle of TiO2, the two work synergistically to achieve in-situ monitoring of the degradation of organic pollutants and enable the self-cleaning and recycling of this composite SERS substrate.

[0034] Characterization of AuNBPs@TiO2 materials To systematically verify the successful synthesis of AuNBPs@TiO2 core-shell composite materials, the AuNBPs@TiO2 core-shell composite materials were analyzed from three dimensions: optical properties, microstructure, and elemental composition using characterization methods such as UV-vis, TEM, and EDS.

[0035] Figure 3Image (a) shows a TEM image of AuNBPs@TiO2, revealing a highly uniform bipyramidal core-shell structure. The AuNBPs core maintains a sharp bipyramidal morphology, while the TiO2 shell uniformly coats the AuNBPs surface without any voids or excessively thick areas. The shell surface is smooth, with no free TiO2 nanoparticles attached, demonstrating the controllability of the coating process. Statistical analysis of over 50 nanoparticles using ImageJ software reveals that the average longitudinal length of the AuNBPs core is 111.1 ± 1 nm, the lateral length is 44.4 ± 2 nm, and the aspect ratio is 2.50. This aspect ratio falls within the optimal LSPR effect range for AuNBPs (2.0–3.0), maximizing the local electromagnetic field intensity at its tip. Meanwhile, the average thickness of the TiO2 shell is 11.1±1 nm. This thickness can protect the AuNBP core from oxidation and aggregation, and also avoid the shell being too thick to hinder MB molecules from approaching the "hot spot" or to prolong the carrier transport path, thus achieving a structural balance between SERS activity and photocatalytic activity. Figure 3 Figure (b) shows the EDS elemental distribution of AuNBPs@TiO2. It can be seen that the Au element is concentrated in a biconical shape, corresponding to the AuNBPs core. The Ti and O elements are uniformly distributed in a ring shape and completely cover the Au element region, which is consistent with the TiO2 shell position observed by TEM, proving the successful construction of the core-shell structure. Figure 3 Figure 3(d) shows the EDS spectrum, which indicates that the material mainly contains three elements: Au (characteristic peak at approximately 2.1 keV), Ti (characteristic peak at approximately 4.5 keV), and O (characteristic peak at approximately 0.5 keV). There are no obvious signals from impurity ions such as Na and Cl, demonstrating the high purity of the material. Combined with elemental quantitative analysis, the atomic ratio of Au, Ti, and O is approximately 1:2.1:4.3, consistent with the theoretical composition of the AuNBPs@TiO2 core-shell structure, further confirming the integrity of the AuNBPs@TiO2 core-shell structure. Figure 3(c) shows the extinction spectra of pure AuNBPs and AuNBPs@TiO2. The characteristic extinction peak of pure AuNBPs is located at 724 nm, corresponding to the LSPR absorption of its bipyramidal structure, while the characteristic extinction peak of AuNBPs@TiO2 is red-shifted to 755 nm, a redshift of 31 nm. This phenomenon stems from the modulation of the dielectric environment of the TiO2 shell: TiO2 is a high dielectric constant material (ε≈80), and after coating, it reduces the oscillation frequency of free electrons on the AuNBPs surface, causing the LSPR absorption peak to shift to the longer wavelength direction; and the redshift amplitude of the extinction peak is positively correlated with the shell thickness. The 31 nm redshift further verifies that the TiO2 shell has been successfully coated, which is consistent with the TEM characterization results.

