Immobilizable fluorescent probes for monitoring the mitochondria microenvironment: a next step from the classic.

Mitochondria play extremely important roles in supplying energy and maintaining the functions of cells. It is essential to monitor mitochondrial microenvironments that reflect the status of this organelle. In this review, we summarize the major progress in the developments and applications of mitochondrial targetable trackers and probes. The newly emerged immobilizable probes for microenvironments are highlighted, and their values are commented. Generally, cationic dyes with appropriate lipophilicity tend to accumulate in the mitochondria due to charge attraction from the negative potential of inner membranes. Following this rationale, numerous fluorescent MitoTrackers have been developed. These probes provide opportunities to investigate mitochondrial morphology and functions. However, such electrostatic interactions are not always reliable since the mitochondrial potential is highly changeable with mitochondria status. The probes will leave when the mitochondria lose their potential. In other words, conventional mitochondrial probes are not suitable for monitoring unhealthy mitochondria that have abnormal mitochondrial potentials. Kim's, Chen's and our teams proposed, separately, new designs of mitochondrial probes that can be immobilized to mitochondria through covalent bonds and monitor microenvironmental factors, including pH, viscosity, polarity and temperature. We believe that the developing of immobilizable mitochondrial fluorescent probes is valuable for tracking and monitoring mitochondrial status accurately. Therefore, this paper reviews and prospects mitochondria immobilizable fluorescent probes of important microenvironmental factors.