Multiphoton imaging of tumor biomarkers with conjugates of single-domain antibodies and quantum dots

Immunofluorescence diagnosis requires a high sensitivity of labeling and discrimination between the fluorescence of the probes and tissue autofluorescence. Recently, we developed conjugates of single-domain antibodies (sdAbs) and quantum dots (QDs), with all sdAb antigen-recognizing sites facing outwards, which considerably increase the nanoprobe sensitivity. Here, we have analyzed the two-photon optical properties of developed conjugates and applied them to imaging of carcinoembryonic antigen (CEA) in normal colon epithelium and pathological human colon carcinoma. The data show that the sdAb-QD conjugates are bright multiphoton nanoprobes with very high signal-to-autofluorescence ratios enabling clear discrimination of CEA-overexpressing tumor areas from normal tissue.144