V_H-Based Mini Q-Body: A Novel Quench-Based Immunosensor

Quenchbodies (Q-bodies), a type of biosensor, are antibodies labeled with a fluorescent dye near the antigen recognition site. In the absence of an antigen, the dye is quenched by tryptophans in the antibody sequence; however, in its presence, the dye is displaced and therefore de-quenched. Although scFv and Fab are mainly used to create Q-bodies, this is the first report where a single-domain heavy chain V_H from a semi-synthetic human antibody library formed the basis. To create a proof of concept “mini Q-body”, a human anti-lysozyme single-domain V_H antibody C3 was used. Mini Q-bodies were successfully developed using seven dyes. Different responses were observed depending on the dye and linker length; it was concluded that the optimal linker length for the TAMRA dye was C5, and rhodamine 6G was identified as the dye with the largest de-quenching response. Three single-domain antibodies with sequences similar to that of the C3 antibody were chosen, and the results confirmed the applicability of this method in developing mini Q-bodies. In summary, mini Q-bodies are an easy-to-use and time-saving method for detecting proteins.