CN104215625B - The Raman spectrum base background signal minimizing technology that electrodeposition process makes - Google Patents

Abstract

The method for removing the background signal of the surface-enhanced Raman spectrum substrate produced by the electrodeposition method provided by the present invention uses the electrodeposition reaction to increase the Raman detection signal on the surface of the substrate, and cleans the impurities left on the surface. The invention modifies the nanometer metal electrode used in the field of electrocatalysis so that it has the SERS effect, thereby being applied in the field of SERS and realizing the detection of trace molecules. On the other hand, from the perspective of the combination of the electrolyte and the cleaning of the surface deposits after electrodeposition, a complex with a larger stability constant than the deposits is selected, and at the same time, the complex itself has no or only small interference to solve the problem. Raman background interference in SERS substrates prepared by electrodeposition.

Description

Surface-enhanced Raman Spectroscopy Substrate Background Signal Removal Method Made by Electrodeposition

technical field

The invention relates to the field of Raman spectroscopy detection, in particular to a method for removing background signals of a surface-enhanced Raman spectroscopy (Electrochemical-Surface enhanced raman scattering, SERS) substrate.

Background technique

The SERS effect is to use laser light and metal particles to form an excimer plasmon resonance effect, so that the detection signal of the molecule to be detected is increased by about 10 ⁴ -10 ⁶ times or even higher. It has great application prospects in the detection of trace molecules. So far, many studies have focused on the development of various substrates with SERS effects, such as rough metal surfaces treated by redox reactions and substrates prepared by electrochemical methods; Particles deposited on substrates of different materials such as glass; metal sols with spherical, rod-shaped, core-shell structures, etc.; MFON in which monodisperse gold or silver nanoparticles are self-assembled on an inert substrate to form an array; photonic crystal lining Bottom etc. Among them, the electrodeposition method can form metal nanoparticles, nanosheets, nanorods, etc. on the surface of the substrate in a short period of time by simply controlling the current, voltage and other conditions. The method is simple and the substrate is easy to obtain. There have been many related reports. However, this type of electrode is mostly used in the field _of electrocatalysis, and is rarely used in the field of Raman spectroscopy detection. Au(SO ₃ ) ₂ ^3- star-shaped gold nano-SERS substrate prepared by electrolyte, gold nanoparticle coating using HAuCl ₄ and NaClO ₄ as electrolyte, etc. Among them, the main difficulty is that when the SERS substrate is prepared by the electrodeposition method, the signal can be increased by more than 10 ⁴ due to the SERS effect, which greatly improves the detection sensitivity of the Raman signal. Therefore, impurities with a very low content on the surface will also produce certain background interference. On the other hand, if the impurities on the surface cannot expose the metal nanoparticles, the SERS effect will also be reduced. However, the reported nano-metal substrates used in the field of electrocatalysis only need to consider the problem of electrical signal interference, and do not need to consider the problem of Raman background signal interference. Therefore, to apply a wide variety of nano-metal substrates in the field of electrocatalysis to Raman detection, a key technical problem needs to be solved, that is, in order to make the prepared substrates applicable to Raman spectroscopy detection, the substrates have no or only relatively small Minor background distractions.

Contents of the invention

In order to overcome the above-mentioned defects of the prior art, the present invention provides a method capable of removing the Raman background signal of the SERS substrate.

The present invention provides a surface-enhanced Raman spectroscopy substrate background signal removal method made by electrodeposition, using electrodeposition reaction to increase the Raman detection signal on the surface of the substrate, and cleaning the impurities left on the surface, including the following steps : (1) Select three or less ion species as the electrolyte to carry out the electrodeposition reaction on the conductive substrate, and the ion pair with less interference to the Raman background should be selected; (2) Use ultrapure water for the substrate after the electrodeposition reaction Cleaning; (3) The sediment remaining on the surface of the substrate is cleaned, and the complex compound with a larger stability constant than the sediment is selected for cleaning, and the complex itself should have no or only a small amount of interference to the Raman back of the matrix; ( 4) Clean the substrate with ultrapure water again.

