Developments And Applications Of Surface-Enhanced Raman Spectroscopy Substrate Material

SERS(Surface-enhanced Raman Spectroscopy)is a spectroscopy technique that can simultaneously realize molecular structure and quantitative analysis,and it has high sensitivity,fast analysis speed,and is suitable for aqueous solutions.The preparation of SERS active substrates with high hot spot density,excellent reproducibility and stability is the key of SERS technology.Coimbining with common sample preparation process in analysis can improve the selectivity of SERS detection and make it suitable for practical conplex systems.In this dissertation,different SERS active substrates were used and prepared.Several rapid detection methods for food safety and environmental analysis were develbped.By using Au NPs combined with thin film microextraction(TFME)meimbranes and preparing two-dimensional and three-dimensional SERS active substrates,the rapid analysis of benzoic acid in carbonated beverages,sorbic acid in beverages and Cr(VI)in water could be realized.The dissertation includes five chapters:Chapter I,introductioa This chapter mainly summarizes the development history of Raman spectroscopy and SERS,the mechanism of SERS and different kinds of SERS active substrates.Afterwards,the application of SERS in the field of food safety testing,environmental analysis and biological analysis were introduced.Finally,the topic selection background and research plan were put forward.Chapter II,silica gel thin-film microextraction coupled to Surface-enhanced Raman scattering for the rapid detection of benzoic acid in carbonated beverages.Commercially chromatography silica gel plates was used as TFME material to extract and separate benzoic acid from liquid matrix,and then Au NPs were dropped onto its surface for SERS detection to develop a quick,easy and sensitive method for detecting benzoic acid in carbonated beverages.Commercially chromatography silica gel plates and Au NPs guaranteed the good reproducibility(RSD ≤10.2%).At the same time,relevant conditions for the extraction process have been optimized,such as thin-layer chromatography silica gel plates brand,extraction temperature,magnetic stirring rate and extraction time.The method was further evaluated based on the optimized conditions.The detection limit of the established method was 3.6 μg mL-1.The recoveries of the method ranged from 85.0%to 103.0%,indicating the good accuracy.Afterwards,this method was applied to the detection of benzoic acid in commercial carbonated beverage samples.The characteristic peak of benzoic acid can be presented clearly and there is no obvious interference of other impurity peaks.The content of benzoic acid in the actual sample obtained by this method is in good agreement with the results of the national standard method,which fully demonstrated this method can meet the actual analytical application requirements.The proposed method improves the selectivity of the SERS technology and realizes rapid,convenient,and e:fficient detection of benzsoic acid in carbonated beverages.Chapter III,preparation of P-Al(O:H)3@Ag SERS substrate and its application in detection of Cr(VI)in water.β-AI(OH)3 was first prepared on the surfiace of glass substrate by liquid deposition method and Ag NPs were modified on the surface of 3－Al(OH)3 through in-sit-u reduction to synthesize a two-dimensional SERS active substrate.The substrate was used for rapid analysis of Cr(VI)in water.The p-Al(OIH)3 substrate and P-Al(OH)3@Ag SERS active substrate were characterized by experiments.The Ag NPs were evenly dristributed on the surfece of β-A1(OH)3 and provided rich hot spots for SERS.4-mercaptopyridine(4-Mpy)was used as the Raman probe to evaluate the SERS performance of P-Al(OH)3@Ag substrate,and the preparation conditions were optimized.The experimental results showed that the substrate has a relatively high SERS sensitivity.At the same time,,the experimentally prepared substrate had good storage resistance.The experiment further used immersion-type TFME to detect Cr(VI)in water.The substrate had good SERS signal response to Cr(VI),and the reproducibility was excellent.At the same time,the selectivity was evaluated experimentally.In the presence of other interfering metal ions,the β-Al(OH)3@Ag substrate still had a high response for Cr(VI).The detection limit can be as lbw as 1.65 nM.The 3-Al(OH)3@Ag SERS substrate has the advantages of simple preparation,low cost and high SERS sensitivity.Applying it to Cr(VI)detection in water can greatly reduce the detection cost,shorten the detection time,and iMdrove the analytical sensitivity.The direct modification of SERS active nanoparticles on the surface of the extraction material provides a new idea for the preparation and application of SERS active substrates.Chapter Ⅳ,Preparation of Ag NPs modified SERS sponge and its application in the determination of sorbic acid in beverages.Three-dimensional melamine sponges were used as scaffolds and Ag NPs were modified on the surface of it by in-situ reduction method.The substrates were applied to the determination of sorbic acid in beverages.The pore structure of the melamine sponge was used as small reaction chambers and Ag NPs were modified on the surface of melamine sponge nanofibers by in-situ reduction method.Ag NPs were tightly arranged on the surface of the fibers to form rich SERS hot spots.4-Aminothiophenol(PATP)molecule was used as the Raman probe and the SERS performance of the prepared SERS sponge was evaluated.The experiment also tested the stability and storage stability of Ag NPs on SERS sponges.Furthermore,the prepared SERS sponge was applied to the determination of sorbic acid in beverages.The detection results ofSERS sponge under different extraction methods were compared.Finally,the instantaneous absorption method was selected.In the interference experiment,SERS sponge has a better selective response to sorbic acid.The detection limit of this method was 27.5(μg mL-1,which was far lower than the maximum allowable amount of sorbic acid in beverage(500 mg kg-1).The recoveries is between 87.1%and 103.0%,indicating good accuracy.The experimental results show that the method is expected to be an efficient,simple,and rapid way for the determination of sorbic acid in beverages.Chapter Ⅴ,summary and outlook.The research work is mainly to combine the extraction technology with different SERS active substrates to realize the analysis of targets.By using Au NPs combined with thin film microextraction(TFME)membranes and preparing two-dimensional and three-dimensional SERS active substrates,the rapid analysis of benzoic acid and sorbic acid in beverages and Cr(Ⅵ)in water could be realized.This chapter summarizes the related work done in this study and look into the future of extending SERS technology to complex systems in food safety,environmental monitoring and public safety.