Photomechanical chemical microsensors

Recently, there has been an increasing demand to perform real-time in situ chemical detection of hazardous materials, contraband chemicals, and explos ive chemicals. The advent of inexpensive mass produced MEMS (microelectrome chanical systems) devices has enabled the use of various microstructures fo r chemical detection. For example, microcantilevers were found to respond t o chemical stimuli by undergoing changes in their bending and resonance fre quency even when a small number of molecules adsorb on their surface. In ou r present studies, we extended this concept by studying changes in both the adsorption-induced stress and photo-induced stress as target chemicals ads orb or desorb on the surface of microcantilevers. We demonstrate that photo -induced bending of microcantilevers depends on the number of absorbed mole cules on their surface. On the other hand, microcantilevers that have under gone photo-induced bending will adsorb a different number of guest molecule s. Depending on the photon wavelength and microcantilever material, the mic rocantilever can be made to bend by expanding or contracting a surface laye r on one of its sides, unequally. Coating the surface of the microstructure with different materials can provide chemical specificity for the target c hemicals. However, by choosing a handful of different photon wavelengths, t unable chemical selectivity can be achieved due to differentiated photo-ind uced response without the need for multiple chemical coatings. We will pres ent and discuss our results on diisopropyl methyl phosphonate (DIMP), trini trotoluene (TNT), two isomers of dimethylnaphthalene (DMN), tetrachloroethy lene (TCE) and trichloroethylene (TRCE). (C) 2001 Elsevier Science B.V. All rights reserved.