Surface plasmon resonance SPR spectroscopy has become a valuable tool for enabling real-time, label free detection of biomolecular interactions in both singular and multiplexed formats. This technique exploits the sensitivity of surface plasmons to changes in the refractive index RI occurring at a metal (typicallz gold or silver) – dielectric interface and has found utility in applications ranging from fundamental studies of the thermodynamics and kinetics of biomolecular interactions to medical diagnostics, environmental monitoring, and food safety.
Propagating surface plasmon polaritons SPPs and localized surface plasmon resonances LSPRs are two types of SPRs used for sensing. SPPs can be excited by light at a metal-dielectric interface using prism, waveguide, or grating couplers. These plasmons propagate along a metal-dielectric interface with an electric field that decays exponentially over hundreds of nanometers into the dielectric. LSPRs are nonpropagating resonances that can be directly excited by light on nanostructured metals, such as nanoparticles and around nanoholes and nanowells in metal films, and have an associated electric field that decays exponentiallt from the surface over tens of nanometers. The decay lengths of the electric fields associated with SPPs and LSPRs impact the linearity and surface sensitivity of techniques that utilize them for sensing.
Two types of plasmonic crystals (quasi 3D and full 3D) is described in this paper which form by soft nanoimprint lithography that enable plasmonic imaging of binding events with micrometer spatial resolution and submonolayer sensitivity in a normal incidence transmission configuration using a common optical microscope and low cost charge coupled device CCD camera. This simple collinear transmission configuration is robust and does not require cumbersome optics or alignment to a specific contrast angle, which allows the devices to be easily incorporated into microfluidic systems, well plates, or portable devices. These crystals exhibit complex optical respnses and support Bloch-wave SPPs (BW-SPPs, the periodic analogue of SPPs), LSPRs, related diffractive effects such as Wood anomalies (WAs), and combinations of these resonant and diffractive phenomena……..
Matthew E Stewart et al, Multispectral Thin film biosensing and quantitative imaging using 3D plasmonic, J Anal Chem, 2009, pp 5980-89