Frontal analysis continuous capillary electrophoresis for predicting polymer nanoparticle interactions with human serum albumin

Thanks to their unique physicochemical properties, polymer nanoparticles (NPs) are promising tools in nanomedicine for drug delivery and therapeutic applications. NPs made of poly(lactic acid) (PLA), a biodegradable and biocompatible polymer, are widely employed for therapeutic molecule encapsulation, offering enhanced efficacy and reduced toxicity. A poly(ethylene glycol) (PEG) coating is often added to confer stealth properties and improve intravenous stability. Upon administration, NPs rapidly interact with plasma proteins, particularly human serum albumin (HSA), influencing their biodistribution and in vivo behavior. In this study, we have formulated PLA and PLA-PEG NPs (100-350 nm, negatively charged) and evaluated their interactions with HSA using a novel frontal analysis continuous capillary electrophoresis (FACCE) method. This approach directly quantifies free HSA post-incubation with NPs, providing excellent reproducibility (RSD <2 %) and linear response over the calibration range (R² > 0.99). Binding constants derived from Langmuir adsorption isotherms showed affinities of 10⁵ M^-1 and 10⁴ M^-1 for PLA NPs and PLA-PEG NPs, respectively clearly confirming the reduced HSA binding upon PEGylation. Compared to conventional methods such as isothermal titration calorimetry or surface plasmon resonance, FACCE proved faster and more robust results leading to analyses completion within 3.5 h. These results highlight the versatility of FACCE for characterizing NP-protein interactions and further stress the key role of PEG moieties in modulating protein binding.