A ratiometric fluorescence probe for bisulfite detection in live cells and meat samples.

The development of reliable probe technology for the detection of bisulfite (HSO3-) in situ in food and biological samples is contributing significantly to food quality and safety assurance as well as community health. In this work, a responsive probe, EHDI, is developed for ratiometric fluorescence detection of HSO3- in aqueous solution, meat samples, and living cells. The probe is designed based on the HSO3- triggered 1,4-addition of electron deficit C = C bond of EHDI. As a result of this specific 1,4-addition, the π-conjugation system was destructed, resulting in blue shifts of the emission from 687 to 440 nm and absorption from 577 to 355 nm. The probe has good water solubility, high sensitivity and selectivity, allowing it to be used for imaging of HSO3- internalization and production endogenously. The capability of probe EHDI for HSO3- was then validated by traditional HPLC technology, enabling accurately detect HSO3- in beef samples. The successful development of this probe thus offers a new tool for investigating HSO3- in situ in food and biological conditions.

Recent Advances in Detection of Hydroxyl Radical by Responsive Fluorescence Nanoprobes.

Hydroxyl radical (•OH), a highly reactive oxygen species (ROS), is assumed as one of the most aggressive free radicals. This radical has a detrimental impact on cells as it can react with different biological substrates leading to pathophysiological disorders, including inflammation, mitochondrion dysfunction, and cancer. Quantification of this free radical in-situ plays critical roles in early diagnosis and treatment monitoring of various disorders, like macrophage polarization and tumor cell development. Luminescence analysis using responsive probes has been an emerging and reliable technique for in-situ detection of various cellular ROS, and some recently developed •OH responsive nanoprobes have confirmed the association with cancer development. This paper aims to summarize the recent advances in the characterization of •OH in living organisms using responsive nanoprobes, covering the production, the sources of •OH, and biological function, especially in the development of related diseases followed by the discussion of luminescence nanoprobes for •OH detection.

Isomorphic Insertion of Ce(III)/Ce(IV) Centers into Layered Double Hydroxide as a Heterogeneous Multifunctional Catalyst for Efficient Meerwein-Ponndorf-Verley Reduction.

The development of highly active acid-base catalysts for transfer hydrogenations of biomass derived carbonyl compounds is a pressing challenge. Solid frustrated Lewis pairs (FLP) catalysis is possibly a solution, but the development of this concept is still at a very early stage. Herein, stable, phase-pure, crystalline hydrotalcite-like compounds were synthesized by incorporating cerium cations into layered double hydroxide (MgAlCe-LDH). Besides the insertion of well-isolated cerium centers surrounded by hydroxyl groups, the formation of hydroxyl vacancies near the aluminum centers, which were formed by the insertion of cerium centers into the layered double hydroxides (LDH) lattice, was also identified. Depending on the initial cerium concentration, LDHs with different Ce(III)/Ce(IV) ratios were produced, which had Lewis acidic and basic characters, respectively. However, the acid-base character of these LDHs was related to the actual Ce(III)/Ce(IV) molar ratios, resulting in significant differences in their catalytic performance. The as-prepared structures enabled varying degrees of transfer hydrogenation (Meerwein-Ponndorf-Verley MPV reduction) of biomass-derived carbonyl compounds to the corresponding alcohols without the collapse of the original lamellar structure of the LDH. The catalytic markers through the test reactions were changed as a function of the amount of Ce(III) centers, indicating the active role of Ce(III)-OH units. However, the cooperative interplay between the active sites of Ce(III)-containing specimens and the hydroxyl vacancies was necessary to maximize catalytic efficiency, pointing out that Ce-containing LDH is a potentially commercial solid FLP catalysts. Furthermore, the crucial role of the surface hydroxyl groups in the MPV reactions and the negative impact of the interlamellar water molecules on the catalytic activity of MgAlCe-LDH were demonstrated. These solid FLP-like catalysts exhibited excellent catalytic performance (cyclohexanol yield of 45%; furfuryl alcohol yield of 51%), which is competitive to the benchmark Sn- and Zr-containing zeolite catalysts, under mild reaction conditions, especially at low temperature (T = 65 °C).

Red-emitting fluorescent probe for hydrogen sulfide detection and its applications in food freshness determination and in vivo bioimaging.

We report the development of a red-emitting fluorescence probe (XDS) for hydrogen sulfide (H2S) detection in biosystems, real-world food samples, and application of this probe for monitoring of H2S production during food spoilage. The XDS probe is developed by coupling of coumarin derivative to rhodanic-CN through a H2S responsive CC bond. Remarkable fluorescence quenching of XDS is observed as a result of the response to H2S. Semi-quantitative detection of H2S in three real-world water and two beer samples and monitoring of H2S production during food spoilage in real-time by "naked-eye" and smartphone colorimetric analysis are then achieved using XDS as the probe. Moreover, XDS is low toxicity, allowing it being used for visualizing endogenous and exogenous H2S in vivo in a mouse model. It is expected that the successful development of XDS could provide an effective tool for investigating the roles of H2S in biomedical system and for future food safety evaluation.

