Detection of Aβ oligomers based on magnetic-field-assisted separation of aptamer-functionalized Fe3O4 magnetic nanoparticles and BaYF5:Yb,Er nanoparticles as upconversion fluorescence labels

A sensitive and stable bioassay for the detection of AP oligomer (A beta o), a potentially promising candidate biomarker for Alzheimer's disease (AD) diagnosis, was developed using Fe3O4 magnetic nanoparticles (MNPs) as the recognition and concentration elements and BaYF5:Yb,Er upconversion nanoparticles (UCNPs) as highly sensitive labels, conjugated with the A beta o aptamer (DNA1) and the complementary oligonucleotide of the A beta o aptamer (DNA2), respectively. The DNA1 hybridized with DNA2 to form the duplex structure on the surface of the MNPs/UCNPs nanocomposites probe. When the target A beta o was introduced, the aptamer DNA1 preferentially bound with A beta o and caused the dissociation of some complementary DNA2, liberating some UCNP-labeled complementary DNA2 and leading to a decreased upconversion fluorescent intensity on the surface of MNPs. The decreased fluorescence intensity of UCNPs was related to the concentration of A beta o in the range of 0.2-15 nM with a detection limit of 36 pM. The developed method then was successfully applied to measure A beta o in artificial cerebrospinal fluid. Benefiting from the magnetic separation and concentration effect of MNPs, the high sensitivity of UCNPs, as well as the selectivity and stability of the aptamer, the present strategy offered valuable information related to early diagnosis of AD process.