Preparation and comparison of FeO@graphene oxide nanoclusters for analysis of glimepiride in urine by surface-assisted laser desorption/ionization time-of-flight mass spectrometry.

Graphene oxide (GO) has the ability to absorb certain compounds, and it can be modified with functional groups for different purposes; for instance, iron oxide (IO) nanoparticles can be used to concentrate analyte by a magnet. Recently, many kinds of GO have been developed, such as single-layer GO (SLGO), two-to-four layers of GO (i.e., few-layer GO, FLGO), and four-to-eight layers of GO (i.e., multi-layer GO, MLGO). However, the abilities of these layered GO coated with IO nanoparticles have not been investigated. In this study, we conducted a novel analysis of glimepiride by using layered GO-coated magnetic clusters of IO nanoparticles that were synthesized through a simple and facile emulsion-solvent evaporation method. The methodology is based on (i) enrichment of glimepiride using the layered GO-coated magnetic clusters of IO nanoparticles (IO@SLGO, IO@FLGO, and IO@MLGO), and (ii) rapid determination using magnetic cluster-based surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOFMS). We found that IO@MLGO, the magnetic cluster with the greatest number of GO layers, had the best limit of detection (28.6 pmol/μL for glimepiride). The number of GO layers played a significant role in increasing the sensitivity of the SALDI-MS, indicating that the size of GO in the magnetic clusters contributed to the desorption/ionization efficiency. To the best of our knowledge, this is the first study to enrich glimepiride using magnetic clusters of different GO types and to show that the glimepiride in HLB purified urine adsorbed by magnetic clusters can be analyzed by SALDI-TOFMS.