β-amyloid peptide (Aβ) aggregates are regarded as a typical neuropathology hallmark for the diagnosis of Alzheimer's disease (AD). Aβ40 aggregates include soluble oligomers (Aβ40O) and insoluble fibrils (Aβ40F). Both of them can simultaneously bind to two different kinds of its aptamer (Apt1 and Apt2). As a mass-sensitive sensing platform, quartz crystal microbalance (QCM) converts changes in mass on the Au chip surface into frequency shift. Here, a dual-aptamer assisted Aβ40 aggregates assay was developed. Taking Aβ40O detection as an example, Apt2 was modified on the surface of Au chip by Au-S bond. Subsequently, the solution consisted of Aβ40O and gold nanoparticles-Apt1 (AuNPs-Apt1) were injected into the QCM chamber. As a result, Aβ40O was specifically recognized and captured by Apt2. AuNPs-Apt1 were also combined on the surface of the Au chip because Aβ40O can simultaneously bind to Apt1. Then, a significant frequency shift occurred because of the large weight of AuNPs. Similarly, this procedure can be used to detect Aβ40F. This QCM biosensor was able to detect Aβ40O with a range of 0.2-10 pM with a detection limit of 0.11 pM, while the linear range for Aβ40F was 0.1-10 pM with a detection limit of 0.02 pM. This QCM biosensor was simple and highly sensitive, which provided a new method for Aβ40 aggregates detection.
Keywords: Alzheimer disease; Aβ(40) aggregates; Gold nanoparticles; Quartz crystal microbalance; β-amyloid peptide.
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