Label-free detection of bovine serum albumin based on a microfiber biosensor with controllable optimized structure

High sensitive bovine serum albumin (BSA) detection is the basis for biosensing experiments. This paper experimentally optimized the microfiber Mach-Zehnder interferometer (MZI) based on taper geometries including taper waist diameter, tapered area length, taper angle, and taper asymmetry. Based on refractive index (RI) sensitivity as the primary criterion and free spectra range (FSR), extinction ratio as secondary factors, an ultrahigh sensitive label -free microfiber with controllable optimized structure was obtained, which exhibited ultrahigh RI sensitivity of 11140.87 nm/ RIU. In the subsequent BSA concentration measurement, experiments demonstrated a high BSA sensitivity of 3.79 nm/(mg/mL) and a low BSA detection limit of 0.0052 mg/mL. Besides, the proposed sensor also had exceptional performance in terms of BSA response time, stability, and repeatability. The superior performance of this biosensor in BSA response proved its potential for biosensing applications.