This paper presents a low-cost, pain-free, and highly sensitive electrochemical biosensor for the detection of α-synuclein in human plasma, a biomarker for Parkinson's disease (PD). The biosensor is based on hierarchical polyglutamic acid/ZnO nanowires decorated with gold nanoparticles (Au NPs) and functionalized with anti-α-synuclein antibodies. The ZnO nanowires were prepared by chemical bath deposition (CBD) and decorated with Au NPs through electrodeposition. Electro-polymerized glutamic acid was grown on the ZnO nanowires and functionalized with anti-α-synuclein antibodies. The biosensor's sensitivity was enhanced by embedding Au NPs into the ZnO nanowires, leading to a synergistic increase in electrode sensitivity. The analytical performance of the biosensor was evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with a Fe(II)(CN)64−/Fe(III)(CN)63− probe. The biosensor exhibited a linear response in the concentration range of 0.5 pg·mL−1 to 10 pg·mL−1, with a limit of detection of 0.08 pg·mL−1. The biosensor showed good reproducibility (5% variation) and stability (90% retention after two months of storage). Clinical tests using plasma samples from PD patients and healthy controls demonstrated the biosensor's ability to discriminate between the two groups, making it a promising tool for non-invasive and rapid diagnosis of PD.This paper presents a low-cost, pain-free, and highly sensitive electrochemical biosensor for the detection of α-synuclein in human plasma, a biomarker for Parkinson's disease (PD). The biosensor is based on hierarchical polyglutamic acid/ZnO nanowires decorated with gold nanoparticles (Au NPs) and functionalized with anti-α-synuclein antibodies. The ZnO nanowires were prepared by chemical bath deposition (CBD) and decorated with Au NPs through electrodeposition. Electro-polymerized glutamic acid was grown on the ZnO nanowires and functionalized with anti-α-synuclein antibodies. The biosensor's sensitivity was enhanced by embedding Au NPs into the ZnO nanowires, leading to a synergistic increase in electrode sensitivity. The analytical performance of the biosensor was evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with a Fe(II)(CN)64−/Fe(III)(CN)63− probe. The biosensor exhibited a linear response in the concentration range of 0.5 pg·mL−1 to 10 pg·mL−1, with a limit of detection of 0.08 pg·mL−1. The biosensor showed good reproducibility (5% variation) and stability (90% retention after two months of storage). Clinical tests using plasma samples from PD patients and healthy controls demonstrated the biosensor's ability to discriminate between the two groups, making it a promising tool for non-invasive and rapid diagnosis of PD.