Ethylenediamine-assisted hydrothermal synthesis of nitrogen-doped carbon quantum dots as fluorescent probes for sensitive biosensing and bioimaging

• Nitrogen-doped carbon quantum dots (N-CQDs) were successfully synthesized through one-pot hydrothermal carbonization of alanine and ethylenediamine.
• The reason for the high quantum yields for the obtained N-CQDs was provided.
• The N-CQDs possess low cytotoxicity and good biocompatibility.
• A novel protocol for NADH determination was established due to the dramatically fluorescence quenching of N-CQDs.

In this work, nitrogen-doped carbon quantum dots (N-CQDs) with high fluorescence quantum yield (46.2%) were successfully synthesized through one-pot hydrothermal carbonization approach assisted by ethylenediamine as surface passivation agent, wherein alanine acted as a single carbon source, ethylenediamine as the surface passivation agent. The obtained biocompatible N-CQDs could effectively label both the MCF-7 cell membranes and the nucleus, suggesting the potential application in biolabeling and bioimaging. Furthermore, the addition of dihydronicotinamide adenine dinucleotide (NADH) could dramatically quench the fluorescence of N-CQDs. Therefore, a novel protocol for NADH determination was established and its mechanism was discussed. This proposed fluorescence sensor displayed an enhanced performance for NADH determination with the linear range up to 80 μM and the detection limit down to 25.1 nM.

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