Phase-stepping technique for highly sensitive microscopic surface plasmon resonance biosensor.

In this paper, the phase-stepping technique is applied to improve a phase-sensitive surface plasmon resonance biosensor based on differential interferometry between focused radially polarized and azimuthally polarized cylindrical vector beams. Detailed analysis is presented for the phase-stepping method, and the least squares unwrapping algorithm is employed to detect the phase distribution in correspondence to the refractive index of sample. Benefiting from the phase-stepping technique, both the measurement speed and sensitivity are improved significantly. The proposed sensor maintains high sensitivity of 9.4×10-7  RIU/1° and a wide dynamic range of 0.35 RIU simultaneously. Furthermore, the real-time binding reaction process of bovine serum albumin with antibody is monitored to verify the system for potential biological applications.