A Novel Method for Detecting Protein Aggregates Using Plasmonic Sensing

Abstract

AbstractBackgroundAmyloid‐beta (Aβ) protein aggregates have been implicated in the pathology of Alzheimer’s disease (AD). These aggregates are difficult to characterise due to their small size, requiring very sensitive techniques. Gold Nanoparticles (AuNPs) form plasmonic cavities when in close proximity to a gold surface. The cavity both enhances and scatters incident light, with a resonant wavelength strongly dependent on the size of the cavity. These plasmonic cavities were used to detect and size Aβ aggregates at ultra‐low concentration using darkfield spectroscopy.MethodsAuNPs were coated with the Aβ specific 6E10 capture antibody, incubated with a synthetic aggregate sample, and centrifuged to isolate the AuNPs. They were then placed on a gold surface, and darkfield scattering spectra were obtained. The peak scattering wavelengths for each AuNP were used to produce a histogram of gap sizes, and thus the size distribution of detected protein aggregates.ResultsSignificant differences were seen in resonant peak position between monomeric samples of Aβ and 24 hour aggregated samples. This allows for easy identification of protein monomer vs fibrillar aggregates. In the case of aggregates, some peaks in the darkfield scattering spectra also appeared strongly polarised, suggesting dimerisation of the AuNPs. This was not present for the case of monomeric sample.ConclusionsWith this novel technique it was possible to clearly distinguish between samples of Aβ monomer and aggregates. This approach can likely be expanded to find the range and proportion of aggregate sizes in serum samples to detect the onset of AD. The AuNP dimerisation when Aβ aggregates are present is also interesting, and may serve as further verification of the size or shape of these aggregates.