Abstract
Alzheimer's disease is the second most common neurodegenerative illness affecting elderly people. Early diagnosis could help to improve a patient's quality of life. The classical sandwich ELISA-based methods are usually costly and time consuming. In this study, we report the design of a label-free immunosensing platform for the sensitive detection of the ApoE protein as a biomarker for Alzheimer's disease. The immunorecognition event induces conformational changes in ferrocenyl alkyl groups tethered to the superficial gold nanoparticles in the vicinity of the antibody. The heavy antigen/antibody complex enhances the electron-transfer (ET) rate constants by bending the ferrocenyl alkyl chain, bringing the ferrocene closer to the gold surface. Determination of the ET rate constants and the analytical performance studies for a series of devices using ferrocenyl alkyl groups with different chain lengths support the proposed mechanism. The best performances and the highest rate constants are observed with sensors having the most flexible chains. The devices are endowed with a large dynamic range (i.e. 0.13 to >1880 ng mL(-1)) and excellent selectivity and specificity.