Two-in-one polydopamine nanospheres for fluorescent determination of beta-amyloid oligomers and inhibition of beta-amyloid aggregation

Beta-amyloid (Aβ) oligomers are the reliable molecular biomarkers and crucial targets for the diagnosis and therapy of Alzheimer's disease (AD). In this work, we reported on a fluorescent platform for the selective detection of Aβ oligomers with polydopamine nanospheres (PDANS) as the nanoquencher. The carboxyfluorescein (FAM)-labeled DNA aptamers specific to Aβ oligomers showed poor fluorescence signal when absorbed onto the surface of PDANS. The specific binding of Aβ oligomer to the FAM-DNA caused the conformation change of the aptamer into a hairpin structure, thus inducing the release of FAM-DNA from the PDANS surface and making the fluorophore far away from the nanoquencher. Aβ oligomers were thus determined based on the increase in the fluorescence signal. The “signal on” fluorescent platform could be used for sensing of Aβ oligomers, but not for the monomers and fibrils. The detection limit was found to be 12.5 nM. More intriguingly, we found that PDANS efficiently prevented the aggregation of Aβ monomers. We believe that the two-in-one PDANS as both the nanoquencher and the inhibitor would found many applications for determination of Aβ oligomers in bodily fluids and drug-therapy of AD.