Unlocking the nanoworld of plant cell walls ! Thanks to optical near-field hyperspectral imaging

With 3000 billion individuals, trees are one of the most widespread materials on Earth, but also one of the most essential for human survival. Their great diversity is expressed in a wide variety of physical and bio-chemical properties giving them different functionalities involved in our daily life, ranging from simple functions such as our breathing, our food or our well-being, to operational functions for building, paper or energy… Surprisingly, this diversity is obtained only from three polymers, namely cellulose, hemicellulose and lignin, which represent more than 90% of wood constituents.

The diversity comes from the arrangement and proportions of these polymers. Trees have a hierarchical structure, i.e. their macroscopic properties and appearances inevitably come from their structures at the micro and nanometric scales. This leads to the question of the relationship between chemical distribution, structural organization and mechanical, thermal and optical properties at the nanoscale. How will nanometric variations influence the global response of the tree? And conversely, how can an external action modify the molecular arrangement and the associated properties? These questions constitute a major societal challenge and to answer them, it is necessary to access nanometric properties.

Our first studies on wood in 2014, using atomic force microscopy (AFM) nanoindentation, allowed us to extract nanomechanical properties of the cell wall. To go further in the understanding of wood morphogenesis, and thus correlate physical properties to chemical distribution, it seemed important to us to move towards a technique combining AFM and optical spectroscopy. We then turned to the company Neaspec gmbh (Attocube) known for its system of diffusive optical near field (s-SNOM) in the infrared, spectral range specific to cellulose, hemicellulose and lignin. Our results gathered in this article show the potential of this technique to access and link mechanical properties, optical constants and in situ chemical distribution of the wood cell wall.

 Partenaires : Ces travaux sont issus d’une collaboration entre le CINaM, l’Institut Fresnel, l’ORNL (Oak Ridge National Lab, USA) et la société Neaspec Gmbh.

Partens : This work is the result of a collaboration between the CINaM, the Institut Fresnel, ORNL (Oak Ridge National Lab, USA) and the company Neaspec Gmbh.

Reference: “In-situ plant material hyperspectral imaging : determination of chemistry and optical properties using multimodal scattering nearfield optical microscopy”, A. Charrier, A. Normand, A. Passian, P. Schaefer and A. L. Lereu, Comm. Mat., 2, 59 (2021).

Contact : Anne CHARRIER, Team PIV