Recent advances in fluorescent probes for extracellular pH detection and imaging

Extracellular pH plays vital roles in physiological and pathological processes including tumor metastasis and chemotherapy resistance. Abnormal extracellular pH is known to be associated with various pathological states, such as those in tumors, ischemic stroke, infection, and inflammation. Specifically, dysregulated pH is regarded as a hallmark of cancer because enhanced glycolysis and poor perfusion in most solid malignant tumors create an acidic extracellular environment, which enhances tumor growth, invasion, and metastasis. Close connection between the cell functions with extracellular pH means that precise and real-time measurement of the dynamic change of extracellular pH can provide critical information for not only studying physiological and pathological processes but also diagnosis of cancer and other diseases. This review highlights the recent development of based fluorescent probes for extracellular pH measurement, including design strategies, reaction mechanism and applications for the detection and imaging of extracellular pH.