Although a lot of mitochondria-targeting biothiol probes have been developed and applied to cellular imaging through thiol-induced disulfide cleavage or Michael addition reactions, relatively few probes assess mitochondrial GSH with high selectivity over Cys and Hcy and with NIR fluorescence capable of noninvasive imaging in biological samples. In order to monitor mitochondrial GSH with low background autofluorescence, we designed a heptamethine-azo conjugate as an NIR fluorescent probe by introducing a tunable lipophilic cation unit as the biomarker for mitochondria and a nitroazo group as the GSH-selective reaction site as well as the fluorescence quencher. The probe exhibited a dramatic off-on NIR fluorescence response toward GSH with high selectivity over other amino acids including Cys and Hcy. Further application to cellular imaging indicated that the probe was highly responsive to the changes of mitochondrial GSH in cells.

An activatable fluorescent probe from indocyanine was developed for the detection of tumor-enriched γ-glutamyltranspeptidase (γGT). The probe exhibited a dramatic fluorescence enhancement (F/F 0 = 10) as well as a bathochromic shift (>100 nm) upon the treatment of γGT with a low limit of detection of 0.15 unit/L and was further successfully applied as a sensitive probe for γGT in the mouse model of colon cancer.

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