Luminescent Blinking from Silver Nanostructures.

Abstract

Silver nanostructures deposited on glass showed luminescent blinking when excited at a high 442 nm irradiance. The irradiance required to photoactivate the silver, was dependent on the nature of the silver nanostructures. Silver fractal-like structures were found to be highly emissive, requiring only ≈30 W/cm 2 for photoactivation as compared to silver island films and spin-coated silver colloids, which required a significantly higher irradiance, > 100 W/cm 2 , to observe similar luminescent emission. In contrast to our recent findings for gold colloids, foci with different color blinking were also observed, with an increase in luminescence intensity as a function of time. We place these findings in context with recent work from our laboratory which employs these silver nanostructures for applications in metal-enhanced fluorescence, a relatively new phenomenon in fluorescence, whereby metallic particles, colloids, and fractal-like structures can modify the intrinsic radiative decay rate of close proximity fluorescent species. These effects are a consequence of localized changes in photonic mode density around the fluorophores, and we can now report are typically observed at significantly lower illumination intensities as compared to those required to photoactivate silver. Subsequently, our findings strongly suggest that the enhanced fluorescence emission of fluorophores positioned in close proximity to metallic silver structures is not due to either intrinsic silver blinking, or indeed the silver luminescence pumping the fluorophore. Further, the intrinsic luminescence properties of silver reported here, suggest a new class of luminescence probes and labels.

Single fluorescent gold nanoclusters

“…Ensemble NCs in solution are photostable, moreover photoinduced fluorescence enhancement was observed for long-time illumination. This photoinduced fluorescence enhancement has been observed for colloidal CdSe QDs [16][17][18] and silver nanoparticles [19], likely due to photoinduced surface passivation. However, when the solvent was evaporated, fluorescence intensity dropped rapidly with illumination time.…”

Water-Soluble Hybrid Nanoclusters with Extra Bright and Photostable Emissions: A New Tool for Biological Imaging

“…Because each individual cluster displayed an unusually bright emission and was resistant to photobleaching, we next examined whether such properties were a result of metalenhanced emission of ThT or an intrinsic fluorescent property of the silver of the nanoclusters. Silver is known to exhibit bright and photostable fluorescence as was previously shown for gaseous silver particles, silver deposited on surfaces, and silver dots encapsulated into dendrimers, but not for silver in aqueous solutions (3,4,22,23). To address this question we compared the emission spectra collected from an area of view densely populated with nanoclusters to spectra recorded from the fibrils prestained only with ThT.…”

“…2 d). Previous studies demonstrated that the agglomeration of noble metals into nanodots and nanocomposites is usually accompanied by the appearance of plasmon absorption, with a maximum between 380 and 600 nm, depending on the size and composition of nanocomposites (3,4,(15)(16)(17). For instance, oligonucleotidebound silver nanoclusters displayed two broad absorption peaks with maxima at 424 nm and 520 nm (5).…”

“…Photoactive nanocomposites of noble metals are of great interest in various fields of physics and chemistry (1). Generation of noble luminescent nanoclusters has been mostly confined to the gaseous and solid phase and does not occur in aqueous solutions at ambient temperatures (2,3). Thus, their practical application in biology has been limited.…”

Optical and photoluminescent properties of Ag/Al2O3 nanocomposite films obtained by pulsed laser deposition

“…Silver nanoparticles (NP), clusters and composite nanostructures based on them demonstrate local surface plasmon resonance (LSPR) [1][2][3], luminescence in the visible spectral range [2][3][4][5][6][7][8], photochromism [2], which opens wide possibilities to study distinctive optical properties of nanoparticles as compared to those in bulk objects as well as to use them in various applications from biosensors to informatics and storage devices. Excitation of LSPR results in creation of strong local fields around the nanoparticles, which causes enhancement of Raman scattering, luminescence, optical non-linearity, etc.…”