Integrated mid-infrared photonic circuits for label-free biochemical sensing

A chip-scale biochemical sensor was developed using mid-Infrared (mid-IR) transparent silicon nitride (SiN) optical waveguides. The label free detection was conducted at λ = 2.70 - 2.81 μm because these spectral regions overlap with the characteristic glucose absorption associated with O-H stretches. Strong intensity attenuation at λ > 2.73 μm was found for the SiN waveguide covered by glucose and a detection limit less than 0.5 ng was experimentally demonstrated. The observed high sensitivity is attributed to a long mid-IR - glucose interaction length owning to the waveguide geometry and an increased sensing surface from the pedestal structure.