An Electrochemical Immunosensor Based on a Self-Assembled Monolayer Modified Electrode for Label-Free Detection of α-Synuclein

This research demonstrated the development of a simple, cost-effective, and label-free immunosensor for the detection of alpha-synuclein (alpha-Syn) based on a cystamine (CYS) self-assembled monolayer (SAM) decorated fluorine-doped tin oxide (FTO) electrode. CYS-SAM was formed onto the FTO electrode by the adsorption of CYS molecules through the head sulfur groups. The free amine (-NH2) groups at the tail of the CYS-SAM enabled the immobilization of anti-alpha-Syn-antibody, which concurrently allowed the formation of immunocomplex by covalent bonding with alpha-Syn-antigen. The variation of the concentrations of the attached alpha-Syn at the immunosensor probe induced the alternation of the current and the charge transfer resistance (R-ct) for the redox response of [Fe(CN)(6)](3-/4-), which displayed a linear dynamic range from 10 to 1000 ng/mL with a low detection limit (S/N = 3) of ca. 3.62 and 1.13 ng/mL in differential pulse voltammetry (DPV) and electrochemical impedance spectra (EIS) measurements, respectively. The immunosensor displayed good reproducibility, anti-interference ability, and good recoveries of alpha-Syn detection in diluted human serum samples. The proposed immunosensor is a promising platform to detect alpha-Syn for the early diagnose of Parkinson's disease, which can be extended for the determination of other biologically important biomarkers.