A hydrothermal strategy for preparing boron and nitrogen codoped carbon quantum dots was studied using the precursors of p-amino salicylic acid, boric acid and ethylene glycol dimethacrylate. The boron and nitrogen codoped carbon quantum dots have high fluorescence intensity, good monodispersity, high stability, superior water solubility, and a fluorescence quantum yield of 19.6%. Their average size is 5 nm. Their maximum excitation and emission wavelengths are 380 and 520 nm, respectively. Permanganate (MnO 4 − ) quenched boron and nitrogen codoped carbon quantum dots fluorescence through inner filter effect and static quenching effects. The linear relation between quenching efficiency and MnO 4 − concentration ranged from 0.05 to 60 μmol/L with a detection limit of 13 nmol/L. In the presence of captopril, MnO 4 − was reduced to Mn 2+ and the fluorescence of boron and nitrogen codoped carbon quantum dots was recovered. The linear range between recovery and captopril concentration was from 0.1 to 60 μmol/L. The limit of detection was 0.03 μmol/L. The developed method can be employed as a sensitive fluorescence sensing platform for MnO 4 − . It has been successfully used for captopril detection in mouse plasma.

S,N-Codoped carbon quantum dots (SNCQDs) with a quantum yield (QY) of 23% have been synthesized using lotus root as a carbon source and glutathione (GSH) as a nitrogen and sulfur source. The obtained SNCQDs exhibited many excellent features such as a simple preparation process, high fluorescence QY, satisfactory photostability, superior water solubility, and biocompatibility. The SNCQDs combined with Cu 2+ were used as a novel off− on nanoprobe for 6-thioguanine (TG). Initial fluorescence is significantly quenched in this sensing system via electron transfer from SNCQDs to Cu 2+ . Fluorescence is recovered after adding TG owing to Cu 2+ −TG complex formation between Cu 2+ and TG. A novel off−on fluorescent nanoprobe was presented for highly sensitive determination of TG. Under optimal conditions, the nanoprobe exhibited a wide linearity range of 0.005−80 μmol/L for TG and a detection limit of 1.6 nmol/L. The designed off−on nanoprobe was successfully utilized for detecting TG in plasma and urine of a leukemia patient and imaging of TG in living T24 cells.

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