Self-assembled covalent capillary coating of diazoresin/carboxyl fullerene for analysis of proteins by capillary electrophoresis and a comparison with diazoresin/graphene oxide coating

• Photosensitive DR/C60-COOH covalent capillary coating is made by self-assembly.
• The self-lubricating coating exhibits excellent protein separation performance.
• Highly toxic and moisture sensitive silane is replaced by DR coupling agent.
• DR/C60-COOH performs better than DR/GO as covalent capillary coating

Self-assembled and covalently linked capillary coatings of carboxyl fullerenes (C60-COOH) were prepared using photosensitive diazoresin (DR) as a coupling agent. Layer by layer (LBL) self-assembled DR/C60-COOH coatings based on ionic bonding was fabricated first on the inner surface of silica capillary, and subsequently converted into covalent bonding after treatment with UV light through a unique photochemistry reaction of DR. The covalently bonded coatings had the ability of suppressing protein adsorption on the inner surface of silica capillary, and thus the baseline separation of lysozyme (Lys), cytochrome c (Cyt-c), bovine serum albumin (BSA) and myoglobin (Mb) was achieved within 13 min by using capillary electrophoresis (CE). The covalently linked DR/C60-COOH capillary coatings presented good chemical stability and repeatability. The reproducibility of the separation of proteins was less than 1%, 2.5%, and 3.5%, respectively, for run-to-run, day-to-day, capillary-to-capillary, respectively; and the RSD of migration time for the proteins are all less than 2.5% after a continuous 100 times running in a coating column. Compared with DR/graphene oxide (GO) coatings prepared by the same method, the DR/C60-COOH capillary coatings showed excellent protein separation performance due to a self-lubrication based anti-fouling mechanism. Because of the replacement of highly toxic and moisture sensitive silane coupling agent by DR in the covalent coating preparation, this method may provide an environmentally friendly and simple way to prepare the covalently coated capillaries for CE.