Biofuels: Analytical and Imaging Technologies for Studying Lignocellulosic Material Degradation

Project Goals: The project is to develop correlated optical (Raman and SH-OCT) and mass spectrometric (SIMS and MALDI MS) imaging approaches for spatial and temporal characterization of lignocellulosic materials at specific processing stages. The ability to efficiently use lignocellulosic materials (LCMs) to feed the biorefinery of the future depends on high-efficiency pre-enzymatic processing to render lignin separable from cellulose/hemicelluloses. The complex 3-D network structure and chemical characteristics of LCMs pose daunting challenges for imaging and molecular characterization: (1) they are opaque and highly scattering; (2) their chemical composition is a spatially variegated mixture of heteropolymers; (3) the nature of the matrix evolves in time during processing. Presently, there are few in situ characterization tools that can be applied to materials with these characteristics, especially during processing—yet acquiring this information is of paramount importance. Here we present a combination of Raman microscopy and mass spectrometric imaging (secondary ion mass spectrometry, SIMS, and laser desorption ionization mass spectrometry, LDI MS) to visualize the structural and chemical changes of LCMs upon various treatments, such as H 2 SO 4 , NaClO 2 , NaOH, etc. Miscanthus x giganteus as a model LCM was sectioned into 50 μm thick, and was investigated in this work. Raman and SIMS imaging results indicated that lignin and cellulose are collocated in the cell wall of raw miscanthus. A globular structure, composed predominantly of hemicellulose and lignin, is associated with the interior cell wall. Pretreatment of Miscanthus using NaOH or NaClO 2 solutions results in the removal of lignin at long processing time. Interestingly, Raman experiments reveal that the H 2 SO 4 treated Miscanthus exhibits a higher autofluorescence, which might be due to the formation of highly conjugated hydrocarbon species during H 2 SO 4 treatment. We are currently correlating these Raman results with mass spectrometric imaging to identify the unknown