Sensitive Electrochemical Immunosensor for Α-Synuclein Based on Dual Signal Amplification Using PAMAM Dendrimer-Encapsulated Au and Enhanced Gold Nanoparticle Labels

A novel electrochemical immunosensor for sensitive detection of α-synuclein (α-SYN), a very important neuronal protein, has been developed based on dual signal amplification strategy. Herein, G4-polyamidoamine dendrimer-encapsulated Au nanoparticles (PAMAM-Au nanocomposites) were covalently bound on the poly-o-aminobenzoic acid (poly-o-ABA), which was initially electropolymerized on the electrode surface to perform abundant carboxyl groups. The formed immunosensor platform, PAMAM-Au, was proved to provide numerous amino groups to allow highly dense immobilization of antigen, and facilitate the improvement of electrochemical responses as well. Subsequently, the enhanced gold nanoparticle labels ({HRP-Ab(2)-GNPs}) were fabricated by immobilizing horseradish peroxidase-secondary antibody (HRP-Ab(2)) on the surface of gold nanoparticles (GNPs). After an immunoassay process, the {HRP-Ab(2)-GNPs} labels were introduced onto the electrode surface, and produced an electrocatalytic response by reduction of hydrogen peroxide (H(2)O(2)) in the presence of enzymatically oxidized thionine. On the basis of the dual signal amplification of PAMAM-Au and {HRP-Ab(2)-GNPs} labels, the designed immunosensor displayed an excellent analytical performance with high sensitivity and stability. This developed strategy was successfully proved as a simple, cost-effective method, and could be easily extended to other protein analysis schemes.