Wavelength Dependence of Fluorescence Quenching of CdTe Quantum Dots by Gold Nanoclusters

Metal nanoclusters (NCs) are well-known for their distinct molecule-like luminescent behaviors. Currently, some research has been conducted concerning their quenching properties for various dyes, but little is known about the interaction between metal NCs and other fluorescent materials such as quantum dots (QM). In this paper, we report efficient quenching of fluorescence emission of mercaptoacetic acid (TGA)-coated CdTe QDs having identical protective layers but differing core diameters (1.04, 1.61, and 2.11 nm) by the bovine serum albumin (BSA)-protected Au-25 NCs (0.8 nm metal core diameter) that have negligible plasmon bands in PBS buffer solution at pH 7.4. With UV-vis absorption spectroscopy and steady-state and time-resolved fluorescence spectroscopy, we found that fluorescence emission of all QDs decreased significantly upon addition of Au NCs, in combination with no decrease in average fluorescence lifetime, which was attributed to static quenching of QDs by Au NCs. Interestingly, the 515 nm emitting QDs are at least 1 order of magnitude more efficiently quenched than the other two QDs in spite of the similar degree of spectral overlap of the emission spectrum with the excitation spectrum of Au NCs. This study not only has brought to light the quenching properties of metal NCs for QDs but also provided fundamental guidelines and new opportunities for further investigations into the interaction between metal NCs and other materials.