Stuides On Ultra-trace Detection Of Heavy Metal Ions Based On Fast-scan Voltammetry

In this paper,the general situation of environmental pollution of cadmium ions and mercury ions,the detection methods for cadmium ions and mercury ions,the application of aptamer,the fast-scan voltammetry technology and functionalized graphene composites were systematically and comprehensively reviewed.Aptamer of functional single-stranded DNA or RNA sequences were obtained from nucleic acid molecular libraries.Aptamer has been widely used in analytical detection due to good chemical stability and specific recognition.In this study,a several of electrochemical biosensors for cadmium ions and mercury ions detection based on the aptamer with specific recognition ability for cadmium ions and mercury ions were constructed by ultrasensitive fast-scan voltammetry technology.The purpose of ultra-trace detection of cadmium ions and mercury ions in water was realized.The specific research contents were described as follows:1.An ultrasensitive method for detecting picomolar levels of cadmium?II?by fast-scan anodic stripping voltammetryThis work reported an approach for the determination of the heavy metal ion cadmium Cd?II?using a bismuth-film electrode?Bi-FE?with fast-scan anodic stripping voltammetry?FSASV?.The experiment was divided into two steps.First,the Bi-FE was prepared by electrodepositing a metallic bismuth-film onto the electrode,and then the target metal ion Cd?II?was electrochemically preconcentrated on the Bi-FE.Second,the target metal was measured with FSASV.At a scan rate of 400 V/s,the anodic stripping peak current increased gradually with increasing Cd?II?concentration,and a linear relationship between the peak current and the logarithm of Cd?II?concentration was obtained from 0.1?mol/L to 1.0 pmol/L,with a detection limit of 0.3 pmol/L?S/N=3?.Furthermore,the method was successfully applied to detect Cd?II?in spiked tap water samples,with sufficient recoveries in the range of 94.0%to 105.2%and corresponding relative standard deviations ranging from 2.9%to 6.4%.Therefore,FSASV is a simple,rapid and ultrasensitive method for the detection of picomolar levels of Cd?II?.2.An ultrasensitive fast-scan voltammetry and electrochemiluminescence dual-channel electrochemical sensor for detection of mercury ionHere,a high sensitivity method for the detection of Hg²⁺was developed based on fast-scan cyclic voltammetry?FSCV?and electrochemiluminescence?ECL?dual-channel electrochemical sensor.Thymine?T?-rich single-stranded DNA?ssDNA?was selected as the capture unit,and ferrocene?Fc?as the signal unit was fixed on one ssDNA end.In the presence of Hg²⁺,it induced conformational changes of ssDNA,the hairpin structure of bended ssDNA was formed.The distance between Fc and the electrode surface were shorted,the electron transfer efficiency and current intensity of the output channel of signal were enhanced.In addition,the electron transfer between Luminol and the electrode from the bended hairpin structure of ssDNA were hindered.The electron transfer efficiency and luminescence intensity of the output channel of signal were weaken.The target metal of Hg²⁺was measured at a scan rate of 400 V/s with FSCV,the peak current increased gradually with increasing Hg²⁺concentration,and a linear relationship between the peak current and the logarithm of Hg²⁺concentration was obtained from 10^-7 to 10^-10 mol/L,with a detection limit of 3×10^-11 mol/L?S/N=3?.The t-test was further used to determine if two sets of data from FSCV and ECL were obviously different from each other.The electrochemical sensors have been broad application prospects in water environment safety detection and field environmental monitoring.3.Fast-scan cyclic voltammetric electrochemical biosensor for detection of mercury ion based on Faraday cage-typeHere,a Faraday cage-type electrochemical biosensor for ultrasensitive detection of Hg²⁺was constructed based on functional graphene?rGO-NH₂?-ferrocene?Fc?-gold nanoparticles?AuNPs?composite?rGO-NH₂@AuNPs&Fc?-aptamer with fast-scan cyclic voltammetry?FSCV?.The multiple of probe DNA chains were used as capture unit.Probe DNA3 and Probe DNA1 of single-stranded DNA with 3?end modified sulfhydryl group?SH?.Probe DNA3 was modified on gold electrode and Probe DNA1 was modified on AuNPs surface based on Au-S bonding.The DNA double helix structure was formed from Probe DNA2 and 3?end of Probe DNA1complement each other.The Probe DNA1 of rigid structure was maintained on AuNPs composite material.In the presence of Hg²⁺,the Hg²⁺was captured due to the formation of thymine?T?-Hg²⁺-thymine(T-Hg²⁺-T)comlplexes by Probe DNA3 and Probe DNA1.A large number of Fc signal units were connected to the rGO surface,in which the signal units were fixed on the electrode surface,resembling a Faraday cage-type structure.In the absence of Hg²⁺,the rGO-NH2@AuNPs&Fc composite material will not be fixed on the electrode,and the current signal was not output.The experimental results show that the peak current increased gradually with increasing Hg²⁺concentration,and a linear relationship between the peak current and the logarithm of Hg²⁺concentration was obtained from 0.1?mol/L to 0.1 pmol/L,with a detection limit of 0.03pmol/L?S/N=3?.The sensor provided an effective method for the highly sensitive detection of Hg²⁺in real water samples.