Synthesis, characterization and application of modified Pd nanoparticles as preconcentration probes for selective enrichment/analysis of proteins via hydrophobic interactions from real-world samples using nanoparticle-liquid-liquid microextraction coupled to matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

We introduce a novel preconcentrating technique by using surface modification of palladium nanoparticles (Pd-NPs) with octadecane thiol (ODT) prepared in toluene for selective and sensitive extraction of proteins (insulin, ubiquitin, lysozyme) from a variety of real-world samples including pancreas, mushroom, soybean and milk using nanoparticle-liquid-liquid microextraction (NP-LLME) coupled to matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-MS). The limit of detection (LOD) values obtained for gramicidin D and insulin in water and urine are between 17-37 nM (17-37 fmol) (with RSDs ranging from 5.3-7.2%) which are 10-20-fold enhancement in detection sensitivity compared with conventional MALDI-MS. The optimal sample pH for highest extraction efficiency of insulin, ubiquitin and lysozyme from biological samples was observed at sample pH ∼ pI which could be due to the enhancement of hydrophobic interactions between proteins with the hydrophobic ligands of Pd-ODT NPs. In addition, we also found that with the addition of 1 M NaCl, signals could be significantly enhanced by using the current approach. It is an efficient, straightforward, sensitive and selective nanoprobe which can be widely applied for separation, enrichment and preconcentration of peptides or proteins from complex biological samples in proteome research.