Identification of peptides using gold nanoparticle-assisted single-drop microextraction coupled with AP-MALDI mass spectrometry

A novel technique, gold nanoparticle-assisted single-drop microextraction (SDME) combined with atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry (AP-MALDI-MS) for the identification of peptides has been described. The SDME of peptides from aqueous solution was achieved using gold nanoparticles prepared in toluene as the acceptor phase. A simple phenomenon of isoelectric point (pI) of the peptides has been utilized successfully to extract the peptides into a single drop of nanogold in toluene. After extraction, a single-drop nano gold solution was directly spotted onto the target plate with an equal volume of matrix, proportional, variant-cyanohydroxy cinnamic acid ( proportional, variant-CHCA) and analyzed in AP-MALDI-MS. The parameters, such as solvent selection, extraction time, agitation rate, and pH effect, were optimized for the SDME technique. Using this technique, in aqueous solution, the lowest concentration detected for Met- and Leu-enkephalin peptides was 0.2 and 0.17 microM, respectively. In addition, the application of this technique to obtain the signal for the selected peptides in a mass spectrum in the presence of matrix interferences such as 1% Triton X-100 and 6.5 M urea has been showed. The application was extended to identify the peptides spiked into urine.