Photothermal cantilever deflection spectroscopy

A real-time technique that does not rely on chemical interfaces or biological receptors for molecular identification of picogram quantities of biomaterials such as DNA molecules in a high throughput fashion is described. This technique combines the extremely high sensitivity of microfabricated bi-material cantilever beams with the high selectivity of mid infrared (IR) spectroscopy to nanomechanically transduce the photon absorption-induced temperature variations of the molecules. Picogram amounts of target molecules were first adsorbed on the cantilever without using any receptors. Illuminating a bi-material cantilever sequentially with a mid-IR radiation results in photon absorption by the molecule at a certain wavelength, which results in a small temperature variation, and the resultant deflection of the bimaterial cantilever. A plot of cantilever deflection as a function of an illuminating wavelength closely follows the IR absorption spectrum of the target molecules. We have used this technique to rapidly identify different DNA strands.