Amphiphilic copolymer fluorescent probe for mitochondrial viscosity detection and its application in living cells

The mitochondrial viscosity measurement with the amphiphilic copolymer fluorescent probe (PP) has been successfully revealed for the first time. PP was synthesized, starting from a hydrophobic rhodamine derivative fluorophore and hydrophilic 2-hydroxyethyl acrylate (HEA) by radical polymerization, which could be used to detect mitochondrial viscosity specifically. The systematic investigation demonstrated that the fluorescence emission of PP with a deep red emission increased about 9-fold when the medium is changed from methanol to 99% glycerol, indicating high viscosity dependence. Moreover, PP could self-assemble into nanospheres with the particle size of about 140 nm in water and the nano-structure enabled PP to enter living cells quickly. Cytotoxicity test showed that the cells survival rate remained above 70% at 70 μg·mL^-1 of PP. Good biocompatibility and low cytotoxicity of PP are promising to provide a high contrast fluorescence imaging. Taken together, the results point the way to development of novel amphiphilic copolymer fluorescent probes-based the detection in solutions, physiology and pathology.