Nitrogen Doped Carbon Quantum Dots as Fluorescence “Turn-Off-On” Sensor for Detection of Fe3+ Ions and Ascorbic Acid in <italic>Moringa oleifera</italic> 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 <italic>Moringa oleifera</italic> and AA in citrus lemon.Graphical abstract: 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 <italic>Moringa oleifera</italic> and AA in citrus lemon. [ABSTRACT FROM AUTHOR]