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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.

In this paper, we synthesized a ratiometric fluorescence probe (IRh-Ly) for lysosomal hypochlorous acid (HOCl) by adopting a through-bond energy transfer (TBET) strategy on rhodamine-imidazo[1,5-a]pyridine platform. IRh-Ly showed brilliant selectivity, rapid response for HOCl. The probe also exhibited high sensitivity with the detection limit calculated to be 10.2 nM. Moreover, we demonstrated its successful application of detecting lysosomal HOCl in living RAW264.7 cells. Notably, the morpholine was integrated into the fluorescent probe IRh-Ly and the results revealed that IRh-Ly could target lysosome and detect the lysosomal HOCl. All the unique features made IRh-Ly particularly suitable for ratiometric HOCl detection and bio-imaging applications.

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.

Hypochlorite (−OCl) has long been recognized as an effective microbicidal agent in immune system. Herein, we report the design, preparation and spectral characteristics of a −OCl fluorescent probe (FI-Mito). The probe exhibited remarkable fluorescence turn-on signal in the red region upon −OCl titration with the detection limit as low as 0.9 nM. FI-Mito displayed specific response for −OCl in completely aqueous solution. Meanwhile, the introduction of quaternized pyridine realized mitochondria-targeting ability. FI-Mito was further applied to monitor the generation of endogenous −OCl in the mitochondria of macrophage cells and mice. Therefore, it was established that FI-Mito may serve as a useful molecular tool for −OCl detection in vivo.

In this study, a novel ratiometric pH probe RNL based on fluorescence resonance energy transfer (FRET) was well developed. It was fabricated by integrating the naphthalimide moiety as an FRET donor with the rhodamine moiety as an FRET acceptor. Meanwhile, 4-(2-aminoethyl)morpholine, which was a lysosome-locating group, was introduced. The sensing mechanism was the integration of PET and FRET processes and the comprehensive effect led to the simultaneous intensity enhancement of naphthalimide and rhodamine along with the pH value decrease. With a pKa of 4.82, the fluorescence intensity ratio (I529/I580) of the probe changed significantly within the pH range from 4.50 to 5.50. The probe showed excellent selectivity among various metal cations, amino acids and ATP. Moreover, RNL has been successfully applied in HeLa cells, and the results demonstrated that it could be used to detect lysosomal pH changes. The probe could also selectively stain lysosome in HeLa cells. Besides, the probe exhibited low cytotoxicity and satisfactory photostability in living HeLa cells.

A novel rhodamine B-based fluorescent probe (RML) for lysosomal pH was developed by integrating a 4-(2-aminoethyl)morpholine moiety, which is a lysosome-targetable group, into a rhodamine B fluorophore, which is associated with rhodamine B dyes possessing spirocyclic (non-fluorescent) and ring-opening (fluorescent) forms with response to pH. The probe responded to acidic pH at low concentration in a short amount of time. In addition, RML showed good membrane permeability and brilliant selectivity among various amino acids and metal cations. RML exhibited an 80-fold increase in fluorescence intensity at 583 nm throughout the pH range of 7.40–4.00 with a pKa of 5.16, which indicates that RML is valuable for studying intracellular acidic organelles. Moreover, RML has been successfully applied in HeLa cells, and the results demonstrated that RML could selectively stain lysosomes in living HeLa cells. Note that RML could be used to detect the pH increase in lysosomes induced by bafilomycin A1 within HeLa cells.

Heat shock is a potentially fatal condition characterized by high body temperature (>40 °C), which may lead to physical discomfort and dysfunctions of organ systems. Acidic pH environment in lysosomes can activate enzymes, thus facilitating the degradation of proteins in cellular metabolism. Owing to the lack of a practical research tool, it remains difficult to exploit relationship between heat shock and lysosome. Herein, a NIR lysosomal pH chemosensor (NRLH) was developed. One typical lysosome-locating group, morpholine, was incorporated into NRLH. The fluorescence intensity showed pH-dependent characteristics and responded sensitively to pH fluctuations in the pH range of 3.0–5.5. NRLH with a pKa of 4.24 displayed rapid response and high selectivity for H+ among common species. We also demonstrated NRLH was capable of targeting lysosomes. Importantly, NRLH was applied in cellular imaging and the data revealed that lysosomal pH increased but never decreased during the heat shock. Therefore, NRLH may act as an effective molecular tool for exploring the mechanisms of heat-related pathology in bio-systems.

