We report a novel approach to the design and development of microcantilever sensors in which photochemical hydrosilylation is used to modify the microcantilever surface. This process enables individual micro cantilevers in multicantilever array chips to be modified separately by focusing the activating UV light sequentially on each particular cantilever. Photochemical hydrosilylation of 11-undecenyltriethyl-ammonium bromide with hydrogen-terminated silicon microcantilever surfaces was carried out to yield a robust quaternary ammonium terminated organic monolayer suitable for chromate detection. The surface functionalities retain their affinity toward Cr(VI), and the organic monolayer is dense enough to generate significant surface stress upon subsequent adsorption of chromate ions from aqueous solutions.