Directing Fluorescence with Plasmonic and Photonic Structures

Abstract

Fluorescence technology pervades all areas of chemical and biological sciences. In recent years, it is being realized that traditional fluorescence can be enriched in many ways by harnessing the power of plasmonic or photonic structures that have remarkable abilities to mold the flow of optical energy. Conventional fluorescence is omnidirectional in nature, which makes it difficult to capture the entire emission. Suitably designed emission directivity can improve collection efficiency and is desirable for many fluorescence-based applications like sensing, imaging, single molecule spectroscopy, and optical communication. By incorporating fluorophores in plasmonic or photonic substrates, it is possible to tailor the optical environment surrounding the fluorophores and to modify the spatial distribution of emission. This promising approach works on the principle of near-field interaction of fluorescence with spectrally overlapping optical modes present in the substrates.In this Account, we present our studies on directional emission with different kinds of planar metallic, dielectric, and hybrid structures. In metal−dielectric substrates, the coupling of fluorescence with surface plasmons leads to directional surfaceplasmon-coupled emission with characteristic dispersion and polarization properties. In one-dimensional photonic crystals (1DPC), fluorophores can interact with Bloch surface waves, giving rise to sharply directional Bloch surface wave-coupled emission. The interaction of fluorescence with Fabry−Peŕot-like modes in metal−dielectric−metal substrates and with Tamm states in plasmonic−photonic hybrid substrates provides beaming emission normal to the substrate surface. These interesting features are explained in the context of reflectivity dispersion diagrams, which provide a complete picture of the mode profiles and the corresponding coupled emission patterns. Other than planar substrates, specially fabricated plasmonic nanoantennas also have tremendous potential in controlling and steering fluorescence beams. Some representative studies by other research groups with various nanoantenna structures are described. While there are complexities to near-field interactions of fluorescence with plasmonic and photonic structures, there are also many exciting possibilities. The routing of each emission wavelength along a specific direction with a given angular width and polarization will allow spatial and spectral multiplexing. Directional emission close to surface normal will be particularly useful for microscopy and array-based studies. Application-specific angular emission patterns can be obtained by varying the design parameters of the plasmonic/photonic substrates in a flexible manner. We anticipate that the ability to control the flow of emitted light in the nanoscale will lead to the development of a new generation of fluorescence-based assays, instrumentation, portable diagnostics, and emissive devices.

Bloch Surface Wave-Coupled Emission at Ultraviolet Wavelengths

“…11–13 The BSW structure, with the 2-AP-PVA coating, was refractive index matched with a cylindrical prism. The excitation light from a 280 nm LED was incident normal to the surface (180°) from the sample (RK) direction (Figure 2).…”

“…10–12 These efforts have been productive as can be seen from recent reviews on plasmon-controlled fluorescence. 13–15 The nanoparticles of Ag and Au are used for probes with visible and near-IR spectral range. Aluminum, platinum and some other metal nanoparticles were reported to enhance signals from ultraviolet probes.…”

Flexible and Adaptable Light‐Emitting Coatings for Arbitrary Metal Surfaces based on Optical Tamm Mode Coupling

“…Plasmonic nanostructures are a means to control the spectral properties, propagation direction, and generation dynamics of light spontaneously emitted by a source, which is of crucial importance in a wide variety of fields such as lighting, [1] sensing, [2] or quantum technology. [3] These effects result from the strict control over the local density of photon states around the emitter they provide.…”

Resonance energy transfer: The unified theory via vector spherical harmonics

“…16,17 The approach has the potential to lead to new physical insights related to the role of relative orientation of chromophores in the energy transfer process, and may also be applicable to the field of near-field quantum optics where emerging technologies such as nanoantennas are currently of interest. [18][19][20][21][22] …”