Sol–gel porous materials with tailored or nanostructured cavities have been increasingly used as nanoreactors for the enhancement of reactions between entrapped chemical reactants. The domains of applications issued from these designs and engineering are extremely wide. This tutorial review will focus on one of these domains, in particular on optical chemical sensors, which are the subject of extensive research and development in environment, industry and health.

An innovative and low-cost method is proposed for the detection and discrimination of indole-positive pathogen bacteria. The method allows the non-invasive detection of gaseous indole, released by bacteria, with nanoporous colorimetric sensors. The innovation comes from the use of nanoporous matrices doped with 4-(dimethylamino)-cinnamaldehyde, which act as sponges to trap and concentrate the targeted analyte and turn from transparent to dark green, long before the colonies get visible with naked eyes. With such sensors, it was possible to discriminate E. coli from H. alvei, two indole-positive and negative bacteria after seven hours of incubation.

In this work, the authors show the capabilities of Surface Acoustic Wave (SAW) devices coupled with various absorbents to probe the properties of gas sensitive materials for the manufacturing of hazardous gas sensors. The great capabilities of cobalt corroles for the trapping of carbon monoxide (CO) were exploited to produce selective sensors. These corroles were deposited on SAW delay lines surfaces and then exposed to carbon monoxide (CO) in standard conditions. Concentrations of a few hundreds of ppb were measured emphasizing the interest of such sensors for the detection of CO. Another type of sensitive layers exhibiting specific porosity adapted to the trapping of formaldehyde (CH₂O) were deposited on similar delay lines. A detection threshold of 140 ppb was shown. These encouraging results pave the way for the development of a functionalized SAW sensors network for multi-gas detection in indoor air.