Study On The Photohormone β-Indole Acetic Acid Electrochemical Biosensor And Other Biosensor

Electrochemical biosensors have been widely applied because of their high sensitivity, simplicity, inexpensive, amenable miniaturization and operating convenience. At present, they have been extensively used in the life science, environmental monitoring, the food and medicine etc. Electrochemical biosensors are the most commonly used class of biosensors. They are based on the fact that during a bio-interaction process, electrochemical species such as electrons are consumed or generated producing an electrochemical signal, which can in turn be measured by an electrochemical detector. Immobilization methods of biomolecules are of the most importance for improving the performances of biosensors. The aim of the immobilization is to preserve inherent biological activity of biomolecules and firmly combine them with base electrode. There are many methods for the immobilization of biomolecules directly or indirectly. Commonly, they are immobilized onto an electrode surface by adsorption, cross-linking, covalent binding and entrapment in gels or polymer. These methods can be combined under different conditions. In this paper, two kind of sensors for determination of auxin and peroxide hydrogen have been developed, which based on the new method for the immobilization of biomolecules and the special performance of mediator. The main works are summarized as follows:1. A novel photohormone indole 3-acetic acid sensor, plant tissue-ferrocene modified carbon paste electrode (PFMCE), has been developed. The features of the electrode were investigated by cyclic voltammetry and the basic conditions needed for the optimal activity of IAA oxidase were also studied. Ferrocene entrapped in the carbon paste was used as a mediator of transferred electron. Under the catalysis of IAA oxidase containing in the pant tissue, IAA can be easily oxidized. The current response on the PFMCE was linear with the IAA concentration in the range of 8-160g/mL. The sensor was applied to the determination of the recovery in the samples with satisfactory results.2. A competitive binding assay used to determine hapten IAA with the aid of HRP-IAA conjugate has been developed. It was based on the ordered, stable mercaptoself-assembled monolayer formed on gold surface, which immobilized IgG with covalent bond. The features of substrate reaction under different conditions were investigated by cyclic voltammetry and the assay conditions were optimized. Under applied potential of -200mV, the response current was linear with the log [IAA].3. A sensitive amperometric sensor for the determination of H2O2 has been proposed. Horseradish peroxidase was successfully immobilized on nano-Au colloids based on the thiol-tailed groups of cysteamine binded to the 2,6-pyridinedicarboxlic acid polymer. With the aid of the hydroquinone in the solution, the sensor displayed excellent electrocatalytical response to the reduction of H2O2 Compared with enzyme-polymer modified sensor, the immobilization of enzyme was simple and the sensor exhibited a better stability and reproducibility.4. A novel amperometric sensor has been constructed for the determination of H2O2. It was based on catalyzing electroreduction of hydrogen peroxide by metal hexacyanoferrate, which were electrodeposited on gold wire electrodes, under a certain potential. The features of modified electrode were investigated by cyclic voltammetry and the assay conditions were optimized. The modified electrodes were further covered with Nafion membrane that could erase the interference. The sensors have the same performance as enzyme modified electrodes reported in literature.