Optimised film thickness for maximum evanescent field enhancement of a bimetallic film surface plasmon resonance biosensor

A surface plasmon resonance (SPR) optical biosensor, with a bimetallic silver–gold configuration that integrates the better evanescent field enhancement of silver, the higher resolution in the reflectivity minimum of silver, and the high chemical resistance of gold is presented. In comparison to most commercial sensors which use single gold films, the enhanced evanescent field of this double-layer configuration at the analyte–metal interface enables the monitoring of biomolecular interactions that occur further into the analyte. In addition, it is shown theoretically and demonstrated experimentally that the double-layer configuration achieves better minimum reflectivity resolution than the single gold film SPR configuration. Finally, the higher stability and better biomolecules adhesion of the proposed configuration, as weighed against a single silver film, makes it be a much better option to be employed for biosensing applications.