An enhanced Raman scattering substrate for chiral molecule detection and its preparation method

Abstract

This invention discloses an enhanced Raman scattering (SERS) substrate and its preparation method for chiral molecule detection, relating to the fields of spectroscopic analysis and chiral recognition technology. By inducing the formation of a helical chiral gold-silver alloy layer on a gold nanorod core with chiral cysteine ​​followed by encapsulation of a zirconium-based metal-organic framework, the synthesized chiral gold rod@MOF material not only exhibits excellent LPSR effect and chiral electromagnetic field, but the MOF layer on its surface can also effectively adsorb analyte molecules into the plasma "hot spot" region, making it a Raman substrate with superior SERS performance. This composite material, through the dual effects of molecular enrichment and electromagnetic enhancement, enables direct differentiation of enantiomers by SERS intensity without the need for labeling or catalytic conversion.

Description

Technical Field

[0001] This invention relates to the fields of spectral analysis and chiral recognition technology, specifically to an enhanced Raman scattering substrate for chiral molecule detection and its preparation method. Background Technology

[0002] The identification and differentiation of chiral enantiomers are crucial in both chemistry and agriculture. Circular dichroism (CD), chromatography, mass spectrometry, nuclear magnetic resonance, and Raman optical activity (ROA) can all be used to identify chiral molecules. However, these methods either rely on the polarity and chromophore of the chiral molecule or on specific chiral probes, which are not conducive to widespread application.

[0003] Raman optical activity (ROA) is a general molecular characterization technique that relies on the vibrational jumping of molecular bonds and shows great promise in the field of enantiomeric detection. However, ROA detection requires stringent conditions, complex instruments, is time-consuming, and produces weak signals, thus necessitating a more general and rapid chiral molecule identification technique. Surface-enhanced Raman scattering (SERS) has been proven to be a feasible method for enantiomeric identification. Localized surface plasmon resonance (LSPR) of plasmonic nanostructures leads to a significant enhancement of the local electric field. The SERS enhancement factor is approximately proportional to the fourth power of the local electric field enhancement. Significant electric field enhancement occurs at the gaps between plasmonic nanoparticles, forming plasmonic "hot spots" that further amplify the SERS enhancement effect.

[0004] Using this method, metallic materials with chiral optical signals are used as Raman substrates. Under linear light irradiation, the SERS signals of chiral Raman molecules with the same chirality as the Raman substrate are significantly enhanced, while those with different chirality are weakened. For example, Shunai Che's group prepared a chiral gold nanofilm, which, when used as a Raman substrate on a conventional spectrometer, enabled the identification of more than one hundred chiral amino acids (regardless of their polarity, size, or chromophore content), demonstrating the universality of SERS in identifying chiral enantiomers. Wenxin Niu's group has demonstrated that using synthesized chiral gold nanocrystals, the chiral electromagnetic field of the chiral gold nanocrystals can be excited by linearly polarized light, effectively distinguishing chiral molecules such as L / D phenylalanine, with a SERS ratio difference of approximately six times. Other metallic structures, such as gold nanostars and nanotriangles, have also been shown to be usable as Raman substrates for differential detection of different chiral enantiomers. However, despite the strong LSPR effect of these single metal nanomaterials, there are challenges in controlling the adsorption of analyte molecules (especially those without metal-specific binding groups) on metal surfaces during SERS applications. Furthermore, commonly used colloidal noble metal nanoparticles have high surface energy and are prone to aggregation, leading to LSPR decay and thus reducing SERS activity. Therefore, the lowest detectable concentration of chiral molecules is approximately 10⁻⁶. -5 M. To prevent the aggregation of colloidal noble metal nanoparticles, many stable materials (such as polymers, transition metals, etc.) have been proposed as protective shells. Such core-shell nanostructures can improve metal-analyte interactions by concentrating the target analyte near the surface of the plasmon nanostructure, thereby generating stronger, more repeatable, and more stable SERS signals.

[0005] Therefore, developing core@shell nanostructured SERS substrates capable of concentrating target molecules into plasma hotspots is highly desirable, but remains a challenge. Summary of the Invention

[0006] The purpose of this invention is to provide an enhanced Raman scattering substrate for chiral molecule detection and its preparation method, which solves the above problems. The method uses a zirconium-based metal-organic framework (MOF) to encapsulate chiral gold nanorods. The synthesized chiral gold rod@MOF material not only has excellent LPSR effect and chiral electromagnetic field, but the MOF layer on the surface can also effectively adsorb the analyte molecules into the plasma "hot spot" region, making it a Raman substrate with excellent SERS performance.