As a preference, the electrolytic solution for electrodeposition of the conductive substrate in step (1) is selected as a mixture of Ag ₂ SO ₄ and H ₂ SO ₄ ; the complex for cleaning the deposit in step (3) is selected as Na ₂ S ₂ O ₃ . Since the stability constant of the Ag ⁺ and S ₂ O ₃ ^2- complex is 10 ^14.15 , which is relatively large, the formed Ag ⁺ and S ₂ O ₃ ^2- complex can be dissolved in water without forming a solid. After cleaning, the nano-silver is exposed. Therefore, the method of removing _Ag2SO4 with more stable and water _- soluble Ag complexes is feasible and can be used to deal with the surface interference of the substrate obtained by this electrodeposition method.

As preferably, in the step (1), select 0.01mol/L of Ag ₂ SO ₄ and the mixed solution of 0.6 mol/L of H ₂ SO ₄ and water as the electrolyte, and electrify the conductive substrate with a constant current of 0.03A for 30s. deposition reaction.

The invention modifies the nanometer metal electrode used in the field of electrocatalysis so that it has the SERS effect, thereby being applied in the field of SERS and realizing the detection of trace molecules. On the other hand, from the perspective of the combination of the electrolyte and the cleaning of the surface deposits after electrodeposition, a complex with a larger stability constant than the deposits is selected, and at the same time, the complex itself has no or only small interference to solve the problem. Raman background interference in SERS substrates prepared by electrodeposition.

Description of drawings

Figure 1 is the laser Raman spectrum of the unwashed substrate surface (a) after electrodeposition, (b) after rinsing with KSCN, and (c) after rinsing with Na ₂ S ₂ O ₃ ;

Fig. 2 is a scanning electron microscope image before (A) and after (B) cleaning.

detailed description

This embodiment takes the modification of the porous silver membrane as an example. Under a certain current density, the electrolyte solution of 0.01mol/l Ag ₂ SO ₄ , 1.5mol/l KSCN and 0-2mol/L NH ₄ Cl can obtain a porous silver film. In the literature, KSCN is selected to prevent the precipitation of Ag ₂ SO ₄ and Cl-, and NH ₄ Cl is used because it can generate a certain amount of H ⁺ to generate hydrogen bubbles, so that the electrode has a porous structure. However, in this electrolyte combination, both AgSCN and AgCl will bring large Raman background interference. Therefore, in the choice of electrolyte, the combination of as few ion species as possible should be selected. In order to obtain a porous silver film, the electrolyte must contain a certain amount of Ag ⁺ and H ⁺ . If AgNO ₃ and HNO ₃ are selected as the electrolyte, since NO ₃ ⁺ can directly dissolve Ag in an acidic environment, after the electrodeposition is completed, the HNO ₃ in the electrolyte will directly react with the deposited silver film and destroy the silver film. Its porous structure excludes AgNO ₃ . Finally, in this embodiment, Ag ₂ SO ₄ and H ₂ SO ₄ are used as electrolytes to conduct electrodeposition on the conductive substrate to obtain a substrate with SERS effect. The electrolyte combination avoids the interference of the Raman spectrum of some ions, and at the same time has a better porous morphology and film thickness at a suitable current density.

Figure 1(a) shows the Raman spectrum of the substrate obtained after deposition at a constant current of 0.03A for 30s in an electrolyte of 0.01mol/L Ag ₂ SO ₄ and 0.6 mol/L H ₂ SO ₄ . It can be seen that there is a peak at 500cm ^-1 , 600cm ^-1 , 1000cm ^-1 , 1200cm ^-1 and 2150cm ^-1 respectively. Considering the presence of substances and possible impurities in the electrolyte, it is suspected that these peaks may be due to electrolysis SO ₄ ^2- in the liquid remains on the electrode surface when it is taken out after the electrode deposition is completed. The pure solid sample of Ag ₂ SO ₄ is tested, and the four peaks at 500cm ^-1 , 600cm ^-1 , 1000cm ^-1 , and 1200cm ^-1 can be obtained, which are the same as the peaks measured under Raman for the pure solid sample of Ag ₂ SO ₄ Therefore, it can be inferred that Ag ₂ SO ₄ exists on the nano-silver on the surface of the prepared substrate, and the peak height of Ag ₂ SO ₄ is very high, which will seriously interfere with the detection of the sample to be tested. In addition, since nano-silver has SERS effect but Ag ₂ SO ₄ does not, Ag ₂ SO ₄ will affect the SERS effect on the substrate surface, so the content of Ag ₂ SO ₄ must be removed or reduced to reduce Raman background interference.