A ratiometric fluorescent probe (RIL) for imaging lysosomal HOCl was prepared, which was designed based on the imidazo[1,5-a]pyridine-rhodamine platform. The probe’s selectivity was excellent, and the detection was not affected by other analytes. Probe RIL responded to HOCl rapidly with a low detection limit of 27 nM. For the biological application, RIL performed well in detecting endogenous HOCl in RAW264.7 cells. Furthermore, the probe could target lysosomes and monitor lysosomal HOCl changes due to the introduction of morpholine moiety, which was identified as a lysosome-targeting group. We believe that RIL had significant potential as a practical molecular tool for HOCl-related research in lysosomes.

A near-infrared fluorescent probe (NRL) for lysosomal pH was presented by integrating 4-(2-aminoethyl)morpholine moiety, a lysosome-targetable group, into the rhodamine derivative. The addition of H+ led to significant fluorescence intensity increase at 739 nm, thus enabling it to monitor pH changes at weakly acidic pH. NRL showed negligible response to common species and short response time. Furthermore, the probe was successfully applied in living cells, and the results indicated that the probe could target lysosomes and detect lysosomal pH. We believe that NRL had great potential as a practical tool for lysosomal pH biology.

A novel ratiometric fluorescent probe ( RIM ) for HOCl was designed on imidazo[1,5 -a ]pyridine-rhodamine FRET platform. Upon addition of HOCl, the imidazo[1,5 -a ]pyridine fluorescence increased and the rhodamine fluorescence increased simultaneously. The ratios (I 585 /I 465 ) displayed brilliant HOCl-dependent performance and responded linearly to HOCl. RIM could respond to HOCl rapidly (within 20 s) with a low detection limit of 24 nM RIM also exhibited high selectivity, and low cytotoxicity. Moreover, it has been successfully applied in fluorescence imaging in living cells and the results confirmed that the probe could selectively stain lysosomes with excellent photostability.

In this study, a new fluorescent probe (LR1) for lysosomal HOCl was developed by integrating a morpholine moiety, a lysosome-targeting group, into the rhodamine framework. LR1 exhibited remarkable fluorescence intensity enhancement at 582 nm upon HOCl titration with a low detection limit (2.6 nM), which indicated that the probe may be capable of monitoring HOCl fluctuations at trace levels. Moreover, the probe was applied in cellular fluorescence imaging, and the results demonstrated that it could sense endogenous HOCl with low cytotoxicity in RAW264.7 cells. In addition, LR1 was found to be capable of monitoring HOCl changes in lysosomes owing to the introduction of morpholine, which served as a lysosome-targeting group. We expect that the probe has great potential as a practical molecular tool for exploring HOCl-related biology in lysosomes.

An imidazo[1,5-a]pyridine-rhodamine-based ratiometric fluorescent probe was designed and successfully synthesized. The probe shows a large Stokes shift (204 nm), high sensitivity and high selectivity. The detection limit was calculated to be as low as 0.93 nM. The probe could quickly (5 min) detect Hg 2+ over a wide pH range from 4 to 10. Furthermore, it could be used for imaging Hg 2+ in living cells.

A novel pyrido[1,2-a]benzimidazole-rhodamine ratiometric fluorescent probe TMUHg-3 for Hg 2+ based on a fluorescence resonance energy transfer mechanism has been developed. In this system, the energy transfer efficiency is 87.3%. The probe can detect Hg 2+ with a very low detection limit of 18.8 nM, and very high selectivity toward Hg 2+ . Furthermore, it can be used for imaging Hg 2+ in living cells.

