Efficiently Writing Bragg Grating in High-Birefringence Elliptical Microfiber for Label-Free Immunosensing with Temperature Compensation

Immunosensor is a powerful tool in healthcare and clinic, food and drug industry, and environmental protection. Label-free fiber-optic immunosensors have shown a myriad of advantages, such as high sensitivity, anti-electromagnetic interference, and afield measurement via the fiber network. However, the fiber-optic based sensor may bear the temperature cross-talk, especially under the warming condition for bio-activating the immune molecules. In this study, we proposed a highly birefringent microfiber Bragg grating for immunosensing with the temperature-compensation. The birefringent microfiber was drawn from the elliptical cladding multimode fiber that was ablated by the CO2 laser. The considerably large energy overlap region offered by the original multimode fiber favored the efficient inscription of FBG with high reflectivity. The dual resonances derived by the orthogonal polarization states presented similar temperature responsivities but significantly different ambient refractive index sensitivities, allowing the temperature-compensational RI sensing. The human immunoglobulin G (IgG) molecules were anchored on the surface of the microfiber grating probe by the covalent functionalization technique to enable the specific detection of the anti-IgG molecule. The proposed method promises a high-efficiency and low-cost design for the microfiber Bragg grating-based biosensor without being subjected to the temperature cross-sensitivity.