A novel dual-response fluorescence probe (XBT-CN) was developed by using a fluorescence priming strategy for quantitative monitoring and visualization of hydrazine (N₂H₄) and hypochlorite (ClO⁻). With the addition of N₂H₄/ClO⁻, the cleavage reaction of C=C bond initiated by N₂H₄/ClO⁻ was transformed into corresponding hydrazone and aldehyde derivatives, inducing the probe XBT-CN appeared a fluorescence “off-on” response, which was verified by DFT calculation. HRMS spectra were also conducted to confirm the sensitive mechanism of XBT-CN to N₂H₄ and ClO⁻. The probe XBT-CN had an obvious fluorescence response to N₂H₄ and ClO⁻, which caused a significant color change in unprotected eyes. In addition, the detection limits of XBT-CN for N₂H₄ and ClO⁻ were 27 nM and 34 nM, respectively. Interference tests showed that other competitive analytes could hardly interfere with the detection of N₂H₄ and ClO⁻ in a complex environment. In order to realize the point-of-care detection of N₂H₄ and ClO⁻, an XBT-CN@hydrogel test kit combined with a portable smartphone was developed. Furthermore, the portable test kit has been applied to the detection of N₂H₄ and ClO⁻ in a real-world environment and food samples, and a series of good results have been achieved. Attractively, we demonstrated that XBT-CN@hydrogel was successfully applied as an encryption ink in the field of information security. Finally, the probe can also be used to monitor and distinguish N₂H₄ and ClO⁻ in living cells, exhibiting excellent biocompatibility and low cytotoxicity.

In this study, a phenothiazine-based ratiometric fluorescent probe PCHO was developed for highly sensitive and specific detection of hydroxylamine (HA). In the presence of HA, the aldehyde group on the PCHO molecule underwent a specific nucleophilic addition with HA to form an oxime group, accompanied by significant changes in fluorescence from green to blue. This detection mechanism was well supported by ¹H NMR titration, HRMS and DFT calculations. The probe PCHO exhibited high sensitivity for HA detection (LOD was 0.19 μM) with a rapid response time (1 min), high selectivity and strong anti-interference performance. Surprisingly, the probe PCHO could selectively distinguish HA from its similar competing agents such as hydrazine and amines. Moreover, paper strips loaded with PCHO were prepared and combined with a smartphone to achieve point-of-care and visual detection of HA. The probe PCHO was further applied for the detection of HA in real water samples, achieving a recovery rate of 98.90% to 104.86% and an RSD of 0.86% to 2.44%, confirming the accuracy and reliability of the method. Additionally, the probe PCHO was used for imaging analysis of HA in living cells, providing a powerful visualization tool for exploring the physiological functions of HA in vivo.