Surface-enhanced raman active substrate and method of making and using same

Abstract

The application discloses a surface-enhanced Raman active substrate and a preparation method and application thereof. The preparation method of the surface-enhanced Raman active substrate comprises the following steps: providing a porous anode plate, wherein the porous anode plate has opposite bottom and top surfaces, and the top surface is provided with nano-pores; placing a metal nanoparticle solution on the top surface of the porous anode plate to form a liquid surface; and applying an electric field between the bottom surface of the porous anode plate and the liquid surface to drive the metal nanoparticles to self-assemble in the nano-pores. The electrically-driven confined self-assembly method is adopted to realize rapid preparation of the surface-enhanced Raman active substrate with good uniformity and high activity.

Description

Technical Field

[0001] This application relates to the fields of analytical chemistry and nanotechnology, and in particular to a surface-enhanced Raman active substrate, its preparation method, and its application. Background Technology

[0002] Surface-enhanced Raman scattering (SERS), as an ultrasensitive analytical detection technique, has been widely researched and applied in fields such as environmental monitoring, food safety, and bioanalysis due to its ability to respond ultrasensitively to the fingerprint information of target molecules. However, some challenges remain in point-of-care testing (POCT) within these fields, such as the activity and homogeneity of the SERS substrate, construction time, and detection time. The requirements for POCT in various fields necessitate the rapid construction of highly active and homogeneous SERS substrates and the quick detection of target analytes using SERS technology.

[0003] Existing technologies disclose a series of methods for creating SERS substrates, with common methods including evaporation self-assembly and template methods. Evaporation self-assembly achieves the self-assembly of noble metal nanoparticles at the gas-liquid interface through precise control of humidity and temperature changes, resulting in a uniform SERS-active substrate. However, this method requires significant time to precisely control humidity and temperature. Template methods utilize photolithography to obtain a template with a nano-uneven array structure. Polymer nanoparticles are then deposited on this template through imprinting to obtain the SERS-active substrate. While this method can rapidly produce highly active and uniform SERS substrates, its fabrication cost is relatively high. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a method for preparing a surface-enhanced Raman active substrate, which is fast, convenient, and low-cost, and produces a substrate with good uniformity and high activity, suitable for rapid on-site preparation and detection.

[0005] In this application, the method for preparing a surface-enhanced Raman active substrate includes:

[0006] A porous anode plate is provided, the porous anode plate having opposing bottom and top surfaces, the top surface having nanopores;

[0007] A solution of metal nanoparticles is placed on the top surface of a porous anode plate to form a liquid surface;

[0008] An electric field is applied between the bottom surface of the porous anode plate and the liquid surface to drive metal nanoparticles to self-assemble within the nanopores.

[0009] Optionally, the porous anode plate is a porous anodic aluminum oxide plate (AAO), with an aluminum layer on the bottom surface and an aluminum oxide layer on the top surface. The aluminum oxide layer is formed by a nano-V-shaped pore array, and a large number of metal nanoparticles can be deposited on or inside the nanopores.

[0010] Optionally, the pore size of the nanopores is 100–450 nm, and the pore depth is 200–900 nm. For example, in one embodiment, the spacing between the nanopores is 125 nm, and the pore depth is 250 nm. Excessive pore depth affects conductivity, while insufficient depth affects filling density; too small a pore spacing makes it difficult for nanoparticles to enter.

[0011] Optionally, the metal nanoparticles are gold nanobipyramidal particles (Au NBPs), gold nanorods (Au NRs), or gold nanospheres (Au NPs).

[0012] Au NBPs are a class of noble metal nanoparticles with superior optical properties. Their structure consists of two pentagonal pyramids, and the sharp ends create a "lightning rod effect," which gives them a high local electromagnetic field strength.

[0013] Optionally, the aspect ratio of the gold nanobipyramidal particles is 3:1 to 3.5:1.

[0014] Optionally, the concentration of the metal nanoparticle solution is 5–15 nM.

[0015] Optionally, the metal nanoparticle solution includes a surfactant; the surfactant coats the surface of the metal nanoparticles, causing the surface of the metal nanoparticles to carry a charge, so that a voltage can be applied to drive the movement of the metal nanoparticles.

[0016] Optionally, the concentration of the surfactant is 0.1 to 0.3 mol / L.

[0017] Optionally, the surfactant is at least one of hexadecyltrimethylammonium chloride (CTAC), hexadecyltrimethylammonium bromide (CTAB), and Tween 20.

[0018] Optionally, the zeta potential of the metal nanoparticle solution is +40 to +50 mV.

