Biosensors based on a light-addressable potentiometric sensor (LAPS) for analysis both aqueous solutions and organic solvents

Characteristics of a light-addressable potentiometric sensor (LAPS) based o n silicon with Ta2O5 dielectric are reported. The pH sensitivity obtained i s 45 mV/pH unit in the pH range from 4.01 to 7.5 (for measurements conducte d in citrate buffer solutions) and 55 mV/pH unit over the pH range from 7.5 to 8.9 (for measurements conducted in Tris-HCl buffer solutions). The kine tic characteristics (K-m, V-m, pH-profile) of different enzymes, i.e., gluc ose oxidase, alpha-chymotrypsin, butyrylcholinesterase, and urease, have be en measured under homogeneous conditions. The values of the Michaelis const ant obtained are very close to analogous data described in the literature. Biosensors were prepared by immobilization of the enzymes on a pH-sensitive matrix. Two methods of immobilization were used: incorporation into a hydr ophilic matrix of bovine serum albumin (BSA) and incorporation into a hydro phobic matrix of modified polyethylenimine (PEI). It is demonstrated that L APS can be used for recording the enzymatic reactions in organic media (mix ture of the solvents).