Radiative Decay Engineering

Abstract

Metallic surfaces can have unusual effects on fluorophores such as increasing or decreasing the rates of radiative decay and the rates of resonance energy transfer (RET). In the present article we describe the effects of metallic silver island films on the emission spectra, lifetimes, and energy transfer for several fluorophores. The fluorophores are not covalently coupled to the silver islands so that there are a range of fluorophore-to-metal distances. We show that proximity of fluorophores to the silver islands results in increased fluorescence intensity, with the largest enhancement for the lowest-quantum-yield fluorophores. Importantly, the metal-induced increases in intensity are accompanied by decreased lifetimes and increased photostability. These effects demonstrate that the silver islands have increased the radiative decay rates of the fluorophore. For solvent-sensitive fluorophores the emission spectra shifted to shorted wavelengths in the presence of the silver islands, which is consistent with a decrease of the apparent lifetime for fluorophores near the metal islands. We also observed an increased intensity and blue spectral shift for the protein human glyoxalase, which displays a low quantum yield for its intrinsic tryptophan emission. In this case the blue shift is thought to be due to increased emission from a buried low-quantum-yield tryptophan residue. Increased intensities were also observed for the intrinsic emission of the nucleic acid bases adenine and thymine and for single-stranded 15-mers poly(T) and poly(C). And finally, we observed increased RET for donors and acceptors in solution and when bound to double-helical DNA. These results demonstrate that metallic particles can be used to modify the emission from intrinsic and extrinsic fluorophores in biochemical systems.

Polyelectrolyte Layer-by-Layer Assembly To Control the Distance between Fluorophores and Plasmonic Nanostructures

“…In general, the quantum yield and lifetime of a fluorophore are described as 9,10 (9) (10) where Γ and k nr are the radiative and nonradiative decay rates, respectively. In proximity to the metallic surfaces and/or particles, eqs 9 and 10 are modified as (11) (12) The radiative decay rate is increased to N r Γ in the presence of plasmonic metal nanostructures. k nr ′ is the nonradiative decay rate in the presence of metal particles.…”

“…1 We have shown that the metal nanoparticles could change the radiative decay rates of fluorophores. [9][10][11][12] These changes occur because of modifications of the photonic mode density near the particle. Using metal nanoparticles, we could engineer changes in the emission based on the fluorophore-metal particle geometries.…”

Enhanced Fluorescence of Cy5-Labeled Oligonucleotides Near Silver Island Films: A Distance Effect Study Using Single Molecule Spectroscopy

“…It is well-known that many factors can result in increased intensities from fluorophores. 42 The absolute and relative brightness of a fluorophore are dependent on the values of the radiative and nonradiative rates. Like a radiating antenna, a fluorophore acts as an oscillating dipole, and nearby metal surfaces can respond to the oscillating dipole and modify the rate of emission and the spatial distribution of the radiated energy.…”

Multicolor Directional Surface Plasmon-Coupled Chemiluminescence

“…We refer to this concept as the radiating plasmon model (RPM). 11,12 In addition, we have also recently reported the first observation of metal-enhanced chemiluminescence (MEC) where Silver Island films (a noncontinuous silver surface) in close proximity to chemiluminescing species significantly enhanced the luminescence intensity. 13,14 This suggested that surface plasmons can be directly excited by chemically induced electronically excited luminophores.…”