Construction And Application Of Heavy Metal Ion Raman Probe Based On Surface Modification

With the current improvement of economic living standards,people are paying more and more attention to the pollution level of their environment.Therefore,the work of environmental testing is gradually receiving more attention.The traditional methods of detecting metal ions in the environment have many limitations in practical applications.Because the environmental sample’s composition is too complicated,it’s often requires complex pre-processing and large-scale equipment,what’s more,it’s requires professional operators.Surface-enhanced Raman spectroscopy can achieve an enhancement of 10⁶.The layer molecules are amplified by a million times,so a clearer surface molecular signal can be obtained.In addition,SERS technology can be used for the detection of complex samples because its narrow peak width provides good resolution,and the presence of portable Raman instruments makes on-site inspection possible.So far,there have been many works to detect heavy metal ions,but there are still have many shortcomings,such as insufficient detection limit,complicated sample preparation,and expensive instruments.In practical applications,it is necessary to select a good,simple and quick method for actual detection.I attempted to study the surface-enhanced Raman technique for the detection of heavy metal ions.The traditional gold-silver nanoparticles are surface-modified with specific molecules to selectively detect Cu²⁺and Hg²⁺metal ions.Trying to establish a simple and rapid method for the detection of heavy metal ions can meet the needs of actual detection and lay a good foundation for the application of Raman spectroscopy in the field of environmental pollutants.The main research contents and results are as follows:I used phytic acid（IP₆）to protect Ag nanoparticles（Ag NPs）to prepare stable SERS substrates,modified with L-cysteine（L-Cys）and rhodamine 6G（R6G）,and R6G as Raman probe.The amino and carboxyl groups on L-Cys will act close to the Ag NPs by the action of Ag NPs,forming more hotspots to enhance the signal of R6G.In the presence of trace amounts of Cu²⁺,L-Cys molecules and Cu²⁺ions occur selective oxidation reduces the R6G signal.In addition,IP₆ with six phosphate groups can enrich Cu²⁺ions through strong interactions.The sensitivity is as low as 10 pM,the linear range is 1×10^-66 to 1×10^-10 M,and the linear relationship is good（R²=0.9907）.Ten experiments are repeated,and the relative standard deviation（RSD）is 10.15%.The recovery rate was between 88.7%and 113.4%,indicating that the method can meet the requirements of practical applications.We have proposed a method for modifying gold nanoparticles by modifying a long-chain lipoic acid（Ta）molecule on the surface of gold nanoparticles,which can increase the distance between gold nanoparticles and reduce the signal of Raman probe,when Hg²⁺is present,competes with the Ta molecule and causes agglomeration of the gold nanoparticles,enhancing the signal of the rhodamine 6G.The Au-Ta/R6G-based SERS protocol is used to rapidly determine Hg²⁺in river water with a sensitivity as low as 0.01 ppb.The recovery of Hg²⁺in river water is between 87.2%and 108.6%.No sample pretreatment is required.In the work of Chapter 3,the surface modification of lipoic acid of gold nanoparticles is easily oxidized by oxygen in the air,which has certain limitations in the actual operation.Therefore,in the work of Chapter 4,consider another sulfhydryl reagent.Trimethyl propyl triethoxy silane（MPTES）is modified on the surface of magnetic Fe₃O₄ nanoparticles,and after incubation with gold nanoparticles,the Au-S chemical bond is formed to connect the two together.And the enrichment by magnetic materials is more convenient and quicker.The method has a minimum detection concentration of 0.01 ppb and a good linear relationship between 10 ppb and 0.01 ppb（R²=0.937）.