Fluorescent Core−Shell Ag@SiO₂ Nanocomposites for Metal-Enhanced Fluorescence and Single Nanoparticle Sensing Platforms

Abstract

The use of fluorescent nanoparticles as indicators in biological applications such as imaging and sensing has dramatically increased since the 1990s. 1 These applications require that the fluorescent nanoparticles are monodisperse, bright, photostable, and amenable to further surface modification for the conjugation of biomolecules and/or fluorophores. Among the many types of fluorescent nanoparticles available today, nanoparticles with core-shell architecture fulfill all these requirements, combining diverse functionalities into a single hybrid nanocomposite. 2 In this work, we have developed core-shell (silver core-silica shell) nanoparticles with various shell thicknesses featuring a variety of fluorophores, to show the versatility of the core-shell architecture, and have demonstrated their applicability for two platform technologies, metal-enhanced fluorescence (MEF) and single nanoparticle sensing. We demonstrate the broad potential applications of our technology by employing near-infrared emitting probes (Rh800) for potential applications in cellular imaging and the use of highly photostable long lifetime (μS) lanthanide probes, probes suitable for off-gating biological autofluorescence. The use of Alexa 647 serves to demonstrate that fluorophores can be readily covalently linked to the core-shell particles also, for metal-enhanced benefits.MEF is an established technology, 3a-d where the interactions of fluorophores with metallic nanoparticles results in fluorescence enhancement, increased photostability, decreased lifetime owing to increased rates of system radiative decay, reduced blinking in single molecule fluorescence spectroscopy, 3b and increased transfer distances for fluorescence resonance energy transfer. 3c Single-molecule fluorescence spectroscopy is the prime tool in single nanoparticle sensing, and it provides several advantages over ensemble measurements, such as, the elimination of averaging of the spectral properties over all members of the ensemble, which can reveal fundamental features otherwise masked in

Plasmonic engineering of singlet oxygen generation

“…Using electromagnetic field calculations to predict electric field distributions, we believe that the extent of enhanced triplet yields and the subsequent rates of singlet oxygen production of luminophores/fluorophores in close proximity to plasmonic structures can be readily predicted. Recently, we reported the solution-based embodiment of MEF in a nanoball architecture (30). These particles were constructed with solid metallic cores with an outer SiO 2 coating.…”

Nanomaterials in fluorescence-based biosensing

“…The silver nanoball was coated with the fluorophore-doped silica shell, and a twentyfold increase in fluorescence was observed with this structure compared to nanobubbles without a silver core (Fig. 2) [62].…”

Polyelectrolyte Layer-by-Layer Assembly To Control the Distance between Fluorophores and Plasmonic Nanostructures

“…[15][16][17][18][19] A detail understanding of the MEF and its distance dependence nature is vital for its potential application in biomedical sensing. [20][21][22] Layer-by-layer (LbL) assembly [23][24][25][26][27][28][29][30][31][32][33][34][35][36] is based on the sequential adsorption of polycations and polyanions from dilute aqueous solution onto a solid substrate as a consequence of the electrostatic interaction and complex formation between oppositely charged polyelectrolytes. Starting from a functionalized solid substrate, it is possible to adsorb a variety of charged species ranging from polyelectrolytes, nanoparticles, and ionic dyes to many biological agents such as viruses, proteins, and DNA.…”