<i>Operando</i> Monitoring of the Polymerization\nProcess of Lignin Monomer and Oligomer Surrogates with Microstructured\nFiber Grating Sensor

The enzymatic depolymerization is a promising route to\nvalorize\nthe lignin polymers by turning the cross-linked polymers into monomers\nor oligomers. However, the lignin polymers cannot be effectively converted\ninto small chemicals, as the oligomers are prone to polymerization,\nwhich is particularly challenging to monitor and thus regulate. Here,\nwe develop a microstructured fiber Bragg grating (mFBG) sensor to\nprobe the dynamic polymerization process of typical lignin oligomer\nsurrogatesguaiacol (monomer) and guaiacylglycerol-β-guaiacyl\nether (GBG, dimer)catalyzed by laccase in an <i>operando</i> way. The mFBG sensor was developed with its reliability well validated\nby control experiments at first. Further, <i>operando</i> monitoring of the polymerization reaction process of the typical\nlignin monomer (i.e., guaiacol) and dimer (guaiacylglycerol-β-guaiacyl\nether, GBG) was demonstrated under various conditions with the mFBG\nsensor. The GC-MS and UV–vis absorption measurements were carried\nout as a further check. Finally, the specific polymerization characteristics\nand reaction mechanism were studied. The mFBG sensor enables <i>operando</i> monitoring of the heterogeneous polymerization\nprocess of lignin monomers and oligomers and can potentially be tailored\nto probe more complex lignin depolymerization processes and unveil\nenzymatic synergistic mechanisms for the biological transition of\nbiomass.