Optimization of Nanoparticle Size for Plasmonic Enhancement of Fluorescence

Abstract

This paper reports on the enhancement of fluorescence that can result from the proximity of fluorophores to metallic nanoparticles (NPs). This plasmonic enhancement, which is a result of the localized surface plasmon resonance at the metal surface, can be exploited to improve the signal obtained from optical biochips and thereby lower the limits of detection. There are two distinct enhancement effects: an increase in the excitation of the fluorophore and an increase in its quantum efficiency. This study focuses on the first of these effects where the maximum enhancement occurs when the NP plasmon resonance wavelength coincides with the fluorophore absorption band. In this case, the excitation enhancement is proportional to the square of the amplitude of the electric field. The scale of the enhancement depends on many parameters, such as NP size and shape, metal type, and NPfluorophore separation. A model system consisting of spherical gold/silver alloy NPs, surrounded by a silica spacer shell, to which is attached a fluorescent ruthenium dye, was chosen and the dependence of the fluorescence enhancement on NP diameter was investigated. Theoretical calculations, based on Mie theory, were carried out to predict the maximum possible enhancement factor for spherical NPs with a fixed composition and a range of diameters. Spherical NPs of the same composition were fabricated by chemical preparation techniques. The NPs were coated with a thin silica shell to overcome quenching effects and the dye was attached to the shell.

The Distance-Dependent Fluorescence Enhancement Phenomena in Uniform Size Ag@SiO2@SiO2(dye) Nanocomposites

“…Additionally the excitation rate intensity was directly proportional to the square of local field amplitude. 11,30 Upon excitation of surface plasmon by light, charges would be concentrated at the metal-dielectric interface resulting in a strong amplification of local electric field (known as "lighting rod effect") which greatly enhanced the excitation rate of fluorescein moities in the vicinity of silver nanoparticles. 33 Enhanced local electro- magnetic field in close proximity to the metal nanoparticles accounted for the increased absorption cross section of the fluorophores which further facilitated enhanced fluorescence emission intensity.…”

Plasmonic Fluorescent Nanocomposites of Cyanines Self-assembled upon Gold Nanoparticle Scaffolds

“…A critical need is to tune the distance between fluorophores and AuNPs in order to overcome nanometal-induced quenching for preparing plasmonic fluorescent nanocomposites. 2 Cyanine dyes are known to form fluorescent J-aggregates upon a wide variety of scaffold materials. 3 During a literature review of chromophore assemblies on metal nanostructures, we found several papers reporting no fluorescent J-aggregates being formed or the fluorescence from such aggregates was quenched or photobleached.…”

A comparison of mono and multivalent linkers and their effect on the colloidal stability of nanoparticle and immunoassays performance

“…Dye-doped silica nanoparticles [13][14][15] (NP) stand out as excellent candidates as it is possible to dope silica NPs with a large number of fluorophores, increasing the total fluorescence of the label significantly [16,17]. Moreover, the fluorophore is protected inside a silica matrix, thereby increasing photostability [18,19] and quantum efficiency [20,21]. Silica NPs are also relatively non-toxic, chemically inert, and can be prepared in a range of sizes [22].…”