Fabrication And Application Of Novel Chemically Modified Electrodes

In electrochemistry, electrodes can be functionally designed for selective detections through chemical modification of the electrode surface. In this thesis, three types of chemically modified glass carbon electrodes (GCEs) have been fabricated using different methods, and their applications in biosensing and chemical sensing have been assayed:The first one, a biomolecule-modified GCE, was fabricated by covalently immobilizing transcription factor Sp1 on the GCE surface and the interaction of immobilized Sp1 with different DNA samples was analyzed using electrochemical impedance spectroscopy (EIS) and difference pulse voltammetry (DPV). Our results show that both the association/disassociation of Sp1 with its consensus sequence (wtDNA) under different conditions and the change of affinity caused by either point mutations or an inhibitor (anticancer drug mithramycin A) can be effectively monitored through Sp1-functionalized GCE, and as low as 1×10?10 mol/L wtDNA can be selectively detected in a DNA pool containing huge access of non-specific DNA fragments.I further developed an enhanced electrode from the above one, taking the advantage of bio-compatible and high electrical conductive carbon nanoparticles (CNPs) derived from glucose by one step hydrothermal oxidation method. To fabricate this electrode, the bare GCE was first modified by CNPs before protein (Sp1) immobilization. The CNPs-modification greatly enhanced the performance of the electrode, and was able to lower the detection limit of Sp1-specific DNA to 1×10?15 mol/L. The CNPs-Sp1-modified GCE exihibits enhanced signal-to-noise ratio, and can be easily regenerated, suggesting a promising approach for rapid and highly sensitive DNA detection.For the last one, L-cysteine modified CNPs were immobilized on the GCE by Nafion. This modified electrode was used to detect trace amount of heavy metal ions by anodic stripping voltammeter. Both Pb²⁺ and Cd²⁺ can be detected concurrently in a mixture, and compare to the bare GCE, the Cys-CNPs modification greatly enhanced the performance of the electrode, successfully lowering the detection limits for Pb2+ and Cd2+ to 1×10^-14 M and 1×10^-9 M, respectively.