Multiphoton imaging of tumor biomarkers in situ using highly oriented conjugates of single-domain antibodies and quantum dots

High-quality imaging for immunofluorescence diagnosis in medical practice requires a high sensitivity of labeling and discrimination between the fluorescence of immunostaining probes and tissue autofluorescence. Multiphoton microscopy with excitation in the near-infrared spectral region, far from the region of excitation of tissue autofluorescence, enables deep imaging of biological tissues. CdSe/ZnS quantum dots (QDs) conjugated to single-domain antibodies (sdAbs) are efficient diagnostic nanoprobes with diameters <;12 nm and the two-photon absorption cross section exceeding 49,000 GM. Such nanoprobes ensure clear discrimination of tumor areas from normal tissue with the ratio of sdAb-QD emission to the autofluorescence for two-photon excitation >40 times higher than that for one-photon excitation.