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 <i>p</i> and <i>s</i> polarizations are interrogated simultaneously. Since SPR affects only the <i>p</i> polarization, the signal due to the <i>s</i> 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<sup>-8</sup> 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.
© 2004 Optical Society of America
S. Y. Wu, H. P. Ho, W. C. Law, Chinlon Lin, and S. K. Kong, "Highly sensitive differential phase-sensitive surface plasmon resonance biosensor based on the Mach–Zehnder configuration," Opt. Lett. 29, 2378-2380 (2004)