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Open AccessFeature PaperArticle

Orientation Matters: Polarization Dependent IR Spectroscopy of Collagen from Intact Tendon Down to the Single Fibril Level

1
Department of Chemistry, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
2
neaspec GmbH, Eglfinger Weg 2, 85540 Munich-Haar, Germany
3
Photothermal Spectroscopy Corp., 325 Chapala St, Santa Barbara, CA 93101, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Kamilla Malek
Molecules 2020, 25(18), 4295; https://doi.org/10.3390/molecules25184295
Received: 31 July 2020 / Revised: 4 September 2020 / Accepted: 17 September 2020 / Published: 19 September 2020
Infrared (IR) spectroscopy has been used for decades to study collagen in mammalian tissues. While many changes in the spectral profiles appear under polarized IR light, the absorption bands are naturally broad because of tissue heterogeneity. A better understanding of the spectra of ordered collagen will aid in the evaluation of disorder in damaged collagen and in scar tissue. To that end, collagen spectra have been acquired with polarized far-field (FF) Fourier Transform Infrared (FTIR) imaging with a Focal Plane Array detector, with the relatively new method of FF optical photothermal IR (O-PTIR), and with nano-FTIR spectroscopy based on scattering-type scanning near-field optical microscopy (s-SNOM). The FF methods were applied to sections of intact tendon with fibers aligned parallel and perpendicular to the polarized light. The O-PTIR and nano-FTIR methods were applied to individual fibrils of 100–500 nm diameter, yielding the first confirmatory and complementary results on a biopolymer. We observed that the Amide I and II bands from the fibrils were narrower than those from the intact tendon, and that both relative intensities and band shapes were altered. These spectra represent reliable profiles for normal collagen type I fibrils of this dimension, under polarized IR light, and can serve as a benchmark for the study of collagenous tissues. View Full-Text
Keywords: collagen type I; tendon; fibrils; far-field infrared spectroscopy; optical photothermal spectroscopy (O-PTIR); scattering-type scanning near-field optical microscopy (s-SNOM); nano-FTIR spectroscopy; polarization imaging and spectroscopy; advances in IR imaging collagen type I; tendon; fibrils; far-field infrared spectroscopy; optical photothermal spectroscopy (O-PTIR); scattering-type scanning near-field optical microscopy (s-SNOM); nano-FTIR spectroscopy; polarization imaging and spectroscopy; advances in IR imaging
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MDPI and ACS Style

Bakir, G.; Girouard, B.E.; Wiens, R.; Mastel, S.; Dillon, E.; Kansiz, M.; Gough, K.M. Orientation Matters: Polarization Dependent IR Spectroscopy of Collagen from Intact Tendon Down to the Single Fibril Level. Molecules 2020, 25, 4295.

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