Gold nano-structures for transduction of biomolecular interactions into micrometer scale movements

Microfabricated cantilevers, similar to those commonly used in scanning probe microscopies, have recently become increasingly popular as transducers in chemical and biological sensors. Surface stress changes that accompany intermolecular interactions on the cantilever surfaces offer an attractive means to develop new generations of microfabricated sensors and actuators that respond directly to chemical stimuli. In the present study, we demonstrate that interfacial molecular recognition events can be converted into mechanical responses much more efficiently when quasi 3-dimensional interfaces with nano-size features are used. Some of the particularly useful approaches to creating such interfaces are surface immobilization of gold nano-spheres and dealloying of co-evaporated Au:Ag films. Preliminary evaluation of these nanostructured surfaces was performed by measuring mechanical stresses generated by receptor modified nano-structures and smooth gold surfaces in response to gas-phase hydrocarbon compounds. The most efficient chemi-mechanical transduction was achieved when the cantilevers were modified with 50 to 75 nm thick dealloyed gold nanostructures. Cantilevers of this type were selected for liquid phase experiments. These cantilevers were found to undergo several micron deflections upon adsorption of protein A and biotin-labeled albumin on nanostructured gold surfaces. Additional micrometer scale movements of the cantilevers were observed upon interaction of the surface bound bioreceptors with, respectively, immunoglobulin G and avidin from the aqueous phase.