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Oxidative stress, a disturbance in the balance between oxidant/antioxidant ratios, is associated with cancer, aging, inflammation, neurodegenerative diseases and other conditions. γ-Glutamyltranspeptidase (GGT) is a redox-related enzyme that plays a key role in mitigating the effects of oxidative stress by maintaining cellular glutathione (GSH) metabolism and homeostasis. Therefore, oxidative stress will upregulate the intracellular GGT level. To better understand the major pathophysiological resist mechanism to oxidative injury in mediating many disease states, we designed and synthesized a novel two-photon (TP) fluorescent turn-on probe, Np-Glu, for GGT detection and bioimaging. Under the optimized conditions, Np-Glu exhibited remarkable fluorescence enhancement (150-fold), good selectivity and high sensitivity (LOD is 0.033 U L−1), with a wide linear concentration range (0–50 U L−1). More importantly, the probe Np-Glu was successfully applied in one-photon and TP fluorescence imaging of GGT activity in an oxidative stress model in living cells and tissues, suggesting Np-Glu as an ideal indicator for clinical and biological samples. [ABSTRACT FROM AUTHOR]

Cellular self-regulation of reactive oxygen species (ROS) stress via antioxidant repair plays an important role in maintaining the redox balance. The redox balance between reducing and oxidizing species within cells is significant in the regulation of a signal pathway and is achieved by a series of elaborate mechanisms. In this work, we employed our previously reported D–π-A-structured naphthalene–BODIPY TBET platform to design an efficient two-photon fluorescent probe for dynamic monitoring of superoxide anion oxidative stress and the GSH reducing repair process. The probe displayed high energy transfer efficiency (91.4%), large pseudo-Stokes shifts upon one-photon excitation, and red fluorescence emission (λem = 596 nm), which is highly desirable for bioimaging applications. The probe exhibits reversibility, rapid response, good photostability, high selectivity and sensitivity for the superoxide anion and GSH. More importantly, the probe was successfully applied for visualizing the redox changes in living cells and tissues. [ABSTRACT FROM AUTHOR]

Formaldehyde (FA) plays an important role in living systems as a reactive carbonyl species (RCS). An abnormal degree of FA is known to induce neurodegeneration, cognitive decrease and memory loss owing to the formation of strong cross-link DNA and protein and other molecules. The development of efficient methods for biological FA detection is of great biomedical importance. Although a few one-photon FA fluorescent probes have been reported for imaging in living cells, probes excited by two photons are more suitable for bio-imaging due to their low background fluorescence, less photobleaching, and deep penetration depth. In this study, a two-photon fluorescent probe FATP1 for FA detection and bio-imaging in living cells and tissues was reported. The detection is based on the 2-aza-Cope sigmatropic rearrangement followed by elimination to release the fluorophore, resulting in both one- and two-photon excited fluorescence increase. The probe FATP1 showed a high sensitivity to FA with a detection limit of 0.2 μM. Moreover, FATP1 enabled the two-photon bio-imaging of FA in live HEK-293 cells and tissues with tissue-imaging depths of 40–170 μm. Furthermore, FATP1 could be applied for the monitoring of endogenous FA in live MCF-7 cells, presaging its practical applications in biological systems. [ABSTRACT FROM AUTHOR]

Lysosomes are acidic organelles (approximately pH 4.5–5.5) and tracking the changes in lysosomal pH is of great biological importance. To address this issue, quite a few of fluorescent probes have been developed. However, few of these probes can realize the tracking of dynamic changes in lysosomal pH. Herein, we report a new lysosome-targeted ratiometric fluorescent probe (FR-Lys) by hybridizing morpholine with a xanthane derivative and an o-hydroxy benzoxazole group. In this probe, the morpholine group serves as a targeting unit for lysosome, the xanthane derivative exhibits a pH-modulated open/close reaction of the spirocycle, while the o-hydroxy benzoxazole moiety shows a pH modulated excited-state intramolecular proton transfer (ESIPT) process. Such a design affords the probe a ratiometric fluorescence response towards pH with pH values ranging from 4.0 to 6.3. The response of the probe to pH was fast and reversible with high selectivity. Moreover, this probe possesses further advantages such as easy synthesis, high photostability and low cytotoxicity. These features are favorable for tracking dynamic pH changes in biosystems. It was then applied for dynamic imaging pH changes in lysosomes with satisfactory results. [ABSTRACT FROM AUTHOR]

This paper described the optimized design, synthesis and application of a novel rhodamine thiospirolactam derivative as an 'off-on' fluorescent probe for the detection of Hg(2+) in aqueous samples. The 'off-on' fluorescence and color signal change of the probe is based on an Hg(2+)-triggered domino reaction which brings on the opened-ring form of the rhodamine spirolactam to regain the conjugated system of the rhodamine skeleton. In the well designed probe, the thiospirolactam serves as both Hg(2+) binding unit and electron-defect carbon centre, a phenolic hydroxyl with very strong nucleophilicity after deprotonation is chosen as the attacking unit, and a benzene ring is introduced on the linker to afford steric effects, which benefits an efficient nucleophilic reaction, with a high sensitivity towards Hg(2+). It exhibits a stable response for Hg(2+) from 1.0 × 10(-8) to 1.0 × 10(-6) M, with a detection limit of 3.0 × 10(-9) M. The response of the probe to Hg(2+) is highly selective and pH-insensitive, with a fast response time. All these unique features make it particularly favorable for cellular Hg(2+) imaging applications. It has been preliminarily used for highly sensitive monitoring of Hg(2+) levels in living cells with satisfying resolution.