Precise and Stable Labeling of Quantum Dots with Engineered Antibodies.

Quantum dots (QDs) are ideal probes for quantitative bioimaging but require controlled surface functionalization to be useful for imaging specific receptors or other cellular targets. Antibodies (Ab) offer high affinities and specificities against a range of targets, but methods for synthesizing QD-Ab conjugates may offer little control over stoichiometry, orient Ab incorrectly, or be reversible or denaturing. Here, we describe a protocol using SpyCatcher proteins, which spontaneously form covalent bonds with paired SpyTag peptides, to stably link Ab to QD surfaces with control over stoichiometry and orientation. Protocols for immunolabeling of CdSe/CdS QDs with miniaturized Ab, their characterization, and their use in live cell imaging are presented.