Stimuli-responsive xanthan gum and diethylaminoethyl dextran multilayer nanofilms: formation, characterization, stability, and interaction with model biomacromolecules.

Abstract

Electrostatically self-assembled multilayer (ML) nanofilms composed of xanthan gum (XG) and diethylaminoethyl dextran (DD) are prepared on gold (Au) substrates via the layer-by-layer (LbL) method under neutral pH conditions. The formation and structural properties of the nanofilms are investigated by surface plasmon resonance (SPR) and quartz crystal microbalance with dissipation (QCM-D). Both techniques clearly demonstrate reproducible linear multilayer growth with total adsorbed masses of approximately 7-15 mg m-2. Low dissipation-to-frequency ratios (<0.4 × 10-6 Hz-1) indicate that the assembled nanofilms retain a compact and predominantly rigid structure. The ML nanofilms display remarkable physicochemical resilience and reversible salt-induced swelling at high salt (0.15 M NaCl) and acidic environment (pH 2.5), suggesting simultaneous electrostatic and hydrophobic stabilization. BSA adsorption displays a switchable pH-dependent interaction mechanism. The adsorbed amount reaches ∼4.5 mg m-2 at pH 7 through rapid electrostatic binding. Slower adsorption kinetics and structural rearrangements within the nanofilm are also revealed. Under acidic conditions (pH 2.5), adsorption decreases to ∼2.6 mg m-2 and is mainly governed by hydrophobic interactions. PGM exhibits strong adsorption (∼3.5 mg m-2), driven by electrostatic attraction together with hydrogen bonding and polymer-mucin entanglement. Partial desorption is also reported under physiological saline conditions. Overall, the integration of tunable biomolecular interactions with intrinsic mucoadhesive properties underscores the translational potential of these nanofilms. They can serve as potentially adaptable platforms for protein immobilization and delivery, as well as controlled release systems and mucoadhesive coatings in biosensing and drug delivery for food and biomedical applications.

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