Diagnostic nanoprobes based on the conjugates of quantum dots and single-domain antibodies for cancer biomarkers detection in immunohistochemistry and flow cytometry

Monoclonal antibodies (mAbs) are often too big for the nanoparticle targeting purpose and the conditions used for their conjugation provide nanoprobes with irregular orientation of mAbs on the surface of nanoparticle. Here, we are reviewing our recent publications reporting on ultra-small nanoprobes engineered through oriented conjugation of quantum dots (QDs) with 13-kDa single-domain antibodies (sdAbs) derived from llama and produced in E. coli. Developed nanoprobes with hydrodynamic diameter below 12 nm contain four homogeneously oriented copies of sdAbs on the surface of each QD. They demonstrated excellent specificity and sensitivity for the quantitative detection of rare biomarker-expressing cells using flow cytometry. The higher diffusibility of sdAbs enables immunohistochemical analysis of thick tissues not accessible to mAbs. The data shows that sdAbs-QD conjugates lead to biopsy tissue labelling displaying an equivalent or even better quality than that obtained with gold standard immunohistochemical diagnostics. Developed sdAbs-QD nanoprobes should find numerous applications in multiplexed high-throughput diagnostics and FRET-based detection platforms.