[0007] This invention discloses a method for preparing an enhanced Raman scattering substrate for chiral molecule detection, which involves inducing the formation of a helical chiral gold-silver alloy layer in a gold nanorod core using chiral cysteine ​​followed by encapsulation of a zirconium-based metal-organic framework, comprising the following steps:

[0008] Step (1) Preparation of Chiral-AuNR

[0009] After centrifuging the gold nanorod solution to remove the supernatant, it was dispersed in a hexadecyltrimethylammonium bromide solution. Then, chiral cysteine ​​molecules were added, and the mixture was stirred at room temperature for 3 hours. Silver nitrate solution was added first, followed by chloroauric acid. After stirring evenly, ascorbic acid was added, and the mixture was stirred evenly. The mixture was then heated at 70°C for 1 hour and centrifuged twice at 5000 r / min for 6 min to purify the product Chiral-AuNR.

[0010] Step (2) Surface modification of Chiral-AuNR

[0011] After centrifugation of the Chiral-AuNR solution, it was resuspended in deionized water. Hexadecyltrimethylammonium bromide and methoxy polyethylene glycol mercapto were added, and the mixture was stirred overnight. After centrifugation, it was resuspended in anhydrous ethanol, and then methoxy polyethylene glycol mercapto was added. The mixture was stirred overnight again. The product was washed with ethanol and resuspended in ethanol or DMF for later use.

[0012] Step (3) Prepare zirconium-based metal node powder;

[0013] Step (4) The zirconium-based metal node powder is placed in a mixed solution of surface-modified Chiral-AuNR solution, DMF and acetic acid, and H4TBAPy solution is added dropwise to form a metal-organic framework structure. The mixture is washed, dried and centrifuged to obtain the Chiral-AuNR@Zr-MOF composite material.

[0014] Preferably, in step (1), the chiral cysteine ​​molecule is L-cysteine ​​or D-cysteine;

[0015] The concentration of the gold nanorod solution was 0.02 mg / mL. The molar ratio of the gold nanorod solution, hexadecyltrimethylammonium bromide solution, and chiral cysteine ​​molecules was 0.01 mg: 92 mol: 0.6 mol. The volume ratio of the gold nanorod solution, silver nitrate solution, chloroauric acid solution, and ascorbic acid was 10:0.07:0.26:0.2.

[0016] Preferably, the volume ratio of Chiral-AuNR to methoxy polyethylene glycol mercapto is 10:1.

[0017] Preferably, in step (4), 36.4 mg of zirconium-based metal node powder is first dissolved in 7.5 mL of LDM solution. The ratio of this solution to the surface-modified Chiral-AuNR solution is 7.5:0.3. The amount of H4TBAPy solution added is 0.1~0.8 mL, and the dropping rate is 0.05 mL / min.

[0018] The present invention also provides an enhanced Raman scattering substrate for chiral molecule detection prepared by the above-described preparation method. The enhanced Raman scattering substrate has a chiral gold nanorod as the core and a Zr-MOF as the shell. The chiral gold nanorod is a helical chiral gold rod with a gold-silver alloy coating on its surface. The smoothness and depth of the spiral on the surface of the chiral gold rod can be changed by changing the gold-silver alloy ratio.

[0019] Preferably, it has excellent LPSR effect and chiral electromagnetic field, and its optical activity corresponds to the chiral nature of chiral cysteine.

[0020] Preferably, the MOF type in the enhanced Raman scattering substrate is NU-901, and the thickness of the Zr-MOF is 2-90 nm.

[0021] This enhanced Raman scattering substrate exhibits excellent ERS performance, enabling the differential detection of enantiomers with different chiralities and distinguishing enantiomers based on differences in Raman signals.

[0022] Preferably, the Chiral-AuNR@Zr-MOF solution is mixed with amino acid molecules and left to stand overnight. Then, 20 μL of the mixed solution is dropped onto a clean silicon wafer. After drying, it is placed in a Raman spectrometer and collected under 532 nm laser excitation. The typical integration time is 10 seconds, and the excitation power is maintained at 0.1 mW.

