Plasmon-Controlled Fluorescence Methods and Applications

Abstract

Fluorescence spectroscopy is an established and widely used technology in physical, chemical, biological, and medicinal research. At present, all aspects (including fluorophore brightness, stability, lasers, and optical components) of far-field fluorescence have developed for maximum capabilities. Accordingly, any developments to the fluorescence technology are more of incremental. However, we still need drastic advances to the technology to use it in some applications. Some examples to note here are the sensitivity of many clinical assays is limited by sample autofluorescence, single-molecule detection is limited by the brightness and photostability of the fluorophores, and the spatial resolution of cellular imaging is limited to about one half of the wavelength of the incident light. We believe a combination of fluorescence, plasmonics, and nanofabrication can fundamentally change and increase the capabilities of fluorescence technology. Surface plasmons are collective oscillations of free electrons in metallic surfaces and particles. We now know that fluorophores in the excited state can create plasmons that radiate into the far field and that fluorophores in the ground state can interact with and be excited by surface plasmons. These reciprocal interactions suggest that the novel optical absorption and scattering properties of metallic nanostructures can be used to control the decay rates, location, and direction of fluorophore emission. We refer to these phenomena as plasmon-controlled fluorescence (PCF). We predict that PCF will result in a new generation of probes and devices. These likely possibilities include ultrabright single-particle probes that do not photobleach, probes for selective multiphoton excitation with decreased light intensities, and distance measurements in biomolecular assemblies in the range from 10 to 200nm. Additionally, PCF is likely to allow design of structures that enhance emission at specific wavelengths and the creation of new devices that control and transport the energy from excited fluorophores in the form of plasmons and then convert the plasmons back to light.