Structure-Interfacial Property Relationships of Thiolated Chitosan Films on Gold Surfaces for Plasmonic Biosensing

Chitosan is a versatile carbohydrate polymer whose chemical modification enables control over interfacial structure, surface chemistry, and biomolecular interactions. Thiolated chitosan (TCh) promotes strong chemisorption onto gold surfaces via Au-S bonds while improving physicochemical properties. However, the adsorption kinetics, interfacial organization, and structure-property relationships of TCh films on metallic substrates remain poorly understood. In this work, chitosan was thiolated to generate a stable three-dimensional polymer film for biomolecule immobilization in surface plasmon resonance (SPR) biosensing. The TCh/gold interface was characterized by FTIR, Raman spectroscopy, AFM, and electrochemical techniques, revealing spontaneous film formation consistent with a potentially thin, stable, and robust interfacial layer, with a surface coverage of 2.4 nmol cm-2 and an apparent surface pKa of 4.5. Real-time SPR measurements enabled a systematic investigation of TCh adsorption kinetics on gold surfaces, providing mechanistic insight into polysaccharide assembly and protein recognition within polymer matrices. Finally, TCh platform was applied to the development of an SPR immunosensor for dengue, successfully discriminating dengue-positive and dengue-negative human serum samples (p = 0.0001) with a detection limit of 3.2 nmol L-1, while also not demonstrating reactivity against Chikungunya-positive samples. Overall, this work elucidates structure-interfacial property relationships of polysaccharide films on gold and highlights thiolated chitosan as a promising carbohydrate-based interface for plasmonic biosensing.