Sensitivity enhancement based on application of multi-pass interferometry in phase-sensitive surface plasmon resonance biosensor

A novel design of multi-pass surface plasmon resonance (SPR) biosensor with differential phase interrogation based on multi-pass interferometry is presented. This new configuration provides an intrinsic phase amplification effect of over twofold by placing the SPR sensor head in a signal arm of the interferometer so that the interrogating optical beam will traverse the sensor surface infinite number of times. Experimental interferometers based on the Michelson and Fabry-Perot configurations have been employed to experimentally verify this amplification effect when they were compared with Mach-Zehnder configuration, results obtained from salt-water mixtures, antibody-antigen.. and protein-DNA binding reaction confirmed the expected phase measurement enhancement, thus leading to the possibility of direct detection of small sized bio-molecules using SPR. (c) 2007 Elsevier B.V. All rights reserved.