(633b) Fluorescence Level Manipulation by Gold Nano Particles

Fluorephore mediated molecular imaging is becoming a leading methodology in medical diagnostic and biotechnology. The ability of fluorescence alteration can be highly beneficial for improving sensitivity and specificity: artificial enhancement in the quantum yield can be highly beneficial to improve the sensitivity. Likewise, if fluorescence can be quenched when the molecule of interest reacts with the target, it can be very useful and also minimizing non-specific signal.

We have been studying alteration of fluorescence using nano metal particles. Gold nano particles (GNPs) are known to generate strong surface plasmon fields when light is applied and this field can effectively be used to quench or enhance fluorescence. GNP is of our interest because of its chemical inertness and ability for easy surface modification. The level of the fluorescence change by GNPs can be from complete quenching to extensive enhancement, depending upon the strength of plasmon field where the fluorophore is placed. The field strength depends upon the particle size and the distance from the particle surface. For a system where the metal type, particle size, and the fluorophore are fixed, the distance between particle and fluorophore can be controlled by placing a molecular spacer at a desired length between the two.

We have manipulated the distance between an NIR fluorophore (Indocyanine Green based) and a GNP, by adding various number of polymer layers of known thickness on the surface of a GNP. The NIR fluorophore was immobilized on the outer layer of the polymer. The distance was also altered by placing bio-compatible molecular spacers at various lengths. The fluorescence was, then, correlated with the distance between the GNP and the NIR fluorophore.

This fluorescence alteration mechanism can be highly beneficially utilized for fluorescent bioimaging with higher contrast. By combining both fluorescence enhancement and quenching in one entity, it is also possible to develop molecular-beacon like, contrast imaging agent with excellent specificity and sensitivity.

The authors acknowledge the financial support from U.S. Army Breast Cancer Program.