We report the integration of a nanomechanical sensor consisting of 16 silicon microcantilevers and polydimethylsiloxane
(PDMS) microfluidics. With our recently developed in-plane photonic transduction method we routinely achieve
microcantilever transduction responsivities in the range of 0.5-1.1 μm-1, which is comparable to the best reported for the
laser reflection readout method used in atomic force microscopy (AFM). Prior work has established that differential
surface stress as low as 0.23 mN/m is readily measurable with our arrays. In this paper we show biotin-streptavidin
sensing with a differential surface stress of ~2.3 mN/m as a first step toward characterizing integrated microcantilever
array/microfluidic sensors.
Microcantilevers show significant promise in sensing minute quantities of chemical and biological analytes in vapor and
liquid media. Much of the reported work on microcantilever sensors has made use of single functionalized
microcantilevers, usually derived from commercially available atomic force microscope (AFM) cantilevers. However,
arrays with hundreds to thousands of microcantilevers on a single chip are required to create sophisticated, broad
spectrum chemical and biological sensors in which individual microcantilevers have different bio- or chemoselective
coatings. Unfortunately, the most sensitive microcantilever readout mechanisms (such as laser beam reflection as used in
atomic force microscopy) are not readily scalable to large arrays. We therefore introduce a new microcantilever
transduction mechanism for silicon-on-insulator (SOI) microcantilevers that is designed to scale to large arrays while
maintaining a very compact form factor and high sensitivity. This mechanism is based on in-plane photonic transduction
of microcantilever deflection in which the microcantilever itself forms a single mode rib waveguide. Light from the end
of the microcantilever is directed across a small gap to an asymmetric receiving waveguide with two outputs that enables
differential detection of microcantilever deflection. Initial noise and optical power budget calculations indicate that
deflection sensitivities in the 10's of picometer range should be achievable.
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