OPTICAL CHEMICAL SENSORS BASED ON SOL-GEL MATERIALS - RECENT ADVANCESAND CRITICAL ISSUES

The use of the sol-gel process to produce materials for optical chemic al sensors and biosensors is attracting considerable interest. This in terest derives mainly from the design flexibility of the sol-gel proce ss and the ease of fabrication. In most applications the sol-gel mater ial is used to provide a microporous support matrix in which analyte-s ensitive species are entrapped and into which smaller analyte molecule s may diffuse. Sensors based on entrapped organic and inorganic dyes, enzymes and other biomolecules have been reported. A range of sensor c onfigurations has been employed, including monoliths, thin films, as w ell as more elaborate structures. In this paper a selection is present ed of recent significant developments in optical chemical sensors whic h employ sol-gel-derived materials. These developments include the tai loring of sol-gel materials to optimise sensor response, advanced wave guide structures and novel probe-tip sensors. Those issues which remai n critical to the eventual deployment of sol-gel sensors are examined. In particular, the problems of leaching, microstructural stability, d iffusion-limited response time, and susceptibility to interferents are discussed and some solutions proposed.