Noninvasive quantitative assessment of collagen degradation in parchments by polarization-resolved SHG microscopy

Abstract

Nondestructive and noninvasive investigation techniques are highly sought-after to establish the degradation state of historical parchments, which is up to now assessed by thermal techniques that are invasive and destructive. We show that advanced nonlinear optical (NLO) microscopy enables quantitative in situ mapping of parchment degradation at the micrometer scale. We introduce two parameters that are sensitive to different degradation stages: the ratio of two-photon excited fluorescence to second harmonic generation (SHG) signals probes severe degradation, while the anisotropy parameter extracted from polarization-resolved SHG measurements is sensitive to early degradation. This approach is first validated by comparing NLO quantitative parameters to thermal measurements on artificially altered contemporary parchments. We then analyze invaluable parchments from the Middle Ages and show that we can map their conservation state and assess the impact of a restoration process. NLO quantitative microscopy should therefore help to identify parchments most at risk and optimize restoration methods.

Proton beam irradiation induces invisible modifications under the surface of painted parchment

“…Further investigations of radiation-induced change of parchment samples using optical coherence tomography (OCT) will be discussed in an upcoming paper (Csepregi et al forthcoming). Another well adapted method would be investigation with multiphoton microscopy 54 .…”

Emerging photonic technologies for cultural heritage studies: the examples of non-linear optical microscopy and photoacoustic imaging

“…Furthermore, non-linear imaging techniques have been applied to extract information from historical coatings samples [45]. Recent works also demonstrated that the degradation procedure in parchments can be revealed by the collection of SHG and PSHG intensity signals [46,47]. The identification of the safe limits for the use of the non-linear techniques for CH studies has been also investigated.…”

Revealing the Wonder of Natural Photonics by Nonlinear Optics

“…Harnessing light–matter interaction in a nonlinear regime, researchers and engineers developed various tools for imaging and spectroscopy analyses of biological samples [ 8 , 62 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 ]. Nonlinear optical imaging and spectroscopy have proved to be versatile and efficient techniques in biomedical and biological research, with many benefits, including an increase in analytic depth and a reduction in photodamage, with respect to classical linear optical techniques [ 8 ].…”