A Label-Free Biosensor Built with Nitride-Based Surface Plasmon Resonance

This 2-year project is to build up a nitride-based surface plasmon resonance (SPR) proteomemicroarrays. The SPR structure comprises a single GaN/InGaN/GaN quantum well coated with a thin Aglayer. Biomolecular interactions are detected by the SPR effect induced at the GaN/Ag interface, where aminute change in refractive index can lead to measurable variation of the emission intensity from thequantum well. Comparing with conventional biosensing techniques, SPR biosensors allow label-free,wash-free, multi-analyte and real-time measurement, which can significantly expedite the assay process.However, most of the current SPR biosensors are made of complicated optical components to achievesufficient detection resolution. In specific, a prism coupled with an Au-coated glass is usually required toattain SPR effect through total internal reflection. The prism-glass complex is not only expensive, but oftenencounters the difficulty in optical coupling between the two components. In this study, we aim to tacklethe problem by replacing the prism-glass complex with a thin GaN-based epi-wafer. Since the refractiveindex of GaN (n = 2.5) is much larger than that (n = 1.5) of the glass, the SPR-inducing total internalreflection can be much easily achieved, simplifying the optical design in the biosensor. More importantly,in addition to the metal layer, the GaN-based epi-wafer offers an extra dimension in maximizing the SPReffect, i.e. the quantum-well structure. The optimized SPR structure should lead to improved detectionresolution because of the enhanced sensitivity in refractive index. Preliminary results show the sensitivityof 10241%/RIU attained with a crude InGaN-based SPR structure, the performance is expected to beconsiderably enhanced once the growth conditions are optimized. The project will be accomplishedthrough the collaboration among the experts in crystal growth, SPR biosensors and proteome microarrays,paving a new route for the development of biosensing techniques.