Determination and Imaging of Small Biomolecules and Ions Using Ruthenium(II) Complex-Based Chemosensors.

Luminescence chemosensors are one of the most useful tools for the determination and imaging of small biomolecules and ions in situ in real time. Based on the unique photo-physical/-chemical properties of ruthenium(II) (Ru(II)) complexes, the development of Ru(II) complex-based chemosensors has attracted increasing attention in recent years, and thus many Ru(II) complexes have been designed and synthesized for the detection of ions and small biomolecules in biological and environmental samples. In this work, we summarize the research advances in the development of Ru(II) complex-based chemosensors for the determination of ions and small biomolecules, including anions, metal ions, reactive biomolecules and amino acids, with a particular focus on binding/reaction-based chemosensors for the investigation of intracellular analytes' evolution through luminescence analysis and imaging. The advances, challenges and future research directions in the development of Ru(II) complex-based chemosensors are also discussed.

Designing an ESIPT-based fluorescent probe for imaging of hydrogen peroxide during the ferroptosis process.

Hydrogen peroxide (H2O2), depending on its levels, plays a crucial role in either modulating various biological processes as a signal molecule, or mediating oxidative damage as a toxin. Therefore, monitoring intracellular H2O2 levels is pivotal for exploring its physiological and pathological roles. Using a modified 2-(2'-hydroxyphenyl) benzothiazole (HBT) as the fluorophore, and a pinacol phenylborate ester as the responsive group, herein we developed an excited-state intramolecular proton transfer (ESIPT)-based probe BTFMB. The probe exhibited turn-on fluorescence response, large Stokes shift (162 nm) and low detection limit (109 nM) toward H2O2, and was successfully applied for monitoring exogenous and endogenous production of H2O2, and identifying accumulation of H2O2 during the ferroptosis process.

Cooperation of ESIPT and ICT Processes in the Designed 2-(2'-Hydroxyphenyl)benzothiazole Derivative: A Near-Infrared Two-Photon Fluorescent Probe with a Large Stokes Shift for the Detection of Cysteine and Its Application in Biological Environments.

A rationally designed near-infrared two-photon fluorescent probe (SDP-A) for selectively detecting cysteine (Cys) has been developed based on a newly designed conjugation-enhanced 2-(2'-hydroxyphenyl)benzothiazole derivative as the fluorophore, an acrylate moiety as the Cys reaction site, and an N-methylpyridinium scaffold as both the unit of organelle targeting and improving water solubility. The probe SDP-A alone essentially emitted no fluorescence, whereas it achieved a superb near-infrared fluorescence emission (713 nm) enhancement within 15 min with a significant Stokes shift (302 nm) in the presence of Cys. The photoluminescence mechanism of the probe SDP-A toward Cys was modulated by excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) processes. It exhibited high selectivity and sensitivity (LOD = 102 nM) for monitoring Cys over other analytes such as Hcy/GSH/H2S owing to a specific conjugate addition-cyclization reaction between Cys and the acrylate moiety. More importantly, the released fluorophore SDP exhibits elevated quantum yields (1.52-18.17%) in different solvents and strong two-photon excited fluorescence with a sizeable two-photon action cross-section (Φ) of 213.5 GM at 820 nm in acetonitrile-PBS medium, which is highly desirable for two-photon fluorescence imaging of the living samples. Therefore, SDP-A was successfully applied to the imaging of Cys in live cells, zebrafish, mouse brain, and abdominal cavity down to a depth of more than 200 µm using a one/two-photon fluorescence microscope.

Rational design of an ESIPT-based fluorescent probe for selectively monitoring glutathione in live cells and zebrafish.

Glutathione (GSH), an extremely important antioxidant, is a major participant in maintaining redox homeostasis and tightly associated with various clinical diseases. Thus, accurate and rapid detection of intracellular GSH is imperative to elucidate its role in physiological and pathological processes. Herein, by modifying 2-(2'-hydroxyphenyl) benzothiazole (HBT) scaffold, we developed an excited-state intramolecular proton transfer (ESIPT)-based fluorescent probe BTFMD for tracking GSH, which exhibited good selectivity, excellent water solubility, a large Stokes shift (181 nm) and fast response rate (within 10 min). Furthermore, the probe was successfully applied for imaging of endogenous GSH in live cells and zebrafish, and probing into the role of GSH in the development of cancer and Parkinson's disease.