Mid-Infrared Opto-nanofluidics for Label-free On-Chip Sensing
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2014 Optical Society of America. A mid-infrared (mid-IR) label-free chemical sensor was developed using optonanofluidics consisting of a Si-liquid-Si slot-structure. A broadband mid-IR lightwave can be strongly confined within a nanofluidic capillary by utilizing the large refractive index contrast (n 2) between the liquid core waveguide and the Si cladding. Through an optical-field enhancement together with a direct interaction between the probe light and the analyte, the sensitivity for chemical detection is increased by 50 times when compared to evanescent-wave sensing. This spectral characterization distinguished several common organic liquids (e.g., n-bromohexane, toluene, isopropanol) accurately, and could determine the ratio of chemical species (e.g., acetonitrile and ethanol) at low concentration (< 5 L/mL) in a mixture through spectral scanning over their characteristic mid-IR absorption peaks. The combination of CMOS-compatible planar mid-IR microphotonics, and a high-throughput nanofluidic sensor system, provides a unique platform for chemical detection.