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

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.

Nanoplasmonics-enhanced label-free imaging of endothelial cell monolayer integrity

“…Cells imaged on the structured film (B) are better resolved than on the unstructured film (A), while maintaining a high image contrast as shown in (C). In a previous work (Banville et al, 2018), we showed by numerical modeling and confirmed experimentally that the attenuation length for a 50 nm unstructured Au film is ~11 µm and ~1.7 µm for the proposed nanostructured film. This reduction in attenuation length improves the spatial resolution, which results in gaps between cells and cell edges being more defined on the nanostructured sensor chip, the plasmonic mode allowing to isolate the structural parts in the immediate vicinity (~100 nm) of the surface.…”

“…The sensor chip metal surface nanostructure geometry (Fig. 1B) was designed numerically as explained elsewhere (Banville et al, 2018) to achieve the optimal compromise between spatial resolution limited by the mode attenuation length, image contrast and sensitivity. The chips are composed of a BK7 glass cover slip (170 μm thick, 22×22 mm, Fisher Scientific), a 3 nm Cr adhesion layer, a 25 nm continuous Au film (h1), 25 nm thick (h2) square Au nanostructures (width w of 200 nm, grating period Λ of 400 nm).…”

“…This hybrid mode benefits from a reduction in mode attenuation distance due to the localized mode properties. In a previous manuscript by our group (Banville et al, 2018), we demonstrated that the nanostructured film geometry can be designed in such a way as to improve spatial resolution while mitigating imaging performance losses. We showed that a trade-off between the attenuation length and the sensitivity is required, while maintaining a high image contrast.…”

A Near-Infrared Multi-Band Perfect Absorber Based on 1D Gold Grating Fabry-Perot Structure

“…For example, gold layer with thickness of 313nm can be deposited on glass substrate by sputtering. Then the traditional photolithography technology is used to make the gold grating graphics [35]- [37].…”

Metamaterial Lensing Devices

“…These devices have gained wide attention and experienced considerable development because they have small dimensions, fast operating speed, and low energy consumption. In particular, lensing and focusing components are widely used in many technologies, such as high-resolution imaging [66,67,68,69,70], nanolithography [71,72,73,74,75], and optical integration [76,77,78,79]. However, due to the diffraction limit which means the resolvable feature size is determined by d=λ2NA (where d is the resolvable feature size, λ is the wavelength of incident light, and NA is the numerical aperture) due to the wave nature of radiation, the imaging resolution of conventional lenses and optical systems is difficult to break through the dimension of half of the incident wavelength.…”