Silver nanoparticles for solvent-free detection of small molecules and mass-to-charge calibration of laser desorption/ionization mass spectrometry

This work aims at the utilization of nanostructured surfaces for advanced mass spectrometry [laser desorption/ionization mass spectrometry (LDI MS)]. The authors demonstrate that prepared nanostructures enable independent mass-to-charge calibration and also effectively substitute protonation agent for low-mass molecules instead of conventionally used matrices. Silver nanostructured surfaces were formed as homogeneous thin film, isolated nanoislands, and spherical nanoparticles. Besides the surface characterization, the paper focuses on the impact of LDI MS laser, irradiating the nanostructured surfaces, which results in the production of charged Ag clusters. Irradiated nanoparticle-based surfaces mostly provide single ionized species Ag⁺ while positive (Ag_n⁺, n ≤ 5) and negative ions (Ag_n⁻, n ≤ 7) were observed from the nanoislands film. It is shown that the ratio between particular ion line intensities can be tailored by the deposition time. The pattern of silver ions Ag_n (due to two natural isotopes) can be used for mass-to-charge calibration up to 1000 m/z. Additionally, the silver protonation improves the identification of small molecules. It is demonstrated on detection of sucrose (342.3 g/mol), fructose (180.2 g/mol), and creatinine (113.1 g/mol) molecules.