Highly selective capture of phosphopeptides using a nano titanium dioxide-multiwalled carbon nanotube nanocomposite

In this study, a titanium dioxide-multiwalled carbon nanotube (TiO2-MWNT) nanocomposite was first used to enrich phosphopeptides as a binding agent. The TiO2-MWNT nanocomposite was synthesized by the hydrothermal reaction process and characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR), and X-ray powder diffraction (XRD). The results demonstrated that the anatase phase TiO2 nanoparticles had been successfully linked by MWNTs. The TiO2-MWNT nanocomposite was applied as a sorbent to enrich phosphopeptides, and the results showed that the performance of the TiO2-MWNT nanocomposite was better than 5 μm TiO2, as confirmed by the analysis of phosphopeptides from a tryptic digest of a standard protein (β-casein and bovine serum albumin) using high-performance liquid chromatography-electrospray ionization-mass spectrometry (HPLC-ESI-MS). The use of lactic acid in the loading buffer significantly enhances the selectivity of the TiO2-MWNT nanocomposite. This nanocomposite material was further applied to enrich the phosphopeptides in a protein digest obtained from nonfat milk successfully.