A Ti4+-immobilized phosphate polymer-patterned silicon substrate for on-plate selective enrichment and self-desalting of phosphopeptides

A circular hydrophobic-hydrophilic-Ti4+ immobilized phosphate polymer is patterned on a silicon wafer. Such a wafer is used as a novel sample support to allow fast selective enrichment, wash-free self-desalting and mass spectroscopy (MS) analysis of phosphopeptides, thanks to the high Ti4+ loading amount, pure phosphate polymer-Ti4+ interface, and strong hydrophobic-hydrophilic attraction pattern. The detection sensitivity was enhanced 300 folds compared with what was obtained using the common MALDI plate. Remarkable selectivity for phosphopeptides can be achieved at a molar ratio as low as 1 : 500 of phosphopeptides (casein digest)/nonphosphopeptides (BSA). High-quality mass spectra can be obtained even in the presence of NaCl (1 M), NH4HCO3 (100 mM), or urea (1 M). These microspots were also used to selectively capture phosphopeptides from milk and human serum, which further demonstrated that they were capable of identifying low-abundance phosphopeptides from real complex samples. They provide a low detection limit (3 fmol mu L-1), small sample size, and excellent enrichment and desalting efficiency. Such a method significantly simplifies the analytical procedures, reduces possible sample loss, and is relatively low cost. Therefore, this on-plate patterned technique is very promising in the high-throughput phosphoproteomic research, especially for the detection of tiny amounts of samples.