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

TLDR

The size, shell thickness, and color of the MEF‑nanoparticles can be tuned for diverse biological applications such as cellular entry, imaging, and localization. The study develops versatile, highly fluorescent Ag@SiO₂ core–shell nanocomposites that enable incorporation of diverse fluorophores onto the silica shell via two simple methods. The authors prepared the nanocomposites by coating silver cores with silica shells and attaching three types of fluorophores—Rh800, a noncovalently linked lanthanide probe, and covalently linked Alexa 647—to demonstrate the method’s versatility. Fluorescent Ag@SiO₂ nanoparticles exhibited up to 20‑fold fluorescence enhancement over control nanobubbles, and the combined 20‑fold intensity increase with a 10‑fold lifetime reduction yielded an overall ~200‑fold increase in detectability for sensing and imaging.

Abstract

We report the development of highly versatile highly fluorescent and photostable core−shell Ag@SiO2 nanocomposites, which allows researchers the flexibility to incorporate just about any fluorophores to the outer silica shell by two simple methods. To show the generality of the preparation technique, we have developed three different fluorescent probes: an organic fluorophore (Rh800) and a lanthanide probe doped (noncovalently linked) and an organic fluorophore (Alexa 647) covalently linked to the silica shell. When compared to the control fluorescent nanoparticles (nanobubbles), fluorescent nanoparticles with silver core−silica shell architecture yielded up to 20-fold (with Rh800) enhancement of the fluorescence signal. In terms of nanoparticle detectability for sensing and cellular imaging applications, a 20-fold increase in fluorescence intensity coupled with a 10-fold drop in lifetime affords a total increased detectability of ∼200-fold as compared to the control sample nanobubbles containing the same number of fluorophores. The size, shell thickness, and color of the new MEF-nanoparticles can be easily controlled and optimized for a variety of biological applications, such as cellular entry, imaging, and localization.