Characterization of biotinylated microcrystalline cellulose fibers. Biotinylated cellulose fibers were treated with alexafluor 647 streptavidin to verify the biotinylation process. Differential interference contrast (DIC) and fluorescence microscopy were used. (a) Microcrystalline cellulose observed under DIC. (b) Fluorescence was observed when microcrystalline cellulose fibers were observed under a Cy5 filter (emission centered at 699 nm). (c) To rule out auto fluorescence of cellulose or background fluorescence, the streptavidin conjugated fibers were observed under a FITC filter (emission centered at 535 nm). No fluorescence was observed under FITC filter (as well as TRITC/Rhodamine/CY3 and DAPI/Hoechst filters, data not shown) indicating absence of auto fluorescence or background fluorescence. The frame size of (a), (b) and (c) is the same. The scale bar is 10 μm for all images.