Time-resolved and steady-state FRET spectroscopy on commercial biocompatible quantum dots

Semiconductor nanocrystals (quantum dots - QDs) possess unique photophysical properties that make them highly interesting for many biochemical applications. Besides their common use as fluorophores in conventional spectroscopy and microscopy, QDs are well-suited for studying Forster resonance energy transfer (FRET). Size-dependent broadband absorption and narrow emission bands offer several advantages for the use of QDs both as FRET donors and acceptors. QD-based FRET pairs can be efficiently used as biological and chemical sensors for highly sensitive multiplexed detection. In this contribution we present the use of several commercially available QDs (Qdot (R) Nanocrystals - Invitrogen) as FRET donors in combination with commercial organic dyes as FRET acceptors. In order to investigate the FRET process within our donor-acceptor pairs, we used biotinylated QDs and streptavidin-labeled dyes. The well-known biotin-streptavidin molecular recognition enables effective FRET from QDs to dye molecules and provides defined distances between donor and acceptor. Steady-state and time-resolved fluorescence measurements were performed in order to investigate QD-to-dye FRET. Despite a thick polymer shell around the QDs, our results demonstrate the potential of these QDs as efficient donors both for steady-state and time-resolved FRET applications in nano-biotechnology.