Spatial resolution in prism-based surface plasmon resonance microscopy

Abstract

Several optical surface sensing techniques, such as Surface Plasmon Resonance (SPR), work by imaging the base of a prism by one of its faces. However, such a fundamental optical concern has not been fully analyzed and understood so far, and spatial resolution remains a critical and controversial issue. In SPR, the propagation length L(x) of the surface plasmon waves has been considered as the limiting factor. Here, we demonstrate that for unoptimized systems geometrical aberrations caused by the prism can be more limiting than the propagation length. By combining line-scan imaging mode with optimized prisms, we access the ultimate lateral resolution which is diffraction-limited by the object light diffusion. We describe several optimized configurations in water and discuss the trade-off between L(x) and sensitivity. The improvement of resolution is confirmed by imaging micro-structured PDMS stamps and individual living eukaryote cells and bacteria on field-of-view from 0.1 to 20 mm(2).

Early detection of bacteria using SPR imaging and event counting: experiments withListeria monocytogenesandListeria innocua

“…The strategy is based on extending the high spatial resolution of SPRI, typically restricted to a narrow band in the middle of the image and falling off towards the edges, to the entire eld of view, thereby signicantly improving the accuracy of the surface kinetics analysis. 40 We demonstrate faster positive signature identication based on single bacteria observation compared to SPRI analysis based on aggregate spots responses. Our observations are conrmed with standard differential interference coherence (DIC) microscopy.…”

“…Prism-based SPRI systems are oen designed with a relatively wide eld of view (around 1 cm 2 ) for parallel measurements on a matrix of spots (spotted microarray) with detection levels as low as 100 pM in the case of DNA-DNA hybridization. 38,39 Though prism-based SPRI systems are limited in spatial resolution to tens of microns or more by geometrical aberrations caused by the prism, 40 this is not a problem for spotted microarray applications since the spots are sufficiently large (100 microns in diameter or more) and spatially well separated. In true imaging applications of biological objects such as bacteria, however, where the morphology and/or dynamical behaviour of individual objects is the basis for the information sought, the low spatial resolution results in loss of important information.…”

Recent advances in surface plasmon resonance imaging: detection speed, sensitivity, and portability

“…However, in prism-based SPRi, the spatial resolution is significantly low, especially along the direction parallel to the surface plasmon wave (SPW) due to the geometrical aberration of the prism and the propagating length of the SPW. An optimized spatial resolution of 1.7 μm perpendicular and 2.8 μm parallel to the SPW has been obtained [8]. So far, the intensity interrogation mode is a straightforward case for 2D arrays.…”

Thickness determination in anisotropic media with plasmon waveguide resonance imaging

“…Finally, it should be stressed that the fitting is based on an approximation by a stack of plane layers. This implicitly assumes that geometrical optics is valid, as discussed in [6], and that only a spatially smoothed version of the topography and index distribution can be measured. Figure 6 shows the result of the isotropic approximation.…”

“…The determination of the spatial distribution of anisotropy characteristics over the sample is a further requirement in biophysical applications, where the existence of lateral heterogeneity (lipid domains [5] or rafts, protein domains as amyloid [3], cell adhesion regions) convey important functional information. In contrast with the good localization properties of SPR or PWR modes in the direction normal to the film, the lateral extension [6] of these modes is only limited by radiation losses. As an example, whereas the penetration depth of a typical SPR mode is ∼ 100 nm, its lateral decay length is more in the range of 10µm, which severely limits the expected spatial resolution [7].…”