Ni-Co alloy coated QCM immunosensor to immobilize multiplex histidine-tagged proteins for label-free immunoassays

This paper presents a QCM immunosensor to immobilize multiplex histidine-tagged proteins for immunoassays. On the silver-plated electrode of QCM, a Ni-Co film was coated as the metal-affinity immobilization layer by electrodeposition. Ni-Co film can provide specific binding with histidine-tagged proteins based on the method of immobilized metal affinity chromatography (IMAC). The adsorption is through the histidine, based on the technique of IMAC and irrelevant to the species of proteins. Thus, multiplex immunoassays of histidine-tagged proteins can be conducted on the same QCM immunosensor. The experimental results show that the Ni-Co layer possesses reliable immobilization ability for different protein concentrations. After immunoreaction, frequency shift caused bylaw abundance of antibody (133 ng/mL) was measured, while the fluorescence intensity was too low to be detected. Moreover, the experiments using 0.5 IA droplets, with each droplet containing one kind of histidine-tagged protein and various antibodies, revealed that His-tagged protein and its corresponding antibody can be immobilized on the Ni-Co coated QCM for immunoassay and measurement. All experiments showed linear relationship between concentration and frequency shift. This feature provides practical implementations for the users to carry out multiplex label-free immunoassays on the same QCM. (C) 2015 Elsevier B.V. All rights reserved.