Revealing Minor pH Changes of Mitochondria by a Highly Sensitive Molecular Fluorescent Probe

Hill-type pH probes

Sensitive detection of the minute and yet pathologically significant pH variation is important and in fact challenging for the conventional pH probes following the Henderson-Hasselbalch equation, i.e., HH-type probes. A paradigm shift to Hill-type pH probes is ongoing. Bestowed by their positive cooperative acid-base chemistry, their pH-responsive profile follows the Hill equation, which exhibits a narrower acid/base transition width than HH-type probes and warrants a higher detection sensitivity. A polymer-based Hill-type pH-responsive material was first developed. More recently, there emerged several distinct small-molecular approaches to achieve Hill-type pH-responsive profiles. They complement the polymer-based sensing materials in applications where membrane permeability is a concern. In this trends article, we rationalize the molecular origins of their positive cooperativity in pH sensing and highlight some interesting proof-of-concept applications. We also discussed future directions of this dynamic research area.

Fluorescence imaging of pathophysiological microenvironments

Abnormal microenvironments (viscosity, polarity, pH, etc.) have been verified to be closely associated with numerous pathophysiological processes such as inflammation, neurodegenerative diseases, and cancer. As a result, deep insights into these pathophysiological microenvironments are particularly beneficial for clinical diagnosis and treatment. However, the monitoring of pathophysiological microenvironments is unattainable by the traditional clinical diagnostic techniques such as magnetic resonance imaging, computed tomography, and positron emission tomography. Recently, fluorescence imaging has shown tremendous advantages and potential in the tracing of pathophysiological microenvironment variations. In this context, a general discussion is provided on the state-of-the-art progress of fluorescent probes for visualizing pathophysiological microenvironments (viscosity, pH, and polarity), since 2016, as well as the future perspectives in this challenging field.

An ESIPT based versatile fluorescent probe for bioimaging live-cells and E. coli under strongly acidic conditions

A BTNN probe undergoes a 146 times increase in fluorescence intensity at 530 nm on lowering the pH from 7.0 to 2.0 and has been deployed for the bioimaging of MG-63 live cells and E. coli bacteria at different pH levels.