Toxicity analysis of graphene nanoflakes by cell-based electrochemical sensing using an electrode modified with nanocomposite of graphene and Nafion

To evaluate the cytotoxicity of nanomaterials, cell-based electrochemical sensing of extracellular H2O2 with a nanocomposite-modified indium tin oxide (ITO) electrode was carried out. The ITO working electrode was modified with a nanocomposite film of Nafion and chemically-driven graphene (G) using the electrospray method. The cyclic voltammetric measurements of H2O2 molecules using the nanocomposite-modified electrode showed a high sensitivity (82.6 μA mM−1 cm−2) due to the enhancement of the electrochemical signal by the nanocomposite. The mini-cell culture system integrated with the nanocomposite electrochemical transducer was used to carry out a toxicity analysis of G nanoflakes under size-, concentration- and time-dependent influences. Quantitative sensing of extracellular H2O2 released from HeLa cells treated with different sizes and concentrations of G nanoflakes was performed by cyclic voltammetry, and optical bioassays were also used to complement the electrochemical measurements. The H2O2 concentrations after treatment by nanoflakes with different concentrations continuously increased up to 1 M, 20-fold higher than the H2O2 concentration of about 50 mM for untreated cells after 24 h. The results also showed that the increased tendency in measured H2O2 concentration as the concentration of the G nanoflakes increased was consistent with the results of the toxicity analysis data obtained by optical bioassays. Also, we confirmed increased cytotoxicity for smaller G size at the same concentration. These toxicity analyses by cell-based electrochemical sensors are of great interest for the toxicity assessment of nanomaterials having various biomedical and environmental applications.