Wavelength-dependent conformational changes in collagen after mid-IR laser ablation of cornea
Yaowu Xiao 1, Mingsheng Guo 2, Peng Zhang 1, Ganesh Shanmugam 1, Prasad L. Polavarapu 1 and M. Shane Hutson 1*
1 Vanderbilt University
2 Fisk University
* To whom correspondence should be addressed. E-mail: shane.hutson{at}vanderbilt.edu.
Submitted on June 5, 2007
Revised on July 16, 2007
Accepted on 24 September 2007
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Abstract |
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We ablated porcine corneas with a free electron laser tuned to either 2.77 or 6.45 µm, two matched wavelengths that predominantly target water or protein respectively. The ejected nonvolatile debris and the crater left behind were examined by circular dichroism, Raman spectroscopy and scanning electron microscopy to characterize the post-ablation conformation of collagen proteins. We find near complete unfolding of collagen secondary and tertiary structure at either ablating wavelength. On the other hand, we find excess fibril swelling and evidence for excess cis-hydroxyproline in the 6.45-µm debris. These results support the hypothesis that the favorable ablative properties of protein-targeting wavelengths rest on selective heating of tissue proteins.
Key Words:
UVCD, amide vibration, fibrils, free-electron laser, proline isomerization, vibrational circular dichroism