[0036] Optimization of SERS substrate preparation conditions TiO2 shell thickness optimization The specific reaction equation for the formation of the TiO2 shell by the hydrolysis of TiCl3 is as follows: ; ; TiO2 shell thickness is a key parameter affecting the SERS and photocatalytic performance of the chip. An excessively thin shell cannot effectively achieve photocatalytic self-cleaning and AuNBP core protection, while an excessively thick shell weakens the LSPR effect of AuNBPs and reduces SERS sensitivity. This invention achieves precise control of TiO2 shell thickness by systematically regulating the reaction time and the amount of NaHCO3 added, as detailed below: (1) Effect of reaction time During the low-temperature crystallization process, the reaction time directly determines the extent of the hydrolysis and condensation reaction of the titanium precursor, which in turn affects the formation efficiency and integrity of the TiO2 shell. Figure 4 Figure (a) shows the extinction spectra of AuNBPs@TiO2 at different reaction times (10 ~ 60 min) during low-temperature crystallization. The peak broadening is obvious at 10 min, indicating that the TiO2 shell coating is not uniform. As the reaction time increases, the peak gradually becomes sharper. At 60 min, the peak is the most symmetrical and the peak position is stable at 755 nm, proving that the shell coating is complete. Figure 4 Figure (b) shows the characteristic absorbance at 755 nm as a function of reaction time. The absorbance gradually increases from 10 to 60 min, and then the increase slows down after 60 min (growth rate <5%). This is because the hydrolysis reaction of the titanium precursor continues over time, the amount of TiO2 generated increases, the shell gradually becomes complete, and the light absorption capacity is enhanced. At 60 min, the titanium precursor reaction is basically complete, and the shell reaches a saturated state. Therefore, 60 min is selected as the optimal reaction time to avoid shell defects caused by insufficient reaction or excessively thick shells caused by excessively long reaction.

[0037] (2) Amount of NaHCO3 added NaHCO3 plays a triple role in the preparation of AuNBPs@TiO2 core-shell structures, regulating pH, controlling reaction rate, and stabilizing dispersion. Its addition directly affects the thickness, morphological uniformity, and particle dispersibility of the TiO2 shell, making it a core parameter for precise shell thickness control. As a weakly alkaline substance, NaHCO3 neutralizes the HCl produced by the hydrolysis of TiCl3, stabilizing the system pH within the optimal range of 6.5–7.5. Secondly, by regulating the hydrolysis rate of the titanium precursor through pH control, it avoids excessively rapid hydrolysis leading to TiO2 aggregation and the formation of irregular shells, while excessively slow hydrolysis prolongs the reaction cycle and reduces synthesis efficiency. Simultaneously, the HCO3 produced by the ionization of NaHCO3... - Adsorbed on the surface of AuNBPs, aggregation is inhibited through electrostatic repulsion; HCO3 -It can also react with titanium precursor hydrolysis intermediates (such as Ti(OH)3) + The interaction between the two particles guides TiO2 to grow directionally along the surface of AuNBPs, preventing the formation of free TiO2 particles and ensuring the uniformity of the shell.

[0038] Figure 5 TEM images of AuNBPs@TiO2 with different NaHCO3 addition amounts (400–600 μL). The results show that when the NaHCO3 addition amount is low (400 μL), the TiO2 shell is granular and amorphous, with a thickness of only 2–3 nm. Figure 5 (Figure (a)) This is mainly because insufficient NaHCO3 leads to excessive acidity in the system, resulting in a too-fast hydrolysis rate and preventing uniform coating of TiO2. When the volume of added NaHCO3 increases to 450 μL, the shell gradually becomes continuous and uniform, with a thickness of 10~13 nm. Figure 5 (Figure b) At this point, the pH and hydrolysis rate are optimal, and TiO2 grows directionally along AuNBPs. When the amount of NaHCO3 added increases to 500-600 μL, the shell thickness increases sharply to 60-70 nm. Figure 5 (Figures (c) and (d)) Due to excessive NaHCO3, the pH is too high, which slows down the hydrolysis rate of the titanium precursor, causing TiO2 to accumulate on the shell surface and form an excessively thick structure. An excessively thin and fragmented TiO2 shell will prevent the photocatalytic activity of the nanomaterial from meeting the requirements of subsequent MB degradation experiments, while an excessively thick shell will hinder AuNBPs from exerting their LSPR effect.

