Applications of silver nanoparticles capped with different functional groups as the matrix and affinity probes in surface‐assisted laser desorption/ionization time‐of‐flight and atmospheric pressure matrix‐assisted laser desorption/ionization ion trap mass spectrometry for rapid analysis of sulfur drugs and biothiols in human urine

Abstract

A strategy is presented for the analysis of sulfur drugs and biothiols using silver nanoparticles (AgNPs) capped with different functional groups as the matrix and affinity probes in surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF MS) and atmospheric pressure-matrix assisted laser desorption/ionization ion trap mass spectrometry (AP-MALDI-ITMS). Biothiols adsorbed on the surface of AgNPs through covalent bonding were subjected to ultraviolet (UV) radiation that enabled desorption and ionization due to the excellent photochemical property of NPs. The proposed method has been successfully applied for the determination of cysteine and homocysteine in human urine samples using an internal standard. The limit of detection (LOD) and limit of quantification (LOQ) for cysteine and homocysteine in urine sample are 7 and 22 nM, respectively, with a relative standard deviation (RSD) of <10%. The advantages of the present method compared with the methods reported in the literature for biothiol analysis are simplicity, rapidity and sensitivity without the need for time-consuming separation and tedious preconcentration processes. Additionally, we also found that the bare AgNPs can be directly used as the matrix in MALDI-TOF MS for the analysis of sulfur drugs without the addition of an extra proton source.