[0023] Therefore, the present invention employs the above-described enhanced Raman scattering substrate and preparation method for chiral molecule detection, which has the following beneficial effects:

[0024] (1) Achieving a synergistic breakthrough in chiral signals and SERS performance

[0025] This invention successfully constructed a Chiral-AuNR@Zr-MOF core-shell material with an tunable Zr-MOF shell (5-90 nm) using a simple room-temperature assembly process, achieving an organic integration of chiral optical activity and surface-enhanced Raman scattering (SERS) performance. Its core innovation lies in simultaneously addressing the dual challenges of low chiral recognition sensitivity and poor molecular enrichment efficiency through three-dimensional structural design: First, L / D-cysteine-modified gold nanorods are used as the core, forming a helical chiral gold-silver layer during alloy growth, endowing the material with intrinsic circular dichroism signals and laying the structural foundation for chiral difference detection; Second, by precisely controlling the MOF shell thickness, it was found that when the shell is thinned to 5 nm, the material exposes more plasmon "hot spots" and generates a strong local electric field, significantly improving SERS activity. At this point, the MOF nanopores can still efficiently enrich target molecules into the hot spot region, breaking through the bottleneck of weak adsorption capacity of traditional chiral substrates. Performance quantitative verification shows that this design pushes Raman detection sensitivity to 10. -9The M level, and exhibits a Raman signal difference of up to 4 times for D / L-chiral molecules, compared to traditional circular dichroism spectroscopy (sensitivity 10). -9 This approach improves upon chiral detection by two orders of magnitude while avoiding complex enzymatic reactions or chromatographic separation steps. This logical chain design, from chiral structure creation to MOF thin-shell optimization of electric field and enrichment, provides a novel material solution for highly sensitive and specific chiral detection.

[0026] (2) The MOF-chiral plasma synergistic mechanism promotes the upgrading of practical applications

[0027] The core value of Chiral-AuNR@Zr-MOF lies in its pioneering achievement of overcoming key technological bottlenecks in in-situ recognition and signal release of chiral molecules through the synergistic effect of porous MOFs and chiral plasmons. Its dual-functional synergistic mechanism manifests in two ways: firstly, the Zr-MOF shell selectively enriches chiral molecules onto the gold rod surface due to its high specific surface area and uniform pore size; secondly, the 5nm thin shell ensures that molecules enter the strong electromagnetic field range of the helical chiral alloy layer, translating chiral configuration differences into measurable Raman signal intensity differences (4-fold). This dual effect of molecular enrichment and electromagnetic enhancement enables direct differentiation of enantiomers through SERS intensity, without the need for labeling or catalytic conversion. This design not only simplifies the detection process but also extends chiral analysis from laboratory research to industrial applications such as the detection of chiral impurities in food and pharmaceuticals, providing a universally applicable technological platform for the rapid screening of chiral substances.

[0028] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the preparation of an enhanced Raman scattering substrate for chiral molecule detection.

[0030] Figure 2 TEM image of the gold nanorods prepared in Example 1;

[0031] Figure 3 TEM image of L-AuNR prepared in Example 2;

[0032] Figure 4 TEM image of D-AuNR prepared in Example 3;

[0033] Figure 5The images shown are TEM images of the products prepared in Examples 6 and 7. Specifically, a is a TEM image of the product prepared in Example 7 with 0.7 mL of H4TBAPy solution added; b is a TEM image of the product prepared in Example 7 with 0.6 mL of H4TBAPy solution added; c is a TEM image of the product prepared in Example 7 with 0.5 mL of H4TBAPy solution added; d is a TEM image of the product prepared in Example 7 with 0.4 mL of H4TBAPy solution added; e is a TEM image of the product prepared in Example 7 with 0.3 mL of H4TBAPy solution added; and f is a TEM image of the product prepared in Example 6.

[0034] Figure 6 Normalized spectra of the products prepared in Examples 1, 2, 3, 6, and 8 are shown, where a is the normalized spectrum of Examples 1, 2, and 6, and b is the normalized spectrum of Examples 1, 3, and 8.

[0035] Figure 7 The CD spectra of the products prepared in Examples 1, 2, 3, 6 and 8 are shown, where a is the CD spectrum of Examples 1, 2 and 6, and b is the CD spectrum of Examples 1, 3 and 8.

[0036] Figure 8 Raman spectra of L / D-Phe molecules detected using AuNR as the Raman substrate;

[0037] Figure 9 Raman spectra of L / D-Phe molecules detected using L-AuNR as the Raman substrate;

[0038] Figure 10 Raman spectra of L / D-Phe molecules detected using D-AuNR as the Raman substrate;

[0039] Figure 11 The image shows the Raman spectrum of L / D-Phe molecules detected using L-AuNR@Zr-MOF as the Raman substrate, where a is 10. -5 ~10 -9 Raman spectrum of M L-Phe on L-AuNR@Zr-MOF (5 nm), b=10 -5 ~10 -9 Raman spectra of M's D-Phe on L-AuNR@Zr-MOF (5 nm);