[0039] To further quantify the effect of NaHCO3 addition on the SERS performance of the material, a 10-1 ratio was used. -3 MMB was used as a model molecule to investigate the 1624 cm⁻¹ molecule under different addition amounts. -1 SERS signal intensity at (MB molecule C=C skeleton vibration peak) Figure 6 ).from Figure 6 As shown in the Raman spectrum of (a), the characteristic peak Raman signal intensity reaches its maximum when 450 μL of NaHCO3 is added, an increase of 47% compared to 400 μL. When the amount added is further increased to 500 μL, the characteristic peak intensity drops to 72% of that of 450 μL. When the amount is increased to 600 μL, the SERS signal intensity decreases significantly, to only 41% of that of 450 μL. This is mainly because the excessively thick shell hinders the contact between MB molecules and the "hot spot," resulting in a significant attenuation of the SERS enhancement effect. Therefore, the optimal volume of NaHCO3 added is 450 μL.

[0040] Preparation of SERS chip AuNBPs@TiO2 concentration optimization The AuNBPs@TiO2 dispersion was concentrated 2–14 times, and the effect of concentration on the performance of the prepared SERS chip was investigated. The results are shown in [Figure number missing]. Figure 7 As shown in Figure 7(a), with the increase of the AuNBPs@TiO2 concentration factor, the concentration at 1624 cm⁻¹... -1 The SERS intensity initially increases and then decreases, reaching its peak at 10-fold concentration. Figure 7 (Figure b) This may be because at lower concentrations, the spacing between nanoparticles is too large, failing to provide sufficiently dense "hot spots," and the contact probability between the detection molecule MB and the substrate is low, resulting in a weak signal. When the substrate concentration is too high, the nanomaterials excessively aggregate to form large aggregates, disrupting the LSPR effect of individual particles. Therefore, choosing AuNBPs@TiO2, which is concentrated 10 times, to prepare the SERS chip can achieve a balance between "hot spot" density and particle dispersion.

[0041] SERS chip performance evaluation SERS performance comparison To verify the feasibility and superiority of AuNBPs@TiO2 as a material for preparing SERS chips, three sets of control experiments were set up: no SERS substrate, pure AuNBPs as the SERS substrate, and AuNBPs@TiO2 as the SERS substrate. SERS detection was performed on MB solutions in each experiment, and the signal enhancement effect was compared and analyzed. Figure 8 Experimental results showed that, even with MB solutions at concentrations as high as 1.0 M, the 1624 cm⁻¹ was not detected in the absence of a SERS substrate. -1 The characteristic peaks at this point are almost invisible, likely because the Raman scattering cross-section of the MB molecule is extremely small, making its signal undetectable by conventional Raman spectroscopy. However, with the help of a SERS chip, even when the detection concentration is reduced to 10... -3 The characteristic peak signals of M and MB were also significantly enhanced, and the enhancement effect of AuNBPs@TiO2 substrate was significantly better than that of pure AuNBPs substrate (1624 cm⁻¹). -1 The peak intensity is increased by approximately 35%. This advantage stems from the noble metal-semiconductor synergistic enhancement mechanism of AuNBPs@TiO2. On one hand, the LSPR effect of the AuNBPs core provides the basic electromagnetic enhancement (EM) for SERS enhancement; on the other hand, the charge transfer (CT) effect between the TiO2 shell and AuNBPs can further enhance the Raman signal of MB molecules. In addition, the TiO2 shell can effectively suppress the aggregation of pure AuNBPs during the detection process. The above results fully demonstrate that AuNBPs@TiO2 has significant feasibility and superiority as a SERS substrate, and is suitable for high-sensitivity detection of organic pollutants.

