Magnetic-assisted catalytic hairpin assembly fluorescent aptasensor for highly sensitive detection of amyloid-beta oligomers as Alzheimer's disease biomarker.

BACKGROUND

The abnormal accumulation of amyloid-beta peptides is a key contributor to Alzheimer's disease. Of these peptides, soluble amyloid-beta oligomers (AβOs) have emerged as potent neurotoxins and early pathological biomarkers. Although AβOs are highly specific biomarkers, their low physiological abundance, structural heterogeneity and matrix interference associated present considerable challenges for conventional diagnostic approaches. Herein, we report a novel fluorescent aptasensor platform for the ultrasensitive detection of AβOs. The platform integrates magnetic preconcentration with a signal amplification strategy based on catalytic hairpin assembly (CHA).

RESULTS

To achieve simultaneous selective recognition of AβOs and efficient CHA initiation, magnetic beads were functionalized with rationally designed double-stranded DNA complexes, which were formed through the hybridization of an AβO-specific aptamer and a CHA-initiator fragment. Upon the specific binding of AβOs, the AβO-specific aptamer competitively dissociates from the magnetic beads, thereby unmasking the surface-tethered initiator to trigger the CHA circuit. The circularly generated CHA products serve as a self-amplifying signal indicator, whereas the magnetic beads enhance target-capturing capacity and facilitate the removal of complex matrix interferences prior to amplification. Experimental results revealed that the proposed system exhibited a broad linear detection range from 10 pg mL-1 to 10 ng mL-1 with a detection limit of 4.1 pg mL-1 (r = 0.9821). Furthermore, to demonstrate its applicability, plasma samples from healthy individuals were analyzed. The results indicated that the AβO level ranged from 87 to 290 pg mL-1.

SIGNIFICANCE AND NOVELTY: These findings demonstrate the potential of integrating aptamer-mediated magnetic capture with CHA-driven signal amplification for ultrasensitive AβO detection. The spatial separation of AβO-aptamer binding and CHA amplification through magnetic beads effectively minimizes matrix interference while permitting large sample volumes. This strategy has the potential to serve as sensitive tool for early Alzheimer's disease diagnosis.