As a group of organic salts consisting entirely of ions (anions and cations), ionic liquids (ILs) have shown great promises as a potential alternative to conventional volatile toxic organic solvents due to their unique and attractive properties including negligible vapor pressure, nonflammability, high chemical/thermal stability, low toxicity and favorable conductivity. These attractive features of ILs have made them as popular candidates in the wide applications of various fields including organic synthesis, extraction/separation, electrochemical analysis, catalysis and chemical sensors. Protein assay has long been a crucial issue in bio-sciences and other related fields. In this respect, the applications of ionic liquids to perform protein assays, including protein stability/activity investigations, protein extraction and isolation/purification, protein crystallization, separation of protein species and their detections, have received increasing attentions in the past few years. This can be attributed to the fact that ionic liquids provides a novel and highly efficient reaction medium, but meanwhile, they also serve as efficient participants in the various chemical/biological reaction processes. The recent applications of ionic liquid-based extraction systems in protein separations and assays are depicted in the present mini-review, including protein extraction in the presence of assistant extractants, direct extraction, aqueous two-phase extraction systems, emulsion extraction systems, crystallization of proteins in the presence of ionic liquids and ionic liquid-based solid-phase extraction systems. Contents
1 Introduction
2 IL-based extraction system in protein separation and assays
2.1 Assistant extraction system
2.2 Direct extraction system
2.3 Aqueous two-phase extraction system
2.4 Emulsion extraction system
2.5 Protein crystallization in the presence of ionic liquids
2.6 IL-based solid-phase extraction system
3 Conclusions and perspectives