Integrated surface plasmon resonance sensor with periodic nanostructures for sensitivity enhancement

Abstract

Surface plasmon resonance (SPR) sensing is now widely used in biosensing applications. There is significant scope to reduce the cost and complexity of existing commercial devices by increasing the level of optical integration, and also of enhancing the sensitivity through the use of periodic nanostructures to increase the electromagnetic field response. We will present a SPR sensor design that addresses these two issues. This design utilizes a diffractive optical element (DOE) which is integrated directly into the sensor-head and which significantly reduces the optical complexity. It is intended for eventual mass replication via a suitable molding technique. This system is designed to be used within an angular sensing scheme and the DOE delivers the required 15° angular beam divergence. A carefully developed signal processing scheme is then used to extract the maximum possible information from the detected signal. The sensor surface incorporates gold nanogratings and guided molecular self-assembly for the immobilization of ligand-specific probes to achieve a higher sensitivity than can be achieved with a flat surface. The nanostructured surface is also designed for eventual reproduction via molding or imprint approaches. The sensor-head modeling was performed using rigorous coupled-wave analysis (RCWA) and the boundary element method (BEM) whereas the beam-steering optics were modeled using ray tracing. The modeling and experimental results will be presented.