This example tries to use Ag ⁺ and SCN ^- complexes (k _w = 10 ^10.8 ) and Ag ⁺ and S ₂ O ₃ ^2- complexes (k _w = 10 ^14.15 ) with larger stability constants than Ag ₂ SO ₄ The surface of the substrate is cleaned so that the cleaning ions and Ag ⁺ form a more stable complex than Ag ₂ SO ₄ , so as to achieve the purpose of eluting SO ₄ ^2- . The electrodeposited substrate was first cleaned with ultrapure water, then soaked in KSCN solution for 3 minutes, and then the surface of the substrate was cleaned with superwater. Because KSCN can form a more stable complex with Ag ⁺ than Ag ₂ SO ₄ , the Ag ₂ SO ₄ on the surface of the substrate can be further converted into a complex of Ag ⁺ and SCN ^2- . The obtained spectrum is shown in Figure 1(b). It can be seen that the original peak of Ag ₂ SO ₄ has almost disappeared, but there is a large peak at around 2200cm ^-1 , and new ones appear at 743cm ^-1 and 888cm ^-1 Two small peaks, it is presumed that this peak is a new interference brought by the AgSCN precipitate, so KSCN cannot be used for cleaning.

Since the stability constant of the Ag ⁺ and S ₂ O ₃ ^2- complex is 10 ^14.15 , which is 4 orders of magnitude higher than that of the Ag ⁺ and SCN ^- complex, and the formed Ag ⁺ and S ₂ O ₃ ^{The 2-} complex is soluble in water without forming a solid. Figure 1(c) is the SERS spectrum of the electrodeposited substrate after rinsing in Na ₂ S ₂ O ₃ . It can be seen that Ag ₂ SO ₄ disappears, and there is only a relatively small peak around 1600cm ^-1 , which is presumed to be the peak of a small amount of residual S ₂ O ₃ ^2- , and the prepared substrate has a better baseline. Further, it can be seen from the scanning electron microscope image (Fig. 2) that the surface of nano-silver is covered with a layer of Ag ₂ SO ₄ before cleaning, but after cleaning, the nano-silver is exposed and Ag ₂ SO ₄ is removed. Therefore, the method of removing _Ag2SO4 with more stable and water _- soluble Ag complexes is feasible and can be used to deal with the surface interference of the substrate obtained by this electrodeposition method.

In summary, the present invention proposes a method for removing the Raman background signal of a SERS substrate made by electrodeposition, which can make nano-metal electrodes commonly used in the field of electrocatalysis through appropriate electrolyte selection and surface Interference removal is applied to Raman spectroscopy detection, which has a great application prospect.

Claims (2)

1. A surface-enhanced Raman spectrum substrate background signal removal method made by electrodeposition method, utilizes electrodeposition reaction to increase the Raman detection signal on the substrate surface, and cleans the impurities remaining on its surface, which is characterized in that it includes the following step: (1) Select Ag ₂ SO ₄ and H ₂ SO ₄ as the electrolyte to perform electrodeposition reaction on the conductive substrate; (2) cleaning the substrate after the electrodeposition reaction with ultrapure water; (3) To clean the sediment remaining on the surface of the substrate, select the S ₂ O ₃ ^2- complex with a larger stability constant than the sediment for cleaning. The complex itself should have no or only a small amount of Raman backing for the substrate. interference; (4) The substrate is washed again with ultrapure water. 2. A surface-enhanced Raman spectrum substrate background signal removal method made by electrodeposition as claimed in claim 1, characterized in that: Ag of 0.01mol/L is selected in step (1) ₂ SO ₄ and 0.6mol/L The mixed solution of H ₂ SO ₄ in L was used as the electrolyte, and a constant current of 0.03A was energized for 30s to carry out electrodeposition reaction on the conductive substrate.