[0042] Stability and reproducibility To investigate the stability of the SERS substrate, 30 detection sites were randomly selected on the same AuNBPs@TiO2 SERS chip for SERS spectrum acquisition. The quantification stability was calculated using thermogram analysis and relative standard deviation (RSD). Figure 9 ).from Figure 9 As shown in the heatmap in Figure (a), the color bands at the same Raman shift at the 30 sites exhibit high uniformity with no significant differences in brightness, directly reflecting the uniformity of the "hot spots" distribution on the substrate surface. Further analysis at 1624 cm⁻¹... -1 and 1401 cm -1 The calculated RSDs of the characteristic peak intensities at the (CN vibrational peak of the MB molecule) are 8.24% and 7.97%, respectively, both less than 10%. Figure 9 (See Figure (b)). This value is far below the industry-recognized stable substrate RSD threshold (<15%), demonstrating that the chip has excellent stability in a single detection and can avoid detection errors caused by uneven distribution of "hot spots".

[0043] To examine the reproducibility of the substrate, six different batches of AuNBPs@TiO2 SERS chips were selected. Three sites were randomly selected from each batch for SERS spectral acquisition. Reproducibility was quantified by spectral consistency and RSD values. Figure 10 ).from Figure 10 As shown in the overlay of 18 SERS spectra in Figure (a), the spectral peaks of different batches of substrates highly overlap, with a peak shape of 1624 cm⁻¹. -1 1401 cm -1 The positions of the characteristic peaks did not shift significantly, with only slight fluctuations in peak intensity, indicating that the "hotspot" distribution pattern of the matrix across batches is consistent with the enhancement mechanism. Further analysis of the 1624 cm⁻¹ peak... -1 The RSD value was calculated based on the characteristic peak intensity. The results showed that the RSD of the six batches of substrates was 5.86%. Figure 10 (See Figure (b)). The results show that the preparation process has excellent controllability and repeatability, and can stably produce SERS substrates with consistent performance, thus ensuring the accuracy of subsequent detection results.

[0044] Sensitivity Using MB as a model molecule, the sensitivity and quantitative analysis capability of the SERS chip were investigated, and the results are as follows: Figure 11 As shown.

[0045] Figure 11 Figure (a) shows different concentrations of MB (10) -8 M-10 -3 The SERS spectrum of M) shows that as the MB concentration gradually increases, the value at 1624 cm⁻¹... -1 The intensity of the characteristic peak gradually increases, even at concentrations as low as 10.-8 At 10 nM, the characteristic peak remains clearly discernible with no significant baseline interference, indicating that the chip has a high signal capture capability for MB molecules. To further verify the feasibility of quantitative analysis, a 10 nM peak was selected. -8 M-10 -3 MB solutions within the M concentration range, at 1624 cm⁻¹ -1 A linear fit was performed on the peak intensity (y) against the logarithm of the MB concentration (x, expressed as lgC), yielding the linear equation y = 1960.37x + 15485.7, with a correlation coefficient R0. 2 =0.9802 (Figure 11(b)). The limit of detection (LOD) was calculated according to the 3σ rule (σ is the standard deviation of the signal in the blank sample). The results showed that the LOD of the chip for MB was 3.3 nM and the linear detection range was 10 nM-1 mM, which is lower than that of the previously reported Au-MoS2 (LOD=10 nM) and Ag / Mn2O3 (LOD=5 nM) substrates, proving that the chip can meet the requirements for accurate quantitative detection of trace MB in the environment.

[0046] In-situ monitoring of MB photodegradation Based on the synergistic characteristics of SERS and photocatalytic activity of AuNBPs@TiO2, in-situ real-time monitoring of the MB photodegradation process is achieved, such as... Figure 12 and Figure 13 . Figure 12 Figure (a) is 10 -5 MMB solution was dropped onto the dry SERS chip surface, and the real-time SERS spectrum was obtained within 90 minutes under xenon lamp irradiation. As the irradiation time increased, the SERS spectrum at 1624 cm⁻¹... -1 The characteristic peak intensity decreased in a stepwise manner; Figure 12(b) shows the peak intensity change curve over time. The intensity decreased rapidly within 0-30 min, dropping to 52% of the initial value, then to 21% at 60 min, and reaching its lowest point at 90 min, only 4% of the initial value. This indicates that MB molecules continued to degrade on the chip surface, and the degradation was basically completed at 90 min. This kinetic trend stems from the photocatalytic reaction mechanism: the initial MB concentration is high, reacting with ·OH and ·O2. - The reaction probability is high and the degradation rate is fast; in the later stage, as the MB concentration decreases, the reaction probability decreases and the rate slows down.

