Quaternized cellulose ester-confined dopamine oligomer complexes with antioxidant, antibacterial and fluorescent properties for fruit preservation and anti-counterfeiting.

Quaternized cellulose ester (QyCE) with tunable alkyl chain lengths was synthesized via esterification followed by the Menshutkin reaction. By direct blending of QyCE and dopamine (DA), water-soluble and transparent DA/QyCE complexes were prepared. QyCE effectively restricted covalent polymerization and non-covalent self-assembly of polydopamine (PDA) through steric confinement, cation-π interactions, hydrophobic interactions, and hydrogen bonding. This confinement resulted in enhanced fluorescence of the DA oligomer/QyCE multifunctional complexes. The DA oligomer/QyCE films formed after drying also exhibited outstanding tensile strength (~45.64 MPa). Furthermore, the resulting samples demonstrated excellent antioxidant activity with a DPPH radical scavenging rate exceeding 93 %, and strong antibacterial activity against Staphylococcus aureus (~99.90 %) and Escherichia coli (~100.00 %). Consequently, as a water-soluble coating material, the complexes effectively reduced dehydration shrinkage and oxidative deterioration of fruits, significantly extending their shelf life. The fluorescence of the film is sensitive to iron ions, enabling pattern design for anti-counterfeiting applications. These findings highlight that DA oligomer/QyCE multifunctional complexes serve as a versatile and sustainable platform with potential in both food preservation and anti-counterfeiting.