Surface Ligand-Dependent Kinetics of α‑Lactalbumin Interaction with Gold Nanoparticles Investigated by SPR

Understanding the kinetic and energetic factors governing protein adsorption onto nanomaterial surfaces is essential for elucidating nanobiointerfacial processes. In this study, the interaction between α-lactalbumin (αLa) and gold nanoparticles (AuNPs) functionalized with different surface ligands (citrate, 3-mercaptopropionic acid (MPA), and polyethylene glycol (PEG 6000)) was investigated by surface plasmon resonance (SPR). Real-time monitoring enabled determination of association and dissociation rate constants, residence times, and activation parameters over a controlled temperature range (285.2-301.2 K). Adsorption proceeded under a rapid kinetic regime for all systems, with both association (10⁷-10⁸ M^-1 s^-1) and dissociation (0.5 s^-1) occurring on short time scales. Despite this overall similarity, the magnitude and thermal dependence of kinetic parameters were strongly influenced by ligand chemistry, with association rates and residence times following the order PEG > MPA ≈ citrate. Activation analyses indicated that formation of the transition state possibly involves contributions from interfacial desolvation and counterion release. For citrate-coated nanoparticles, temperature-dependent parameters were obtained, suggesting the involvement of conformational changes on αLa upon binding. These findings provide mechanistic insights into how surface functionalization governs the kinetic and energetic pathways of protein adsorption at gold nanobiointerfaces.