Numerical Modelling of a Sinusoidal Grating-Based Surface Plasmon Coupled Emission Biosensor

V. Sukhotskiy, N.C. Cady, I.V.A.K. Reddy, E.P. Furlani
University at Buffalo SUNY,
United States

Keywords: surface plasmon resonance, SPR grating, biosensing, sinusoidal grating

Summary:

We present a full-wave computational model to study the optical behavior of a versatile sinusoidal grating-based surface plasmon-coupled emission (SPCE) biosensor. Surface plasmons (SPs) are coherent oscillations of conduction electrons on a metal surface excited by incident light at the metal-dielectric interface. The sensitivity of the surface plasmon resonance (SPR) to the refractive index (RI) change at the interface has led to the development of SPR sensing systems, which typically use prisms to couple light into a single SP mode on a flat, continuous metal film (typically gold). Commercial prism-based wavelength/angular-modulated SPR sensors can provide a resolution of 10-7 RIU (refractive index units) for single point detection. However, their large detection spot and the need of bulky prisms limit their effectiveness for compact and miniaturized biosensing. Nanoplasmonic biosensors employing nanoscale topographies are attractive miniaturized platforms for label-free, high throughput and sensitive monitoring of biochemical analytes. When receptor molecules are immobilized on metal surfaces, the binding of target biomolecules changes the local RI, affecting the optical properties of the SP modes and permitting optical detection. In this work, we present rigorous full-wave analysis of a sensor composed of a SiO2 substrate coated with Titanium (Ti) adhesion layer and a 45nm gold layer as shown in Fig.1 (c), Fig. 2(a). We use the finite-element based RF module from COMSOL (www.comsol.com) for the analysis. In the model, TM polarized light is incident on the grating and we perform parametric analysis of optical performance as a function of key device parameters. Our predictions are in agreement with recorded data. We demonstrate the model and its potential for the rational design of new sensor systems.