Imaging Secondary Structure of Individual Amyloid Fibrils of a β₂-Microglobulin Fragment Using Near-Field Infrared Spectroscopy

Abstract

Amyloid fibril diseases are characterized by the abnormal production of aggregated proteins and are associated with many types of neuro- and physically degenerative diseases. X-ray diffraction techniques, solid-state magic-angle spinning NMR spectroscopy, circular dichroism (CD) spectroscopy, and transmission electron microscopy studies have been utilized to detect and examine the chemical, electronic, material, and structural properties of amyloid fibrils at up to angstrom spatial resolution. However, X-ray diffraction studies require crystals of the fibril to be analyzed, while other techniques can only probe the bulk solution or solid samples. In the work reported here, apertureless near-field scanning infrared microscopy (ANSIM) was used to probe the secondary structure of individual amyloid fibrils made from an in vitro solution. Simultaneous topographic and infrared images of individual amyloid fibrils synthesized from the #21-31 peptide fragment of β(2)-microglobulin were acquired. Using this technique, IR spectra of the amyloid fibrils were obtained with a spatial resolution of less than 30 nm. It is observed that the experimental scattered field spectrum correlates strongly with that calculated using the far-field absorption spectrum. The near-field images of the amyloid fibrils exhibit much lower scattering of the IR radiation at approximately 1630 cm(-1). In addition, the near-field images also indicate that composition and/or structural variations among individual amyloid fibrils were present.

Characterization of semiconductor materials using synchrotron radiation-based near-field infrared microscopy and nano-FTIR spectroscopy

“…For wavelengths in the IR regime this technique has already been applied to many different sample systems, e.g. for mapping of free carriers in transistors [27], determination of doping profiles in semiconductor structures and nanowires [28], mapping of the composition of polymers [29][30][31] and biological samples [32,33], measurement of strain fields due to small spectral bandshifts [34], and the excitation of plasmons in metal nanostructures and graphene layers [35,36]. For IR spectroscopic characterization of samples with unknown material composition it is desirable to have radiation sources capable of covering a large frequency range in the mid-IR regime.…”

Structural analysis and mapping of individual protein complexes by infrared nanospectroscopy

“…However, broadband nano-FTIR spectra of protein complexes have neither been observed so far nor shown to be suitable for the analysis of their structure. Biological objects such as protein fibrils and membranes have been already studied by s-SNOM imaging at selected wavelengths2526272829 but it has not been demonstrated that the most important secondary structures—α-helical and β-sheet structures—can be identified on the level of individual protein complexes.…”

Nanoscale-resolved chemical identification of thin organic films using infrared near-field spectroscopy and standard Fourier transform infrared references

“…By sequential imaging of the sample at different wavelengths, infrared near-field spectra can be obtained. [5][6][7][8][9][10][11][12][13][14][15] Alternatively, in nano-FTIR spectroscopy, the tip is illuminated by broadband infrared radiation and the interferometer is used as an asymmetric 16 Fourier transform spectrometer, yielding infrared near-field spectra with a spatial resolution of about 20 nm. 3,4,17,18 Importantly, the interferometric detection yields both near-field amplitude s and phase u.…”