Missions

Prepared from animal skins, parchment is essentially composed of collagen fibers and is sensitive to various alteration factors, mainly water (hydrolysis) and heat (oxidation). A crucial challenge in defining suitable treatments or conservation conditions is to determine the state of conservation of collagen non-invasively and thus prevent irreversible parchment degradation, also called gelatinization. The aim of this project is to measure and characterize the physico-chemical and morphological modifications of collagen as a function of temperature and humidity conditions, and to understand their origins.
Our approach is based on non-linear optical microscopy (NLO), also known as multiphoton microscopy, a non-invasive micrometer-scale technique for characterizing fibrillar collagen. A key advantage of NLO microscopy is its ability to combine different intrinsic contrast modes that depend on the structure and chemical nature of the materials: two-photon excited fluorescence (2PEF), emitted by a large number of fluorophores, and second harmonic generation (SHG), specific to non-centrosymmetric structures such as fibrillar collagen [1]. Previuos collaborative projects between LOB and CRC have shown that NLO microscopy has the major advantage of being sensitive to collagen alteration, offering a non-invasive alternative for assessing its state of preservation in skin-based materials [2]. A strong SHG signal, characteristic of intact collagen, is obtained on preserved areas of parchment, while this signal decreases and may even disappear and be replaced by fluorescence signal in altered areas. A first metric is thus based on the ratio of fluorescence and SHG signals. In addition, polarization-resolved SHG signals, which is a probe of local disorder on the submicrometer scale, i.e. the scale of collagen fibrils, show sensitivity to the early stages of parchment degradation [3,4].
At the same time, multiscale infrared analysis techniques allow us to monitor alterations from a chemical point of view. Preliminary experiments, in collaboration with ICP, have shown that the chemical processes responsible for changes in NLO signals take place at the scale of the collagen fibril (diameter less than 100 nm) [2]. These chemical modifications were explored by Infrared (IR) nanospectroscopy, using the AFMIR technique which couples atomic force microscopy (AFM) with IR spectroscopy [5]. Well-preserved areas have been distinguished from degraded ones, with a broadening of the amide I band, an IR absorption band characteristic of the protein family, and thus here of collagen, and the onset of a carbonyl band in conjunction with the emergence of the fluorescence signal [2].
The main issue of this project is to establish the link between the different scales probed (from nanometer to micrometer) and the different physico-chemical signals from collagen in parchment. The research will be carried out on modern and ancient parchments, artificially aged with exposition to heat and humidity. Preserved samples and individual extracted fibers will be analyze. The aims of the project are to
1. identify the physico-chemical characteristics associated with each alteration condition (hydrolysis, oxidation): decrease of SHG signals, increase of fluorescence signals, local disorder of collagen fibrils, study of IR spectra,
2. a more detailed interpretation of the physico-chemical origin of these signals (NLO and IR) at the scale of an isolated fiber during alteration. This analysis on the scale of the fiber is essential to access to a better understanding of the alteration processes and the evolution of the various physico-chemical characteristics.
[1] S. Bancelin et al., Nature Communications (2014) - https://doi.org/10.1038/ncomms5920
[2] G. Latour et al., Scientific Reports (2016) - https://doi.org/10.1038/srep26344
[3] M. Schmeltz et al., Science Advances (2021) - https://doi.org/10.1126/sciadv.abg1090
[4] G. Galante et al., APL Photonics (2025) - https://doi.org/10.1063/5.0250484
[5] J. Mathurin et al., Journal of. Applied Physics (2022) - https://doi.org/10.1063/5.0063902

Activités

- Parchment characterizauion by using nonlinear optical microscopy (two-photon excited fluorescence and second harmonic generation)
- Determination and anlysis of polarization-resolved SHG signals
- AFMIR data acquisition (AFM microscopy coupled to infrared spectroscopy)
- Artificial aging of parchment in heat- and humidity-controlled chambers
- Data processing and correlation of multi-scale and multi-modal information

Compétences

The candidate will have a PhD in physics, with an expertise in optics, data processing or physico-chemical analysis. The candidate should be familiar with experimental optics, understanding microscopy techniques and light-matter interaction. Knowledge in programming and image processing will also be appreciated, in order to be able to extract quantitative information from the collected data. Skills in physical chemistry and AFM microscopy will be an asset. An interest in cultural heritage science and an ability to work in a highly interdisciplinary environment will also be essential.

Contexte de travail

The post-doctoral project will take place mainly at the Laboratoire d'Optique et Biosciences (LOB, Ecole Polytechnique site, Palaiseau) under the supervision of Gaël Latour and Marie-Claire Schanne-Klein. The person will be integrated into the advanced microscopy team and will benefit from biophotonics facilities (microscopes, biology laboratory, image processing software). Further information: https://lob.ip-paris.fr/recherche/advanced-microscopies-and-tissue-physiology
Ecole Polytechnique is located on the Saclay plateau, accessible from Paris by public transportation. The campus offers a pleasant living environment, with numerous activities (sports, culture, associations). For more information: https://www.ip-paris.fr.
Regular travel is required to the Centre de Recherche sur la Conservation (CRC, site of the Museum National d'Histoire Naturelle de Paris, Laurianne Robinet) for additional analyses using non-linear optical microscopy, and to the Institut de Chimie Physique (Orsay, Ariane Deniset and Jérémie Mathurin) and the Laboratoire Institut photonique d'analyse non-destructive européen des matériaux anciens (IPANEMA, Saint-Aubin, Mathieu Thoury) for infrared spectroscopy.

Contraintes et risques

The candidate will work with class IV lasers and will receive appropriate training and supervision.