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Alzheimer’s disease (AD) is a common neurodegenerative disease characterized by cognitive and memory function impairment. Studies have shown that the amyloid-beta (Aβ) plays an important role in the disease progression. The monomeric Aβ has been associated with biological functions, such as memory, learning, and neuroprotection, while the soluble Aβoligomers are the primary toxic agents and the resultant amyloid fibrils are relatively benign. Thus, the conformation detection of Aβ is quite necessary for AD research. IR spectroscopy is an excellent technique used for protein conformational analysis, for the C=O stretching vibration of the peptide is sensitive to the range of 1600-1700cm- 1. In this research, we proposed a method that detects the conformation of soluble Aβ by using Fourier transform infrared (FTIR) spectroscopy with a transmission approach. Although the attenuated total reflectance (ATR) accessory made from zinc selenide or germanium is the most popular approach for recording liquid spectra of the peptides, the volume requires almost 5 mL of soluble Aβ to cover the crystal to achieve a higher signal. Herein we designed a 25×4 mm calcium fluoride (CaF2) substrate with the center has a groove with 5μm deep and 10 mm diameter, it just needed 2uL of soluble amyloid β-peptide to fill the groove and also achieved a high transmission signal. Moreover, based on this method, we found that the process of oligomer-to-fibrils transition occurred much faster within the first 24 hours, and the secondary structure changed slowly in the following time of 48-96 h. These results demonstrated that FTIR is an exquisite way to characterize the aggregation process of peptides, it not only economizes the reagents but also enables give an almost continuous structural view of such process.
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