Q-body is a new type of antibody-based probes that are highly innovative, versatile, and sensitive in detecting their corresponding antigens. It is constructed based on the principle of antigen-mediated fluorescent signal release. A Q-body is comprised of a fragment antibody (Fab or scFv) that is covalently modified by a fluorophore whose signal is, in the absence of the corresponding antigen, quenched by tryptophan (Trp) residues in the antibody. Upon antigen interaction, due to the change in antibody conformation, the Trp quenching effect is levitated, releasing the fluorescent signals. In principle, any antibody can be converted into a Q-body with proper protein engineering and conjugation strategies. The quenching effect is facilitated by adding of a small flexible linker that crosslinks the fluorophore to the Nt of the Fab or scFv antibody.
