UV-Absorbing Ligand Capped Gold Nanoparticles for the SALDI-MS Analysis of Small Molecules

We report that modifying the surface of gold nanoparticles (Au NPs) with 2-mercaptopyridine-3-carboxylic acid (MPyCA) enhances surface-assisted laser desorption/ionization (SALDI) performance in the analysis of small molecules. The MPyCA ligand has a strong UV absorbance at the wavelengths of the typical MALDI laser at 337 nm, resulting in efficient thermal/energy transfer from the Au NPs to analytes during pulse-laser irradiation. In addition, the MPyCA ligand contains carboxylic acid and pyridine groups, providing affinity to various analytes through acid-base interactions. Irganox1010, glucose and meropenem were utilized as model analytes to evaluate SALDI performance because these molecules are generally ionized with difficulty by conventional MALDI-MS. Our results demonstrate that the MPyCA-Au NP based SALDI-MS could detect Irganox1010, glucose and meropenem with stronger ion peaks for these molecules compared to MALDI-MS using CHCA. The limit of detection (LOD) for meropenem was much lower in the case of SALDI (LOD=1 ng/mL) compared to MALDI (LOD=10 μg/mL).