Nitrogen-doped carbon dots coupled with morin-Al 3+ : Cleverly design an integrated sensing platform for ratiometric optical dual-mode and smartphone-assisted visual detection of fluoride ion.

Ratiometric fluorescence sensor has high selectivity and good sensitivity; however, its development is limited by intricate design, tedious synthesis, etc. Herein, a facile and effective ratiometric fluorescence sensing platform for fluoride ion (F ^- ) detection was developed by simply combining nitrogen-doped carbon dots (N-CDs) and morin-Al ³⁺ based on inner filter effect (IFE). The competitive binding of F ^- to Al ³⁺ obviously decreased morin-Al ³⁺ fluorescence and increased N-CDs fluorescence, attributing to the inhibition of IFE between N-CDs and morin-Al ³⁺ . The as-constructed ratiometric fluorescence sensing platform can be used for F ^- detection with a wide linear range (0.5-150 μM) and a low detection limit (55.8 nM). Interestingly, with the introduction of F ^- into the N-CDs/morin-Al ³⁺ sensing platform, a distinguishable change in fluorescence color from green to blue enabled the N-CDs/morin-Al ³⁺ system to be used as a smartphone-assisted visual sensing platform for F ^- detection with a detection limit of 2.09 μM. This platform was successfully applied for the onsite monitoring of F ^- in various water samples with satisfying results. These findings provide a novel guidance for the facile construction of a ratiometric optical dual-mode and smartphone-assisted sensing platform based on CDs, revealing the broad application prospect of CDs in environmental monitoring field.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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