Phase-sensitive surface plasmon resonance biosensor using the photoelastic modulation technique

In this paper, a novel biosensing technique based on detecting the phase difference between p- and s-polarization associated with the surface plasmon resonance (SPR) effect is presented. This is a single beam system in which a photoelastic phase modulator produces a carrier frequency so that the phase quantity can be extracted by measuring the relative amplitude of the first harmonic signal. From the phase quantity, we can directly calculate the shift of refractive index in the analyte. The presence of SPR not only enhances the phase change but also confines the volume of interrogation very close (approximately 200 nm) to the sensing surface. Such properties are important to affinity biosensors. We have used the setup to perform measurement on refractive index changes associated with varying the concentration of glycerin/water mixtures. In addition, real-time monitoring of binding reaction between bovine serum albumin (BSA) and BSA antibodies is also demonstrated.