Nitrogen Doped Carbon Quantum Dots as Fluorescence "Turn-Off-On" Sensor for Detection of Fe3+ Ions and Ascorbic Acid in Moringa oleifera and Citrus Lemon.

In recent year, the uses of carbon quantum dots (CQDs) have increased in many fields. Herein we report, synthesis of fluorescent nitrogen doped carbon quantum dots (N-CQDs) by simple and ecofriendly hydrothermal method. The as-synthesized N-CQDs were characterized by various techniques and the quantum yield was also calculated. Then, application of N-CQDs were performed as a sensor for detection of ferric ions (Fe³⁺) based on static quenching mechanism (turn-off) which occurred due to formation of non-fluorescent complex between N-CQDs and Fe³⁺ ions. Interestingly, fluorescence intensity of quenched N-CQDs has been significantly recovered (turn-on) by addition of ascorbic acid (AA). The recovery mechanism is based on the redox reaction between Fe³⁺ ions and AA. Thus, N-CQDs has been used as fluorescence "turn-off-on" sensor for detection of Fe³⁺ ions and AA. Further this detection system is used for detecting Fe³⁺ ions in Moringa oleifera and AA in citrus lemon.