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

Characteristics of a light-addressable potentiometric sensor (LAPS) based on silicon with Ta₂O₅ dielectric are reported. The pH sensitivity obtained is 45 mV/pH unit in the pH range from 4.01 to 7.5 (for measurements conducted 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 kinetic characteristics (K _m ³ V _m ⁵ pH-profile) of different enzymes, i.e., glucose oxidase, α-chymotrypsin, butyrylcholin esterase, and urease, have been measured under homogeneous conditions. The values of the Michaelis constant 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 in to a hydrophilic matrix of bovine serum albumin (BSA) and incorporation into a hydrophobic matrix of modified polyethylenimine (PEl). It is demonstrated that LAPS can be used for recording the enzymatic reactions in organic media (mixture of the solvents).