Preparation Of Novel SERS Sensors For The Detection Of Mycotoxins

With the continuous improvement of people's living standards,food safety issues have increasingly become the focus of special attention of the public,and more and more people have continuously raised the requirements for food safety.Mycotoxins,as a class of small molecule secondary metabolites,have caused great harm to human and animal health.Surface-enhanced Raman scattering?SERS?is a new type of spectroscopy technology,which has the advantages of high sensitivity,molecular fingerprinting,photobleaching resistance,etc.It has broad application prospects in trace detection.Therefore,preparing the new SERS sensors and using them rapidly,sensitively,and efficiently detecting the mycotoxins in complex samples are evidently critical in the field of food safety.Here,the thesis starts with the preparation of highly active SERS substrates and combines the advantages of DNA nanotechnology to develop a series of methods for SERS detection of mycotoxins,which provides new ideas for food safety detection.The detailed contents and results are described as follows:1. Preparation of cauliflower-inspired 3D SERS substrate and its application in multiple mycotoxins detection.Due to the intrinsic feature of low contents of mycotoxins and the traditional SERS substrate being severely disturbed by the sample,it is impossible to achieve the goal of sensitive detection.To overcome this drawback a cauliflower-inspired 3D SERS substrate sensor was designed and prepared for the rapid and sensitive detection of aflatoxin B₁?AFB₁?,zearalenone?ZON?,and deoxynivalenol?DON?in corn.The cauliflower-inspired3D SERS substrate with intense hot spots was prepared through sputtering Au nanoparticles?Au NPs?on the surface of polydimethylsiloxane?PDMS?coated porous anodized aluminum?AAO?complex substrate?PDMS@AAO?.Under the optimal conditions,this SERS substrate possessed a low detection limit of 10^-12 mol/L,excellent enhancement uniformity?relative standard deviation,RSD=4.57%?and high enhancement factor?2.2×10⁶?for 4-mercaptobenzoic acid?4-MBA?.Furthermore,the results of Raman showed that the 3D-Nanocauliflower SERS substrates could realize the simultaneous label-free detection for AFB₁,ZON,and DON in maize for the first time.The experimental results showed that the limit of detection?LOD?of AFB₁,ZON,and DON was 1.8 ng/m L,47.7ng/m L,and 24.8 ng/m L,respectively.All of the results meet the requirements of national standards?GB 2761-2017?.Finally,the spiked recovery and real samples were used to further verify the feasibility and practicability of the SERS sensor.2. Programmable DNA tweezer-actuated SERS probe for the sensitive detection of.In order to improve the sensitivity and specificity of mycotoxins detection,a DNA nano tweezer was designed for the sensitive detection of AFB₁.This chapter is based on DNA nanotechnology,using aptamers as recognition elements,small-sized silver nanoparticles?Ag NPs?as SERS-enhanced substrate,and 4-nitrothiophenol?4-NTP?as signal probe.The DNA nano tweezer could dynamically control the distance between two Ag NPs.Activation of the Raman intensity was achieved by the state transformation of DNA tweezer from open to closed.At this time,the distance between two Ag NPs decreased from 8.1±2.7 nm to3.2±0.8 nm,which greatly enhanced the SERS signal.The results showed that the SERS sensor has a good specificity.The developed biosensing system exhibited a good linear relationship when the concentration of AFB₁ ranged from 1 ng/m L to 0.01 pg/m L,and the limit of detection?LOD?was 5.07 fg/m L.3. CHA assisted signal amplification combined with magnetic nanochains SERS biosensor for simultaneous detection of multi-mycotoxins.In order to achieve the purpose of high-throughput mycotoxins detection and further improve the sensitivity of mycotoxins detection,Raman reporter embedded gold-core-silver-shell nanoparticles?Au@probe@Ag NPs?and gold-coated magnetic nanochains?Au@MBCs?with nano-stirring function,combined with catalytic hairpin assembly?CHA?as a signal amplification tool was used to form a SERS sensor.Simultaneous and rapid quantitative analysis of three mycotoxins was achieved.When the target mycotoxins existed,due to the specific binding of the aptamer to the target,the CHA reaction was triggered.And the hairpin DNA H1 on the surface of Au@probe@Ag NPs and the hairpin DNA H2 on the surface of Au@MBCs were successively opened successively.As a result,more and more Au@probe@Ag NPs were bound to the surface of Au@MBCs,serslting in a high SERS signal.By detecting changes in the SERS signal,simultaneous and sensitive detection of aflatoxin B₁,ochratoxin A,and zearalenone could be achieved.The LOD of the three mycotoxins was 0.81 fg/m L,1.07 fg/m L,and 11.38 fg/m L,respectively.