A promising approach for detecting biomolecules follows their binding to immobilized probe molecules on microfabricated cantilevers; binding causes surface stresses that bend the cantilever. We measured this deflection, which is on the order of tens of nanometers, by embedding a metal-oxide semiconductor field-effect transistor (MOSFET) into the base of the cantilever and recording decreases in drain current with deflections as small as 5 nanometers. The gate region of the MOSFET responds to surface stresses and thus is embedded in silicon nitride so as to avoid direct contact with the sample solution. This approach, which offers low noise, high sensitivity, and direct readout, was used to detect specific binding events with biotin and antibodies.

The label-free detection of cholera toxin is demonstrated using microcantilevers functionalized with ganglioside nanodiscs. The cholera toxin molecules bind specifically to the active membrane protein encased in nanodiscs, nanoscale lipid bilayers surrounded by an amphipathic protein belt, immobilized on the cantilever surface. The specific molecular binding results in cantilever deflection via the formation of a surface stress-induced bending moment. The nanomechanical cantilever response is quantitatively monitored by optical interference. The consistent and reproducible nanomechanical detection of cholera toxin in nanomolar range concentrations is demonstrated. The results validated with such a model system suggest that the combination of a microcantilever platform with receptor nanodiscs is a promising approach for monitoring invasive pathogens and other types of biomolecular detection relevant to drug discovery.

We explore various metal-oxide-semiconductor field-effect transistor (MOSFET)-embedded microcantilever designs to assess their performance as an efficient nanomechanoelectronic signal transduction platform for monitoring deflection in microcantilever-based phenomena such as biochemical sensing and actuation. The current-voltage characteristics of embedded MOSFETs show current noise in the nanoampere range with a large signal-to-noise ratio sufficient to provide measureable output signal. The change in drain current with cantilever deflection is consistent with the effect of stress on carrier mobility and drain current reported in previous studies, validating that the MOSFET cantilevers can directly transduce deflection of a microcantilever into reproducible change in electrical signal.

A batch fabricated microcantilever array with embedded metal oxide semiconductor field effect transistor (MOSFET) is demonstrated to behave as an actuator as well as a strain sensor. Actuation is made possible through MOSFET self-heating effect and metal-silicon bimaterial thermal expansion mismatch. Precise cantilever deflection is achieved with gate modulated saturation current. Controllable deflection and oscillation are demonstrated, with amplitude of 212 nm measured through laser interferometry near first resonant frequency. Higher amplitude is attainable through higher bias. Such in situ actuation and sensing promises to have applications ranging from nanolithography to microfluidic mixing, among others, which require precise and controllable nanoscale deflection.

No abstract