Polyaniline / Horseradish Peroxidase Or Polyphenol Oxidase Biosensor Of The Building

PANI synthesized in proton acid solution losts its redox activity and conductivity at pH over 4. The drawback restricts its application in enzyme biosensor. So we will improve the properties of PANI through changing the experiment conditions. The PANI synthesized in a solution containing ionic liquid, 1-ethyl-3-methylimidazolium ethyl sulfate (EMIES), is an electroactive polymer at pH over 4. The following results indicate that PANI is an ideal material for the construction of biosensor.The hydrogen peroxide biosensor is constructed by cross-linking between horseradish peroxidase (HRP) and polyaniline (PANI) using glutaraldehyde as a cross linking agent on F-doped tin oxide (FTO) electrode. It is easy to characterize the biosensor due to the excellent optical transparency of FTO. The process of immobilized HRP is unrelated to isoelectric point of the enzyme and is particularly mild. The response current increases linearly with increasing hydrogen peroxide concentration up to 20 mmol dm^-3. The maximum response current (I_max) and the Michaelis-Menten constant ( k_m') are 1.189μA and 27.11 mmol dm^-3 respectively. The response current of the biosensor increases with increasing temperature below 40℃. The activation energy (E_a) of the HRP catalytic reaction is 39.1 kJ mol^-1 in the B-R buffer. The biosensor is also characterized with SEM and CV.The catechol biosensor is constructed by cross-linking between polyphenol oxidase (PPO) and polyaniline (PANI) using glutaraldehyde as a cross-linking agent. The PANI can protect the immobilized PPO due to the biocompatible microenvironment of PANI film. In the presence of catechol as a substrate, the biosensor exhibits a linear range up to 80μmol dm^-3. The maximum response current (I_max) and the Michaelis-Menten constant ( k_m') are 9.44μA and 117μmol dm^-3, respectively. The value of the Michaelis-Menton constant k_m' indicates that the interaction between immobilized PPO and catechol is stronger than that between free PPO and catechol. The effects of pH and operating potential are also explored to optimize measurement conditions. The activation energy (E_a) of the PPO catalytic reaction is 30.23 kJ mol^-1 in the B-R buffer. Electrochemical impedance spectroscopy (EIS), UV-vis and SEM are used to characterize the PANI-PPO biosensor. The biosensor exhibits good long-term stability.A PANI/PPO biosensor for the determination of benzoic acid is reported. The biosensor functioning is based on the inhibition effect of benzoic acid on the biocatalytic activity of the enzyme. The kinetic parameters Michaelis-Menten constant (k_m') and maximum current (I_max) in the absence and in the presence of benzoic acid are also evaluated. The kinetic analyses show that the inhibition of benzoic acid on the PPO activity is reversible and competitive with the inhibition constant determined to be 28.7μmol dm^-3. A limit of detection of 0.3μmol dm^-3 benzoic acid is obtained. The I_0.5 value is estimated to be 35μmol dm^-3. The biosensor has good sensivity and high stability. So it can be used as a new approach for the determination of benzoic acid.