Electrochemical Sensors For Determination Of Heavy Metal Ions

Heavy metals,especially Pb²⁺,Hg²⁺,Cd²⁺and Cu²⁺,have attracted huge attention around the world for the high toxicity which may directly or indirectly affect human health.Therefore,it is of great significance to pursue a sensitive,fast,convenient,efficient and low-cost electrochemical sensor for trace heavy metal ions detection.This dissertation intends to use fluorine doped tin oxide（FTO）to construct electrochemical sensors for copper ion and lead ion detection including the following three aspects:1.A sensitive electrochemical sensor for the detection of Cu²⁺was constructed based on the self-assembly of 4-mercaptobenzoic acid（4-MBA）on the surface of gold nanoparticles（AuNPs）.Firstly,AuNPs were electrochemically deposited on fluorine doped tin oxide.Then,4-MBA containing carboxyl chelator,was self-assembled on the surface of AuNPs through S-Au bond.The strong chelation of Cu²⁺with 4-MBA formed a stable Cu²⁺-4-MBA complex.Square wave voltammetry（SWV）was applied to determine the concentration of Cu²⁺.Under optimized condition,the oxidation peak current of Cu²⁺-4-MBA complex is proportional to the concentration of Cu²⁺in the range of 10–1500 nM with limit detection of 8 nM.The proposed electrochemical sensor showed excellent selectivity towards Cu²⁺.In addition,the sensor could be used to determine the concentrations of Cu²⁺in Huangpu River.2.A novel metal-enhanced electrochemical sensor based on 4-mercaptobenzoic acid（MBA）modified silver nanoparticles（AgNPs）signal amplification was presented for highly sensitive determination of Cu²⁺.AuNPs were electrochemically deposited on FTO,and then MBA was self-assembled onto the surface of gold nanoislands through S-Au bond.The carboxyl of MBA could be chelated with target analyte Cu²⁺in solution.Subsequently,MBA-AgNPs nanoprobes could be chelated with captured Cu²⁺on the electrode as well as Cu²⁺in solution through the carboxyl,forming AgNPs-MBA-Cu²⁺-MBA-AgNPs architecture on the electrode surface.In this way,large amount of Cu²⁺were captured on the modified electrode.Herein,instead of directly probing the electro-oxidation peak of captured Cu²⁺,the concentration of Cu²⁺was determined by measuring the electrochemical oxidation signal of AgNPs.Under optimum conditions,the electrochemistry sensor of Cu²⁺performed a good linear range of 0.1–100 nM with low detection limit of 0.08 nM.3.Highly sensitive electrochemical signal enhanced sensor of Pb²⁺based on glutathione-modified silver nanoparticles（GSH-AgNPs）and reduced graphene oxide（rGO）was developed.Firstly,FTO was utilized as the substrate of the electrodeposition of reduced graphene oxide/gold nanoparticles（rGO/AuNPs）,and then glutathione（GSH）was self-assembled on the surface of AuNPs.The GSH molecules on the AuNPs could be chelated with Pb²⁺in aqueous solution and then Pb²⁺could be chelated with GSH-AgNPs to form a stable complex immobilized on the surface of the modified electrode.The electrodeposited rGO/AuNPs and the synthesized GSH-AgNPs nanoprobe were used for amplification.The rGO/AuNPs could improve the conductivity of the modified electrode.The GSH-AgNPs nanoprobe captured more Pb²⁺in solution and formed a stable AgNPs-GSH-Pb²⁺-GSH-rGO/AuNPs structure.In this way,large amount of Pb²⁺were captured on the modified electrode.Thus,we could use SWV to detected Pb²⁺by measuring the electrochemical oxidation signal of AgNPs.The sensor had good analytical performance,including wide linear range,high sensitivity,low detection limit and good repeatability which had promising potential in detecting Pb²⁺in real samples.