Radiative decay engineering 8: Coupled emission microscopy for lens-free high-throughput fluorescence detection

Abstract

Fluorescence spectroscopy and imaging are now used throughout the biosciences. Fluorescence microscopes, spectrofluorometers, microwell plate readers and microarray imagers all use multiple optical components to collect, redirect and focus the emission onto single point or array imaging detectors. For almost all biological samples, except those with regular nanoscale features, emission occurs in all directions. With the exception of complex microscope objectives with large collection angles (NA ≤ 0.5), all these instruments collect only a small fraction of the total emission. Because of the increasing knowledge base on fluorophores within near-field (< 200 nm) distances from plasmonic and photonic structures we can anticipate the development of compact devices in which the sample to be detected is located directly on solid state detectors such as CCDs or CMOS cameras. Near-field interactions of fluorophores with metallic or dielectric multi-layer structures (MLSs) can capture a large fraction of the total emission. Depending on the composition and dimensions of the MLSs, the spatial distribution of the sample emission results in distinct optical patterns on the detector surface. With either plain glass slides or MLSs the most commonly used front focal plane (FFP) images reveal the x-y spatial distribution of emission from the sample. Another approach, which is often used with two or three-dimensional nanostructures, is back focal plane (BFP) imaging. The BFP images reveal the angular distribution of the emission. The FFP and BFP images occur at certain distances from the sample which is determined by the details of the optical components. Obtaining these images requires multiple optical components and distances which are too large for the compact devices. For devices described in this paper, the images will be detected at a fixed distance between the sample and some arbitrary distance below the MLS which is determined by the geometry and thicknesses of the components. We refer to measurements at these locations as out-of-focal plane (OFP) imaging. Herein we describe a method to measure the optical fields at micron and multi-micron distances below the MLS, which will represent the images seen by an optically coupled array detector. The possibility of sub-surface optical images is illustrated using five different multi-layer structures. This is accomplished using an optical configuration which allows measurement at a front focal plane (FFP), back focal plane (BFP) or any OFP locations. Our OFP imaging method provides a link between the FFP images which reveals the surface distribution of fluorophores with the BFP images that reveal the angular distribution of emission. This linkage can be useful when examining structures which have nanoscale features due to fluorescence or leakage radiation from nanostructures.

Quantification of Material Fluorescence and Light Scattering Cross Sections Using Ratiometric Bandwidth-Varied Polarized Resonance Synchronous Spectroscopy

“…Light/matter interactions are the most fascinating phenomena in nature that have remained as central research topics since the inception of modern science. − Applications exploiting light/matter interactions encompass essentially every imaginable scientific discipline that ranges from molecular sciences to space exploration. − Depending on their optical properties in the UV–vis wavelength region, all materials can be divided into the following five categories: (1) approximate pure light absorbers with no significant light scattering and emission, (2) pure light scatterers with no significant light absorption and emission, (3) simultaneous light absorbers and scatterers with no significant photon emission, such as metal nanoparticles, − (4) simultaneous light absorbers and emitters with no significant photon scattering, all the way to (5) simultaneous light absorbers, scatterers, and emitters, including synthetic fluorescent nanoparticles and supramolecules . Many emerging functional materials, especially nanoscale photonic materials, are highly optically complicated because they can simultaneously absorb, scatter, and emit light in the same wavelength regions. − Reliable determination of the material photon extinction, absorption, scattering, and emission activities is critical for material characterizations, designs, and applications.…”

k-space optical microscopy of nanoparticle arrays: Opportunities and artifacts

“…The potential of k-space optical microscopy for autofocusing applications in optical microscopy still needs to be investigated further. 74 Yet the technique presented here is, in principle, compatible with existing imaging techniques such as those based on sample photoluminescence or nonlinear coherent emission processes. In these cases, the excitation light propagating back from the filter cube of the microscope may be imaged in Fourier space on a remote camera, just by inserting a semi-reflective component in the light beam before the entrance port of the microscope.…”

Nd2O3-Ag Nanostructures for Plasmonic Biosensing, Antimicrobial, and Anticancer Applications

“…The emitter dipoles in the “hot spots” , of the cavity environment between the NdAg FP and the Ag thin film experienced a striking polarization switching from p to s in the SPCE platform. There is a lineup of experimental and theoretical studies (Radiative Decay Engineering) ,, undertaken by Lakowicz and co-workers on the decay and lifetime of quantum emitters on the SPCE platform. Despite these studies and the fact that >50% fluorescence signal is collected based on directionality, the emission polarization always remains explicitly transverse magnetic (TM) .…”