An ancient plant for the synthesis of a novel carbon dot and its applications as an antibacterial agent and probe for sensing of an anti-cancer drug.

An innovative, facile, low- cost and one-pot hydrothermal synthesis was developed for preparing a high fluorescence carbon dots (CDs). In this report for the first time, Lawsonia inermis (Henna) plant as a carbon source was used to produce CDs without adding any chemical reagent and it was characterized by different techniques. The as-synthesized CDs exhibit high stability under various conditions and exceptionally solubility in hydrophilic solvents such as water and ethanol. In addition, the CDs were employed as a biocompatible probe for determination of methotrexate (MTX) in the range of 0.02 μmol L^-1 to 18 μmol L^-1 with a detection limit as 7 nmol L^-1. Highly selective and sensitive determination of MTX was carried out through the fluorescence resonance energy transfer (FRET) mechanism. It is noteworthy that, the antibacterial studies of this CDs lead to interesting results which suggested Henna CDs kill Gram-positive and Gram-negative bacteria like an antibiotic drug. Also, compared with the henna plant, CDs show antibacterial properties in much lower concentrations.