The smartphone-assisted fluorescent and colorimetric dual-mode sensor based on novel graphitic carbon nitride quantum dots for environmental sensing and bioimaging of hypochlorite

The novel graphitic carbon nitride quantum dots (g-C₃N₄ QDs) as dual-mode sensor for fluorescent and colorimetric detection of hypochlorite (ClO^-) was prepared via a low-temperature solid thermal polymerization method. g-C₃N₄ QDs exhibited yellow fluorescence at 518 nm. Upon reaction with ClO^-, the -NH₂ groups on the QDs surface were oxidized to N=O, leading to static quenching and a decrease in absorbance. Based on this mechanism, g-C₃N₄ QDs were used as a dual-mode sensor for ClO^- with a response time of only 10 s. A linear range of 0.1-70 μM and detection limit of 32 nM (fluorescent method) and 37 nM (colorimetric method) were acquired. Interestingly, the smartphone-integrated sensing platform can portably and visually evaluate ClO^- changes due to sensitive color changes. This functionality was complemented by its successful application in complex real-world samples, including tap water, swimming pool water, and 84 disinfectants, demonstrating robust practical utility. g-C₃N₄ QDs were applied to visualize ClO^- in cells, zebra fish and a tumor-bearing mouse model. This work presented a novel approach for synthesizing g-C₃N₄ QDs and dual-mode rapidly monitoring ClO^- in environment. Moreover, g-C₃N₄ QDs was expected as a potential tool for early diagnosis of cancer via monitoring ClO^-.