Nano-Fluidic Millimeter-Wave Lab-on-a-Waveguide Sensor for Liquid-Mixture Characterization

This paper reports on a miniaturized lab-on-a-waveguide liquid-mixture sensor, achieving highly accurate nanoliter liquid sample characterization, for biomedical applications. The nanofluidic-integrated millimeter-wave sensor design is based on a near-field transmission-line technique implemented by a single loop slot antenna operating at 91 GHz, fabricated into the lid of a photolaser-based subtractive manufactured WR-10 rectangular waveguide. The nanofluidic subsystem, which is mounted on the top of the antenna aperture, is fabricated by using multiple polytetrafluoroethylene layers to encapsulate and isolate the liquid sample during the experiment, hence, offering various preferable features, e.g., noninvasive and contactless measurements. Moreover, the sensor is reusable by replacing only the nanofluidic subsystem, resulting in a cost-effective sensor. The novel sensor can measure a liquid volume of as low as 210 nanoliters, while still achieving a discrimination accuracy of better than 2% of ethanol in the ethanol/deionized-water liquid mixture with a standard deviation of lower than 0.008 from at least three repeated measurements, resulting in the highest accurate ethanol and DI-water discriminator reported to date. The nanofluidic-integrated millimeter-wave sensor also offers other advantages, such as the ease of design, low fabrication and material cost, and no life-cycle limitation of the millimeter-wave subsystem.