Sensitive Detection Of Trace Heavy Metal Ions Based On Surface-enhanced Raman Spectroscopy And Nucleic Acid Amplification

Heavy metal ions can be enriched in the environment.Because of its harmful effects,heavy metal pollution has aroused increasing attention.Traditional methods for the detection of heavy metal ions are limited in their application by the problems of complex sample preparation,time-consuming analysis,expensive equipment and large sample volumes.Therefore,it is necessary to develop a simple,rapid and highly sensitive method for heavy metal detection.Surface-enhanced Raman spectroscopy（SERS）is an ideal method for the detection of heavy metal ions because of its simplicity of operation,rapid analysis,non-contact and non-damaging effect on the sample.To further improve the sensitivity of the SERS sensor for the detection of heavy metals,this work attempts to combine SERS with an efficient nucleic acid amplification strategy.While improving the performance of the SERS sensor,the signal detection intensity was also significantly increased.Two SERS biosensors combining SERS and nucleic acid amplification strategies for Pb²⁺detection were designed and worked out as follows.（1）A DNAzyme-mediated rolling circle amplification SERS-based biosensor was designed for the sensitive detection of trace Pb²⁺.First,the hairpin DNA is circularly cleaved by specific recognition of the Pb²⁺-assisted DNAzyme,and the cleaved product is passed through the RCA reaction to produce a long single strand with a large number of repeating structures.Then,the SERS probe modified with Rox is incubated with the long single strand for Raman detection.The concentration of Pb²⁺in the sample is quantified by measuring the intensity of the resulting Raman signal.The design is based on the synergistic effect of RCA and SERS to multiply the detection signal and achieve the goal of ultra-sensitive detection of trace Pb²⁺.The SERS biosensor has a good linear relationship in the range of 0.1 fM～2 pM,and the detection limit is as low as 0.031 fM.In addition,the present strategy provides a new and effective idea for the detection of heavy metal ions.（2）A Pb²⁺detection platform based on the combination of dendritic DNA nanoassembly signal amplification and SERS was constructed.The heavy metal ion signal was converted into a DNA signal through the specific recognition properties of Pb²⁺by the aptamer.The signal is then continuously amplified by triggering an enzyme-free dendritic DNA nanoassembly process induced by the trigger DNA.Subsequently,Raman signal detection is performed with the introduction of a SERS probe on the substrate.The results showed that the method is fast and sensitive,with good linearity in the range of 0.1 pM～5 nM and a detection limit as low as 45.3 fM.The method was used to detect Pb²⁺in real water environments with recoveries in the range of 96.2%～104.8%.This indicates that the SERS biosensor is practical for the detection of real samples and has some potential for development.