Effect of Glucose Oxidase Immobilizing Techniques on Performances of Nano Scale Polypyrrole Glucose Biosensors

Abstract

Characteristic dependency of nano scale polypyrrole (PPy) glucose biosensors, achieved by three different immobilizing techniques namely, coentrapment, physical adsorption and a two step method of coentrapment superimposed with physical adsorption is reported. Different enzyme loading and material properties resulted in varied immobilizing methods lead to dissimilarities in characteristics. In this study, Pt coated AnodiscTMs (0.2 µm) were used as electrodes to polymerize PPy at 0.3 mA cm-2 using a solution containing 0.05 M Pyrrole and 0.1 M NaPF6. The polymerization time was optimized to 90 s. In the coentrapment method, glucose oxidase (GOx) (1 mg ml-1) was added to the monomer solution while an aliquot of GOx (5 µl) was placed on the pre-polymerized electrode for physical adsorption. A combined procedure of these two techniques was used as the last immobilization technique. Physical adsorption method gave a sensitivity of 3 mA cm-2 M-1 and a linear range of 0.5–13 mM with a response time of a 3 s. Sensitivity in the case of coentrapment was 3.75 mA cm-2 M-1 while it showed a value of 4.45 mA cm-2 M-1 in two step immobilization thus giving 25 and 48% increases respectively. Response times of 9 and 8 s in latter cases reveal the possible repercussion taking place at enzyme immobilization in three dimensional (3-D) PPy matrix and the delay occur in glucose to reach the enzyme. Linear range of the two step method was extended up to 16 mM due to the reinforced enzyme loading.