Covalent monofunctionalization of peptide-coated quantum dots for single-molecule assays.

Fluorescent probes for biological imaging of single molecules (SM) have many stringent design requirements. In the case of quantum dot (QD) probes, it remains a challenge to control their functional properties with high precision. Here, we describe the simple preparation of QDs with reduced size and monovalency. Our approach combines a peptide surface coating, stable covalent conjugation of targeting units and purification by gel electrophoresis. We precisely characterize these probes by ensemble and SM techniques and apply them to tracking individual proteins in living cells.