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Abstract
In this study, we investigated the sensitivity enhancement in nanowire-based surface plasmon resonance (SPR) biosensors using rigorous coupled wave analysis (RCWA). The enhancement, enabled by the excitation of localized surface plasmons in gold nanowires, offers improved performance in sensitivity as well as in reproducibility and customizability. Calculation results found that a T-profile provides higher sensitivity than an inverse T-profile in general and also determined optimum design parameters. Our study on a nanowire-enhanced SPR biosensor demonstrates the potential for significant improvement in the sensitivity through the nanowire-mediated localized SPR.
Highlights
IntroductionSurface plasmon resonance (SPR) has been widely used in a variety of sensing applications, since it provides rapid, label-free and array-based real-time sensing capability of detecting biochemical reactions on a surface.[1,2,3] The highest sensitivity that was reported of an SPR biosensor based on a traditional configuration is approximately 1 pg/mm[2], corresponding to a change of 5 x 10-7 in refractive index.[4,5] While other sensing mechanisms, such as cantilever based ones using an atomic force tip to mount antibodies for specificity which result in different resonance vibrations with binding, are known to offer comparable sensitivity,[6] an SPR based biosensor is extremely simple in structure and has been commercially available as an economic solution to many sensing needs
In order to investigate the impact of nanowire geometries that affect the sensitivity enhancement, different profiles of gold nanowires were selected for the analysis using parameters shown in the inset of Fig. 1, where wtop and wbottom denoting the width of the nanowire top and bottom are either 20 nm or 40 nm
As a quantitative measure of the sensitivity improvement, we introduce a sensitivity enhancement factor (SEF) that represents the impact of nanowires on the Surface plasmon resonance (SPR) sensitivity in reference to a conventional SPR biosensor without nanostructures as SEF = ∆θ NWSPR = θ NWSPR − θ NWSPR, (1)
Summary
Surface plasmon resonance (SPR) has been widely used in a variety of sensing applications, since it provides rapid, label-free and array-based real-time sensing capability of detecting biochemical reactions on a surface.[1,2,3] The highest sensitivity that was reported of an SPR biosensor based on a traditional configuration is approximately 1 pg/mm[2], corresponding to a change of 5 x 10-7 in refractive index.[4,5] While other sensing mechanisms, such as cantilever based ones using an atomic force tip to mount antibodies for specificity which result in different resonance vibrations with binding, are known to offer comparable sensitivity,[6] an SPR based biosensor is extremely simple in structure and has been commercially available as an economic solution to many sensing needs. We are interested in the impact of geometrical parameters such as nanowire period and its profile and size on the coupling of LSPs in nanowires and the sensitivity enhancement in a nanowire-based SPR biosensor
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