Lignocellulosic Biomass (LB) encompasses a variety of plant samples like trees (both softwood and hardwood), grasses as culture residues or dedicated crops (switchgrass, Miscanthus…), or plant byproducts (sawdust, bagasse, bark…) (Yousuf et al., 2020). As most dry LB consists of plant cell wall, biomass is mainly composed of three biopolymers:-

Cellulose & hemicelluloses, which are polysaccharides (Cai et al., 2017),

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Lignins, which are heteropolymer of para-hydroxyphenyl, guaiacyl, and syringyl units, respectively labelled H, G and S (del Río et al., 2020).

LB's richness in polysaccharides (more than 60 % of dry weight) makes it valuable for conversion into monosaccharides by saccharification and then into various chemicals by fermentation. Thus, LB is considered a suitable renewable feedstock to replace fossil resources, mitigating greenhouse gas and pollutant emissions (Chen et al., 2023a). However, thorough LB multiscale characterization is needed to understand and optimize its transformation (Biswas et al., 2022), especially the enzymatic hydrolysis process, which is challenging, as its efficiency depends mainly on biomass physicochemical properties.

Chemical imaging includes various methods to map the sample's chemical composition, hence simultaneously providing chemical and topological information. Chemical sampling usually involves the irradiation by electromagnetic waves or particles leading to the sample excitation. Absorption or emission processes are thus recorded and then correlated with chemical information. As excitation sources can either be focalized at a precise point or irradiate the whole sample at once, images can be recorded by using a position detection system, by moving the sample or the irradiation beam (Adams and Collingwood, 2019).

Although chemical imaging seems to be a promising field for LB analysis, no review article on this subject has been published to this date. The objective of this paper is then to highlight the different chemical imaging techniques that are useful for LB study. This review aims to present up-to-date methods of the three main fields of chemical imaging: microspectrometry, MSI and MRI complemented by Time-Domain and other solid-state NMR methods, as well as compare these methods between themselves (see Table 1).