[0040] Figure 12 The image shows the Raman spectrum of L / D-Phe molecules detected using D-AuNR@Zr-MOF as a Raman substrate, where a is 10. -5 ~10 -9Raman spectrum of M's D-Phe on D-AuNR@Zr-MOF (5 nm), b=10 -5 ~10 -9 Raman spectra of M's L-Phe on D-AuNR@Zr-MOF (5 nm);

[0041] Figure 13 This image shows the Raman spectra of L-Phe molecules detected when L-AuNR@Zr-MOF with different Zr-MOF thicknesses were used as Raman substrates. Here, a represents the enhancement of L-phenylalanine molecules (10) when L-AuNR@Zr-MOF with Zr-MOF thicknesses of 40 nm, 70 nm, and 90 nm were used as Raman substrates. -6 Raman spectra of M), b is the L-AuNR@Zr-MOF-enhanced L-phenylalanine molecules with Zr-MOF thicknesses of 5 nm, 15 nm and 30 nm (10 -6 Raman spectrum of M). Detailed Implementation

[0042] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0043] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. These other embodiments are also covered within the scope of protection of this invention.

[0044] like Figure 1 As shown, this invention discloses a method for preparing an enhanced Raman scattering substrate for chiral molecule detection. The method involves inducing the formation of a helical chiral gold-silver alloy layer on a gold nanorod core using chiral cysteine, followed by encapsulation of a zirconium-based metal-organic framework. The method includes the following steps:

[0045] Step (1) Preparation of Chiral-AuNR

[0046] After centrifuging the gold nanorod solution to remove the supernatant, it was dispersed in a hexadecyltrimethylammonium bromide solution. Then, chiral cysteine ​​molecules were added, and the mixture was stirred at room temperature for 3 hours. Silver nitrate solution was added first, followed by chloroauric acid. After stirring evenly, ascorbic acid was added, and the mixture was stirred evenly. The mixture was then heated at 70°C for 1 hour and centrifuged twice at 5000 r / min for 6 minutes to purify the product Chiral-AuNR.

[0047] Step (2) Surface modification of Chiral-AuNR

[0048] After centrifugation of the Chiral-AuNR solution, it was resuspended in deionized water. Hexadecyltrimethylammonium bromide and methoxy polyethylene glycol mercapto were added, and the mixture was stirred overnight. After centrifugation, it was resuspended in anhydrous ethanol, and then methoxy polyethylene glycol mercapto was added. The mixture was stirred overnight again. The product was washed with ethanol and resuspended in ethanol or DMF for later use.

[0049] Step (3) Preparation of zirconium-based metal node powder

[0050] Zirconium n-butoxide and benzoic acid were added to 1-propanol, stirred, and sonicated for 10–20 minutes. The mixture was then heated and stirred for 12 hours, resulting in layering: a clear solution on top and a white precipitate on the bottom. Excess 1-propanol was removed by vacuum heating to obtain a white solid. After thorough washing with 1-propanol, the solid was vacuum dried at room temperature to obtain zirconium-based metal node powder.

[0051] Step (4) The zirconium-based metal node powder is placed in a mixed solution of surface-modified Chiral-AuNR solution, DMF and acetic acid, and H4TBAPy solution is added dropwise to form a metal-organic framework structure. The mixture is washed, dried and centrifuged to obtain the Chiral-AuNR@Zr-MOF composite material.

[0052] In step (1), the chiral cysteine ​​molecule is either L-cysteine ​​or D-cysteine, which enhances the optical activity of the Raman scattering substrate and corresponds to the chiral nature of the chiral cysteine.

[0053] The concentration of the gold nanorod solution was 0.02 mg / mL. The molar ratio of the gold nanorod solution, hexadecyltrimethylammonium bromide solution, and chiral cysteine ​​molecules was 0.01 mg: 92 mol: 0.6 mol. The volume ratio of the gold nanorod solution, silver nitrate solution, chloroauric acid solution, and ascorbic acid was 10:0.26:0.07:0.2.

[0054] The volume ratio of Chiral-AuNR to methoxy polyethylene glycol mercapto is 10:1.

[0055] In step (4), 36.4 mg of zirconium-based metal node powder is first dissolved in 7.5 mL of LDM solution. The ratio of this solution to the surface-modified Chiral-AuNR solution is 7.5:0.3. The amount of H4TBAPy solution added is 0.1~0.8 mL, and the dropping rate is 0.05 mL / min.

