A gold nanoparticles/sol–gel composite architecture for encapsulation of immunoconjugate for reagentless electrochemical immunoassay

A highly hydrophilic, non-toxic and conductive colloidal gold nanoparticle/titania sol–gel composite membrane with a low contact angle was prepared on a glassy carbon electrode via a vapor deposition method. With human chorionic gonadotrophin (hCG) as a model antigen and encapsulation of horseradish peroxidase-labeled hCG antibody (HRP-anti-hCG) in the composite architecture, this membrane could be used for reagentless electrochemical immunoassay. It displayed a porous and homogeneous composite architecture without the aggregation of the immobilized protein molecules. The presence of gold nanoparticles provided a congenial microenvironment for adsorbed biomolecules and decreased the electron transfer impedance, leading to a direct electrochemical behavior of the immobilized HRP. The formation of immunoconjugate by a simple one-step immunoreaction between hCG in sample solution and the immobilized HRP-anti-hCG introduced a barrier of direct electrical communication between the immobilized HRP and the electrode surface. Under optimal conditions, the hCG analyte could be determined in two linear ranges from 0.5 to 5.0 mIU/mL and 5.0 to 30 mIU/mL with a relatively low detection limit of 0.3 mIU/mL at 3σ. The hCG immunosensor exhibited good precision, high sensitivity, acceptable stability, accuracy and reproducibility. This composite membrane could be used efficiently for the entrapment of different biomarkers and clinical applications.