Low-cost, mass-produced biosensing systems needing minimal sample preparation and user intervention are required for many applications, ranging from food safety, water quality and security to personal and preventative medicine and rapid point-of-care diagnostics. Optical techniques have traditionally played a major role in quantitative chemical analysis and remain the mainstay of detection in “lab-on-chip” systems, but the degree of optical functionality integrated within these systems remains limited. Mid-infrared (MIR) absorption spectroscopy at wavelengths between 2.5 µm and 25 µm is widely used for quantitative analysis of biochemical species, as the fundamental vibrations of many biomolecules take place at these frequencies, offering the potential for label-free biosensing through analysis of molecular “fingerprints. However, while telecommunications applications have caused a revolution in photonic materials, devices and integration in the near-infrared, progress in biosensing systems has been hampered by the lack of integrated photonic platforms which can operate over the MIR wavelength region. Improvements in MIR sources and detectors combined with increasing demand for biochemical information to improve understanding of biological systems and to target medical treatment more effectively are driving research into materials and processes for MIR waveguide biosensors. Progress on new materials and approaches for high-sensitivity waveguide evanescent spectroscopies in the MIR which would enable new opportunities for sensitive, selective, label-free biochemical analysis will be described.
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