In situ monitoring the aggregation dynamics of amyloid-β protein Aβ42 in physiological media via a raman-based frequency shift method

Amyloid-β protein (Aβ) is a major biomarker candidate for the diagnosis of Alzheimer's disease (AD). It is known that the core segment of Aβ42 tends to aggregate into neurotoxic soluble oligomeric species and finally into fibrillar structures associated with AD; however, much remains to be learned about the conformational changes and dynamic aggregation processes of Aβ protein in solution. Herein we exploit the selectivity of affinity peptides, singled out by biopanning a phage display library, to recognize and capture Aβ42 and its fibers. The sensitivity of surface-enhanced Raman spectroscopy (SERS) to subtle electronic changes of a Raman reporter upon Aβ42 binding, that is, the frequency shift SERS assay, is employed to develop a reliable sensor for both in situ Aβ42 aggregation monitoring and Aβ42 monomers and fibers detection. Atomic force microscope (AFM) imaging is used to investigate the dynamic aggregation processes of Aβ42 on mica and confirms the conclusions of the SERS studies. Finally sensing of Aβ42 and its fibers in fetal bovine serum (FBS) solution is shown to have a limit of detection of ~10-9 mol/L.