Single shot embedded surface plasmon microscopy with vortex illumination

Abstract

In previous work we demonstrated how a confocal microscope with a spatial light modulator in the back focal plane could perform accurate measurement of the k-vector of a propagating surface plasmon. This involved forming an embedded interferometer between light incident close to normal incidence (reference beam) and light incident at the angle to excite surface plasmons (sample beam). The signal from the interferometer was extracted by stepping the phase of the reference beam relative to the sample beam using a spatial light modulator; this requires at least 3 phase steps, which limits the speed of operation. To overcome this and extract the same information with a single measurement, we project an azimuthal varying phase between 0 and 2π in the central region of the back focal plane; corresponding to small angles of incidence. This projects a vortex beam as the reference, so that the phase of the reference beam varies with azimuthal angle. By extracting the interference signal from different portions of the reference beam, different phase steps between the reference and the sample are obtained, so all the values required for phase reconstruction can be extracted simultaneously. It is thus possible to obtain the same information with a single shot measurement, at each defocus position, without additional changes to the back focal plane illumination. Results are presented to show that the vortex illuminated sample provides similar results to the phase stepped version, whose values are, in turn, validated with ellipsometry and surface profilometry.

Analysis of Effects of Surface Roughness on Sensing Performance of Surface Plasmon Resonance Detection for Refractive Index Sensing Application

“…In other words, the rougher surface led to the worse refractive index sensing capability. This contour was then normalized to the maximum calculated FOM and curve-fitted to polynomial function FOM(h, cl), as expressed in Equation (12), with an R 2 of 99.98%, using the built-in curve-fitting toolbox in MATLAB. Figure 16b shows the curve-fitted contour based on the curve-fitting model.…”

“…Table 2 shows the performance parameters calculated for the idealized smooth surface and different plasmonic gold sensor roughness reported in the literature for different deposition technologies and surface treatments calculated using Equations ( 8)- (12). The surface RMS reported in the literature were extracted from each of the referenced articles in Table 2 and then converted to corresponding h and cl values using Equation (2), assuming the h and 1/cl had a similar length, as reported by Agarwal et al [51].…”

“…This phenomenon can generate a resonating effect when illuminated by an external electric field called surface plasmon resonance (SPR) [ 2 ]. The theory of SPR has been utilized for numerous sensing technology and applications, including host–pathogen detection [ 3 , 4 ], protein interactions [ 5 , 6 ], ultrasonic detections [ 7 ], refractive index sensing [ 8 , 9 ], voltage sensing [ 10 ], and microscopic imaging application [ 11 , 12 ]. For example, Lan et al [ 13 ] reported the binding kinetics of SARS-CoV-2 and angiotensin-converting enzyme 2 (ACE2) using SPR measurement.…”

Performance Analysis of Non-Interferometry Based Surface Plasmon Resonance Microscopes

“…The k sp,BSA uniform and k sp,WATER uniform are the plasmonic angles measured for the uniform layer of the BSA protein and the bare gold sensor, respectively. (18) where Ct ,water grating and Ct ,BSA grating are the measurement crosstalk at the center of the water region and the center of the BSA region in the grating sample, respectively.…”

“…Thanks to the development in high numerical aperture (NA) objective lenses, they have made SP excitation more convenient under a conventional optical microscope configuration [ 16 , 17 ]. Several SPR microscope configurations [ 18 , 19 ] can achieve good sensitivity without compromising the spatial resolution. The SPR microscopes have demonstrated their capability in microscopic scale biosensing applications, such as recently, an SPR microscope has been employed to measure the binding kinetics of spike protein in SARS CoV-2 or COVID-19 virus with angiotensin-converting enzyme 2 (ACE2) [ 20 ].…”