Recent developments in organically doped sol-gel sensors: A microns-scale probe; successful trapping of purified polyclonal antibodies; solutions to the dopant-leaching problem

We describe recent advances made in our laboratories in the general field of organically and bio-organically doped sol-gel sensors. The developments described are: (a) The first miniaturization of a sol-gel sensor down to the microns scale, with potential applications to near-field optical microscopy, using a fluorescent pH-indicator. (b) The first successful sol-gel encapsulation of purified polyclonal antibodies, and in particular an anti-nitroaromatics immunoglobulin, with which selective sensing of nitroaromatics, an important class of environmental pollutants, was demonstrated. (c) The leaching problem, occasionally encountered in doping procedures, is solved by two methodologies: First, TMOS polymerization at high acidity and low water content was found to result in non-leachable yet reactive matrices, as demonstrated with O₂ sensing by excited state pyrene and with H⁺ sensing by excited state pyranine; and second, doping with molecules capable of forming a covalent bond within the encapsulating cage results in the permanent anchoring of the dopant. Thus, Methyl-Red, a pH indicator, was derivatized with a silylating residue, and a polymerizing TMOS was doped with it forming a pH-shifted indicator. With both methodologies, leachability was practically zero.