Enzyme immobilization on nitrocellulose film for pH-EGFET type biosensors

This investigation evaluated an EGFET biosensor in which the enzyme was immobilized on a nitrocellulose film. A porous nitrocellulose layer, formed by an inverse phase process, was deposited directly on a SnO2/ITO gate by spin-coating. To ensure optimal surface chemistry conditions under which the EGFET had appropriate pH sensitivity and protein-immobilizing capacity, the nitrocellulose film manufacturing conditions were investigated, and were found to be determined by the inverse phase process, the rate of the spin coater, and the concentration of nitrocellulose. To determine the protein-immobilizing capacity of the nitrocellulose-modified EGFET, urease was immobilized on the nitrocellulose film, and was adopted as a urea biosensor. The device exhibited a response of 136 mV for urea at a concentration of 64 mg/dl. The porous surface of nitrocellulose constitutes a low diffusion barrier, and has a fast response time of 20 s. In a stability test, the sensor maintained its excellent performance in detecting urea in 27 measurements performed over 60 days. The developed nitrocellulose-modified EGFET was therefore proved to have potential application as a biosensor for determining enzymes or antigen-antibody reactions.