[0019] Optional, see Figure 1 The preparation method includes the following steps:

[0020] A solution of metal nanoparticles is dropped onto the top surface of a porous anode plate;

[0021] A guide wire is used as the first electrode, which contacts a droplet on the top surface of a porous anode plate, and a second electrode is provided on the bottom surface of the porous anode plate.

[0022] A voltage is applied between the first electrode and the second electrode.

[0023] Optionally, the guide wire is a platinum wire; the second electrode is a copper sheet disposed on the bottom surface of the porous anode plate.

[0024] Optionally, the first electrode is connected to the positive terminal of the power supply, and the second electrode is connected to the negative terminal of the power supply.

[0025] Optionally, the voltage is 1.4 to 1.5V, and the voltage application time is 0.5 to 4 minutes. For example, in one embodiment, the voltage is 1.5V, and the voltage application time is 2 minutes.

[0026] This application also provides a surface-enhanced Raman active substrate prepared by the above preparation method.

[0027] This application also provides the application of surface-enhanced Raman active substrates in the detection of 4-mercaptobenzyl mercaptan (4-NTP).

[0028] Specifically, the application includes the following steps:

[0029] 4-NTP solution was dropped onto the surface of a surface-enhanced Raman-active substrate;

[0030] Detection was performed using a portable Raman spectroscopy system.

[0031] Optionally, the 4-NTP solution is 10 μM.

[0032] Optionally, the laser power for Raman detection is 500mW and the exposure time is 3s.

[0033] Compared with existing technologies, this application employs electrically driven induction of metal nanoparticle self-assembly within nanopores on a porous anode plate, enabling rapid preparation of a surface Raman-active substrate with good uniformity and high activity. This preparation method is simple and easy to operate. The surface Raman-active substrate is used for the detection of 4-NTPs, enabling rapid detection. Attached Figure Description

[0034] Figure 1 This is a schematic diagram illustrating the preparation of the Au NBPs-AAO SERS active substrate;

[0035] Figure 2A Characterization diagram (1 μm) of Au NBPs-AAO SERS active substrate;

[0036] Figure 2B Characterization image (300 nm) of Au NBPs-AAO SERS active substrate;

[0037] Figure 3 Optimization diagram of preparation time for Au NBPs-AAO SERS active substrate;

[0038] Figure 4A Raman spectra of 4-NTPs at different points on the Au NBPs-AAO SERS active substrate;

[0039] Figure 4B Au NBPs-AAO SERS active substrate at different points 1346 cm⁻¹ -1 A histogram of the intensity at the characteristic peak;

[0040] Figure 4C Raman spectra of 4-NTPs were obtained from different batches of Au NBPs-AAO SERS active substrates.

[0041] Figure 4D Different batches of Au NBPs-AAO SERS active substrates were tested at 1346 cm⁻¹. -1 A histogram of the intensity at the characteristic peak. Detailed Implementation

[0042] The technical solutions described in this application will be further explained below with reference to specific embodiments, but this application is not limited thereto.

[0043] Preparation Example 1: Preparation of Au NBPs

[0044] Following the 2017 article published in JACS by Professor Luis M. Liz-Marzán's research group, gold bipyramidal nanoparticles were synthesized. The synthesis process consisted of two parts:

[0045] 1) Synthesis of gold seeds: 0.25 mL of freshly prepared 25 mM sodium borohydride solution was added to 10 mL of mixed solution (0.25 mM chloroauric acid, 50 mM CTAC, 5.0 mM citric acid) and reacted at 80 °C for 90 min.

[0046] 2) Synthesis of gold bipyramidal nanoparticles: The above 8.0 mL gold seed solution was added to a mixed solution containing 200 mL of 100 mM MCTAB, 10 mL of 10 mM chloroauric acid, 2.0 mL of 10 mM silver nitrate, 4.0 mL of 1.0 M hydrochloric acid, and 1.6 mL of 100 mM ascorbic acid, and the reaction was carried out for 2 h.

[0047] Example 1: Preparation of Au NBPs-AAO SERS active substrate

[0048] In size 3.0×3.0mm 210 μL of 10 nM Au NBPs was dropped onto the V-shaped AAO (pore size 125 nm, pore depth 250 nm) surface on both sides. A platinum wire was used as the positive electrode, contacting the top of the droplet, and the bottom of the AAO was used as the negative electrode. A voltage of 1.5 V was applied between the two. After energizing for 2 minutes, excess solution on the surface was quickly removed from top to bottom using filter paper. After 1 minute, the Au NBPs-AAOSERS active substrate was obtained. The relevant operating principle is as follows: Figure 1 As shown. The substrate was characterized using high-resolution scanning electron microscopy (SEM), as shown. Figure 2A , 2B As shown, the nanopores contain a large number of uniformly packed Au NBPs.

