Optical biosensors based on nitrogen-doped graphene functionalized with magnetic nanoparticles

Nanocomposites from nitrogen-doped graphene (NG) and magnetic nanoparticles (MNPs) are prepared via an edge-functionalized ball milling approach, followed by a coprecipitation method. Catalytic peroxidase-like activity of the resulting MNP/NG is investigated. The as-synthesized MNP/NG nanocomposites are used to catalyze the colorimetric reaction between hydrogen peroxide (H₂O₂) and 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) diammonium salt (ABTS). Typical absorption peaks associated with the oxidation of ABTS are found to increase linearly with increasing H₂O₂ concentrations up to 10.0 × 10⁻³ m with a detection limit of 17.1 × 10⁻⁶ m. Rapid detection of H₂O₂ with the use of MNP/NG is confirmed further by a glucose biosensor. Concentrations of glucose could be monitored by detection of H₂O₂ since H₂O₂ is generated during oxidation of glucose by glucose oxidase (GOx). The absorption intensity increases significantly with increasing glucose amounts up to 18.0 × 10⁻³ m glucose, with a detection limit of 59.7 × 10⁻⁶ m, indicating a high performance for glucose detection.