Ultrasensitive and label-free detection of annexin A3 based on quartz crystal microbalance

Cadmium sulfide (CdS) quantum dots (QDs) were coupled to an Au nanoimmunosensor on a quartz crystal microbalance (QCM) to form the basis of an ultrasensitive and label-free sensor of annexin A3 (ANXA3), a lung and prostate cancer biomarker protein. Polyclonal anti-ANXA3 antibody was covalently immobilized on the CdS QDs, which had previously been functionalized with carboxyl groups and bound to a cystamine self-assembled monolayer on the Au/QCM. Frequency changes induced by the binding of ANXA3 to the anti-ANXA3 on the probe's surface allowed the very sensitive detection of GST-ANXA3 with a detection limit of 0.075 ± 0.01 ng/mL. The sensor could detect ANXA3 at 0.1 ng/mL in spiked human blood and urine samples in less than 15 min without any interference from other proteins.

A QCM-based nanoimmunosensor was fabricated in three steps: a CYS self-assembled monolayer was formed by incubating the Au/QCM electrode in CYS solution for 2 h; CdS QDs functionalized by carboxylic acid groups (COOH-CdS) were covalently attached to the CYS on the SAM/QCM electrode by incubating the electrode in a solution of COOH-CdS for 30 min; finally, anti-ANXA3 antibody was covalently immobilized onto the QDs/SAM/QCM. The immunosensor could detect ANXA3 in phosphate buffer solution, human urine, and human serum.Figure optionsDownload as PowerPoint slide