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A dual-mode pH sensor based on nitrogen-doped carbon dots (N-CDs) with the source of o-phenylenediamine and tryptophan has been constructed. Under the stimulation of pH, the N-CDs exhibited prominent both color and fluorescence changes, leading to the rarely discovered colorimetric and fluorescent dual-readouts for the evaluation of pH. The mathematic relationship was established between pH and fluorescence intensity of N-CDs, and between pH and the UV–Vis absorbance ratio at 630 nm and 488 nm of N-CDs, respectively, over a quite broad pH range of 2.2 to 12.0. Multiple techniques are used to explore the dual-mode pH-responsive mechanism, and the preliminary explanation is put forward. The experimental results show that the N-CDs have visualized pH sensing applicability for actual samples, including various water samples and HeLa cell. Furthermore, the N-CD ink is developed for successful information encryption and anti-counterfeiting. This work might provide valuable insights into the sensing mechanism of CDs, and the application potential of CDs in broader fields. [ABSTRACT FROM AUTHOR]

Oxoisoaporphine (OA) is a plant phototoxin isolated from Menispermaceae, however, its weak fluorescence and low water solubility impede it for theranostics. We developed here 4-hydroxyl-oxoisoaporphine (OHOA), which has good singlet oxygen-generating ability (0.06), strong fluorescence (0.72) and improved water solubility. OHOA displays excellent fluorescence for cell imaging and exhibits light-induced cytotoxicity against cancer cell. In vitro model of human cervical carcinoma (HeLa) cell proved that singlet oxygen generated by OHOA triggered photosensitized oxidation reactions and exert toxic effect on tumor cells. The MTT assay using HeLa cells verified the low cytotoxicity of OHOA in the dark and high phototoxicity. Confocal experiment indicates that OHOA mainly distributes in mitochondria and western blotting demonstrated that OHOA induces cell apoptosis via the mitochondrial pathway in the presence of light. Our molecule provides an alternative choice as a theranostic agent against cancer cells which usually are in conflict with each other for most traditional theranostic agents. [ABSTRACT FROM AUTHOR]

Biothiols, including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play key roles in biological processes, and detecting such thiols selectively is critical for understanding functions of biothiols. In this work, a pyridazine annelated perylene–based fluorescent probe PAPC is synthesized for highly selective detection of Cys. PAPC exhibits strong blue emission in PBS, while the red emission at 605 nm can be observed in the presence of Cys. The probe PAPC shows ratiometric fluorescence (I605/I460) detection of Cys with wide linear range of 1–120 μM and low detection limit of 0.19 μM. Super large Stokes shift (170 nm) and ratiometric fluorescence endow the probe low background signal. The discrimination of Cys over Hcy and GSH can be achieved through the difference of the ratiometric fluorescence. In addition, the probe has been proven to track Cys in real samples such as urine and HeLa cells. Therefore, PAPC probe is a promising candidate for detecting Cys in practical application. [ABSTRACT FROM AUTHOR]

Fluorescence detection of H2S in living organisms is greatly advantageous because it is nondestructive and can be used for in situ analysis. We have constructed a novel rhodamine analogue dye (Rho630) by extending the conjugated system of rhodamine to create a novel cell-trappable H2S fluorescent probe Rho630-AM-H2S with red light emission. Its application for H2S fluorescence detection in living HeLa cells and zebrafish was investigated. As expected, Rho630-AM-H2S showed a huge fluorescence turn-on response of about 20-fold at 630 nm and good selectivity toward H2S in solution. An MTT assay demonstrated that the probe showed negligible cytotoxicity in the concentrations typically used in fluorescence imaging experiments. Cell imaging experiments revealed that compared with compound 4 without cell-trappable unit modification, Rho630-AM-H2S exhibited remarkably enhanced cell penetration ability, as an enormous fluorescence signal increase was observed at the red channel within 5 min after Rho630-AM-H2S was incubated with HeLa cells. Finally, the probe Rho630-AM-H2S was used to detect H2S in living HeLa cells and zebrafish with great fluorescence enhancement in the red channel. [ABSTRACT FROM AUTHOR]

On account of long wavelength emission and high stability, a hemi-cyanine skeleton of 2,3,3-trimethyl-1-(3-sulfopropyl)-3H-benzo[f]indolinium was condensed with 6-hydroxy-7-morpholin-4-yl-methyl-naphthalene-2-carbaldehyde in the presence of acetic anhydride. The new probe displays a sensitive absorption and fluorescence according to the pH value changes and exhibits an excellent linearity of the relative emission intensity (I670/I580) vs. pH in the pH range of 7.0–9.5 with a correlation coefficient of 0.993. Moreover, compared to the commercialized LysoTracker Green DND-26 the probe is targeting to the lysosomal imaging in HeLa cells and, thus, can be further used as a near-infrared fluorescent probe for cellular research. [ABSTRACT FROM AUTHOR]

As a structural analogue of pyridylthiazole, 2-(2-benzothiazoyl)-phenylethynylquinoline (QBT) was designed as a fluorescent probe for Hg(II) based on an intramolecular charge transfer (ICT) mechanism. The compound was synthesized in three steps starting from 6-bromo-2-methylquinoline, with moderate yield. Corresponding studies on the optical properties of QBT indicate that changes in the fluorescence ratio of QBT in response to Hg(II) could be quantified based on dual-emission changes. More specifically, the emission spectrum of QBT before and after interactions with Hg(II) exhibited a remarkable red shift of about 120 nm, which is rarely reported in ICT-based fluorescent sensors. Finally, QBT was applied in the two-channel imaging of Hg(II) in live HeLa cells. [ABSTRACT FROM AUTHOR]

Fluorescence recognition of Zn in 100 % aqueous medium using 2-((1, 3 dihydroxy-2-(hydroxymethyl)propan-2 ylimino) methyl) phenol (SALTM) as ratiometric probe is reported. Moreover, SALTM can discriminate Zn from Cd very effectively. The binding constant and detection limit of the probe for Zn is 2.2 × 10 M and 2.79 × 10 M respectively. Interestingly, corresponding naphthalene derivative (HNTM) having less water solubility fails to be a ratiometric sensor. SALTM can detect intracellular Zn in HeLa cervical cancer cells under fluorescence microscope. Moreover, DFT and TD-DFT studies support experimental findings. [ABSTRACT FROM AUTHOR]