Infrared (IR) spectroscopy is an invaluable tool to study the biophysical properties of amyloid aggregates. Although historically used as a tool for composition analysis of chemical compounds as it measures the vibrational energy of chemical bonds, IR spectroscopy provides measures to analyse the size and rigidity of amyloid fibrils. Coupling of IR spectroscopy to an optical microscope (OPTIR) is a new method that allows users to obtain chemical information of biological macromolecules from cells and tissues at submicron resolution. Using OPTIR for investigating the biophysical properties of amyloid fibrils in cells and tissues has been challenging since amyloid fibrils cannot be easily identified by conventional light microscopy. Therefore, Oxana Klementieva and her research group at Lund University in Sweden combined epifluorescence imaging and OPTIR in a single instrument. Their “Fluorescence-Located” OPTIR or FL-OPTIR allows precise targeting using epifluorescence signals to locate amyloid-rich regions for OPTIR analysis. In a recent study published in Journal of Medicinal Chemistry, Prater et al. used fixed sections of APP/PS1 transgenic mouse brain and labelled amyloids using Amytracker 520. Guiding OPTIR measurements via the fluorescent signal from Amytracker 520, detailed biophysical analysis of amyloids in the core, corona, and outside of the plaque could be performed indicating a high degree of heterogeneity in the distribution of β-sheet structures within the amyloid plaque. Therefore, the FL-OPTIR method with the optotracer Amytracker might be valuable in studying amyloids in cells or tissue.
Image: FL-OPTIR spectra recorded from the outside, core, and plaque corona as indicated by the markers of the corresponding colour on the inset representing an amyloid plaque stained with Amytracker 520. Image from Figure 2D, Prater et al. (2023) Journal of Medicinal Chemistry 66(4), 2542–2549 (CC BY 4.0).