Surface modified silver selinide nanoparticles as extracting probes to improve peptide/protein detection via nanoparticles-based liquid phase microextraction coupled with MALDI mass spectrometry.

We report the first use of functionalized Ag(2)Se nanoparticles (NPs) as effective extracting probes for NPs-based liquid-phase microextraction (NPs-LPME) to analyze hydrophobic peptides and proteins from biological samples (urine and plasma) and soybean in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Surface modified functional groups such as octadecanethiol (ODT) and 11-mercaptoundecanoic acid (MUA) on Ag(2)Se NPs were found to play an important role for efficient extraction of peptides and proteins from test samples through hydrophobic interactions. The peptides can be efficiently extracted using functionalized Ag(2)Se NPs as extracting probes in the presence of high concentration of matrix interferences such as 4M urea, 0.5% Triton X-100 and 3% NaCl. Ag(2)Se@ODT NPs have shown better extraction efficiency and detection sensitivity for peptides than Ag(2)Se@MUA NPs, bare Ag(2)Se NPs and conventional MALDI-MS. The LODs are 20-68 nM for valinomycin and 100-180 nM for gramicidin D using Ag(2)Se@ODT NPs-LPME in the MALDI-MS. The current approach is highly sensitive and the target analytes can be effectively isolated without sample loss and efficiently analyzed in MALDI-MS.