The effect of water on the optical properties and concentration of carbon nanodots (CND), prepared by microwave heating of a mixture of polyethylene glycol 200 (PEG-200) and water, was studied. It was shown that the presence of water as a substrate leads to the synthesis of CND with lower yield and optical properties and it is better to use only PEG-200 as the substrate. Microwave power and irradiation time as two important variables in the synthesis of CND from a single substrate (PEG-200) were optimized to obtain CND with a high yield. The CND obtained under the best conditions were characterized by TEM, XRD, UV-Visible, fluorescence spectroscopy and fluorescence imaging. Consequently, photostability of the prepared CND in acidic and alkaline mediums was studied. Finally, it was shown that the produced CND can be used as a green and cheap reagent for fast detection of metronidazole based on fluorescence quenching.
