Construction And Application Of Several Functional Nucleic Acid Based Heavy Metal Ion Sensors

In this thesis, by the using of functional nucleic acid as recognition element, and combined with nanomaterials, protein enzymes and DNA self-assembling technique for signal amplification, several novel biosensors have been developed for the sensitive detection of heavy metal ions. There have six chapters in this thesis. The main contents are listed as follows:In chapter 1, we provided a brief introduction to the detection progress of heavy metal ions and the application of biosensors in their detection. The applications of functional nucleic acid and signal amplification technique in the biosensor were also described. The research purpose and contents of this thesis were summarized at last.In chapter 2, a novel highly sensitive and selective electrochemical sensor based on DNAzyme and rolling circle amplification (RCA) for the determination of Pb2+ was developed. The RCA reaction was initiated by Pb2+, which producing a long ssDNA with repeating sequence at last. Subsequently, numerous QDs can be captured through the hybridization for electrochemical detection. Ultra-low level (7.8 pM) of Pb2+ could be detected by this method. The linear range was in the range of 0.01 nM～1.0μM.In chapter 3, a new enzyme-free and ultrasensitive electrochemical Pb2+ biosensor was developed. In the presence of Pb2+, a long cascade DNA structure can be formed as well as assemble of numerous QDs for signal amplification. Under the optimal conditions, a detection limit as low as 6.1 pM can be obtained for Pb2+ with a linear range from 10.0 pM to 500.0 nM.In chapter 4, a novel label-free electrochemical sensor has been developed for the highly sensitive and selective detection of Hg2+. Hg2+ were first captured on the modified electrode surface through the specific T-Hg2+-T coordination, and then catalytic the HAuCl4/NH2OH reaction for the formation of gold nanoparticles (AuNPs). By the introduction of graphene to accelerate electron transfer and amplify the electrochemical signal of AuNPs, a detection limit as low as 0.06 nM could be obtained for Hg2+.In chapter 5, by the using of graphene oxide (GO) as catalytic probes, a novel label free electrochemical biosensor has been fabricated for sensitive detection of Pb2+. The configuration of DNA was changed after interaction with Pb2+, and then producing free ssDNA for the capture of GO. The Ag+ reduction process can be accelerated by the captured GO, which resulted in the formation of silver nanoparticals on GO surface. The detection limit of this assay for Pb2+was 0.08 nM with a linear range from 0.1 nM to 10.0 μM.In chapter 6, a new label free colorimetric sensor has been developed for the highly sensitive detection of Hg2+ based on the DNA hybridization chain reaction (HCR) and silver nanowire for signal amplification. The HCR reaction was initiated by Hg2+ and formed a long cascade dsDNA. The silver nanoparticles were then formed along with the dsDNA template, which resulted in an amplified colorimetric signal. The detection of Hg2+ was achieved with a linear range from 50.0 pM to 3.0 nM and a detection limit of 45.0 pM.