Sensitive Electrochemical Detection of Phosphorylated-Tau Threonine 231 in Human Serum Using Interdigitated Wave-Shaped Electrode

The development of an electrochemical biosensor for the detection of phosphorylated-tau threonine 231 (p-tau231), a biomarker of Alzheimer’s disease (AD), has yet to be achieved. Therefore, in this study, we developed a simple, small size, cheap, and sensitive electrochemical biosensor based on an interdigitated wave-shaped electrode via an activated self-assembled monolayer to preserve a specific anti–p-tau231 antibody (IWE/SAM/EDC-NHS/anti–p-tau231). Detection of p-tau231 in human serum (HS) using the biosensor was undertaken using electrochemical impedance spectroscopy (EIS). The change in charge-transfer resistance (R(ct)) in the EIS analysis of the biosensor indicated the detection of p-tau231 in HS within a wide linear range of detection (10(−4)–10(1) ng mL(−1)), and a low limit of detection (140 pg mL(−1)). This lower limit is less than the detection level of p-tau231 in cerebrospinal fluid (CSF) (700 pg mL(−1)) of AD patients and the level of CSF p-tau231 of patients with mild cognitive impairment (501 pg mL(−1)), demonstrating the possibility of using the biosensor in detection of p-tau231 at early stage AD. A high binding affinity and low dissociation constant (K(d)) between anti–p-tau231 and p-tau231 in HS was demonstrated by using a biosensor and K(d) was 7.6 pM, demonstrating the high specific detection of p-tau231 by the biosensor. The good selectivity of the biosensor for the detection of p-tau231 with differential analytes was also examined in this study.