Controlled-pore glasses embedded in plastic optical fibers for gastric pH sensing purposes

The present work is concerned with the development of an optical-fiber pH sensor for gastric monitoring. Bromophenol blue is used as a chromophore, which is immobilized on controlled-pore glasses (CPGs) by means of a silylation process. As far as the optoelectronic unit is concerned, light-emitting diodes as sources and an appropriate electronic circuit as detection system are utilized. Treated CPGs are fixed at the end of two plastic optical fibers (core diameter = 500 ?m) by means of a proprietary process; a reflector made of Teflon, anchored to the distal end of the fibers, ensures good fibers/probe coupling efficiency. The behavior of the realized probe is carefully investigated, with particular attention devoted to the presence of hysteresis, to ionic strength and temperature effect, and to its lifetime. The fast response time, thanks to the absence of a mechanical envelope, the small dimensions of the probe, and the biocompatibility of the utilized materials make this sensor suitable for in vivo measurements.