Selective Enrichment of Phosphopeptides and Phospholipids from Biological Matrixes on TiO 2 Nanowire Arrays for Direct Molecular Characterization by Internal Extractive Electrospray Ionization Mass Spectrometry.

Rapid analysis of phosphopeptides and phospholipids in biological matrixes is of significant interest in multiple disciplines of life sciences. Herein, trace phospholipids in human plasma, whole blood, and undiluted human urine as well as phosphopeptides in protein digest were selectively captured on a homemade array of TiO ₂ nanowires for sensitive characterization by internal extractive electrospray ionization mass spectrometry (TiO ₂ -iEESI-MS). Sequential release of captured chemicals from TiO ₂ array was achieved by tuning pH of the extraction solvent. A single sample analysis, including sample loading, chemical extraction and MS detection, was accomplished within 3 min. As far as the quantification of phospholipids, acceptable linearity ( R ² ≥ 0.9985) and relative standard deviations (RSDs ≤ 8.9%) were obtained within the range of 0.1-500 μg L ^-1 for LysoPC(14:0) and LysoPC(16:0) in raw urine samples. Limit of detection (LOD) ≤ 0.025 μg L ^-1 and recovery rates of 94.8-101.6% were obtained for these phospholipids. As far as the quantification of phosphopeptides, R ² ≥ 0.9994 and RSDs ≤ 9.2% within the range of 0.3-200 μg L ^-1 were obtained for two phosphopeptides in nonphosphopeptides mixtures. LODs ≤ 0.09 μg L ^-1 and recovery rates of 83.4-107.0% were obtained for these phosphopeptides. On the basis of the orthogonal partial least-squares discriminant analysis, TiO ₂ -iEESI-MS patterns from the blood of 46 patients with ovarian cancer were confidently discriminated from the MS patterns of 46 healthy volunteers. Our results indicate the strong potential of TiO ₂ -iEESI-MS approach for the selective detection of trace phosphopeptides and phospholipids in various biological matrixes with high sensitivity, high specificity, low sample consumption, and high throughput.