Photomechanical chemical microsensors

Abstract

Recently, there has been an increasing demand to perform real-time in situ chemical detection of hazardous materials, contraband chemicals, and explosive chemicals. The advent of inexpensive mass produced MEMS (microelectromechanical systems) devices has enabled the use of various microstructures for chemical detection. For example, microcantilevers were found to respond to chemical stimuli by undergoing changes in their bending and resonance frequency even when a small number of molecules adsorb on their surface. In our present studies, we extended this concept by studying changes in both the adsorption-induced stress and photo-induced stress as target chemicals adsorb or desorb on the surface of microcantilevers. We demonstrate that photo-induced bending of microcantilevers depends on the number of absorbed molecules on their surface. On the other hand, microcantilevers that have undergone photo-induced bending will adsorb a different number of guest molecules. Depending on the photon wavelength and microcantilever material, the microcantilever can be made to bend by expanding or contracting a surface layer on one of its sides, unequally. Coating the surface of the microstructure with different materials can provide chemical specificity for the target chemicals. However, by choosing a handful of different photon wavelengths, tunable chemical selectivity can be achieved due to differentiated photo-induced response without the need for multiple chemical coatings. We will present and discuss our results on diisopropyl methyl phosphonate (DIMP), trinitrotoluene (TNT), two isomers of dimethylnaphthalene (DMN), tetrachloroethylene (TCE) and trichloroethylene (TRCE).