SPR biosensors: simultaneously removing thermal and bulk-composition effects

Surface plasmon resonance (SPR) is an established method for sensing analytes by monitoring changes in the plasmon dispersion relation (PDR) at the inter-face of a thin metal film and a fluid. When SPR is used in sensors for specific analytes, the changes in the plasmon dispersion relation of interest are generated by the binding of analytes to receptors immobilized to the metal film. However, changes in the PDR can also be generated by changes in the index of refraction of the bulk solution containing the analytes via changes in composition or temperature. Thus, there exist inherent systematic errors in SPR based chemical sensing when temperature and/or concentration conditions are not carefully controlled. We have demonstrated the efficacy of a single, simple, and inexpensive method for simultaneously discriminating both effects from those of binding and/or debinding of analytes with a two-element SPR sensor array. Although two-element SPR arrays have been used before, their ability to simultaneously discriminate out both thermal and bulk-composition (TAB) effects (in both SPR spectroscopic and spectrophotometric schemes) has not been previously addressed. We show an example of a relatively inexpensive SPR biosensor instrument using a compensator element and its stability over a period of days. This demonstration has implications for the development of reliable SPR based chemical sensors for environmental and remote sensing applications. (C) 1999 Published by Elsevier Science S.A. All rights reserved.