Au nanostructures by colloidal lithography: from quenching to extensive fluorescence enhancement

Abstract

Enhanced local electric fields are created by nanoparticles when pumped at wavelengths corresponding to Localised Surface Plasmon Resonance (LSPR) modes, leading to Metal Induced Fluorescence Enhancement (MIFE). This paper describes the fluorescent enhancement due to reproducible and tuneable Au nanostructures on glass substrates fabricated over large areas by colloidal lithography. Interparticle separation, particle resonance, and the fluorescent dye properties (quantum yield and emission/ excitation wavelengths) are all important factors influencing the fluorescent enhancement. A maximum fluorescence enhancement of 69 times from near infra-red (NIR) dye Alexa FluorÒ 790 was observed.

Nanoscale control of Ag nanostructures for plasmonic fluorescence enhancement of near-infrared dyes

“…Polystyrene monolayer templates were prepared by using a modified colloidal lithography method described in detail in reference [17].…”

“…Since the discovery of the Purcell effect [9], efforts to increase the sensitivity of fluorescence detection have focused on controlling the local electromagnetic (EM) environment of the fluorophores and taking advantage of the interaction between an emitter and its surroundings. The dielectric environment has a profound influence on the emission of a fluorophore, through its spontaneous emission rate and local modifications of the electromagnetic field: fluorescence quenching [10] [12], fluorescence enhancement [13]- [15] or both [16] [17] have all been reported. It has been shown experimentally, and supported by theoretical calculations, that the fluorescence enhancement factors of metal nanostructures depend on the particle size, shape, interparticle separation, surrounding dielectric medium, as well as the particle arrangement geometry and distance between the metal and fluorophore.…”

Gold nanodisc arrays as near infrared metal-enhanced fluorescence platforms with tuneable enhancement factors

“…5 Recently, selfassembled monolayers obtained through nanosphere lithography (NSL) have been used as templates for the fabrication of metal nanostructured arrays. 19,20,25 This method allows the production of regular arrays over large surface areas. These arrays are low cost and have flexible tuning parameters.…”

“…15,16 In the literature, the magnitude of fluorescence enhancement, or quenching, has been shown to depend on particle size and shape, interparticle separation distance, surrounding dielectric medium, as well as particle geometry and distance between the metal and the fluorophore. [17][18][19] MEF also critically depends on the spectral overlap between the LSPR of metal nanoparticles with the spectral properties (i.e. excitation and emission) of fluorophores.…”

“…These arrays are low cost and have flexible tuning parameters. 19,20 In our own work, by combining NSL and subsequent O2 plasma treatment, arrays of Ag triangular-like nanoparticles were fabricated, with controlled size, shape, particle separation and, more importantly, with tuneable optical features in the NIR. 20 These arrays allowed extensive NIR fluorescence enhancement of ~2 orders of magnitude, but the tunability of their sensitivity was not investigated.…”