The influence of silver nanostructures formed in-situ in silica sol-gel derived films on the rate of Förster resonance energy transfer

There is growing interest in the detection of target analytes in biological systems which can be achieved by the development of suitable biosensors and lab-on-a-chip devices[1]. Media produced using the sol-gel method are suitable host materials for such biological based applications[2]. These robust glass-like materials are highly porous and exhibit large internal surface areas and previously we have reported upon the incorporation of enzymes entrapped within sol-gel derived hosts. This made use of fluorescent dyes to characterise the sol-gel manufacture and help elucidate protein conformation, along with guest-host interactions[3]. Recently there has been increased research in the use of metal surfaces in order to influence the fluorescence emission, which can be advantageous as the radiative decay rate can be enhanced. We have previously put this to use to show the influence of silver nanostructures formed in-situ using a compact time-resolved fluorescence microscope system on the fluorescence of a tagged protein adsorbed onto a sol-gel derived film[4].

In this work we will demonstrate a model biosensor system employing enhanced Förster resonance energy transfer (FRET) in the presence of locally created silver colloids. The system is based on a sol-gel film containing silver salts, from which we can produce localised silver colloids in-situ via light irradiation. The presence of these silver nanostructures was ascertained via UV-vis and atomic force microscopy (AFM). Silane molecules with an NH2 group were attached to the surface of the sol-gel film. A fixed distance between a fluorescent donor molecule (Rhodamine 6G), which was located within the sol-gel matrix, and an acceptor was therefore achieved by covalently binding the acceptor molecule to the NH2 group of the silane spacer. The effect of the localised silver colloids on FRET was monitored. Our model system employs Texas Red as the acceptor molecule, however in future applications this could be a biomolecule such as a protein or DNA, thus demonstrating the potential application of this methodology to developing a molecular recognition system.