Metal enhanced fluorescence solution-based sensing platform 2: Fluorescent core-shell Ag@SiO2 nanoballs

In recent years our laboratories have reported the favorable effects for fluorophores placed in close proximity to surface immobilized silver nanostructures. These include; greater quantum yields, re-duced lifetimes (increased photostability) and directional emission. However, while these findings are likely to find multifarious applications for surface assays based on enhanced fluorescence detec-tion, a solution based enhanced sensing platform has yet to be realized. In this short, note, we show how SiO2-coated silver colloids, indeed provide for a solution based enhanced fluorescence sensing platform with a 3–5 fold enhancement typically observed. KEY WORDS: Radiative decay engineering; metal-enhanced fluorescence; solution assays. Recently our laboratories have fabricated numerous noble-metal surfaces for metal-enhanced fluorescence de-tection whereby fluorophores can undergo modifications in their radiative decay rate, , Fig. 1 [1–8]. Silver island films (SiFs), formed an APS-coated glass slides by the re-duction of silver nitrate by glucose, have proved a versatile surface, providing up-to 10 fold increases in fluorescence signal of appropriate fluorophores [1–5]. Silver colloid coated surfaces have yielded up-to 50-fold enhancements [6], while silver-fractal-like coatings have been shown to increase fluorescein emission, several thousand fold [7,8]. These findings have been most encouraging and suggest the use of metallic nanostructures in surface assays and high-throughput screening plate-well formats. However, to date, little attention has been given to solution-based systems. This is in part due to the complexities associated with working with nano-or picomolar concentrations o