Highly sensitive differential phase-sensitive surface plasmon resonance biosensor based on the Mach–Zehnder configuration

TLDR

The paper presents a high‑sensitivity SPR biosensor using a Mach–Zehnder interferometer. The sensor employs a Wollaston prism to simultaneously measure p‑ and s‑polarization phases, using the s‑polarization as a reference to cancel common‑path noise and isolate the SPR‑induced phase shift. Experimental tests with glycerin–water mixtures show a sensitivity limit of 5.5×10⁻⁸ RIU per 0.01° phase change, surpassing gold‑based sensors, and the device successfully monitored BSA–antibody binding, indicating its potential to replace fluorescence‑based biosensing.

Abstract

A high-sensitivity surface plasmon resonance (SPR) biosensor based on the Mach–Zehnder interferometer design is presented. The novel feature of the new design is the use of a Wollaston prism through which the phase quantities of the p and s polarizations are interrogated simultaneously. Since SPR affects only the p polarization, the signal due to the s polarization can be used as the reference. Consequently, the differential phase between the two polarizations allows us to eliminate all common-path phase noise while keeping the phase change caused by the SPR effect. Experimental results obtained from glycerin–water mixtures indicate that the sensitivity limit of our scheme is 5.5×10-8 refractive-index units per 0.01° phase change. To our knowledge, this is a significant improvement over previously obtained results when gold was used as the sensor surface. Such an improvement in the sensitivity limit should allow SPR biosensors to become a possible replacement for conventional biosensing techniques based on fluorescence. Monitoring of the bovine serum albumin (BSA) binding reaction with BSA antibodies is also demonstrated.