Label-free detection of breast cancer marker HER-2/neu with an acoustic biosensor

Abstract

Surface acoustic wave (SAW) biosensors based on horizontally polarized surface shear waves enable label-free, sensitive and cost-effective detection of biomolecules in real time. Binding reactions on the sensor surface are detected by determining changes in surface wave velocity caused mainly by mass loading in the sensing layer. Typically, SAW devices are coated with biochemically sensitive layers including analyte-specific capture molecules (e.g., antibodies) or ligands. The covalent binding of antibodies to intermediate hydrogel layers (e.g., dextran or polyethylene glycol) tends to result in undirected orientation of capture molecules and leading to a lower signal response in a subsequent analyte binding experiment. Therefore, a coupling procedure was developed using two linkers, neutravidin and biotinylated protein A, allowing directed orientation of capture antibodies. This assembly enables label-free and direct detection of the breast cancer marker HER-2/neu at a concentration of 10 ng/ml (threshold: 13–20 ng/ml).