Design of a Dual-Wavelength Ratiometric Electrochemiluminescence Immunosensor for Sensitive Detection of Amyloid-β Protein in Human Serum

Alzheimer's disease (AD) threatens the health of elderly people. Amyloid-β protein (Aβ42) is considered to be a critical protein in the development of AD and a predictive biomarker for the diagnosis of AD. In this study, a dual-wavelength ratiometric electrochemiluminescence (DWR-ECL) sensor was developed for sensitive detection of Aβ42. A Ru@TiO2@Au nanomaterial was used as the energy receptor, and gold nanoparticles (AuNPs)-modified graphitic carbon nitride nanosheets (g-C3N4NSs) were employed as the energy donor. Au-g-C3N4NSs exhibits a highly stable ECL signal with an emission center at 460 nm, which overlaps with the Ru@TiO2@Au UV–vis absorption spectrum also well stimulates the emission of Ru(bpy)32+ at 620 nm, manufacturing ECL resonance energy transfer (RET) with a good performance. Therefore, an ECL-RET system was established. AuNPs functionalized the surface of g-C3N4NSs, not only providing a good substrate to fix primary antibodies (Ab1) (Au–N) but also increasing the electron transport rate of g-C3N4NSs on the surface of the electrode. Furthermore, titanium dioxide nanoparticles (TiO2NPs) due to high specific surface area were applied to load numerous Ru(bpy)32+ and AuNPs, and the obtained Ru@TiO2@Au nanomaterials were introduced to combine secondary antibody (Ab2), thus remarkably amplifying the ECL signal. Under optimal experiments, on the basis of the ratio of I460nm/I620nm (I is the ECL intensity), the linearity range of Aβ42 is from 1 × 10–5 to 200 ng/mL with a limit of detection (LOD) of 2.6 fg/mL (S/N = 3). The results indicate that the designed DWR-ECL immunosensor has satisfactory stability, high sensitivity, good reproducibility, and excellent specificity, and it can be applied in clinical diagnosis.