Microfabricated mechanical biosensor with inherently differential readout

We report measurements with a micromachined mechanical biosensor that inherently suppresses background effects by producing a differential signal with respect to a reference. The sensor comprises two adjacent cantilevers with interdigitated fingers between them that allow interferometric detection of the differential, i.e., relative bending. We demonstrate that differential detection can efficiently suppress unspecific chemical effects that result in cantilever bending. We show that the differential deflection noise is up to an order of magnitude lower than the absolute deflection noise in the low-frequency range of 0.0003-1 Hz, where many types of biologically relevant reactions occur. We also demonstrate the sensor's applicability to biological receptor-ligand systems by reporting experimental results on direct differential detection of biotin-streptavidin binding. (C) 2003 American Institute of Physics.