Photothermal Deflection Spectroscopy

One approach that can provide exceptional selectivity and reproducibility is photothermal deflection spectroscopy (PDS). PDS is a technique that can combine the extremely high sensitivity of a microcantilever and the selectivity of mid-infrared (IR) spectroscopy. Resonant excitation of specific vibrations of adsorbed molecules on a bimaterial cantilever results in thermal bending when resonantly excited with an IR wavelength which, when plotted as a function of illuminating wavelength, replicates vibrational IR spectra of the adsorbed molecules. It is assumed that absorption of IR photons by the molecules results in a certain amount of non-radiative decay that excites phonons in the bi-material cantilever resulting in a slight increase in temperature. By using a differential technique, a cantilever with and without adsorbed molecules, it is possible to detect and identify (molecular speciation) adsorbed molecules with high selectivity and sensitivity by plotting the cantilever bending response as a function of the illumination wavelength.