Spatial resolution versus contrast trade-off enhancement in high-resolution surface plasmon resonance imaging (SPRI) by metal surface nanostructure design.

Frederic A Banville,Paul G Charette,Mitradeep Sarkar,Mondher Besbes,Julien Moreau,Michael Canva

doi:10.1364/oe.26.010616

Abstract

Surface plasmon resonance imaging (SPRI) is an optical near-field method used for mapping the spatial distribution of chemical/physical perturbations above a metal surface without exogenous labeling. Currently, the majority of SPRI systems are used in microarray biosensing, requiring only modest spatial resolution. There is increasing interest in applying SPRI for label-free near-field imaging of biological cells to study cell/surface interactions. However, the required resolution (sub-µm) greatly exceeds what current systems can deliver. Indeed, the attenuation length of surface plasmon polaritons (SPP) severely limits resolution along one axis, typically to tens of µm. Strategies to date for improving spatial resolution result in a commensurate deterioration in other imaging parameters. Unlike the smooth metal surfaces used in SPRI that support purely propagating surface modes, nanostructured metal surfaces support "hybrid" SPP modes that share attributes from both propagating and localized modes. We show that these hybrid modes are especially well-suited to high-resolution imaging and demonstrate how the nanostructure geometry can be designed to achieve sub-µm resolution while mitigating the imaging parameter trade-off according to an application-specific optimum.

Highlights

Surface plasmon resonance (SPR) sensing is an optical near-field based method for detecting minute material or physical changes that occur within a thin volume on the dielectric side of a metal/dielectric interface [1, 2]
Surface plasmon resonance imaging (SPRI) is an optical near-field method used for mapping the spatial distribution of chemical/physical perturbations above a metal surface without exogenous labeling
The majority of SPRI systems are used in microarray biosensing, requiring only modest spatial resolution

Summary

Introduction

Surface plasmon resonance (SPR) sensing is an optical near-field based method for detecting minute material or physical changes that occur within a thin volume on the dielectric side of a metal/dielectric interface [1, 2]. A typical propagating-type SPR sensor is a planar waveguide that supports a single TM-polarized guided mode propagating at a metal/dielectric interface with a field profile that decays exponentially on either side, i.e. a surface wave This mode, commonly referred to as “surface plasmon polaritons (SPP)” or as “surface plasmons”, can be excited by input light with a matching wavevector in a number of ways, to guided modes in photonic waveguides. The nanostructure design process, involving numerical modeling and parameter estimation from the experimental data, is described below in a case study based on one of the most common SPRI biosensing system configurations: a dielectric fluid medium atop a 50 nm uniform gold film at an operating wavelength of λ = 830 nm This particular choice of wavelength is motivated by the fact that longer operating wavelengths yield higher SPR sensitivity and that 830 nm is considered the practical upper limit for systems based on silicon photodetectors. The dielectric material system in the case study is based on biological cells

Numerical analysis

Experimental results and parameter estimation

Conclusion