Metal Nanostructure Enhanced Luminescence
Coupling of luminescent molecules such as fluorophores to Localized Surface Plasmons (LSPs) Figure 1) yields dramatic emission enhancement via mechanisms that are still under investigation. Enhanced luminescence occurs when lumiphores are in close association (<30 nm) with nanoparticles having LSPs. The depiction in Figure 1 is not to scale; silver nanoparticles typically 20 – 100 nm in diameter are interacting with fluorophores that are roughly 1 nm and the plasmon field (shown as shading around nanoparticle) extends approximately 30 nm from the particle surface. The presence of LSPs results in the nanoparticles having an extinction profile (extinction is a combination of absorption and scattering). The overlap of this extinction profile with the fluorophore’s peak emission represents the intensity of any enhancement and, as a result, the phenomenon can be specifically tuned.
The fundamental phenomenon of enhanced luminescence exploits localized surface plasmons generated by oscillation of free electron densities in metal nanostructures. The LSPs are quanta produced by certain metals at sizes that are greater than single atoms and smaller than the level of the bulk continuous material. Several different metals have demonstrated this phenomenon but most of the published literature utilizes silver or gold. The size, shape and metal composition of nanoparticles impact performance relative to the wavelength of light that can be enhanced.
Although we use a fluorophore to depict the phenomenon, all forms of luminescence have demonstrated enhanced perform in association with LSPs. The effect of LSP association on fluorophores includes dramatic enhancements in emission, substantial decreases in fluorescence life-time and long-term photo-stability. Direct association experiments, where the fluorophore is deposited on a nanoparticle surface, have demonstrated a million-fold enhancement. Recent academic studies have demonstrated feasibility for practical assay applications with enhancements of 10- to 1000-fold routinely demonstrated.
Plasmonix is exploiting these luminescent enhancements in development of multiple consumables for bioanalysis including QuantArray microarray substrates and QuantaWell microtiter plates, both coated with nanoparticles, and QuantaNP surface-derivatized nanoparticles as detection components.
Several non-life-science industrial product opportunities have been identified including cosmetic additives, reflective material for apparel, paints and other applications for which Plasmonix is pursuing partnership and licensing opportunities.