Aqueous one-step fiber-surface modification of paper with alkyl-terminated low-molecular-weight cellulose for hydrophobized all-cellulose biointerfaces

Paper is an attractive, sustainable substrate for biointerfaces, yet controlling wettability without sacrificing capillary transport remains challenging. Here, we report an aqueous, one-step, all-cellulose route to moderately hydrophobize cellulose paper by depositing crystalline assemblies of alkyl-terminated cello-oligosaccharides onto fiber surfaces. Hexyl- (CEL-C6) and octyl-terminated (CEL-C8) cello-oligosaccharides, prepared by enzymatic synthesis, were dissolved in NaOH and neutralized in situ to trigger self-assembly and heterogeneous nucleation within the paper matrix. Attenuated total reflection-Fourier transform infrared absorption spectroscopy revealed formation of the cellulose II allomorph, and scanning electron microscopy showed nanoscale hairy deposits on fibers, confirming surface-localized assembly (with CEL-C8 additionally showing some network formation in voids). Contact angle measurements indicated successful, yet moderate, hydrophobization that preserved imbibition after brief swelling. The modified papers promoted hydrophobic interaction-driven adsorption of diverse proteins, such as laccase, trypsin, β-galactosidase, and horseradish peroxidase-conjugated immunoglobulin G, enabling on-paper catalysis with enhanced product formation relative to pristine paper, whereas nonalkylated cello-oligosaccharides suppressed adsorption. Protein loading exhibited a saturating dependence on modifier amount, suggesting an optimal coverage regime. This green, single-step approach yields tunable, functional, all-cellulose biointerfaces suitable for assays, immobilized enzymes, and diagnostic devices.