Benzothiazole-Based Fluorescent Probe as a Simple and Effective Platform for Functional Mitochondria Imaging

Mitochondrial imaging is crucial for studying disease pathogenesis and diagnosis. However, commercially available mitochondria-specific fluorescent probes are limited due to the difficulty in modifying cationic probes for functional bioimaging of mitochondria. To address this, we prepared a hydroxythiophene-conjugated benzothiazole (BzT-OH) as a platform for the design of functional fluorescent probes. Two probes, BzT-OAc and BzT-OAcryl, were synthesized by substituting the hydroxy group in BzT-OH with acetate and acrylate groups, respectively. BzT-OAc demonstrated blue fluorescence that shifted to green emission after enzymatic cleavage of the acetate group, allowing for monitoring of endogenous esterase activity. BzT-OAcryl showed high selectivity for cysteine at pH > 8.0, owing to its pH-responsive property, and could detect pH perturbations caused by mitochondrial dysfunction. Both probes exhibited high biocompatibility, quantum yield, and large Stokes shifts in mitochondria. BzT-OH can be easily conjugated with other functional groups and substrates of various enzymes for designing fluorescent probes for functional mitochondrial imaging. The photofunctional property of the probe can be changed due to the involvement of the hydroxyl group in the excited state intermolecular proton transfer.