Quartz crystal microbalance immunoassay with dendritic amplification using colloidal gold immunocomplex

A novel dendritic amplification procedure has been developed for microgravimetric quartz crystal microbalance (QCM) immunosensing by the application of antibody-functionalized Au nanoparticles as the primary amplifying probe and a dendritic-type immunocomplex of protein A- and antibody-modified Au nanoparticles as the secondary amplifying probe. Goat anti-human immunoglobulin G (IgG) antibody is orientedly immobilized on the Au electrode surface of QCM through pre-assembled protein A and acts as the sensing interface to recognize the analyte, human IgG. The primary amplification of the recognition process is implemented via the interaction of the sensing interface with the antibody-functionalized Au nanoparticles, and the secondary dendritic amplification is performed through interaction with the immunocomplex of protein A- and antibody-modified Au nanoparticles. The dendritic-type amplified sensing procedure is also confirmed by the UV–vis absorption measurements. The frequency decreases of the primary amplified and the secondary amplified sensing process are observed to be linearly dependent upon the IgG concentration in the range of 10.9 ng ml−1 to 10.9 μg ml−1 with a detection limit of 3.5 ng ml−1, while in the absence of the amplification processes, the antigen–antibody recognition event can only be detected for a IgG concentration as high as 10.9 μg ml−1.