[0047] To verify the substrate's suitability for degradation of different concentrations of MB, 10... -4 M, 10 -5 M, 10 -6 MMB solution and blank sample (without substrate) were subjected to a 90-minute photodegradation experiment, and the change in degradation rate was monitored. Figure 13 ).from Figure 13The SERS spectra of (a) to (b) show that 10 -4 MMB still showed a weak characteristic peak at 90 min, indicating that degradation was incomplete; while at 10 -6 The characteristic peak of MMB completely disappeared at 60 min, indicating that degradation was completed prematurely. Figure 13 (c) The degradation rate curves of MB at different concentrations show that 10 -4 MMB achieved a degradation rate of 95.96% in 90 minutes, 10 -5 MMB achieved a degradation rate of 98.96% in 90 minutes, 10 -6 The degradation rate of MB reached 100% after 60 minutes and remained completely degraded after 90 minutes, while the degradation rate of the blank sample was only 12.3% after 90 minutes. These results confirm that the SERS chip has highly efficient photocatalytic degradation capabilities, and the degradation efficiency increases with decreasing MB concentration. This may be because at lower concentrations, the contact probability between MB molecules and the active sites on the chip surface is higher, and the interaction between ·OH and ·O2... - It can effectively attack MB molecules, accelerating the degradation process. Simultaneously, the dynamic changes in SERS signal intensity show a good correlation with the MB degradation rate, proving that the substrate can serve as a "real-time sensor" to accurately track changes in pollutant concentration during photodegradation.

[0048] Self-cleaning cycle performance test Self-cleaning recycling capability is a key indicator for evaluating the greenness and economy of SERS substrates. This study evaluated the recycling performance of SERS chips through a "MB adsorption-photodegradation-re-adsorption" cycle experiment. Figure 14 A cycle of 90 minutes was used (i.e., MB was added at t0, and t...). 90 Degradation is completed at a certain time (record the time t0 and t1 of each cycle). 90 The SERS spectrum was obtained, and the value at t0 (1624 cm⁻¹) was calculated. -1 The attenuation rate of the peak intensity. From Figure 14 As can be seen in Figure (a), the characteristic peak at time t0 within each cycle is clearly visible. 90 The characteristic peaks almost completely disappeared, indicating that MB can be completely degraded after each cycle, leaving no residual contaminants on the chip surface and achieving effective self-cleaning. Figure 14Figure (b) shows the relationship between the number of cycles and the SERS intensity. After 8 cycles, the SERS intensity of the chip remained at 89% of its initial intensity, and after 12 cycles, it still remained at 70%, with a photocatalytic degradation rate still exceeding 90%. After multiple photocatalytic cycles, a small amount of TiO2 shell peeled off slightly, leading to the exposure and oxidation of some AuNBPs, and a slight reduction in the number of "hot spots." However, even after 12 cycles, the chip maintained good SERS and photocatalytic activity, demonstrating that the AuNBPs@TiO2 substrate has excellent self-cleaning stability, which can significantly reduce detection costs, reduce secondary pollution, and meet the requirements of green and environmentally friendly detection.

