Photothermal Sensing of Chemical Vapors Using Microcantilevers

Although microfabricated cantilevers have been used for detecting a variety of chemicals with high sensitivity, their selectivity appears to be poor. This selectivity problem is directly related to the poor selectivity of chemical interfaces immobilized on cantilever surfaces. Here we discuss two cantilever-based techniques that can be used for obtaining orthogonal signals for multimodal operation for enhanced selectivity. The first technique is based on photothermal deflection spectroscopy where selectivity is achieved through a mechanical response due to optical absorption by the adsorbed molecules on a cantilever. In the second technique, the position of the resonance frequency peak of the cantilever is monitored for shifting due to mass loading. This technique allows the precise measurement of the mass of the surface-adsorbed molecules. These two methods are demonstrated for adsorbed explosives.