Enthalpy-Driven Biomolecular Stabilization of Au Nanodomains Enabling Polaron Engineering in Polyaniline for Accelerated Interfacial Charge Transfer

Abstract Polyaniline (PANI)–gold nanoparticles (AuNPs) nanocomposites have emerged as promising electroactive interfaces due to enhanced interfacial charge-transport properties. In situ polymerization is a highly effective synthesis strategy for PANI/AuNPs; however, its effectiveness is often limited by the aggregation of citrate-capped AuNPs in acidic conditions essential for aniline polymerization. Herein, we report a chitosan-mediated in situ polymerization, wherein chitosan acts as a multifunctional macromolecular stabilizer, providing electrostatic and steric hindrance that preserves the nanoscale dispersion of metallic Au nanodomains under strongly acidic polymerization conditions. Isothermal titration calorimetry (ITC) revealed thermodynamically favorable binding interactions between chitosan and Au nanodomains relative to ANI/HCl–AuNPs interactions, confirming enthalpy-driven stabilization in an acidic environment. Spectroscopic investigations (UV–Vis and ESR) demonstrated enhanced polaron generation within the PANI emeraldine salt backbone, indicating strong electronic coupling between the π-conjugated polymer chains and embedded Au nanodomains. Microscopic analysis (FESEM and TEM) confirmed a nanofibrous morphology with uniformly distributed metallic nanodomains, forming continuous charge percolation pathways. Subsequent electrochemical studies revealed improved interfacial charge-transfer kinetics marked by an increased anodic peak current in cyclic voltammetry (1030 μA) and reduced charge-transfer resistance (704 Ω) in electrochemical impedance spectroscopy. Furthermore, its applicability as an electroactive interface was validated by leveraging its natural affinity toward hyaluronic acid, enabling quantification in the linear range of 50 ng/mL to 450 ng/mL with a detection limit of 7.07 ng/mL. Thus, the resulting polaron-engineered PANI/AuNP composite with superior structural and electrochemical properties establishes a robust platform for accelerated interfacial charge transport and electroanalytical applications. Additionally, CS-mediated in situ polymerization presents a feasible choice for hybridizing PANI and citrate-capped metal nanoparticles, which has broader prospects in electroanalytical and optoelectronic applications.