Enhanced sensitivity of quartz crystal microbalance immunosensor via back-conjugation of biofunctionalized magnetic beads with an external magnetic field

A new signal amplification strategy based on back-conjugation of biofunctionalized magnetic beads holds promise to improve the sensitivity/detection limit of quartz crystal microbalance (QCM) immunosensor toward target carcinoembryonic antigen (CEA, a kind of tumor marker) with the help of an external magnetic field. To construct such an affinity reactor, anti-CEA capture antibody was initially immobilized onto a 10 MHz quartz crystal resonator by using mercaptopropionic acid, whilst detection antibody was covalently conjugated to carboxylated magnetic beads via a typical carbodiimide coupling. Sandwich-type protocol was successfully introduced to develop a new high-efficiency QCM immunosensor through interaction of the carried magnetic beads with external magnetic field. Under the optimal conditions, the linear range and limit of detection (LOD) of the QCM immunosensor were 1.0⿿15 ng mL⿿1 and 0.86 ng mL⿿1 CEA without external magnetic field, and 0.05⿿10 ng mL⿿1 and 0.013 ng mL⿿1 CEA in the presence of magnetic field, respectively. In addition, our system also exhibited good precision and reproducibility, high selectivity, acceptable stability (90.3% of the initial signal after a storage period of 24 days), and could be utilized for detection of real human serum samples with consistent results comparable to those obtained from commercially available enzyme-linked immunosorbent assay (ELISA) method.