[0056] This invention also provides an enhanced Raman scattering substrate for chiral molecule detection, prepared using the above-described method. The substrate comprises a chiral gold nanorod as the core and a Zr-MOF shell. The chiral gold nanorod is a helical chiral gold rod coated with a gold-silver alloy. The smoothness and depth of the spiral threads on the surface of the chiral gold rod are altered by changing the gold-silver alloy ratio. It exhibits excellent LPSR effect and chiral electromagnetic field.

[0057] The MOF in an enhanced Raman scattering substrate for chiral molecule detection is NU-901, and the thickness of the Zr-MOF is 2-90 nm.

[0058] The aforementioned enhanced Raman scattering substrate for chiral molecule detection serves as a Raman substrate with excellent SERS performance to detect differences in chiral enantiomers, distinguishing enantiomers by differences in Raman signals.

[0059] Chiral-AuNR@Zr-MOF solution was mixed with amino acid molecules and allowed to stand overnight. Then, 20 μL of the mixed solution was dropped onto a clean silicon wafer. After drying, the wafer was placed in a Raman spectrometer and collected under 532 nm laser excitation. The typical integration time was 10 seconds, and the excitation power was maintained at 0.1 mW.

[0060] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0061] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0062] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. These other embodiments are also covered within the scope of protection of this invention.

[0063] Reagents and their types used in the examples: hexadecyltrimethylammonium bromide (CTAB, ≥99%, Aladdin), sodium borohydride (NaBH4, ≥98%, Aladdin), sodium oleate (NaOL, >98.0%, Maclean), chloroauric acid (HAuCl4·H2O, ≥99.995%, Sigma-Aldrich), silver nitrate (AgNO3, ≥99.9%, Alfa Aesar), ascorbic acid (AA, ≥99.99%, Aladdin), hydrochloric acid (HCl, 37 wt % in Water (testing required), concentrated sulfuric acid (H2SO4, ≥98%, testing required), hydrogen peroxide (H2O2, ≈30%, testing required), L-phenylalanine (L-Phe, ≥99%, Aladdin), D-phenylalanine (D-Phe, ≥99%, Aladdin), L-tyrosine (L-Tyr, ≥99%, Aladdin), D-tyrosine (D-Tyr, ≥99%, Aladdin), L-cysteine ​​(L-Cys, ≥99%, Aladdin), D-cysteine ​​(D-Cys, ≥99%, Aladdin), mercapto-substituted polyethylene glycol (CH3O(CH2CH2O)). n CH2CH2SH, mPEG-SH, Mw≈6000, ≥97%, Sigma-Aldrich), anhydrous ethanol (≥99.9%, Aladdin), 1-propanol (≥99.5%, Maclean), zirconium n-butoxide (Zr(OBu)4, 80 wt%, Maclean), benzoic acid (≥99%, Maclean), N,N-dimethylformamide (DMF, ≥99.5%, Sinopharm), 4-mercaptobiphenylnitrile (C 13 H9NS, ≥98%, Sigma-Aldrich), acetic acid (≥99.5%, Guangshi).

[0064] Example 1

[0065] This embodiment provides a method for preparing gold nanorods, including the following steps:

[0066] 0.0378 g NaBH4 was dissolved in 10 mL of deionized water under ice-water bath conditions to prepare a 0.1 M solution, which was then diluted to 0.01 M. 5 mL of 0.5 mM HAuCl4 was mixed with 5 mL of 0.2 M CTAB, and 0.6 mL of 0.01 M NaBH4 was added while stirring vigorously. The solution turned brownish-yellow, and the mixture was stirred for another 2 minutes. The solution was then allowed to stand at room temperature for 1 hour to obtain the seed culture. Next, the growth medium was prepared. 2.8 g CTAB and 494 mg NaOL were dissolved in 100 mL of 50°C warm water. After cooling to 30°C, 9.6 mL of 4 mM AgNO3 was added, and the mixture was allowed to stand for 15 minutes. Then, 100 mL of 1 mM HAuCl4 was added, and the mixture was stirred at 700 rpm for 90 minutes until the solution became colorless. 0.6 mL of 37% HCl was added to adjust the pH, and the mixture was stirred at 400 rpm for another 15 minutes. Then, 0.5 mL of 64 mM ascorbic acid was added and stirred vigorously for 30 seconds. Finally, 80 μL of seed culture was added, stirred for 30 seconds, and then allowed to stand at 30°C for 12 hours. The product was centrifuged twice to obtain a gold nanorod solution. Figure 2 The image shows a TEM image of the gold nanorods prepared in this embodiment. The gold nanorods in the image exhibit a typical elongated or rod-shaped structure with rounded ends, regular overall shape, high aspect ratio, smooth surface, and clear edges.

