An optical fiber biosensor based on anomalous reflection of gold

We propose a simple and sensitive optical sensing method for biological applications. Since gold behaves as a dielectric with a large extinction index under blue or violet light, presence of a transparent surface layer on gold produces a large decrease in the reflectivity of the gold surface due to multiple reflections in the surface layer. We call this phenomenon anomalous reflection (AR) of the gold surface. AR is applicable to affinity biosensors based on fiber optics, so that inexpensive and disposable micrometer-sized biosensor probes are possible based on this technique. Here, we demonstrate the application of AR to real-time measurements of the adsorption process of octadecanethiol (ODT) on gold and the affinity of streptavidin to a biotin-labeled monomolecular layer on gold.