| The food safety issues caused by heavy metals pose a serious threat to both the safety of food production and people’s lives.As a result,heavy metal testing has become a necessary means of ensuring food safety.However,traditional testing methods are often associated with drawbacks such as long detection times,high costs,and unsuitability for on-site testing.Therefore,the development of a simple,rapid,accurate,and low-cost testing method is of great academic and practical significance.Electrochemical methods are widely used in the field of rapid heavy metal detection due to their advantages such as simplicity,rapidity,accuracy,high sensitivity,and real-time performance.In this study,carbon-based nanomaterials were used to modify the electrode surface in order to improve the electrochemical performance of the sensor.To achieve high-selectivity detection of metal ions,molecular recognition elements were introduced as recognition units,and a novel electrochemical sensor was constructed and successfully used for the detection of lead and cadmium ions.The main research content and results are as follows:(1)A carbon-based DNA electrochemical sensor was designed for cadmium ion(Cd2+)detection.In this chapter,a competitive electrochemical sensing method was constructed based on a transition metal carbide-methylene bluecomplementary DNA(MXene-MB-cDNA)probe for Cd2+ detection.Gold nanoparticles(AuNPs)were electrodeposited onto a glassy carbon electrode surface and assembled with Cd2+ aptamer(Cd2+Apt)through Au-S bonding to achieve specific recognition and capture of Cd2+.Additionally,MXene was used as a nanocarrier to provide multiple binding sites for cDNA binding and MB adsorption.The presence of Cd2+led to a conformational change in the DNA structure,causing the MB-cDNA-loaded MXene material to move away from the electrode surface.A significant change in MB signal peak value was observed at-0.3 V,providing the basis for Cd2+detection.After the method was constructed,experimental parameters such as Cd2+Apt concentration,Cd2+ Apt incubation time,cDNA concentration,cDNA incubation time,MXene concentration,and Cd2+incubation time were optimized.Under the optimal experimental conditions,when the concentration of Cd2+ varied in the range of 0.01-1.6 mg·L-1,the peak current exhibited a good linear relationship with its concentration,with an R2 of 0.991 and a limit of detection(LOD)of 0.034 mg·L-1.The specificity and stability of the electrochemical method were investigated,and the sensor was applied to the determination of Cd2+content in Xiangjiang water and fish samples.The recoveries of the method ranged from 96.85%to 104.65%with the relative standard deviations(RSD)not exceeding 4.28 in real samples.(2)Based on the first chapter,a novel sensing method was constructed using a composite nanomaterial of reduced graphene oxide-carboxylated carbon nanotubes-nanogold-glutathione(rGO-MWCNT-COOH/AuNPs/GSH)for simultaneous detection of lead ions(Pb2+)and cadmium ions(Cd2+).In this experiment,efficient adsorption of heavy metal ions was achieved by modifying the glassy carbon electrode surface with the composite nanomaterial rGO-MWCNT-COOH/A uNP s/GSH.The three-dimensional hybrid network structure of rGO-MWCNT-COOH served as the substrate and exhibited a synergistic effect in the composite nanomaterial,increasing the adsorption capacity of heavy metal ions.AuNPs,as intermediates between rGO-MWCNT-COOH and GSH,were grown in situ on the surface of the rGO-MWCNT-COOH three-dimensional hybrid network structure by sodium citrate reduction,providing active sites for adsorption of heavy metal ions.At the same time,as the adsorption component of Pb2+and Cd2+,glutathione(GSH)formed a complex with heavy metals through its own thiol group,and was connected to the rGO-MWCNT-COOH/AuNPs surface through an Au-S bond.The three-component composite nanomaterial of rGO-MWCNT-COOH,AuNPs,and GSH exhibited a synergistic effect,and simultaneous detection of Pb2+and Cd2+was achieved by square wave anodic stripping voltammetry(SWASV).After the method was constructed,experimental parameters such as the amount of composite material added to the reaction system,the proportion of rGO-MWCNT-COOH,solution pH value,deposition voltage,and deposition time were optimized.Under the optimal conditions,within the concentration range of 1-70 μg·L-1,the peak current intensity at-0.8 V exhibited a good linear relationship with Cd2+ concentration,with an R2 of 0.998 and a limit of detection(LOD)of 0.2 μg·L-1(S/N=3).Within the concentration range of 1-80μg·L-1,the peak current intensity at-0.56 V exhibited a good linear relationship with Pb2+ concentration,with an R2 of 0.989 and an LOD of 0.31 μg·L-1(S/N=3).Subsequently,the repeatability,stability,and anti-interference ability of the constructed electrochemical method were investigated,and quantitative detection of Pb2+ and Cd2+content in tap water and fish samples was achieved.The recoveries of the method ranged from 97.10%to 100.70%with the relative standard deviations(RSD)not exceeding 3.83 in real samples. |
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