[0049] This invention successfully fabricated a self-cleaning, recyclable SERS chip based on an AuNBPs@TiO2 core-shell structure and achieved in-situ monitoring of organic pollutant degradation. We employed a combined strategy of "seed growth method for AuNBPs core preparation - hydrolysis method for TiO2 shell coating" to successfully synthesize AuNBPs@TiO2 nano-core-shell composite materials with regular morphology and uniform size. Through systematic optimization of reaction parameters, 60 min was determined as the optimal reaction time and 450 μL as the optimal amount of NaHCO3 added, allowing precise control of the TiO2 shell thickness to approximately 10 nm. This core-shell structure design achieves a synergistic effect between the LSPR effect of AuNBPs and the photocatalytic performance of TiO2, effectively solving the problem of balancing SERS activity and recyclability in traditional composite substrates. After further optimization of material concentration, the prepared AuNBPs@TiO2 SERS chip exhibited excellent sensitivity, stability, and reproducibility, with a detection linear range of 10 nM to 1 mM for megohmmeter (MB) and a low LOD of 3.3 nM. Meanwhile, the chip exhibits outstanding stability and reproducibility; the RSD of detection at 30 random sites on the same chip and at 6 different batches of chips is less than 10%, ensuring the accuracy and consistency of the detection results. Furthermore, the chip can track the dynamics of MB photodegradation in real time in situ, and under xenon lamp irradiation, it can effectively detect 10... -4 M, 10 -5 M, 10 -6 The degradation rates of MMB solutions reached 95.96%, 98.96%, and 100% after 90 min, respectively. Simultaneously, the chip exhibited excellent self-cleaning and recycling performance; after 12 cycles, the SERS signal intensity remained at 70% of its initial value, and the photocatalytic degradation rate remained above 90%, significantly reducing detection costs while avoiding secondary pollution. In summary, the self-cleaning and recyclable SERS chip constructed in this study achieves an integrated function of "trace detection - high-efficiency degradation - recycling," providing a green, efficient, and stable analytical method for in-situ monitoring of the degradation of organic pollutants such as MB. It has significant practical application value and promotion potential in fields such as environmental pollutant analysis and food safety testing.

[0050] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. AuNBPs@TiO2-based self-cleaning recyclable SERS chip, characterized in that, The AuNBPs@TiO2 core-shell structure composite material comprises AuNBPs at the core and a TiO2 shell layer covering the AuNBPs.

2. The AuNBPs@TiO2-based self-cleaning recyclable SERS chip according to claim 1, wherein, The thickness of the TiO2 shell layer in the AuNBPs@TiO2 core-shell structure composite material is 10-13 nm.

3. The preparation method of the AuNBPs@TiO2-based self-cleaning recyclable SERS chip according to claim 1 or 2, characterized in that, The method comprises the following steps: Preparation of gold nanobipyramids; At a temperature of 30-40°C, a titanium precursor solution and a morphology control agent are added to water to perform a hydrolysis reaction, then an aqueous NaHCO3 solution and the gold nanobipyramids are sequentially added, low-temperature crystallization is performed at a temperature of 120-140°C, amorphous TiO2 is converted into an anatase phase, and finally the obtained precipitate is separated, washed, and dispersed in a dispersant to obtain an AuNBPs@TiO2 dispersion liquid; The substrate is subjected to hydrophilization pretreatment, then immersed in an aqueous polydiallyldimethylammonium chloride solution, and finally taken out and dried to obtain a substrate with positive charges; The AuNBPs@TiO2 dispersion liquid is concentrated and then added dropwise to the surface of the substrate with positive charges, and after drying, an AuNBPs@TiO2-based self-cleaning recyclable SERS chip is obtained.

4. The production method according to claim 3, characterized by, The titanium precursor solution is a TiCl3 solution.

5. The preparation method according to claim 4, characterized in that, The volume ratio of the titanium precursor solution to the aqueous NaHCO3 solution is 10:45, and the concentration of the aqueous NaHCO3 solution is 1.0 M.

6. The preparation method according to claim 3, characterized in that, The low-temperature crystallization time is 50-70 min.

7. The production method according to claim 6, wherein The low-temperature crystallization time is 60 min.

8. The preparation method according to claim 3, characterized in that, The morphology control agent is a solution containing fluoride ions.

9. The preparation method according to claim 3, characterized in that, The substrate is a silicon wafer, a glass wafer or a quartz wafer.

10. An AuNBPs@TiO2-based self-cleaning recyclable SERS chip for in-situ monitoring of organic contaminant degradation according to claim 1 or 2.

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