Exploring Interactions of Aptamers with Aβ40 Amyloid Aggregates and Its Application: Detection of Amyloid Aggregates

The exhaustive investigating interactions between recognition probes and amyloid aggregates, especially simultaneous recognition events, are challenging and crucial for the design of biosensing probes and further diagnosis of amyloid diseases. In the present work, the interactions of aptamers (Apts) with β-amyloid (Aβ) aggregates were explored thoroughly by single-molecule force spectroscopy (SMFS). Indeed, it was found that the interaction of aptamer1 (Apt1)-amyloid aggregates was different from that of aptamer2 (Apt2)-Aβ₄₀ aggregates at the single-molecule level. Especially, the interaction force of Apt1-Aβ₄₀ fibril showed a double distinguishing Gaussian fitting. The only unimodal distribution of the force histogram was displayed for the interactions of Apt2-Aβ₄₀ oligomer, Apt2-Aβ₄₀ fibril, and Apt1-Aβ₄₀ oligomer. More intriguingly, two Apts could bind to amyloid aggregates simultaneously. With the assistance of two Apts recognition, a novel sensitive dual Apt-based surface plasmon resonance (SPR) sensor using Au nanoparticles (AuNPs) was developed for quantifying Aβ₄₀ aggregates. The dual Apt-based SPR sensor not only avoided the limitation of steric hindrance and epitope but also employed simple operation as well as inexpensive recognition probes. A detection limit as low as 0.2 pM for Aβ₄₀ oligomer and 0.05 pM for Aβ₄₀ fibril could be achieved. Moreover, the established sensor could be successfully applied to detect Aβ₄₀ aggregates in artificial cerebrospinal fluid (CSF) and undiluted real CSF. This work could provide a strategy to monitor a simultaneous recognition event using SMFS and broaden the application of Apts in the diagnosis of neurodegenerative diseases.