Carbon Dot-MnO2 Nanosphere Composite Sensors for Selective Detection of Glutathione

Herein, a fluorescent nanosensor based on carbon dots (Cdots) and different-size MnO2 nanospheres has been synthesized for rapid detection of glutathione (GSH). Water-soluble and highly fluorescent Cdots were prepared by the microwave method using ascorbic acid as the precursor. MnO2 nanospheres of different sizes (large, medium, and small) were prepared by varying the concentration ratio of methionine and KMnO4 at room temperature, which was confirmed by HRTEM analysis. The different sizes of MnO2 nanospheres in Cdots result in quenching of the fluorescence intensity, quantum yields, and average lifetime values, which suggest that the fluorescence resonance energy transfer mechanism occurs between the Cdots and MnO2 nanospheres. The variations of all the photophysical parameters and fluorescence turn off properties of Cdots are significantly tuned depending on the size of the nanospheres. Moreover, detection of GSH in the presence of different-size Cdots@MnO(2 )systems has been explored. GSH causes the redox reaction in the presence of MnO2, which leads to transformation from MnO2 to Mn2+. As a result, fluorescence restoration (turn on) of Cdots was observed. The large MnO, nanospheres showed the lowest detection limit of 15 mu M for GSH. The synthesized sensing system was very fast, simple, economical, and environmentally-friendly for the detection of the GSH level.