Metal-Enhanced Fluorescence and FRET in Multilayer Core-Shell Nanoparticles

Abstract

In recent years, various methods for the synthesis of fluorescent core-shell nanostructures were developed, optimized, and studied thoroughly in our research group. Metallic cores exhibiting plasmonic properties in the UV and visible regions of the electromagnetic spectrum were used to increase substantially the brightness and stability of organic fluorophores encapsulated in silica shells. Furthermore, the efficiency and range of Förster resonant energy transfer (FRET) between donor and acceptor molecules located in the vicinity of the metallic core was shown to be enhanced. Such multilayer nanoparticle architectures offer, in addition to the aforementioned advantages, excellent chemical and physical stability, solubility in aqueous media, low toxicity, and high detectability. In view of these enviable characteristics, a plethora of applications have been envisioned in biology, analytical chemistry, and medical diagnostics. In this paper, advances in the development of multilayer core-shell luminescent nanoparticle structures and selected applications to bioanalytical chemistry will be described.

Plasmon‐Enhanced Fluorescence Resonance Energy Transfer

“…Note that there is a 15‐fold signal intensity when the metal core for the dye‐to‐metal separation is present (Figure a) and for Ag@SiO 2 @SiO 2 +FiTC NPs there is a 14‐fold fluorescence enhancement (Figure b) . Moreover, find that the metal‐enhanced fluorescence (MEF) phenomenon indeed occur in the process of measuring the fluorescence lifetime . Note that the emittance of the acceptor around 545 nm was tripled for adding the donor label layer, although the same concentration of acceptor in the two types of nanocomposites (Figure ).…”

“…Reported that the metal core of composite nanoparticles (NPs) can provide strong plasmon resonance, and the interaction with surrounding fluorescent molecules significantly improves the rate of excitation and emission . What's more, multilayer core‐shell NPs have many desirable properties for fluorescent probes, such as excellent stability of chemical and photophysical, high optical detection sensitivity, high water solubility, large excitation cross‐section, low toxicity, and easy binding to target biological molecules …”

“…(Figure ). They compared the fluorescence spectra of Ag@SiO 2 @SiO 2 +EiTC NPs (45 nm nuclear diameter) with those of corresponding non‐nuclear samples, and recorded the fluorescence spectra of Ag@SiO 2 @SiO 2 +eosin@SiO 2 +fluorescein and acceptor‐only Ag@SiO 2 @SiO 2 +eosin nanocomposites …”

The local field dependent effect of the critical distance of energy transfer between nanoparticles

“…FRET can be used as spectroscopic ruler in various areas such as the interaction of biological molecules in vitro and in vivo assays in cellular research, nucleic acid analysis, signal transduction, light harvesting and metallic nanomaterial etc. Based on the mechanism of FRET a variety of novel chemical sensors and biosensors have been developed [1][2][3][4][5]. Conventional FRET exhibits the R À 6 dependence law of energy transfer rate and characterized by the Förster distance or critical distance R 0 , which defined as the distance at which the energy transfer efficiency is 50%.…”

Effect of Silver Nanoparticles on Fluorescence Spectra of C480 dye

“…This behavior may be due to the remarkable optical properties displayed by metal nanostructures, in particular the coupling between the free electrons responsible for surface plasmon resonance and nearby fluorophores can enhance the emission rates and decrease the lifetimes of excited states. This phenomenon termed metal-enhanced fluorescence (MEF) as agreement with [15]. All procedure was same in the first case except that the silica had been replaced by PMMA layer.…”