A highly sensitive disposable immunosensor through direct electro-reduction of oxygen catalyzed by palladium nanoparticle decorated carbon nanotube label

A palladium nanoparticle decorated carbon nanotube was designed as a label for preparation of a highly sensitive disposable immunosensor. The immunosensor was constructed by assembling the capture antibody on gold nanoparticles decorated graphene nanosheets modified screen printed carbon working electrode. With a sandwich immunoassay mode, the palladium nanoparticle decorated carbon nanotubes were captured to the immunocomplex and showed strong electrocatalytic activity toward oxygen reduction. The use of carbon nanotube carrier offered a high amount of palladium nanoparticles on each immunoconjugate, hence amplified the detectable signal from the electro-reaction of dissolved oxygen. The graphene nanosheets and gold nanoparticles improved the electronic conductivity and the hydrophilicity of electrode surface for immobilization of the capture antibody, respectively. Under optimal conditions, a linear detection range from 50 pg/mL to 10 ng/mL and a limit of detection of 44 pg/mL (0.3 pM) were achieved for human IgG. Using dissolved oxygen as a signal reporter, the detection process avoided deoxygenation. The immunosensor showed acceptable stability, precision and accuracy, indicating potential applications in clinical diagnostics.