Amperometric Biosensing Studies Base On Electrodeposited Chitosan And The Polymer From Dopamine Oxidation

The enzymatic electrode is one kind of electrochemical biosensorsthat combines highly specific enzymatic catalytic reactions with highlysensitive electrochemical detection, which has developed very rapidly inthe past decades.The electrochemical quartz crystal impedance analysis (EQCIA) isan important analytical method for monitoring the processes ofchemo-/bio-modification on electrode surfaces, via a simultaneous andrapid measurement of the electroacoustic impedance for the piezoelectricquartz crystal (PQC) resonance, from which multiple chemical/physicalparameters and material-relevant characteristics during anelectrochemical perturbation can be acquired, such as electrode-masschanges down to the nanogram level, the solution viscodensity, and theelasticity of modified films.In the present thesis, we have carried out some innovative researcheson the electrodeposition of chitosan (CS), the immobilization of glucoseoxidase (GOD) and constructions of enzymatic electrodes. The maincontents are as follows,1. The concept and construction of the biosensors, mainly involvingimmobilization methods for biomolecules, as well as the principle andapplication of the electrochemical quartz crystal microbalance(EQCM), have been briefly reviewed.2. A novel method to immobilize GOD in 1,4-Benzoquinoneelectroreduction-induced deposition of thickness-controllableenzyme-chitosan-MWCNT nanocomposite film has been proposed. The EQCIA technology was used to monitor the process of chitosandeposition on the Au electrode. The result suggested that the chitosanfilm deposited by electroreduction was nonrigid hydrogel. A glucosebiosensor with good performance was thus fabricated, and comparedwith the sensors via H₂O₂ or H₂O electroredution method. The effectsof experimental parameters on the sensor performance, includingapplied potential, solution pH were examined. At an optimal potentialof 0.7 V vs SCE, the current response of the biosensor in selectedphosphate buffer (pH 7.0) was linear with glucose concentration from0.005 to 8 mM, with lower limit of detection of 2μM (S/N=3), shortresponse time (within 15s), The Michaelis constant (K_m^app) wasestimated as 6.8 mM.3. The EQCIA technology was used to monitor the process ofelectrodeposition of Prussian blue (PB) on Au electrode. A hydrogenperoxide (H₂O₂) biosensor with good performance was constructed,via the quantity optimization for PB, and effects of experimentalparameters on the sensor performance, including applied potential,solution pH and electroactive interferents, were examined. At anoptimal potential of-0.25 V vs SCE, the current response of thebiosensor in the selected phosphate buffer (pH 7.0) was linear with theconcentration of H₂O₂ from 1μM to 5 mM, with a lower limit ofdetection of 0.27μM (S/N=3), short response time (within 10s). Thebiosensor exhibited good storage stability.4. A new enzymatic electrode with cost effectiveness and goodperformance for glucose detection was developed by codepositingglucose oxidase into the polymer from electrochemical oxidation of dopamine (DA) on a Pt-modified 8B pencil lead electrode. Effects ofconcentrations of phosphate buffer, DA and GOD were investigated.At the optimal potential of 0.65 V versus the KCl-saturated calomelelectrode (SCE), the current response of the biosensor in the selectedphosphate buffer (pH 7.0) was linear with the concentration of glucosefrom 0.05 to 12 mM, with a lower detection limit of 6μM (S/N=3),short response time (within 15s) and good anti-interferent ability. TheMichaelis constant (K_m^app) was estimated to be 9.21 mM. Thebiosensor exhibited good storage stability, i.e. 97% of its initialresponse was retained after 7-day storage in the selected phosphatebuffer at 4℃, and even after another three weeks the biosensorretained 93% of its initial response.