Label-Free Electrochemiluminescence Detection of Urinary AD7c-NTP Using Structurally Optimized Iridium(III) Complexes on Boron-Doped Diamond Electrodes

Evaluation of Alzheimer’s disease-associated neuronal thread protein (AD7c-NTP) in urine holds significant potential as a noninvasive and accessible biomarker for the early diagnosis of Alzheimer’s disease (AD). In this study, a novel label-free and ultrasensitive electrochemiluminescence (ECL) sensor for detection of AD7c-NTP was designed based on a structurally optimized iridium(III) complex ([(piq) 2 Ir(CH 3 CN) 2 ]BF 4 ) as the luminescent probe at a boron-doped diamond (BDD) electrode. After modifying the antibody on the surface of the amino-functionalized BDD electrode, AD7c-NTP molecules were first captured, and then a sandwich immunoassay system was constructed by introducing aptamer-modified gold nanoparticles (AuNPs). Subsequently, [(piq) 2 Ir(CH 3 CN) 2 ]BF 4 was intercalated into the DNA double-helical structure via electrostatic adsorption, thereby enabling ECL signal detection. Based on the metal-to-ligand charge transfer of iridium complexes at the π–π* energy level and the acceleration of electron transfer from the complexes to the BDD electrode by AuNPs, the established ECL immunosensor exhibited high sensitivity, with a linear range of 0.001–100 ng/mL and an ultralow detection limit of 17.7 fg/mL (S/N = 3). The practicability of the assay was confirmed by the test of AD7c-NTP in human urine, providing valuable information for early screening of AD.