Application Of Electrochemical Sensors Based On Nanostructured Materials For Heavy Metal Detection In Water

Heavy metal contamination is persistent and bioaccumulative and may cause serious damage even in trace amounts.The heavy metals in water may destroy the balance of water ecosystem,and on the other hand,also threaten the safety of human beings at all times.Therefore,it is very important to develop highly sensitive,rapid and low-cost detection technologies for heavy metals.Compared with traditional detection technologies of heavy metals,the electrochemical sensors have many advantages such as fast response,simple equipment,low detection cost,and they are easy to carry and realize the automation and real-time online monitoring,which make their application prospect broader.As a hotspot in recent years,nano structured materials possess many unique physical and chemical properties compared with ordinary macroscopic materials,which provide a great space for the development of electrochemical sensors.Electrochemical sensors based on nanostructured materials usually exhibit some excellent properties such as smaller volume,faster detection speed,higher sensitivity and wider linear detection range.Based on some nanostructured materials,this paper constructed a series of electrochemical sensors for detection of common heavy metal ions in water combining with electrochemical analysis techniques adequately.In the second chapter,a reusable electrochemical biosensor was developed for highly sensitive detection of mercury ion(Hg2+)using an anionic intercalator,which was based on Hg2+-induced conformational change of a thymine-rich,single-stranded DNA supported on the platform of ordered mesoporous carbon(OMC)and self-doped polyaniline(SPAN)nanofibers.In the presence of Hg2+,the mercury-specific oligonucleotides were induced and folded into hairpin structure from random coils,and then the indicators intercalated into the hairpin structure and increased electric signal.The OMC and SPAN nanofibers modified glassy carbon electrode exhibited excellent electron transfer ability and provided a good platform for DNA immobilization.Under the optimal conditions,the detection limit for Hg2+was 0.6 fM(S/N=3).Furthermore,the sensor could be easily regenerated by cysteine for cyclic utilization.To investigate its practical application ability,some environmental samples including lake sediment pore water and tap water were analyzed by the developed sensor,and the relatively satisfactory results indicated that it provided a green and promising strategy for detection of trace Hg2+ in the practical application.In the third chapter,a glassy carbon electrode was modified with SPAN nanofibers and mesoporous carbon nitride(MCN)for simultaneous determination of trace cadmium ion(Cd2+)and lead ion(Pb2+)by square wave anodic stripping voltammetry in the presence of bismuth.The morphology property of MCN was characterized by transmission electron microscopy,and electrochemical properties of the modified electrode were characterized by cyclic voltammetry and electrochemical impedance spectroscopy.Experimental parameters such as supporting electrolyte solution and deposition time were optimized.Under the optimum conditions,the constructed electrochemical sensor exhibited exhibited excellent detection performance,the linear detection ranges were both from 5 to 80 ?g L-1 for Cd2+ and Pb2+.The detection limit were 0.7 ?g L-1 for Cd2+ and 0.2 ?g L-1 for Pb2+(S/N=3).The experimental results also showed that the sensor have good repeatability,reproducibility,anti-interference ability and practical application ability.In the fourth chapter,we proposed a construction method of electrochemical biosensor for detection of silver ions(Ag+)based on gold nanoparticles(AuNPs)and specific DNAzyme.A glassy carbon electrode modified with AuNPs was used as an immobilization platform for an Ag+ specific DNAzyme.In the presence of Ag+,the DNA zyme can be induced to catalyze the cleavage of the complementary substrate chain at the cleavage site,thereby causing a change of electrical signal.In the process of detection,methylene blue(MB)was used as the signal indicator.Besides,the DNA probes labeled with AuNPs was used as a signal amplifier to adsorb a large amount of MB for further enhancing the signal response.The experimental results indicated that the design and detection strategy of the electrochemical biosensor is feasible.The sensor showed an excellent response to Ag+,which has the significance of further study.