Nano-antenna enhanced two-focus fluorescence correlation spectroscopy

Abstract

We propose two-focus fluorescence correlation spectroscopy (2fFCS) on basis of plasmonic nanoantennas that provide distinct hot spots that are individually addressable through polarization, yet lie within a single diffraction limited microscope focus. The importance of two-focus FCS is that a calibrated distance between foci provides an intrinsic calibration to derive diffusion constants from measured correlation times. Through electromagnetic modelling we analyze a geometry of perpendicular nanorods, and their inverse, i.e., nanoslits. While we find that nanorods are not suited for nano-antenna enhanced 2fFCS due to substantial background signal, a nanoslit geometry is expected to provide a di tinct cross-correlation between orthogonally polarized detection channels. Furthermore, by utilizing a periodic array of nanoslits instead of a single pair, the amplitude of the cross-correlation can be enhanced. To demonstrate this technique, we present a proof of principle experiment on the basis of a periodic array of nanoslits, applied to lipid diffusion in a supported lipid bilayer.

Double moiré localized plasmon structured illumination microscopy

“…Nonetheless, the challenge is to simultaneously enhance the strength of the evanescent orders and gain control to manipulate their phase independently to shift hot spots through the unit cell. Previously proposed far-field mechanisms, that could enable control over near-field hot spots in a plasmonic grating, are based on time-reversal [41,42], polarization multiplexing [43,44] or spatial phase modulation [45,46]. For instance, using nanocubes, as in the study by Mårsell et al [47], or two orthogonally aligned slab antennas, as in the study by Langguth et al [44], as the unit cell could allow for a larger shift of the nanoparticle nearfields upon rotation of the incident polarization.…”

“…Previously proposed far-field mechanisms, that could enable control over near-field hot spots in a plasmonic grating, are based on time-reversal [41,42], polarization multiplexing [43,44] or spatial phase modulation [45,46]. For instance, using nanocubes, as in the study by Mårsell et al [47], or two orthogonally aligned slab antennas, as in the study by Langguth et al [44], as the unit cell could allow for a larger shift of the nanoparticle nearfields upon rotation of the incident polarization. A further challenge as compared to creating multi-moiré patterns with just propagating waves is that evanescent waves inherently have a complicated polarization state, making high interference contrast harder [48].…”

Microscale Spectroscopic Mapping of 2D Optical Materials

“…Based on this unique natural property, different materials can be detected and imaged for measurements and analyses, especially in biotechnology and medical diagnostics . By photoluminescence imaging, the localization and distribution of materials on the detected surface can be revealed . Figure a shows a combination of both photoluminescence and absorption spectroscopy.…”

A scanning planar Yagi-Uda antenna for fluorescence detection

“…In general, low excitation cross-sections at room temperature, low quantum yields of molecules and their dipolar emission patterns are only some of the problems that we have to face to detect low fluorescence signals. To overcome these issues a lot of different techniques have been developed over the years, ranging from simple ones such as the use of high numerical aperture (NA) mirrors and objectives [1,2] to the complicated fabrication techniques for creating nanostructures that can change the optical properties of the emitters and facilitate their detection, such as optical microcavities [3,4], photonic nano-wires [5,6] and nano-antennas [7,8]. For example, in the vicinity of plasmonic nanoparticles illuminated by laser light, the excitation intensity can increase by orders of magnitude [9,10].…”