ABSTRACTWe 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.
Sol–gel-entrapped pH indicator for monitoring pH variations in cementitious materials