Intracellular K+plays an important role in apoptotic process.However,real-time concentration changes of mitochondrial K+during cell apoptosis remained unknown,thus the relationship between apoptosis and mitochondria K+are difficult to explore.Herein,the first mitochondria-targeting NIR fluorescent sensor(TAC-Rh)was designed and developed,which consisted of rhodamine analogs as the fluorophore and triazacryptand(TAC)as K+recognition unit.