A combination of surface-initiated controlled radical polymerization (SET-LRP) and Click-Chemistry for the chemical modification and fluorescent labeling of Cellulose Nanofibrils: STED super-Resolution imaging of a Single fibril and a Single fibril embedded in a composite

A strategy is developed to modify cellulose nanofibril (CNF) surfaces with a combination of Cu 0 -mediated radical polymerization (SET-LRP) and Cu I -catalyzed azide-alkyne click-chemistry (CuAAC). CNFs were grafted with statistical copolymers of di(ethylene glycol) ethyl ether acrylate (DEGEEA) and acrylic acid 3-trimethylsilyl-prop-2-ynyl ester (TMSPgA) that allows labeling of multiple fluorescent dyes, e.g. AF488 and ATTO633, special dyes for confocal laser scanning microscopy and stimulated emission depletion (STED) microscopy. Through our strategy and these microscopic techniques, we visualized isolated fibrils and fibrils embedded in a PVA composite in a high resolution. This work also provides new insight into the effect of the clickable entity/precursor on the compatibility of modified fibrils with the composite matrix.