Novel Approach to Prepare Ultrathin Lignocellulosic Film for Monitoring Enzymatic Hydrolysis Process by Quartz Crystal Microbalance

The applications of quartz crystal microbalance (QCM) rely heavily on the preparation of ultrathin films. So far, techniques on direct lignocellulosic film making without components isolation have been hardly investigated. In this work, a novel approach was developed to prepare spin-coated ultrathin films based on the complete dissolution of ball-milled wood in LiCl/DMSO solvent system. The surface analysis and elemental composition of the films respectively using atomic force microscopy and X-ray photoelectron spectroscopy proved that an even-textured lignocellulosic film could be formed on QCM gold sensors. The prepared ultrathin films were successfully applied on monitoring the enzymatic hydrolysis process in situ and in real time by QCM. The changes of QCM frequency showed clearly that the enzymatic hydrolysis of lignocellulosic materials could be divided into three stages, including cellulase adsorption, fast substrate hydrolysis, and slow substrate hydrolysis. The adsorption and hydrolysis processes were fitted with Lagergren and Boltzmann-sigmoidal kinetic models, respectively, indicating that cellulase adsorption on lignin and cellulose is competitive and that lignin inhibits the enzymatic hydrolysis of cellulose.