Turn-on fluorescence sensor for intracellular imaging of glutathione using g-C₃N₄ nanosheet-MnO₂ sandwich nanocomposite.

Herein, a novel fluorescence sensor based on g-C3N4 nanosheet-MnO2 sandwich nanocomposite has been developed for rapid and selective sensing of glutathione (GSH) in aqueous solutions, as well as living cells. The graphitic-phase C3N4 (g-C3N4) nanosheet used here is a new type of carbon-based nanomaterial with high fluorescence quantum yield and high specific surface area. We demonstrate a facile one-step approach for the synthesis of a g-C3N4 nanosheet-MnO2 sandwich nanocomposite for the first time. The fluorescence of g-C3N4 nanosheet in this nanocomposite is quenched, which attributing to fluorescence resonance energy transfer (FRET) from a g-C3N4 nanosheet to the deposited MnO2. Upon the addition of GSH, MnO2 is reduced to Mn(2+), which leads to the elimination of FRET. As a result, the fluorescence of g-C3N4 nanosheet is restored. Importantly, the chemical response of the g-C3N4-MnO2 nanocomposite exhibits great selectivity toward GSH relative to other electrolytes and biomolecules. Under the optimal conditions, the detection limit of 0.2 μM for GSH in aqueous solutions can be reached. Furthermore, the g-C3N4-MnO2 nanocomposite is confirmed to be membrane-permeable and have low cytotoxicity. Moreover, we successfully apply this sensor for visualizing and monitoring change of the intracellular GSH in living cells. Moreover, the proposed sensor shows satisfying performance, such as low cost, easy preparation, rapid detection, good biocompatibility, and turn-on fluorescence response.