Spatial imaging of modifications to fluorescence lifetime and intensity by individual Ag nanoparticles

Abstract

Highly ordered periodic arrays of silver nanoparticles have been fabricated which exhibit surface plasmon resonances in the visible spectrum. We demonstrate the ability of these structures to alter the fluorescence properties of vicinal dye molecules by providing an additional radiative decay channel. Using fluorescence lifetime imaging microscopy (FLIM), we have created high resolution spatial maps of the molecular lifetime components; these show an order of magnitude increase in decay rate from a localized volume around the nanoparticles, resulting in a commensurate enhancement in the fluorescence emission intensity.

Plasmonic engineering of silver films for enhanced fluorescence and Raman scattering

“…Any effects originating from an increased excitation field should be greatly reduced, and similar for both samples [15]; hence, any differences in the fluorescent properties of the two samples will result from changes in resonant coupling of emission radiation to plasmons in the metal nanoparticles, as discussed below. nanoparticles is much greater than that measured in the far-field: within a confocal spot of ∼400 nm diameter, only those fluorophores within approximately 10-20 nm of the nanoparticle will show significant enhancement [26,27]; this corresponds to <5 % of the excitation region. For the control sample, the essentially uniform fluorescence intensity indicates that any enhancement effects from the nanoparticles are negated by quenching close to the metal.…”

Strong coupling of localized plasmons and molecular excitons in nanostructured silver films

“…10 Furthermore, localized surface plasmon resonances (LSPRs) can be engineered to produce large modifications in fluorescence intensity and lifetime. 11,12 Due to this, the interaction between localized plasmon modes and excitonic states has been studied recently for a variety of nanostructured systems: these include nanoparticles, 13,14 nanorods, 15 nanovoids, 16 and subwavelength hole arrays. 17 For all these systems, strong coupling is manifested as an anticrossing behavior in the dispersion curve of the plasmon mode at the energy of the uncoupled exciton mode, indicating the formation of a hybridized exciton-plasmon polariton state; the resulting mode splitting is determined by the coupling strength of the two systems.…”

Plasmonic Enhancement of Fluorescence and Raman Scattering by Metal Nanotips

“…In both cases, there is an identical long-lived component originating from unmodified fluorophores in the polymer layer; this has a monoexponential decay >3 ns and implies that there are no significant concentration-induced, nonradiative channels [30]. A Figure 6e, f shows maps of the preexponential intensities α m and α 0 for the two modal lifetime components; the 0.5-ns component is localized (resolution limited) around the nanotips, whereas the 3.6-ns component has a uniform intensity (standard deviation < 2%) consistent with the homogeneous coverage of fluorophores [31]. For this sample, the R6G (in polymer) layer thickness is comparable to the axial confocal excitation depth; hence, fluorophores at different distances from the nanotips will contribute differently to the total signal measured.…”