Nanomechanics of organic/inorganic interfaces: a theoretical insight

Microfabricated arrays of cantilevers coated with active layers represent ultrasensitive devices for the label-free detection of chemical and biochemical reactions. The development of these sensors for practical applications requires an understanding of the mechanism of transduction of chemical or physical changes in the active layer of the cantilever into its mechanical bending. In order to eliminate non-specific effects, differential detection with respect to reference cantilevers with an inert coating is used. However, the convolution of different specific effects leading to cantilever bending does not allow their direct decoupling based on experiments alone. We propose a quantitative mesoscopic model showing that there are two competing components to the differential deflection: the component associated with specific chemical or physical reaction on the active cantilever and the component due to a difference in elastic properties of the active and reference coatings. We apply the model to study the origin of the chemomechanical response in cantilever arrays for experimentally studied reactions, including deprotonation of pH sensitive self-assembled monolayers, DNA hybridization and swelling of polyelectrolyte brushes. We show that for all these diverse systems the theoretical model gives good quantitative agreement with the experimental data and provides a guide for designing cantilever sensors with significantly improved sensitivity.