Modification Of Fe₃O₄/Ag Magnetic SERS Substrates And Its Application In The Detection Of Perchlorate

Surface enhanced Raman spectroscopy（SERS）is a new type of spectroscopy technology that uses the surface enhancement effect of precious metals or semiconductor materials,which greatly increase the intensity of molecular Raman signals.SERS can identify and detect low-concentration target molecules,even achieve single-molecule sensitivity.SERS has important application prospects in the fields of environmental monitoring and trace monitoring of explosives because of its high sensitivity,quickness,simplicity and on-site detection.In this paper,an iron oxide magnetic SERS substrate supported by silver nanoparticles was prepared.This SERS substrate after functional modification applies to the detection of various inorganic explosives（perchlorate,sulfate,nitrate,etc）.The main content of this paper is as follows:（1）Using 3-aminopropyltriethoxysilane（APTES）as a bridging agent,the surface of nano-Fe₃O₄was modified in anhydrous ethanol environment,combined with in-situ chemical reduction method to load Ag nanoparticles onto the modified Fe₃O₄surface,a silver-based magnetic SERS substrate was prepared.The magnetic SERS substrate was further functionalized with 2-dimethylaminoethanethiol（DMAE）to form a positively charged self-assembled monolayer on the surface.The functionalized SERS substrate was used for perchlorate detection.The results show that this method can achieve sensitive detection of perchlorate with a detection limit as low as 0.1 ppm,which is 10 times more sensitive than commercial substrates functionalized with DMAE.The quantitative linear range is 0.5 ppm～200 ppm,which showing good reproducibility（the relative standard deviation of 40 tests is 14.3%）.Mechanism analysis shows that under suitable p H conditions,DMAE molecules can adsorb perchlorate through electrostatic adsorption,realizing the sensitive detection.（2）A magnetic SERS substrate modified with cysteamine instead of DMAE was prepared for detecting perchlorate and other inorganic explosives.Compared with the DMAE functionalized substrate,after surface modification with cysteamine,the Zeta potential of the SERS substrate is more positive and the cysteamine steric hindrance is smaller,so it is more conducive to the enrichment and detection of explosive anions.The SERS signal of cysteamine itself is simpler and has less spectral interference to explosive anions.The detection limit of perchlorate on the magnetic Ag/Fe₃O₄substrate modified by cysteamine can be as low as 0.01 ppm,and the relative standard deviation of signal reproducibility is only 12.9%.Quantitative detection can be carried out in the range of 0.5ppm～50 ppm.The substrate shows good stability,after dispersed and stored in water for75 days,its signal attenuation rate is less than 10%.This method has been successfully used in the detection of explosive anions in actual soil samples,which demonstrating its practical application prospects.