In this study, a benzo[e]indole[2,1-b][1,3]benzooxazine derivative 2-nitro-5a-(2-(2-thiophene)-ethylene)-6,6-dimethyl-5a,6-dihydro-12H-benzo[e]indolo[2,1-b][1,3]benzooxazi-ne (TEO) was explored as a sensitive probe for CN−. Unlike conventional spiropyrans that possess a 3H-benzo[e]indole cation and a 4-nitrophenolate anion in the same conjugated structure, TEO enhances the positive charge of the 3H-benzo[e]indole cation, which considerably improves its sensitivity and reaction speed. UV–visible spectrophotometry was used to detect CN− with a detection limit of 0.1 μM and a rate constant of 0.528s−1. In this study, TEO probe showed high selectivity and sensitivity to CN−. Therefore, this probe allows overcoming the limitations of prevailing techniques against the S2− interference. In addition to UV titration for the determination of CN−, we also added fluorescence titration experiments. CN− of 0.1 μM can also be detected by fluorescence titration. Moreover, the probe was successfully used to detect amygdalin content in almonds. Compared with high-performance liquid chromatography (HPLC), this method avoids the complexity of the extraction process and the interference of polar components. Furthermore, the results are consistent with those obtained by the HPLC method.

A ratiometric fluorescent probe (NR) for HOCl based on a new naphthalimide-rhodamine platform involving through-bond energy transfer (TBET) process is presented. Rhodamine B thiohydrazide and naphthalimide derivative were linked to form a structure of monothio-bishydrazide. Free NR only emitted the fluorescence of naphthalimide. The treatment of NR with HOCl converted the monothio-bishydrazide into 1,2,4-oxadiazole. As a result, naphthalimide donor and rhodamine acceptor were connected with electronically conjugated bonds, and the spiro ring of rhodamine was opened. Hence, a typical TBET process took place, resulting in the increase of rhodamine emission at 582 nm as well as the decrease of naphthalimide emission at 532 nm. I582/I532 ratios showed desirable HOCl-dependent performance and responded linearly to minor changes of HOCl concentration (0–5 μM). The detection limit was determined to be 14.5 nM. NR exhibited high selectivity, rapid response and low cytotoxicity. Moreover, NR has been employed for the imaging of artificially loaded HOCl and endogenously produced HOCl with satisfying results. Therefore, NR may act as a practical molecular tool for monitoring HOCl fluctuations in biological systems.

A novel fluorophore pyrido[1,2-a]benzimidazole was synthesized and used as a donor to construct FRET system. The probe shows a large Stokes shifts (190 nm), high selectivity, fast response (within 2 min), and high sensitivity toward Cu2+ (detection limit 42 nM). A significant colour change from colourless to pink could be observed, enabling naked-eye detection of Cu2+. Furthermore, it could be used for imaging Cu2+ in living cells which demonstrated its value of practical applications in biological systems.

In this study, a ratiometric fluorescent probe (IRP) for −OCl was designed based on the fluorescence resonance energy transfer (FRET) platform. The probe was fabricated by integrating an imidazo[1,5-a]pyridine moiety (donor) with a rhodamine moiety (acceptor). We evaluated its properties for recognizing −OCl and the results implied that IRP possessed high selectivity, a real-time detection possibility and brilliant photostability. The fluorescence intensity ratios (I575/I467) of IRP displayed desirable −OCl-dependent performance and responded linearly to −OCl in the concentration range of 0.5–3.5 μM. Also, IRP was applied to image endogenous −OCl with a mitochondria-targeting ability, due to the introduction of the quaternized pyridine moiety. Therefore, IRP may be used for further mitochondrial −OCl-related studies.

An indolizine–rhodamine-based ratiometric fluorescent probe was designed and successfully synthesized. The probe shows a large Stokes shift (204 nm), high sensitivity and high selectivity. The detection limit was calculated to be as low as 8.76 nM. The probe could quickly (5 min) detect Hg2+ over a wide pH range from 5 to 10. Furthermore, it could be used for imaging Hg2+ in living cells.

A new fluorophore pyrido[1,2-a]benzimidazole was synthesized and used as a ratiometric fluorescent probe based on an intramolecular charge transfer (ICT) mechanism for sensing sulfite. The probe showed high selectivity and sensitivity toward SO32− with a fast response time (10 s) and a detection limit of 10.6 nM. Furthermore, the probe showed great potential for the detection of SO32− in real samples (dry white wine).

