Bioconjugation of anti estrogen alpha antibody with CdSSe/ZnS quantum dots for molecular sensing of a breast cancer antigen

• CdSSe/ZnS QDs have been conjugated with a breast cancer marker anti-ERα.
• Emission spectra of the QD-(anti-ERα) complex overlaps with the excitation spectra of FITC-ERα.
• FRET based molecular sensing of ERα is demonstrated.
• Sensing of the antigen is achieved over wide concentration range with detection limit approaching 120 pM.

In this present work, amine functionalized CdSSe/ZnS (core/shell) QDs have been conjugated with an anti-ERα antibody, which is a specific antibody against breast cancer antigen ERα. The bioconjugation reaction has been optimized with respect to the pH, reaction time and ionic strength of the media. Molecular interaction between the QDs conjugated antibodies and a dye (FITC) labeled ERα antigen provided a fluorescence resonance energy transfer (FRET) based pathway for quantitative detection of antigen. Upon excitation with 465 nm light, the PL intensity of FRET donor (QDs) decreases proportionally with increasing antigen concentration. Simultaneously, increase in the PL intensity of the FRET acceptor was observed. FRET immunoassay of ERα is sensitive and a wide linear range of detection (10–300 ng mL−1 ERα) observed. FRET efficiency of ∼70% has been achieved. Estimated limit of detection of ERα is 120 pM.