Surface plasmon microscopy: resolution, sensitivity and crosstalk

Abstract

SummaryThis paper develops the theoretical framework to understand the capability of the interferometric surface plasmon microscope to quantify sample properties in a confined region. We use rigorous diffraction theory to quantify the ability of the system to measure local properties and eliminate crosstalk from adjacent regions. We argue that the interferometric system in the defocused condition defines the measured point of excitation and reradiation of the surface plasmons; which greatly improves localisation. We also present results for the noninterferometric microscope, which confirm that the interferometric based system can perform quantitative measurements over smaller regions.

Ultrastable embedded surface plasmon confocal interferometry

“…9, the longer the range of defocus used to calculate the wave vector of the SP, the more accurate the measurement, on the other hand, reducing the maximum defocus improves the lateral resolution. 5 We used the artificial plasmon method to measure the local gradient over a narrow range of defocus corresponding to the flat region from 22400 to 22100 nm. By phase stepping the region with predominant p-polarization, we obtained curves for the variation of w(z) shown in Figure 6 for the five regions of the sample; we see that the R2 curve is approximately horizontal, whereas R0 and R1 have positive gradients and R3 and R4 have negative gradients as expected.…”

“…Extending the 'flat' artificial plasmon range will improve the signal to noise even more as demonstrated in Ref. 5 for the system with the normal reference beam. Approaches to extend the flat region are discussed below.…”

“…5 We have shown previously 6 how a defocused confocal microscope acts as an interferometer in which two principal optical paths form the two beams of an interferometer, which are shown as the black rays P1 and P2 in Figure 1a and 1b. These paths consist of a beam illuminating the sample close to normal incidence and another which is converted to a SP which propagates along the sample surface reradiating continuously.…”

“…The use of radial polarization incident in the back focal plane has often been advocated in SP microscopy which means the light incident on the sample is p-polarized for all azimuthal angles, so that more energy is coupled in SPs and the focus is tight and circularly symmetrical. 5 Our new interferometer, however, relies on linear polarization to generate interfering p-and s-polarized beams hitting the sample at similar incident angles. Examining Equation (1), we can see that an interferometer formed between a path generating a SP and one in which the incident light is primarily s-polarized will allow us to form an interferometer in which the sample and reference beams are incident on the sample at essentially the same angle of incidence.…”

Surface plasmon microscopic sensing with beam profile modulation

“…In recent years there has been a growing interest in performing surface plasmon (SP) measurements within a microscopic environment [1][2][3][4][5][6]; this offers the possibility of obtaining localized high resolution measurements of local changes in refractive index as well as performing valuable imaging of cell attachment [7][8][9]. We have shown that the lateral resolution of SP microscopy is optimized with an interferometric arrangement and we have more recently demonstrated that similar performance can be achieved with a confocal microscope arrangement [5].…”