Small-molecule ligands strongly affect the Förster resonance energy transfer between a quantum dot and a fluorescent protein.

We report herein the study of Förster resonance energy transfer (FRET) between a CdSe/ZnS core/shell quantum dot (QD) capped with three different small-molecule ligands, 3-mercaptopropionic acid (MPA), glutathione (GSH), and dihydrolipoic acid (DHLA), and a hexa-histidine (His(6))-tagged fluorescent protein, mCherry (FP). The Förster radius (R(0)) and the corresponding donor-acceptor distances (r) for each of the QD-FP FRET systems were evaluated by using the Förster dipole-dipole interaction formula. Interestingly, both the FRET efficiency (E) and r were found to be strongly dependent on the capping small-molecule ligands on the QD surface, where E ≈ 85% was obtained at a FP:QD copy number of 2:1 for the MPA capped QD, while that for the DHLA capped QD was <25% under the same conditions.