N-doped multi-fluorescent carbon dots for 'turn off-on' silver-biothiol dual sensing and mammalian cell imaging application

Bright multi-fluorescent carbon dots (C-dots) were synthesized using prolonged time microwave assisted heating (PT-MAH) method. C-dots were found to be spherical, monodispersed, uniformly distributed with the ultra-small size of about 3.3 +/- 0.4 nm. The C-dots showed high oxygen content and nitrogen-doping (N-doped), thereby elucidating a competitive quantum yield ( QY: 17.73%). The presence of silver ions (Ag+) in drinking water needs to be monitored to prevent related human health hazards. Biothiols especially glutathione (GSH) plays a vital role in numerous biological processes. Alteration of GSH concentration from normal level is observed in various diseases and disorders. We demonstrate 'turn-off' dynamic fluorescence-based sensing of Ag+ ions and 'turn-on' fluorescence-based on sensing of GSH using C-dots as dual-sensor. Wide range concentrations of Ag+ ions (1-1000 mu M) were detected when Ag+ ions were spiked in C-dots suspended in three representative solutions: Milli-Q, purifier and tap water. The addition of GSH (1-200 mu M) to the C-dots-Ag+ complex recovered fluorescence in linear correlation with good recovery. Furthermore, the C-dots showed excitation-dependent fluorescence, which was utilised for multicolor in vitro cellular imaging in fibroblasts. The C-dots showed high cyto-compatibility and no deterring effect on cellular morphology. Thus, this study illustrates the potential of C-dots utility for silver and biothiol dual sensing and applicability intracellular imaging. (C) 2017 Elsevier B.V. All rights reserved.