Study of an Ultrasensitive\nLabel-Free Electrochemiluminescent\nImmunosensor Fabricated with a Composite Electrode for Detecting the\nGlutamate Decarboxylase Antibody

Abstract

Antibody\ntesting for the glutamic acid decarboxylase\n65 antibody\n(GADA) is widely used as a golden standard for autoimmune diabetes\ndiagnosis, while current methods for antibody testing are not sensitive\nenough for clinical usage. Here, a label-free electrochemiluminescent\n(ECL) immunosensor for detecting GADA in autoimmune diabetes is fabricated\nand investigated. In the designed immunosensor, a composite film including\nthe multiwalled carbon nanotubes (MWCNTs), zinc oxide (ZnO), and Au\nnanoparticles (AuNPs) was prepared through nanofabrication processes\nto improve the performance of sensor. The MWCNTs, which can provide\na larger specific surface area, ZnO as a good photocatalytic material,\nand AuNPs that can enhance the ECL signal of luminol and immobilize\nthe GAD65 antigen were applied to prefunctionalize indium tin oxide\n(ITO) glass based on a nanofabrication process. The GADA concentration\nwas detected using the ECL immunosensor after incubating with GAD65\nantigen-coated prefunctionalized ITO glass. After a direct immunoreaction,\nit is found that the degree of decreased ECL intensity has a good\nlinear regression toward the logarithm of the GADA concentration in\nthe range of 0.01 to 50 ng mL^–1 with a detection\nlimit down to 10 pg mL^–1. Human serum samples positive\nor negative for GADA all nicely fell in the expected area. The fabricated\nimmunosensor with excellent sensitivity, specificity, and stability\nhas potential capability for clinical usage in GADA detection.