Abstract.  Fluorescent labels have long been utilized in studies of in vitro and in vivo biochemical processes. In view of the widespread applications of monolayer-protected gold nanoparticles (AuNP) in biosensor design and medical diagnostics, their interactions with photoluminescent dyes became of a major focus. We report herein results of an investigation of the fluorescence resonance energy transfer (FRET) between photoluminescent dyes: Coumarin 4, acting as the donor, and Coumarin 7, acting as the acceptor. We have found that in the presence of spherical gold nanoparticles, the fluorescence energy transfer occurs primarily from both dyes to the nanoparticles and the FRET between the dyes is hindered. The high efficiency of fluorescence quenching by gold nanoparticles has been evaluated from the viewpoint of non-Forster distance dependence and molecular orientation of dyes adsorbed on gold nanoparticles. We have also evaluated the quenching effectiveness of Coumarin 4 fluorescence by spherical gold nanoparticles and nanorods.

Figure 1. Fluorescence spectra for AuNP5nm in the presence of 50 uM coumarin 4; AuNP concentration [nM]: (1) 0, (2) 0.63, (3) 1.27, (4) 1.9, (5) 2.53, (6) 3.17, (7) 3.8, (8) 4.43, (9) 5.07, (10) 6.33, (11) 6.97. Excitation wavelength: (a) lex = 363 nm and (b) lex = 355 nm.