Study On Electrochemical Immunosensor Based On Interdigitated Microelectrode

Biosensor is analytical device composed of a biological recognition element coupled to a chemical or physical transducer. It has many advantages such as high sensitivity, quick response, simple and convenient manipulation, low cost and continuous detection. The composition, basic principle and development of biosensor are introduced, the application of biosensor in the field of life science, biomedicine, environmental inspection, food production and military defense are summarized. The prospect of biosensor development is also prognosticated. In this thesis, the interdigitated microelectrodes have been prepared by help of the UV-LIGA method and also applied in the electrical immunosensor field. The positive effect of this notable and novel biosensor will be sustained both in business and research lab in future.(1) Interdigitated microelectrodes were prepared using UV-LIGA method. With the rapid development and application of MEMS (Micro Electro Mechanical System) in the recent years, the micro-fabrication technology is improving. UV-LIGA technology is a micro-fabrication technology derived from LIGA. Comparing with LIGA, UV-LIGA has notable characteristics of simple exposure process and low cost, and it attracts much attention and research. By the method of UV-LIGA, the typical dimensions of an individual microband finger are 0.1 m in height, 5 m in width; 3mm in length, with a gap of 5 m between the fingers.(2) A novel ultra-sensitive electrical immunosensor using an interdigitated microelectrode was proposed based on an enzyme-linked immunoassay format with enzymatic silver deposition for the detection of an antigen of hIgG. The capture antibody was covalently immobilized on the gaps through a silanization layer. The presence of hIgG resulted in the formation of a sandwiched complex of IgG with the capture antibody and the detection antibody conjugated with alkaline phosphatase, which could catalyze the production of a reductive agent ascorbic acid. The reduction of Ag+ ions by ascorbic acid yielded dispersed silver deposits over the microgaps, allowing the interdigitated electrodes to be electrically connected with a readily detectable increase in electrical conductance. This strategy was the first demonstration of incorporating enzymatic deposition of conductive materials in electrical detection for the development of biosensors. Such enzyme-based transformation was analyse-specific, highly efficient, and easily controlled, thereby offering the possibilities of enormous signal amplification without side effects from interfering enhancement reactions. The results revealed that the electrical conductance signal showed linear dependency on IgG concentration over a range from 1.0 fg mL-1 to 100 ng mL-1.(3) A novel electrochemical sensor was developed for sensitive and selective detection of mercury (II) based on thymine-Hg²⁺-thymine coordination chemistry. This strategy exploited the cooperativity of proximate poly-T oligonucleotides in coordination with Hg²⁺. Ferrocene-tagged poly-T oligonucleotides were immobilized on the electrode surface via self-assembly of the terminal thiol moiety. In the presence of Hg²⁺, a pair of poly-T oligonucleotides could cooperatively coordinate with Hg²⁺, which triggered a conformational reorganization of the poly-T oligonucleotides from flexible single strands to relatively rigid duplex-like complexes, thus drawing the Fc tags away from the electrode with a substantially decreased redox current. In addition, this sensor could be implemented using minimal reagents and working steps with excellent reusability through mild regeneration procedure. It was expected that this cost-effective electrochemical sensor might hold considerable potential in on-site applications of Hg²⁺ detection.