Easy and Versatile Synthesis of Bulk Quantities of Highly Enriched 13C-Graphene Materials for Biological and Safety Applications

The preparation of bulk quantities of( 13)C-labeled graphene materials is relevant for basic investigations and for practical applications. In addition, C-13-labeled graphene materials can be very usef u l in biological and environmental studies, as they may allow the detection of graphene or its derivatives in cells or organs. In this paper, we describe the synthesis of C-13-labeled graphene materials (few-layer graphene, FLG, and graphene oxide, GO) on a tens of mg scale, starting from C-13-labeled methane to afford carbon fibers, followed by liquid-phase exfoliation (FLG) or oxidation (GO). The materials have been characterized by several analytical and microscopic techniques, including Raman and nuclea r magnetic resonance spectroscopies, thermogravimetric analysis, X-ray photoelectron spectroscopy, and X-ray powder diffraction. As a proof of concept, the distribution of the title compounds in cells has been investigated. In fact, the analysis of the C-13/C-12 ratio with isotope ratio mass spectrometry (IRMS) allows the detection and quantification of very smal l amounts of material in cells or biological compartments with high selectivity, even when the material has been degraded. During the treatment of( 13)C-labeled FLG with HepG2 cells, 4.1% of the applied dose was found in the mitochondrial fraction, while 4.9% ended up in the nuclear fraction. The rest of the dose did not enter into the cel l and remained in the plasma membrane or in the culture media.