Enrichment of phospholipids using magnetic Fe3O4/TiO2 nanoparticles for quantitative detection at single cell levels by electrospray ionization mass spectrometry

Abstract

Quantitative detection of phospholipids at the single cell level remains in challenge. Herein, the TiO2-coated Fe3O4 nanoparticles were synthesized to selectively enrich trace phospholipids from single cell, which were then eluted using 1.5% ammonia/methanol (w/w) for sensitive detection by electrospray ionization mass spectrometry. Under the optimal experimental conditions, eighteen phospholipids in single cell samples were detected and identified by MS/MS experiments. The limit-of-detections (LODs) were 0.012 μg/L for phosphatidylcholine (PC, 34:1) and 0.014 μg/L for phosphatidylcholine (PC, 36:2) in PBS matrix, with the linear range of 0.05–50 μg/L (R2 ≥ 0.999). The recovery rates of 94.90–104.00% were obtained, with the relative standard deviations (RSDs ≤ 6.90%). Quantitative determination of PC in real unicellular samples was also achieved, with the concentration of 1.82–2.11 μg/L for PC(34:1) and 1.25–1.65 μg/L for PC(36:2) in six types of single cell, opening up possibilities for quantitative analysis of trace compounds in complex bio-samples. A set of 6 types of tumor cells were analyzed and further differentiated by the partial least squares-discriminant analysis (PLS-DA). Conclusively, a facile method for the direct quantification of phospholipids in single cell samples has been developed, showing potential applications for advanced investigation of phosphorylated substance at the single cell level.