A novel ratiometric probe (RCP) for -OCl was developed based on the fluorescence resonance energy transfer (FRET) platform. The probe was constructed by integrating the coumarin moiety (FRET donor) with the rhodamine moiety (FRET acceptor). Upon treatment with -OCl, the coumarin emission at 483 nm decreased and the rhodamine emission at 570 nm increased, enabling the probe to provide accurate detection of -OCl (in the concentration range of 0-50 μM). The probe exhibited brilliant selectivity and sensitivity, rapid response and low cytotoxicity. More importantly, the introduction of the quaternized pyridine moiety can not only manage to increase the solubility, but also achieve mitochondria-targeting. The probe was applied successfully to imaging endogenous -OCl in mitochondria, highlighting its potential applications in bioanalysis.

A new fluorescence probe (PML) for sensing HSO3− was developed based on a Michael addition reaction mechanism. The probe was composed of carbazole and 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene)malononitrile moieties and can be easily synthesized. The carbazole-based probe can selectively detect HSO3− and shows good sensitivity with the limit of detection of 2.08 × 10−6 M in a PBS : DMF = 1 : 1 buffer solution. Upon addition of HSO3−, the intense fluorescence of the probe was quenched, and the color markedly changed from red to colorless. In addition, the probe can be used to detect HSO3− in dry white wine.

In this paper, ratiometric imaging of lysosomal HOCl was realized with a molecular probe (CR-Ly) based on fluorescence resonance energy transfer by using coumarin as the donor and rhodamine as acceptor. CR-Ly showed high sensitivity and fast response to HOCl. Moreover, CR-Ly exhibited excellent selectivity and sensitivity for HOCl over other biologically relevant species. Furthermore, it was successfully utilized to image the endogenous HOCl with low cytotoxity. And CR-Ly was capable of targeting lysosomes and monitoring lysosomal hypochlorous acid changes owing to the presence of the morpholine moiety. We believe that probe CR-Ly would be helpful to further research on the HOCl-associated diseases in lysosomes.

A rhodamine B-based derivative (RL1) was developed as a specific fluorescent probe for HOCl. Meanwhile, morpholine moiety was introduced into the probe. It was found that the probe could display highly selective, sensitive and naked-eye detection upon the addition of HOCl. And the detection limit (LOD) was calculated to be as low as 2.8 nM. Furthermore, cellular confocal microscopic studies revealed that the introduction of morpholine moiety realized the lysosome-targeting capability. Moreover, RL1 was successfully applied for the imaging of endogenous HOCl with low cytotoxicity. Therefore, all the desirable features made probe RL1 particularly suitable for HOCl detection in aqueous buffer solution samples as well as the bio-imaging applications.

In this study, we developed a coumarin–rhodamine based fluorescence resonance energy transfer (FRET) system RC1 as a ratiometric pH probe. The probe with a pKa of 4.98 was constructed by integrating a coumarin moiety as an FRET donor with a rhodamine moiety as an FRET accepter. Upon addition of H+, the coumarin emission at 477 nm decreased and the rhodamine emission at 582 nm increased simultaneously. The fluorescence intensity ratio (I477/I582) displayed excellent pH-dependent performance and responded linearly to minor pH changes in the range of 4.20–6.00. The probe exhibited brilliant selectivity among different amino acids, metal cations and the ATP. Moreover, it has been successfully applied in fluorescence imaging in HeLa cells and the results indicated that the probe could selectively stain lysosomes with low cytotoxicity and excellent photostability. We also applied RC1 to monitor intracellular pH variations induced by dexamethasone. Therefore, RC1 could act as a practical tool for the detection of pH in weakly acidic conditions and provide essential information in medicinal analysis and real biological systems.

A new simple-structure fluorescent probe RL based on the special affinity of Pd2+ to double bond ligands has been designed and synthesized. RL shows high selectivity and sensitivity for Pd2+ with a detection limit of 21.3 nM (2.3 ppb) in the presence of other competing metal ions in aqueous media. Furthermore, RL has potential applications in Pd2+ analysis in natural water and in a reactor involving a Pd2+catalytic reaction.