Highly Reversible "Off-On-Off" Dual-channel Fluorescence Probe Based on Amino Pyrazole and Phenothiazine for Sensing Extremely Alkaline Solution

Acid-base balance is related to many cell functions, and its disorders can lead to many diseases. Real-time detection of intracellular pH fluctuation is very important to prevent many diseases and environmental water samples. Here, we report a dual-channel fluorescence probe PTZ-aminopyrazole based on low-cost phenothiazine and 3-aminopyrazole, which can detect pH fluctuation highly sensitively through protonation under acidic condition and deprotonation under alkaline condition. The probe exhibits a fluorescence intensity and UV absorbance characteristics in the extreme acidity range of 2.6-5.5 and especially in the extreme alkaline range of 11.1-13.8, respectively. In addition, PTZ- aminopyrazole has high pH-selective reaction to metal ions, good reversibility and excellent photostability. Furthermore, PTZ-aminopyrazole can be fixed on a test paper, which shows a rapid and reversible colorimetric response to HCl/NaOH vapor with naked-eye.