Analysis of the extreme scattering effect for particles inside and above a noble metal film via the discrete sources method

Abstract

In this paper the discrete sources method is applied to analyze the extreme scattering effect for particles located both inside and on a gold film deposited on a glass prism. The extreme scattering effect is an effect of the sharp increase of the scattered intensity for P-polarized excitation which occurs in the evanescent wave region behind the critical angle. Moreover, the intensity enhancement appears not only in the transmission direction but in the backscattering direction as well. The effect does not depend on the thickness of the metal film or particle diameter, but it is strongly affected by the film material. Different scattering characteristics, such as transmission cross section and reflection cross sections and their correlation with the surface plasmon resonance in the film, are investigated and discussed in this paper. The analysis of the influence of a thin transparent spacer layer between particle and gold film on the scattering characteristics has been performed. The differential scattering cross section is considered to examine the field distribution in the forward and backscattering directions.

Optical imaging of single-protein size, charge, mobility, and binding

“…The overall reflected light detected by the camera (I) is given by [44][45][46][47][48][49][50][51][52] ,…”

“…One reason for this difference is that evanescent wave scattering can greatly enhance the scattering cross section. It has been reported that over three orders of magnitude scattering cross section enhancement for nanoparticles in evanescent field generated by p-polarized excitation 52,53 . It is possible that other less understood effects also contribute to the scattering cross section enhancement given that the surface condition is more complex than that in iSCAT.…”

“…When a protein is present on the surface, it scatters the evanescent wave, generating a scattered wave ( u s ), given by where r ′ is the location of the protein and r is the location on the image, β is a scattering coefficient related to the polarizability of the molecule, d is the decaying constant of the evanescent wave, and k is the wave number of evanescent wave. The superposition of the two waves, together with light reflected from the ITO surface ( u r ), is The overall reflected light detected by the camera ( I ) is given by 44 – 52 , The image contrast of the particle is described by where the last term is the background image in the absence of the protein. For weak scattering, is small, and Eq.…”

Surface Plasmon Resonance Imaging: What Next?

“…Only recently, the interaction of a P-or S-polarized plane wave (λ = 670 nm) with a AuNP (52 nm in diameter) deposited above a multilayered structure, composed of a Au film (thicknesses of 53 and 46 nm) deposited on a LASF46A prism, has been simulated by using the discrete source method (DSM). 49 The simulated system considered the upper half-space filled with air. The critical angle at which evanescent waves were generated was calculated to be 31.52°.…”

“…DDA, instead, describes the NP as an array of polarizable dipolar elements organized on a lattice. Only recently, the interaction of a P- or S-polarized plane wave (λ = 670 nm) with a AuNP (52 nm in diameter) deposited above a multilayered structure, composed of a Au film (thicknesses of 53 and 46 nm) deposited on a LASF46A prism, has been simulated by using the discrete source method (DSM) . The simulated system considered the upper half-space filled with air.…”