FRET studies between CdTe capped by small-molecule ligands and fluorescent protein

Water-soluble luminescent semiconductor nanocrystals also known as quantum dots (QDs) that have prominent photostability, wide absorption cross sections and tunable narrow emission, have been shown as promising probes in immunoassays. QDs are often used as donors in fluorescence resonance energy transfer (FRET) based sensors using organic dyes or fluorescent proteins as acceptors. Here, the FRET between a QD donor and fluorescent protein acceptors has been studied. The fluorescent protein (FP) mCherry appended with a hexa-histidine-tag could effectively self-assemble onto CdTe to produce small donor-acceptor distances and hence highly efficient FRET (efficiency > 80%) at relatively low FP:CdTe copy numbers (ca.1). Using the Förster dipole–dipole interaction formula, the Förster radius (R0) and respective donor acceptor distances for the CdTe-FP FRET systems have been calculated. The binding constants (Kd) of the QD-FP systems have also been evaluated by the emission spectra.