[0049] Example 2: Optimization of Voltage Application Time

[0050] In size 3.0×3.0mm 2 10 μL of 10 nM Au NBPs was dropped onto the surface of a V-shaped AAO (pore size 125 nm, pore depth 250 nm). A platinum wire was used as the positive electrode, contacting the top of the droplet, and the bottom of the AAO was used as the negative electrode. A voltage of 1.5 V was applied between the two electrodes. Different Au NBPs-AAO SERS active substrates were prepared under different energizing times (0.5 min, 1 min, 2 min, 3 min, 4 min). Subsequently, these SERS active substrates were tested using 4-NTP as the target compound.

[0051] like Figure 3 As shown, before 2 minutes, with the extension of the energizing time, the analyte 4-NTP at 1346 cm⁻¹... -1 The Raman signal intensity at the characteristic peak gradually increases, and after 2 minutes, the 4-NTP signal intensity at 1346 cm⁻¹ increases. -1 The Raman signal intensity at the characteristic peak remained essentially unchanged. This indicates that 2 minutes of energizing is the optimal time, and the SERS-active substrate prepared after 2 minutes will be used in subsequent applications.

[0052] Example 3: Au NBPs-AAO SERS active substrate for 4-NTP detection

[0053] 10 μL of 10 μM 4-NTP solution was dropped onto the surface of the Au NBPs-AAO SERS active substrate prepared under the above optimal conditions. Subsequently, a portable Raman spectrometer was used to detect the substrate at five different locations under the conditions of 500 mW laser power and 3 s exposure time, with a detection time of 10 s.

[0054] The results are as follows Figure 4A As shown in Figures B and C, the relative standard deviation (RSD) of the Raman intensity is 5.04%, indicating good homogeneity of the substrate.

[0055] Three Au NBPs-AAO SERS active substrates from different batches were prepared using the above method, and 10 μL of 10 μM 4-NTP solution was dropped onto their surfaces. Subsequently, detection was performed using a portable Raman spectrometer under conditions of 500 mW laser power and 3 s exposure time. Figure 4C As shown in Figures D, an RSD of 7.79% indicates that the substrate has good reproducibility.

[0056] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. Those skilled in the art can also make appropriate changes and modifications to the above embodiments. Therefore, this application is not limited to the specific embodiments disclosed and described above, and some modifications and variations to the present invention should also fall within the protection scope of the claims of this application.

Claims

1. A method for preparing a surface-enhanced Raman active substrate, characterized in that, include: A porous anode plate is provided, the porous anode plate having opposing bottom and top surfaces, the top surface having nanopores; A solution of metal nanoparticles is placed on the top surface of a porous anode plate to form a liquid surface; An electric field is applied between the bottom surface of the porous anode plate and the liquid surface to drive metal nanoparticles to self-assemble within the nanopores; The porous anode plate is a porous anodic aluminum oxide plate, the bottom surface is an aluminum layer, the top surface is an aluminum oxide layer, and the aluminum oxide layer is formed by a nano-V-shaped pore array; The nanopores have a pore size of 100 ~ 450 nm and a pore depth of 200 ~ 900 nm; The metal nanoparticles are gold bipyramidal nanoparticles; The aspect ratio of the metal nanoparticles is 3:1 to 3.5:1; The concentration of the metal nanoparticle solution is 5~15 nM; The metal nanoparticle solution includes a surfactant; The surfactant is at least one of hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide and Tween 20; The preparation method includes the following steps: A solution of metal nanoparticles is dropped onto the top surface of a porous anode plate; A guide wire is used as the first electrode, which contacts a droplet on the top surface of a porous anode plate, and a second electrode is provided on the bottom surface of the porous anode plate. A voltage is applied between the first electrode and the second electrode; The voltage is 1.4 ~ 1.5 V, and the voltage is applied for 0.5 ~ 4 min.

2. The preparation method according to claim 1, characterized in that, The guidewire is a platinum wire; The second electrode is a copper sheet disposed on the bottom surface of the porous anode plate.

3. The surface-enhanced Raman active substrate prepared by the preparation method according to claim 1 or 2.

4. The application of the surface-enhanced Raman active substrate according to claim 3 in the detection of 4-mercaptobenzyl mercaptan.

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