The efficient detection of Fe 3+ and MnO 4 - in a water environment is very important and challenging due to their harmful effects on the health of humanity and environmental systems. Good biocompatibility, sensitivity, selectivity, and superior photophysical properties were important attributes of carbon dot-based CDs sensors for sensing applications. In this work, we synthesized N, P- co -doped carbon dots (N/P CDs) with guanosine 5'-monophosphate (GMP) as a green carbon source, with high fluorescence quantum yield in water (QY, 53.72%). First, the luminescent N/P CDs showed a three-state "on-off-on" fluorescence response upon the sequential addition of Fe 3+ and F - , with a low detection limit of 12 nM for Fe 3+ and 8.5 nM for F - , respectively. Second, the N/P CDs also exhibited desirable selectivity and sensitivity for toxic MnO 4 - detection with the limit of detection of 18.2 nM, through a turn-off mechanism. Moreover, the luminescent N/P CDs successfully monitored the aforementioned ions in environmental water samples and in Escherichia coli ., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Wang, Liu, Nong, Song, Zhang, Shen, Jian, Chen, Li and Xu.)