Advances in amino acid-derived aqueous biphasic systems for eco-friendly separation processes

Aqueous biphasic systems (ABSs), recognized for their mild operational conditions and low environmental impact, provide a versatile platform for the extraction, separation, purification, and enrichment of various biomolecules and other valuable materials and therefore are key in advancing sustainable separation technologies. Among various ABSs, those based on amino acids offer enhanced biocompatibility, reduced toxicity, and a diminished environmental footprint, establishing them as promising alternatives to traditional solvent-based methods. Compared to salting-out methods, the amino acid-induced phase separation technique (“amino aciding-out”) is simpler, more stable, cost-effective, and reduces equipment corrosion. This review provides a comprehensive overview of recent developments in amino acid-based ABSs, focusing on polymer-amino acid, ionic liquid (IL)-amino acid, and surfactant-amino acid ABSs, as well as ABSs formed by amino acid-based ILs (AAILs), including AAIL – salt, AAIL – polymer, AAIL-surfactant and AAIL-organic solvent systems. Unlike previous review, M.G. Freire, A.F.M. Claudio, J.M.M. Araujo, J.A.P. Coutinho, I.M. Marrucho, J.N.C. Lopes, L.P.N. Rebelo, Aqueous biphasic systems: a boost brought about by using ionic liquids, Chem. Soc. Rev. 41 (2012) 4966–4995., which was limited to the IL–amino acid systems and covered only two studies, this work provides the first comprehensive and quantitative analysis of all amino acid-based ABSs reported up to 2024. We delve into the molecular and thermodynamic mechanisms that govern phase behaviour and stability in these systems, highlighting the role of amino acids as soluting-out agents. Our analysis covers the influence of structural and environmental parameters on system efficacy, including the effects of temperature, amino acid type, and the physicochemical properties of co-solutes. Practical applications are discussed, with a focus on the extraction and purification processes for biomolecules and value-added compounds, underscoring the systems' versatility and efficiency. The review identifies current challenges within the field, and proposes future directions that emphasize innovation, sustainability, and broader application scopes. By consolidating existing knowledge and suggesting pathways for future research, this work aims to catalyze further advancements in green separation technologies using amino acid-based ABSs. All types of amino acid-based ABSs. • Design principles proposed for amino acid–induced phase separation. • Unified overview of seven amino acid–based aqueous biphasic systems. • Thermodynamic insights reveal entropy-driven phase formation mechanism. • Databases compiled for phase constituents, extraction targets, and methods. • Roadmap outlined for green, scalable, and sustainable separation processes.