Nonlinear Label-Free Biosensing With High Sensitivity Using As₂S₃ Chalcogenide Tapered Fiber

We demonstrate an experimentally feasible fiber design, which can act as a highly sensitive, label-free, and selective biosensor using the inherent high nonlinearity of an As₂S₃ chalcogenide tapered fiber. The surface immobilization of the fiber with an antigen layer can provide the possibility to selectively capture antibody biomolecules. This increase of the layer thickness directly affects the group velocity dispersion of the fiber and, thus, the modulation instability (MI) gain spectrum changes (location of the anti-Stokes and Stokes wavelengths) when pumping the fiber close to the zero-dispersion wavelength. The sensitivity of the sensor was predicted to be ∼18 nm/nm, defined as the shift in resonance wavelength per nanometer biolayer thickness, which is almost twice the current record sensitivity of nonlinear MI-based fiber optical biosensors. Importantly, due to the strong nonlinearity of As₂S₃, this high sensitivity can be obtained using a low-power 1064-nm microchip laser.