Highly Sensitive Fluorescence Molecular Switch for the Ratio Monitoring of Trace Change of Mitochondrial Membrane Potential.

As one of the earliest events in apoptosis, trace change of mitochondrial membrane potential (MMP) greatly affects cell health. The local MMP, as an intracellular variable factor, differs considerably from one area to another in an extremely fine cell structure-mitochondrial membrane, which increases the difficulty for the real-time monitoring of MMP trace change in living cells. More regrettably, so far, no ratio fluorescence probe for MMP is available. Such a probe is a kind of precision analysis tool that detects a trace change of MMP in the complex biological systems at subcellular level. In this study, a molecular switch (hemicyanine derivative, TPP-CY) was reported as a ratio fluorescence probe for real-time detection of trace change of MMP in living cells. Given the formation of the "C-O" bond in the probe molecule, the probe exhibits a remarkable ratio of fluorescence intensity change (I563/I663) within seconds during the response process for MMP, that is, TPP-CY transforming to TPP-SP. Furthermore, TPP-CY at a low concentration (0.23 μM) can present extremely high sensitivity for the trace change of MMP in living cells. The detection limit can be as low as -0.16 mV. More importantly, a trace change of MMP and mitochondrial morphology at the subcellular level during cell apoptosis can be accurately monitored by TPP-CY with excellent selectivity and high resolution. TPP-CY could be used as a potential tool for evaluating cell health.