Sustainable depletion of high-abundance serum proteins using aqueous biphasic systems based on glycine-betaine analogue ionic liquids for the detection of masked biomarkers.

The detection of protein biomarkers in human serum using more sustainable analytical strategies remains constrained by the predominance of high-abundance proteins, particularly human serum albumin (HSA) and immunoglobulin G (IgG), which limits access to low-abundance targets. To address these limitations, aqueous biphasic systems (ABS) comprising glycine-betaine analogue ionic liquids (AGB-ILs) are introduced as a green sample preparation strategy for the selective depletion of high-abundance serum proteins. After synthesizing and characterizing AGB-ILs, including their thermal properties and ecotoxicity, these were combined with a citrate buffer and screened for ABS formation. HSA and IgG were efficiently depleted in a single step via interfacial precipitation, allowing the detection of previously suppressed analytes such as transferrin using size-exclusion high-performance liquid chromatography with UV detection (SE-HPLC-UV). This demonstrates that effective sample pretreatment can enable the use of simpler analytical techniques compared to immunoassay- and mass spectrometry-based approaches. The sustainability profile of the proposed approach was evaluated using the AGREE (Analytical GREEnness), AGREEprep (Analytical GREEnness for sample PREParation), and BAGI (BioAnalytical Greenness Index) metrics, confirming low toxicity, reduced reagent consumption, and potential for improved workflow integration. Ultimately, this work extends the applicability of IL-based ABS for protein depletion, establishing bio-inspired ILs as promising tools for green bioanalytical workflows.