Detection of nucleoside monophosphates through surface-assisted laser desorption/ionization mass spectrometry using CTAB-adsorbed gold nanoparticles

In this paper, we demonstrate the determination of nucleoside monophosphates through surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using hexadecyltrimethylammonium bromide (CTAB)-adsorbed gold nanoparticles (CTAB-Au NPs) as the surface. The binding of four nucleoside monophosphates - adenosine 5'-monophosphate (5'-AMP), guanosine 5'-monophosphate (5'-GMP), uridine 5'-monophosphate (5'-UMP), and cytidine 5'-monophosphate (5'-CMP)-to the surfaces of the CTAB-Au NPs induced their aggregation, allowing selective concentration of the four analytes from sample solutions. The analyte-adsorbed CTAB-Au NPs were subjected directly to SALDIMSmeasurement-that is, withoutmixing the analytes with organicmatrices. The presence of CTAB improved the ionization efficiency of the analytes and suppressed the MS background signals arising from Au clusters. By using CTAB-Au NPs prepared from a mixture of 0.4 μM CTAB and 1.8 nM Au NPs, this SALDI-MS approach provided limits of detection (signal-to-noise ratio = 3) for 5'-AMP, 5'-GMP, 5'-UMP, and 5'-CMP of 5, 10, 25, and 25 nM, respectively. The SLADI-MS method established was also employed for the analyses of nucleoside monophosphates in mushroom extracts and a commercial sample of monosodium glutamate. 5'-AMP, 5'-GMP, 5'-UMP, and 5'-CMP were found in the samples. This system has several advantageous features - simplicity, sensitivity, and reproducibility (shot-to-shot variation: < 15%) - that allow its use for the determination of the concentrations of nucleoside monophosphates in biological samples.