The Research Of Surface Enhanced Raman Spectroscopy Biosensing Technology For Quantitative Detection Of Heavy Metal Ions

Heavy metal ions are highly toxic,bioaccumulative,and hard to degrade.With the rapid development of the economy,heavy metal ion pollution is becoming more and more serious,which seriously threatens the organism's health and sustainable development of the environment.The development of a rapid,sensitive,and highly specific detection method for heavy metal ion is the key to early warning of heavy metal pollution.Biosensing technology has the advantages of high sensitivity,fast response,low cost,and continuous monitoring.It provides a new idea for high sensitivity,high specificity,simple and rapid detection of heavy metal ions in the environment.Among the identification elements of biosensing systems,nucleic aptamers can effectively replace traditional identification elements such as enzymes and antibodies due to their unique advantages such as strong specificity,low molecular weight,stable structure,wide range of target molecules,flexible signal output mechanism,and ease of synthesis and modification.Nucleic aptamers become one of the best choice for biosensing system identification components.Surface-enhanced Raman Scattering(SERS)is a vibrational spectroscopy technique with many inherent advantages such as high sensitivity,resistance to photobleaching,short response time,high spectral resolution,and rich spectral fingerprint information.The SERS sensing technology based on SERS possesses many flash points as high specificity,highly sensitivity,high throughput detection,simple operation,no sample pretreatment,and so on,which has made it become one of the most promising detection tools in the field of analytical chemistry.It is widely used in food safety Monitoring,environmental pollutant detection,biomedicine and many other fields.However,how to obtain a stable,reproducible SERS signal to improve the accuracy of SERS quantitative detection and increase its sensitivity is a key challenge for current SERS biosensing technology.This paper addresses the cutting edge issues of current SERS technology in the field of biosensing inspection,in order to take full advantages of both SERS and biosensing technologies.The cysteine-functionalized“signal-enhanced" SERS biosensing method and the ratiometric nucleic acid aptamer SERS sensing method have been developed.The main research contents of the thesis are as follows:1."Signal-enhanced"SERS sensing technology for quantitative detection of Cu2+(Chapter 2)For the current situation that Cu2+ detection methods are complex in operation,insufficient in sensitivity and the "signal attenuation" type sensing method is prone to“false positive”result.Based on the distance dependence of the optical properties of precious nanoparticles and the strong coordination of amino and carboxyl groups in cysteine(Cys)with Cu2+,a "Signal enhanced" SERS sensing technology based on the Cys-Cu2+-Cys ternary coordination system was developed for the detection of Cu2+.Au@Ag NPs with strong SERS enhancement effect was used as the substrate,the substrate co-functionalized with 4-thiopyridine(4-Mpy)and Cys serves as a SERS probe.In the presence of Cu2+,the complexation between Cu2+ and Cys leads to agglomeration of the nanoparticle substrate,which results in a strong enhancement of the SERS signal of 4-Mpy.Based on the change in the SERS signal intensity of 4-Mpy,quantitative detection of Cu2+ was achieved.The method has a high sensitivity and exhibits a LOD of 5 nM.More importantly,the method is easy to operate,quick in response,and requires no tedious marking process.And it is expected to develop into a universal method for the detection of other heavy metal ions.2.Ratio metric nucleic ap tamer SERS sensing technology for quantitative detection of Ag+(Chapter 3)Aiming at the problem of poor stability and reproducibility of SERS signals in SERS sensing technology,combining with the advantages of ratiometric strategies and aptamer.This chapter presents a ratiometric nucleic aptamer SERS sensing technique for the quantitative detection of Ag+.Using pyridine(Dpy)as an internal standard molecule,The C-rich nucleic acid strands double-labeled with thiol and Raman reporter Rox are immobilized on the SERS substrate surface as recognition probes,and hybridized with the complementary strand to form a rigid double-stranded structure.The recognition probe can specifically recognizes Ag+ and forms stable C-Ag+-C hairpin structure,thus reducing the distance between Rox and the substrate surface.Then the SERS signal intensity of Rox is significantly enhanced,while the signal intensity of Dpy remains almost unchanged.The ratio of the signal intensity of the two Raman signal molecules is used as the quantitative standard.This detection method has wide detection range and high sensitivity.In the range of 0.1 to 100 nM,there is a good linear relationship between the ratio of two SERS signals intensity and the Ag+concentration with a correlation coefficient of 0.989,and the LOD is 50 pM.Moreover,the method showed good stability and reproducibility,and the standard deviation of SERS signal intensity for different batches was 6.2%.This method can also be used for the determination of the Ag+ in Real samples,the recoveries are in the preferable range of(96.9-106.1%),and the results obtained in this method are basically the same as those detected by the standard AFS method.This method can effectively improve the accuracy of quantitative detection of SERS technology.