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Ulcerative colitis, a kind of inflammatory bowel disease (IBD), is caused by dysregulated immune response of intestinal bacteria. This chronic disorder can lead to a deficiency of O

Ulcerative colitis is a prevalent inflammatory disease caused by the intestinal bacterial infection. And it is related to the hypoxic degrees in the colon microenvironment. Hypoxia, a condition of imbalance in O

Mitophagy, a mitochondria-selective autophagy process, plays critical roles in maintaining intracellular homeostasis by removing the damaged mitochondria and recycling the nutrients in a lysosome-dependent manner. Mitophagy process could result in the changes of mitochondrial pH. So fluorescent probes for detecting mitochondrial pH during mitophagy are highly needed for exploring the functions of mitochondria. Herein, a series of near-infrared pH probes were designed based on the rhodamine framework. The probes showed high sensitivity for pH with the tunable pKa from 4.74 to 6.54. Particularly, for probe 5 (with the pKa of 6.54), a linear relationship between fluorescence intensity and pH in the range of 5.6-7.2 was observed, which was suitable for mitochondrial pH detection. The probe displayed excellent mitochondria-targeting ability. It was applied to monitor pH changes during mitophagy caused by starvation. Besides, in vivo non-invasive visualization of tumor pH variations was achieved via the fluorescence imaging in the near-infrared region. We anticipate that the probe may be a useful tool for revealing essential information about mitophagy-related research and clinical tumor diagnosis.

Cyanide (CN

Mitochondria are the powerhouses in cells, providing the energy needed for cellular activities. However, the abnormalities in the mitochondrial microenvironment (e.g., the increased viscosity) can lead to mitochondrial dysfunctions and diseases. Herein, we develop a series of near-infrared (NIR) fluorescence probes for the detection of viscosity. After screening, probe CQ-4 is selected since it shows a great fluorescence enhancement (89-fold) in the NIR window. Its specific response to viscosity is not influenced by pH, polarity and biological species. Under stimulation with monensin or nystatin, CQ-4 can measure the cellular viscosity changes with good biocompatibility. In addition, we can observe an increase of viscosity during starvation. CQ-4 is applied to distinguish cancer cells from normal cells based on the viscosity differences. Furthermore, the probe has been successfully applied to image viscosity in inflamed and tumor-bearing mice in vivo. Therefore, CQ-4 may contribute to the future study about viscosity in the physiological and pathological processes.

Cyanide (CN−) is a highly toxic compound that exists in many substances and is harmful to the environment and human health. Therefore, it is of great significance to develop excellent CN− ion probes, especially solvent-induced on–off fluorescent probes. Based on the condensation reaction of indolo[2,1-b] [1] , [3] oxazine molecules with aldehydes, probes (E)-13a-(2-(9-ethyl-9H-carbazol-3-yl)vinyl)-14,14-dimethyl- 10-nitro-13a,14-dihydro-8H-benzo[e]benzo [5] , [6] , [1] , [3] oxazino[3,2-a]indole (NCO) and (E)-13a-(2-(9-benzyl-9H-carbazol-3-yl)vinyl)-14,14-dimethyl-10-nitro-13a,14-dihydro-8H-benzo[e]benzo [5] , [6] , [1] , [3] oxazino[3,2-a]indole (NBO) were synthesized to detect CN−. Compared with other cyanogen ion probes, NCO and NBO have special carbazole ring structures and large conjugate systems. When CN− is added to the probe-detection solution, color changes that are visible to the naked eye can occur. The UV–vis spectrum test using differential spectroscopy shows that the probe (i) has excellent solvent-induced switching characteristics and stability (CH3OH–H2O) and (ii) high selectivity, anti-interference ability, and sensitivity for the detection of CN−. The fluorescence limit of detections (LODs) are 1.05 µM for NCO and 1.34 µM for NBO. The UV LODs are 0.83 µM for NCO and 0.87 µM for NBO. Fluorescence spectroscopy shows that the probe has remarkable fluorescence properties. Fluorescence titration experiments, liver cancer cell (Hep G2) imaging, and cytotoxicity experiments all show that the probes have high biocompatibility, low toxicity, high cell permeability, and high sensitivity for the detection of CN− in cells. In addition, NCO and NBO have been successfully used for the detection of cyanogenic glycosides in the seeds of ginkgo, crabapple, apple, and cherry. Test strips were fabricated to detect CN−. After adding CN−, the color of the test strip changed significantly—from brown to light yellow; thus, the test strips have a high application value in the fields of drug quality control, drug safety testing, and pharmacological research.

A colorimetric fluorescence probe 1-nitro-(8-ethylene-11- (14-diethylaminophenyl)-benzoindo oxazine (ZBO) based on indoleoxazine structure was prepared for detection of cyanide ions (CN−). The introduction of UV difference spectroscopy provides a guarantee for the accuracy of CN− detection. Results indicate that ZBO can achieve the desired recognition of CN− with excellent anti-interference performance. The minimum detection concentration of CN− is 0.1 μM. For practical applications, ZBO test strips were prepared for the convenient and qualitative detection of CN−. The low-concentration solution of ZBO can facilitate the qualitative detection of CN− in peach kernel, loquat seed, and cassava samples. In addition, low cytotoxicity and cell imaging experiments suggested that ZBO can be used for detect CN− in living cells.

Nitroreductase (NTR) is a highly expressed endogenous enzyme in hypoxic tumor cells, which is associated with the hypoxic degree in tumors. Therefore, it is particularly important to develop low-toxicity and high-sensitivity fluorescent probes for NTR. Herein, we report an NTR-activated near-infrared probe with good selectivity and sensitivity. More importantly, the background fluorescence signal is effectively reduced due to the quenching effect of nitro group as well as the spironolactone (ring-closed) form of rhodamine moiety. Upon reaction with NTR, the probe exhibits a remarkable fluorescence off-on response at 740 nm (about 32-fold intensity enhancement), with an extremely low detection limit of 1.09 ng/mL. Moreover, the probe is able to target mitochondria. With this probe, we have achieved the visualization of NTR overexpression in hypoxic cancer cells, as well as in hypoxic tumors in vivo as revealed in the tumor-bearing mouse model. By using this probe, some essential information may be revealed about hypoxia-relevant diseases.

As a member of the reactive oxygen species, hydrogen peroxide (H2O2) plays critical roles in oxidative stress and cell signaling. Intracellular abnormal levels of H2O2 production are closely related to many diseases. Therefore, the real-time monitoring of H2O2 in the cells is important. In this work, we designed a novel fluorescent probe (Mito-H2O2) for the specific detection of H2O2 based on the hemicyanine skeleton, with bright near-infrared fluorescence emission. Mito-H2O2 displayed fast response, excellent water-solubility and great fluorescence intensity enhancement after the addition of H2O2. Furthermore, Mito-H2O2 has been successfully applied to image both of the exogenous and endogenous H2O2 in cells and mice with negligible cytotoxity.