[0067] Example 2

[0068] This embodiment provides a method for preparing Chiral-AuNR, including the following steps:

[0069] The gold nanorod stock solution prepared in Example 1 (0.5 mL, 0.02 mg / mL) was centrifuged to remove the supernatant, then dispersed in 9.2 mL of 10 mM CTAB solution. Next, 0.1 mL of 6 mM L-Cys was added, and the mixture was stirred at room temperature for 3 hours. Then, 70 μL of 0.01 M silver nitrate solution was added, followed by 260 μL of 5 mM chloroauric acid. After thorough mixing, 200 μL of 0.1 M AA was added, and the mixture was stirred until homogeneous. The mixture was then heated at 70°C for one hour, followed by centrifugation twice at 5000 r / min for 6 min to purify the product. This product was named L-AuNR. Its TEM image is shown below. Figure 3 As shown, chiral molecules are aggregated on the surface of gold nanorods, and the surface has a helical structure.

[0070] Example 3

[0071] This embodiment provides a method for preparing Chiral-AuNR. The preparation steps are the same as in Example 2, the only difference being that D-Cys is used in this embodiment, and the product is named D-AuNR. Its TEM image is shown below. Figure 4 As shown, chiral molecules are aggregated on the surface of gold nanorods, and the surface has a helical structure.

[0072] The absorption spectra and CD spectra of L-AuNR and D-AuNR are as follows: Figure 6 As shown, the absorption spectra show that both types of particles have two LSPR resonance absorption peaks, indicating that they have excellent LSPR effects. Furthermore, the corresponding CD spectra show that two distinct symmetrical peaks appear near the LSPR peak of the chiral gold nanorods, exhibiting a positive and a negative state, indicating that the originally chiral gold nanorods have been endowed with chiral optical activity by chiral molecules.

[0073] Example 4

[0074] This embodiment provides a Chiral-AuNR surface modification method, the steps of which are as follows:

[0075] First, centrifuge 10 mL of the L-AuNR solution prepared in Example 2 and resuspend it in 50 mL of deionized water to adjust its concentration to 1 nM and CTAB concentration to 2 mM. Add 4 mL of mPEG-SH at a concentration of 10 mg / mL and stir overnight. The next day, centrifuge and resuspend in 50 mL of anhydrous ethanol, then add 800 μL of mPEG-SH at a concentration of 10 mg / mL and continue stirring overnight. Finally, wash with ethanol and resuspend the product in 5 mL of ethanol or DMF.

[0076] Example 5

[0077] This embodiment provides a Chiral-AuNR surface modification method. The preparation steps are the same as in Example 4, except that the L-AuNR is prepared in Example 3.

[0078] Example 6

[0079] This embodiment provides a method for preparing Chiral-AuNR@Zr-MOF composite material, the steps of which are as follows:

[0080] 15 mL of 80 wt% zirconium butoxide and 100 g of benzoic acid were added to 300 mL of 1-propanol, stirred, and sonicated for 10–20 minutes. The mixture was then heated and stirred for 12 hours, resulting in layering: a clear solution on top and a white precipitate on the bottom. Excess 1-propanol was removed by vacuum heating to obtain a white solid. After thorough washing with 1-propanol, the solid was vacuum dried at room temperature to obtain zirconium-based metal node powder.

[0081] 36.4 mg of zirconium-based metal node powder was dispersed in approximately 7.5 mL of DMF, and 1.82 mL of acetic acid and 0.3 mL of a 10 nM solution of surface-modified chiral gold nanorods prepared in Example 4 were added. At room temperature, 0.1 mL of a 2 mg / mL H4TBAPy solution was added dropwise at a rate of 0.05 mL / min using a titration pump to form a metal-organic framework structure. The reaction was vigorously stirred for 12 hours after the addition to promote the reaction. After the reaction was complete, the product was washed three times with DMF by centrifugation to remove unreacted substances and impurities. After the third wash, a solvent exchange was performed, replacing the DMF with acetone, and the mixture was ultrasonically dispersed and allowed to stand for 12 hours. Finally, the product was centrifuged and redispersed in 5 mL of acetone or methanol to obtain the final L-AuNR@Zr-MOF composite material, wherein the Zr-MOF thickness was 5 nm.

