Facile synthesis of magnetic graphene and carbon nanotube composites as a novel matrix and adsorbent for enrichment and detection of small molecules by MALDI-TOF MS

In this work, for the first time, we synthesized magnetic graphene and carbon nanotube (graphene/CNT) composites via a simple solvothermal synthesis of magnetite particles in the presence of CNTs and graphene. The magnetic graphene/CNT composites possess a unique structure in which CNTs are coated by magnetite particles and deposit on graphene sheets, which not only provides strong magnetic responsiveness for separation, but also prevents the self-aggregation of graphene and CNTs. By using their magnetic separability and large surface areas accessible for guest molecules, this novel composite has been successfully employed as a matrix and adsorbent for the analysis and enrichment of small molecule compounds using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). It is found that the graphene/CNT composites have several advantages such as higher sensitivity, facile desorption/ionization process, higher efficiency in analyte desorption/ionization and higher peak intensities for aromatic analytes, which are attributed to the distinct structure of magnetic graphene/CNTs comprised of pi-conjugated networks with a highly exposed surface. Additionally, they exhibited very high salt tolerance, which makes them a good candidate for application in analysis and enrichment of small molecules present in complex media, such as urine samples.