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 (R2) 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.