Microfabricated transducers enable the label-free detection of biological molecules in nanoliter sized samples. Integrating microfluidic detection and sample-preparation can greatly leverage experimental efforts in systems biology and pharmaceutical research by increasing analysis throughput while dramatically reducing reagent cost. Microfabricated resonant mass sensors are among the most sensitive devices for chemical detection, but degradation of the sensitivity in liquid has so far hindered their successful application in biology. This thesis introduces a type of resonant transducer that overcomes this limitation by a new device design: Adsorption of molecules to the inside walls of a suspended microfluidic channel is detected by measuring the change in mechanical resonance frequency of the channel. In contrast to resonant mass sensors submersed in water, the sensitivity and frequency resolution of the suspended microchannel resonator is not degraded by the presence of the fluid. Our device differs from a vibrating tube densitometer in that the channel is very thin, and only molecules that bind to the walls can build up enough mass to be detected; this provides a path to specificity via molecular recognition by immobilized receptors.
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