Surface modified BaTiO3 nanoparticles as the matrix for phospholipids and as extracting probes for LLME of hydrophobic proteins in Escherichia coli by MALDI-MS.

In this paper, we report the dual function of 12-hydroxy octadecanoic acid (HOA)-modified barium titanate nanoparticles (BaTiO3 NPs) as the matrix for phospholipids (PLs) and as hydrophobic affinity probes for liquid-liquid microextraction (LLME) of hydrophobic proteins in Escherichia coli prior to their identification by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-MS). FT-IR, SEM and TEM were used for the characterization of the HOA-modified BaTiO3 NPs. The surface modified BaTiO3 NPs acted as multifunctional probes (as extracting probes and as the matrix) for the analysis of PLs by MALDI-MS. Compared to 2,5-dihydroxybenzoic acid (2,5-DHB), the HOA-modified BaTiO3 NPs provided good PLs mass spectra with similar or improved signal-to-noise (S/N) ratio, which demonstrated the potentiality of HOA-modified BaTiO3 NPs as a PLs purpose matrix. This method was found to be linear in concentration ranges of 1.0-5.0 μM and 1.0-10.0 μM for L-A-phosphatidyl-l-serine (PS) and L-A-phsophatidic acid sodium (PA) with correlation coefficient (R(2)) values from 0.9905 to 0.9987. The detection limits were 0.20-0.35 μM and 0.25-0.40 μM for PS and PA, respectively. We also demonstrated the HOA-modified BaTiO3 NPs as extracting and as preconcentrating probes for the LLME of hydrophobic proteins in E. coli prior to their identification by MALDI-MS. Thus, the surface modified BaTiO3 NPs-assisted LLME coupled with MALDI-MS provides a simple methodology for the efficient extraction and determination of hydrophobic molecules in biological samples.