Terahertz microfluidic sensor based on a parallel-plate waveguide resonant cavity

We describe a terahertz optical resonator that is ideally suited for highly sensitive and noninvasive refractive-index monitoring. The resonator is formed by machining a rectangular groove into one plate of a parallel-plate waveguide, and is excited using the lowest-order transverse-electric (TE(1)) waveguide mode. Since the resonator can act as a channel for fluid flow, it can be easily integrated into a microfluidics platform for real-time monitoring. Using this resonator with only a few microliters of liquid, we demonstrate a refractive-index sensitivity of 3.7 x 10(5) nm/refractive-index-unit, the highest ever reported in any frequency range. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3251079]