Abstract
Since first discovered in 1902, surface plasmon resonance (SPR), which is the collective oscillation of free electrons at interface of metal-dielectric interface, has been widely studied and become a mature biosensing technique. Different from conventional detection assays, SPR sensors particular present further advantages such as label-free detection, capability of dynamic molecular interaction analysis, small required sample volume, and ultra sensitivity. In recent years, the necessity for low cost, comfortable and rapid medical test which is so called point-of care test gradually moves the advancement of SPR sensor toward more convenient and portable devices. Among all the progression, surface plasmon resonance imaging (SPRI), which is originally utilized in monitoring molecular interaction within dots arrays, allows users to distinguish slight variation of sensing region simply using CCD camera instead of complex spectrum analysis. This characteristic brings about development of color SPR imaging, where SPR response is no longer just interpreted as shift of SPR curve but significant color change. However, to further meet request for POCT, it is essential to increase color contrast that is easier to be observed and identified. Accordingly, this issue is worth of studying because it is highly corresponding to sensitivity possessed by color SPR. In our work, we have presented a color SPR platform based on wavelength interrogation which provides broaden linear range than conventional SPRI to directly observe the bio-interaction through CCD camera. The optimized 35 nm-sliver/5nm-Au bimetallic film was first fabricated based on simulation and glucose with different concentration was introduced as tested analyte to verify the enhancement of sensitivity. It depicted that sliver/Au bimetallic film possess 2.54 folds larger in sensitivity and 10 folds higher in color contrast than bare Au. Besides, we also demonstrated feasibility in detection of biomolecular using Biotin-Streptavidin binding pairs. The results suggest that streptavidin as small as 10-7M could be discernible for naked eyes by telling color difference and the simplified detection assay is of great potentiality in developing POC based SPR sensing technology.