[0082] Example 7

[0083] This embodiment provides a method for preparing Chiral-AuNR@Zr-MOF composite material. The steps are the same as in Example 6, except that the amount of H4TBAPy solution added is 0.3 mL, 0.4 mL, 0.5 mL, 0.6 mL and 0.7 mL, and the thicknesses of the synthesized Zr-MOF after adding different volumes of H4TBAPy solution are 15 nm, 30 nm, 40 nm, 70 nm and 90 nm, respectively.

[0084] TEM images of the products prepared in Examples 6 and 7 are shown below. Figure 5 As shown in Figure af, the results indicate that zirconium-based metal-organic frameworks (Zr-MOFs) nucleate and grow on the surface of gold nanorods. The thickness of Zr-MOF in Example 7 is significantly greater than the 5 nm thickness of Zr-MOF in Example 6, indicating that the nucleation and growth rate of MOFs can be significantly affected by changing the amount of precursor added. Therefore, by adjusting the amount of precursor H4TBAPy added, the thickness of zirconium-based metal-organic frameworks (Zr-MOFs) nucleated and grown on the surface of gold nanorods (AuNR) can be controlled.

[0085] Example 8

[0086] This embodiment provides a method for preparing Chiral-AuNR@Zr-MOF composite material. The preparation steps are the same as in Example 6, except that the surface-modified chiral gold nanorod solution used is the one prepared in Example 5, and the product is named D-AuNR@Zr-MOF, wherein the Zr-MOF thickness is also 5 nm.

[0087] The normalized spectra of Examples 1, 2, and 6 are as follows: Figure 6 As shown in Figure a, the normalized spectra of the products prepared in Examples 1, 3, and 8 are as follows. Figure 6As shown in b; the CD spectra of Examples 1, 2, and 6 are shown in Figure 1. Figure 7 As shown in Figure a, the CD spectra of Examples 1, 3, and 8 are as follows. Figure 7 As shown in b; the results indicate that due to surface modification and the isolating effect of surface MOF, the CD peak values ​​of composite materials with different chiralities all decreased.

[0088] Application examples

[0089] The products prepared in Examples 1-3, 6, and 8 were used as Raman spectroscopy substrates to test their enhancement effect on two amino acid molecules with different chiralities, L / D-phenylalanine (L / D-Phe). The concentration of the amino acid molecules was 10. -5 M, 10 -6 M, 10 -7 M, 10 -8 M, 10 -9 M.

[0090] The testing procedure was as follows: 100 μL of the product solution prepared in the above examples was mixed with amino acid molecules of different concentrations and allowed to stand overnight. Then, 20 μL of the mixed solution was dropped onto a clean silicon wafer, dried, and placed in a Raman spectrometer for detection. All Raman spectra were acquired using a confocal micro Raman spectrometer (Renishaw InVia Reflex) under 532 nm laser excitation, with a typical integration time of 10 seconds and an excitation power maintained at 0.1 mW.

[0091] From the appendix Figure 8 , 9 As can be seen from 10, at the same L / D-Phe amino acid molecule concentration of 10 -5 Under M conditions, both AuNR and L / D-Chiral-AuNR enhance the Raman signal of phenylalanine molecules. However, when L / D-Chiral-AuNR is used as the Raman substrate, the enhancement effect on isochiral phenylalanine molecules is better than that on heterochiral molecules, with a difference of about four times.

[0092] Then from the appendix Figure 11 , 12 As can be seen, using L / D-Chiral-AuNR@MOF (5nm) as the Raman substrate to enhance the sensitivity of SERS not only allows for the differential recognition of amino acid molecules with different chiralities, but also enables the detection of molecules as low as 10 - 9 M, this is due to the adsorption effect of the surface MOF, which adsorbs the analyte molecules to the vicinity of the substrate surface, allowing more analyte molecules to enter the plasma "hot spot" region, thus enhancing SERS sensitivity. Furthermore, experiments have shown that the thickness of the Zr-MOF layer also has a certain impact on SERS performance, as shown in the attached figure. Figure 13As shown, when the Zr-MOF layer is greater than 30 nm, the Raman signal cannot be detected; when the Zr-MOF layer is less than 30 nm, the Raman signal begins to appear.

[0093] Therefore, this invention provides an enhanced Raman scattering substrate for chiral molecule detection and its preparation method. The method uses zirconium-based metal-organic frameworks (MOFs) to encapsulate chiral gold nanorods, so that the synthesized chiral gold rod@MOF materials not only have excellent LPSR effect and chiral electromagnetic field, but also the MOF layer on the surface can effectively adsorb the analyte molecules into the plasma "hot spot" region, thus serving as a Raman substrate with excellent SERS performance.

