USE OF PHOTOPOLYMERIZABLE MEMBRANES BASED ON POLYACRYLAMIDE HYDROGELSFOR ENZYMATIC MICROSENSOR CONSTRUCTION

The construction of enzymatic microsensors based on semiconductor tech nology and photo-curable membranes is reported in this work. A planar three-microelectrode cell and a pH-sensitive Ion Selective Field-Effec t Transistor (ISFET) with Si3N4 membrane have been used as transducers for glucose and urea measurements, respectively. Polyacrylamide has b een employed as matrix material for the immobilization by entrapment o f the enzyme. This hydrogel permits the membrane deposition and patter ning by photolithographic techniques which are compatible with semicon ductor technology. It also provides reproducible and thin membranes du e to the possible automatization of the whole process. In order to imp rove the longterm stability of the sensor, the introduction of glutara ldehyde in the membrane for inter-enzyme cross-linking has been tested . Both methods of membrane preparation, with the cross-linker and with out it, have been compared observing an increase of the long-term stab ility of around two times for glucose and urea sensors. The response c haracteristics of glucose and urea sensors using several membrane prep arations have been studied under different measurement conditions. A s ensitivity of 45-67 nA mM(-1) in a linear range 4x10(-3)-1 mM dependin g on the membrane thickness and enzyme concentration has been observed for the amperometric glucose sensor. A sensitivity from 50 to 58 mV p er decade in a concentration range 0.2-8 mM urea depending on the memb rane preparation has been obtained for the urea enzymatic Field-Effect Transistor (ENFET) sensor. (C) 1997 Elsevier Science B.V.