One-pot synthesis of dopamine dithiocarbamate functionalized gold nanoparticles for quantitative analysis of small molecules and phosphopeptides in SALDI- and MALDI-MS

The sensitivity and efficiency of SALDI-MS or MALDI-MS is mainly dependent on the nature of matrix. A novel approach is proposed for one-pot synthesis of dopamine dithiocarbamate-functionalized gold nanoparticles (DDTC-Au NPs). Their application to quantification of small molecules by surface assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF-MS) and rapid identification of phosphopeptides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is investigated. The synthesized DDTC-Au NPs were characterized by UV-visible and FT-IR spectroscopy, H1NMR, SEM and TEM. DDTC-Au NPs offers marked improvement on analyte ionization and effectively suppressed the background noise which leads to clean mass spectra. We also demonstrated the use of DDTC-Au NPs as affinity probes for selective enrichment of phosphopeptides from the solutions of microwave tryptic digested casein proteins. Compared with a conventional matrix, DDTC-Au NPs exhibited a high desorption/ionization efficiency for accurate quantification of small molecules including amino acid (glutathione), drugs (desipramine and enrofloxacin) and peptides (valinomycin and gramicidin D) and successfully utilized as novel affinity probes for straightforward and rapid identification of phosphopeptides from casein proteins (α-, β-casein and nonfat milk), showing a great potentiality to the real-time analysis.