Distance-Dependent Metal-Enhanced Intrinsic Fluorescence of Proteins Using Polyelectrolyte Layer-by-Layer Assembly and Aluminum Nanoparticles

Abstract

Previously reported studies indicate that aluminum nanostructured substrates can potentially find widespread use in metal-enhanced fluorescence (MEF) applications particularly in the UV or near-UV spectral region toward label-free detection of biomolecules. MEF largely depends on several factors, such as chemical nature, size, shape of the nanostructure and its distance from the fluorophore. A detailed understanding of the MEF and its distance-dependence are important for its potential application in biomedical sensing. Our goal is to utilize intrinsic protein fluorescence for label-free binding assays. This is made possible by the use of metallic nanostructures which provide localized excitation and enhanced fluorescence of UV fluorophores and will also provide a way to separate the surface-bound proteins from the bulk samples. We evaluated varied probe distances from plasmonic nanostructures by the well-established layer-by-layer (LbL) technique. The investigated proteins were adsorbed on different numbers of alternate layers of poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH). Bovine serum albumin (BSA) was electrostatically attached to the positively charged PAH layer, and goat and rabbit IgG were attached to negatively charged PSS layer. We obtained a maximum of a ~ 9 fold increase in fluorescence intensity from BSA at a distance of ~9 nm from the Al nanostructured surface. Approximately 6- and 7- fold increases were observed from goat and rabbit IgG at a distance of ~8 nm, respectively. The minimum lifetimes were about 3-fold shorter than those on bare control quartz slides for all three proteins. The time-resolved intensity decays were analyzed with a lifetime distribution model to understand the distance effect on the metal–fluorophore interaction in detail. The present study indicates the distance dependence nature of metal-enhanced intrinsic fluorescence of proteins and potential of LbL assembly to control the metal-to-fluorophore distance in the UV wavelength region.

In situ induced metal-enhanced fluorescence: A new strategy for biosensing the total acetylcholinesterase activity in sub-microliter human whole blood

“…The fluorescence signal increased when the fluorophore was fixed to the outer-silica shell. The fluorescence enhancement factor was optimized by modulating the shell thickness (Arifin and Lee 2013;Akbay et al, 2012).…”

Coupling of Deep-Ultraviolet Photons and Electrons

“…With the aid of photon localization and enhancement by DUV-LSPR [59][60][61] LSPR, the output power of LEDs is expected to improve [62][63][64][65]. Huang et al demonstrated for the first time that the enhanced emission of DUV-LEDs coupled to LSPRs generated by Al nanoparticles prepared on quantum wells (QWs) [66,67].…”

Fluorescence enhancement in large-scale self-assembled gold nanoparticle double arrays

“…Therefore, smaller distances suggest an enhanced absorption by the fluorophore. 2,14,18,[21][22][23][24] Second, the radiative decay rate of the fluorophore can be increased in the vicinity of nanoparticles. This increases its emission and influences its quantum yield, shortens the fluorophore life time, and improves its photostability by reducing the chances of photo-bleaching.…”

“…1,[12][13][14][15]22 As a result and considering the concerted action of all processes, there is an optimal distance for the fluorophore from the particle's surface to maximize the fluorescence. 12,16,19,21,26,30 Therefore, it is essential to control the distance between the fluorophores and the particles surface. 12,14,16,19,21,26,31 In order to achieve such distance control, the use of different types of spacers has been reported such as silica, 22,24,[32][33][34][35] polymers, 7,19,21,[36][37][38][39] and biomolecules.…”

“…12,16,19,21,26,30 Therefore, it is essential to control the distance between the fluorophores and the particles surface. 12,14,16,19,21,26,31 In order to achieve such distance control, the use of different types of spacers has been reported such as silica, 22,24,[32][33][34][35] polymers, 7,19,21,[36][37][38][39] and biomolecules. 28,[40][41][42] However, one important factor is yet unconsidered.…”