Enantiomeric separation by open-tubular capillary electrochromatography using bovine-serum-albumin-conjugated graphene oxide–magnetic nanocomposites as stationary phase

In this work, a novel chip-based enantioselective open-tubular capillary electrochromatography (OT-CEC) was developed employing bovine serum albumin (BSA)-conjugated graphene oxide–magnetic nanocomposites (GO/Fe3O4) as stationary phase. GO/Fe3O4 nanocomposites with high magnetic responsivity, excellent solubility, and high dispersibility in water were prepared through a facile and controllable in situ chemical deposition strategy. BSA was then adsorbed onto the GO/Fe3O4 surface to form GO/Fe3O4/BSA conjugates, which were then locally packed into PDMS microchannels with the help of magnets. The resultant GO/Fe3O4/BSA conjugates not only have the magnetism of Fe3O4 NPs that make them easily manipulated by an external magnetic field, but also have the larger surface and excellent biocompatibility of graphene, which can incorporate much more biomolecules and well maintain their biological activity. In addition, the successful BSA decorations endowed GO/Fe3O4/BSA conjugates with pH-tunable water solubility related to the isoelectric point of BSA (pI 4.7) and led to enhanced stability against high ionic strength. Compared with the native PDMS microchannel, the modified surfaces exhibited more stable and suppressed electroosmotic mobility and less nonspecific adsorption toward analytes. Successful separation of tryptophan, threonine, and propranolol enantiomers were achieved in less than 80 s with resolution factors of 1.22, 1.9, and 2.1, respectively, utilizing a separation length of 37 mm coupled with in column amperometric detection. The presented on-chip enantioselective OT-CEC protocol simplifies the protein immobilization methodology and has the potential to provide a platform for high-throughput screening of enantiomer candidates.