Detection of aminothiols through surface-assisted laser desorption/ionization mass spectrometry using mixed gold nanoparticles.

We have employed mixtures of two differently sized (average diameters: 3.5 and 14 nm) gold nanoparticles (Au NPs) as selective probes and matrices for the determination of aminothiols using surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). When using 38 and 150 pM solutions of the 3.5- and 14-nm Au NPs, respectively, as the probe and matrix, SALDI-MS provided limits of detection (signal-to-noise ratio = 3) of 2, 20, and 44 nM for 1.0 mL solutions of glutathione (GSH), cysteine (Cys), and homocysteine, respectively. The signal intensities of these analytes varied by less than 20% for SALDI-MS analyses recorded over 50 sample spots; in contrast, they varied by as much as 60% when using a conventional matrix (2,5-dihydroxybenzoic acid). We validated the practicality of this approach - with its advantages of sensitivity, reproducibility, rapidity, and simplicity - through the analysis of GSH in MCF-7 cell lysates and Cys in plasma.