Sensitive electrogravimetric immunoassay of hepatitis B surface antigen through hyperbranched polymer bridge linked to multiple secondary antibodies

A method for using a hyperbranched polymer (HBP) as a bridge to link multiple secondary antibodies at HBP branches to amplify the detection response signal on a quartz crystal microbalance (QCM)-based sandwich-type immunosensor is reported. Carboxyl groups were prepared at multiple branches of HBP to make possible chemical binding between HBP and secondary antibodies via the carboxyl-amine reaction. The total mass of HBP and its linked multiple secondary antibodies were used to enhance the signal on a QCM chip in comparison with a simple sandwich-type immune reaction. By contrast, the proposed method could cause one antigen to analogously react with multiple secondary antibodies as a result of the branch structure of HBP. The strategy of using HBP as a bridge to link multiple secondary antibodies succeeded in quantitatively detecting the hepatitis B surface antigen (HBsAg). By employing demonstrated HBP bridge-linking, the frequency shift on a QCM chip was approximately 5 times greater than conventional methods without modification at secondary antibodies. The limit of detection of HBsAg was achieved as 2.0 ng mL −1 , lower than most of the values recorded in the literature measured by the QCM technique. Taking into account the general chemical interaction of immunoreaction, this method has the potential to amplify the signal in sensing many other analytes of interest.