[0094] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and does not limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an enhanced Raman scattering substrate for chiral molecule detection, characterized in that, The process involves encapsulating a zirconium-based metal-organic framework by inducing the formation of a helical chiral gold-silver alloy layer on a gold nanorod core using chiral cysteine, followed by the following steps: Step (1) Preparation of Chiral-AuNR After centrifuging the gold nanorod solution to remove the supernatant, it was dispersed in a hexadecyltrimethylammonium bromide solution. Then, chiral cysteine ​​molecules were added, and the mixture was stirred at room temperature for 3 hours. Silver nitrate solution was added first, followed by chloroauric acid. After stirring evenly, ascorbic acid was added, and the mixture was stirred evenly. The mixture was then heated at 70°C for 1 hour, and the product was purified by centrifugation twice at a speed of 5000 r / min for 6 minutes. In step (1), the chiral cysteine ​​molecule is either L-cysteine ​​or D-cysteine; The concentration of the gold nanorod solution was 0.02 mg / mL. The molar ratio of the gold nanorod solution, hexadecyltrimethylammonium bromide solution, and chiral cysteine ​​molecules was 0.01 mg: 92 mol: 0.6 mol. The volume ratio of the gold nanorod solution, silver nitrate solution, chloroauric acid solution, and ascorbic acid was 10:0.07:0.26:0.

2. Step (2) Surface modification of Chiral-AuNR After centrifugation of the Chiral-AuNR solution, it was resuspended in deionized water. Hexadecyltrimethylammonium bromide and methoxy polyethylene glycol mercapto were added, and the mixture was stirred overnight. After centrifugation, it was resuspended in anhydrous ethanol, and then methoxy polyethylene glycol mercapto solution was added. The mixture was stirred overnight again. The product was washed with ethanol and resuspended in ethanol or DMF for later use. Step (3) Prepare zirconium-based metal node powder; Step (4) Assembly of zirconium-based metal-organic frameworks Zirconium-based metal node powder was placed in a mixed solution of surface-modified Chiral-AuNR, DMF, and acetic acid, and H4TBAPy solution was added dropwise to form a metal-organic framework structure. After washing, drying, and centrifugation, Chiral-AuNR@Zr-MOF composite material was obtained, which is an enhanced Raman scattering substrate for chiral molecule detection. In step (4), 36.4 mg of zirconium-based metal node powder is first dissolved in 7.5 mL of LDM solution. The ratio of this solution to the surface-modified Chiral-AuNR solution is 7.5:0.

3. The amount of H4TBAPy solution added is 0.1-0.8 mL, and the dropping rate is 0.05 mL / min.

2. The method for preparing an enhanced Raman scattering substrate for chiral molecule detection according to claim 1, characterized in that, The volume ratio of Chiral-AuNR solution to methoxy polyethylene glycol mercapto solution is 10:

1.

3. An enhanced Raman scattering substrate for chiral molecule detection, characterized in that, The enhanced Raman scattering substrate is prepared by the preparation method described in any one of claims 1-2, wherein the enhanced Raman scattering substrate has a chiral gold nanorod as the core and a Zr-MOF as the shell, and the chiral gold nanorod is a helical chiral gold rod with a gold-silver alloy coating on its surface. The smoothness and depth of the helix on the surface of the chiral gold rod are changed by changing the gold-silver alloy ratio.

4. The enhanced Raman scattering substrate for chiral molecule detection according to claim 3, characterized in that, It exhibits excellent localized surface plasmon resonance effect and chiral electromagnetic field, enhancing the optical activity of Raman scattering substrates and the chiral correspondence of chiral cysteine.

5. The enhanced Raman scattering substrate for chiral molecule detection according to claim 3, characterized in that, The MOF type in the enhanced Raman scattering substrate is NU-901, and the thickness of the Zr-MOF is 2-90 nm.

6. The enhanced Raman scattering substrate for chiral molecule detection according to claim 3, characterized in that, Chiral-AuNR@Zr-MOF composite material, as a Raman substrate with excellent SERS performance, was used to detect differences in chiral enantiomers and to distinguish enantiomers by differences in Raman signals.

7. The enhanced Raman scattering substrate for chiral molecule detection according to claim 6, characterized in that, Chiral-AuNR@Zr-MOF solution was mixed with amino acid molecules and allowed to stand overnight. Then, 20 μL of the mixed solution was dropped onto a clean silicon wafer. After drying, the wafer was placed in a Raman spectrometer and Raman spectra were collected under 532 nm laser excitation. The typical integration time was 10 seconds, and the excitation power was maintained at 0.1 mW.

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