Reactive oxygen (ROS) and nitrogen (RNS) species cause oxidative and nitrosative stresses, respectively. These stresses are implicated not only in diverse physiological processes but also in various pathological processes, including cancer and neurodegenerative disorders. In addition, some ROS and RNS in the environment are pollutants that threaten human health. As a consequence of these effects, sensitive methods, which can be employed to selectively monitor ROS and RNS in live cells, tissues and organisms as well as in environmental samples, are needed so that their biological roles can be understood and their concentrations in environmental samples can be determined. In this review, fluorescent, luminescent and colorimetric ROS and RNS probes, which have been developed since 2011, are comprehensively discussed.

Recent progress in the development of fluorescent, luminescent and colorimetric probes for detection of reactive oxygen and nitrogen species

Coumarins are a very large family of compounds containing the unique 2H-chromen-2-one motif, as it is known according to IUPAC nomenclature. Coumarin derivatives are widely found in nature, especially in plants and are constituents of several essential oils. Up to now, thousands of coumarin derivatives have been isolated from nature or produced by chemists. More recently, the coumarin platform has been widely adopted in the design of small-molecule fluorescent chemosensors because of its excellent biocompatibility, strong and stable fluorescence emission, and good structural flexibility. This scaffold has found wide applications in the development of fluorescent chemosensors in the fields of molecular recognition, molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, as well as in the biology and medical science communities. This review focuses on the important progress of coumarin-based small-molecule fluorescent chemosensors during the period of 2012-2018. This comprehensive and critical review may facilitate the development of more powerful fluorescent chemosensors for broad and exciting applications in the future.

Coumarin-Based Small-Molecule Fluorescent Chemosensors.

Metal cations and anions are essential for versatile physiological processes. Dysregulation of specific ion levels in living organisms is known to have an adverse effect on normal biological events. Owing to the pathophysiological significance of ions, sensitive and selective methods to detect these species in biological systems are in high demand. Because they can be used in methods for precise and quantitative analysis of ions, organic dye-based ratiometric fluorescent probes have been extensively explored in recent years. In this review, recent advances (2015-2019) made in the development and biological applications of synthetic ratiometric fluorescent probes are described. Particular emphasis is given to organic dye-based ratiometric fluorescent probes that are designed to detect biologically important and relevant ions in cells and living organisms. Also, the fundamental principles associated with the design of ratiometric fluorescent probes and perspectives about how to expand their biological applications are discussed.

Synthetic ratiometric fluorescent probes for detection of ions

Colour Chemistry  By R L M Allen Pp xii+336 (Thomas Nelson and Sons: London, 1971) £5

Dyes and Pigments

Biothiols such as cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) play crucial roles in maintaining redox homeostasis in biological systems. This Minireview summarizes the most significant current challenges in the field of thiol-reactive probes for biomedical research and diagnostics, emphasizing the needs and opportunities that have been under-investigated by chemists in the selective probe and sensor field. Progress on multiple binding site probes to distinguish Cys, Hcy, and GSH is highlighted as a creative new direction in the field that can enable simultaneous, accurate ratiometric monitoring. New probe design strategies and researcher priorities can better help address current challenges, including the monitoring of disease states such as autism and chronic diseases involving oxidative stress that are characterized by divergent levels of GSH, Cys, and Hcy.

Fluorescent Probes with Multiple Binding Sites for the Discrimination of Cys, Hcy, and GSH.

Heat stroke (HS) can cause serious organism damage or even death. Early understanding of the mechanism of heat cytotoxicity can prevent or treat heat stroke related diseases. In this work, probe Ly-NT-SP was synthesized, characterized, and used for sulfur dioxide (SO2) detection in lysosomes. PBS solutions of probe Ly-NT-SP at pH 5.0 present a marked broad emission band in the green zone (535 nm). After UV irradiation, the spiropyran group in Ly-NT-SP isomerizes to the merocyanine form (Ly-NT-MR), which presented a weak red-shifted emission at 630 nm. In addition, photocontrolled isomerization of Ly-NT-SP to Ly-NT-MR generated a C═C-C═N+ fragment able to react, through a Michael addition, with SO2 to yield a highly emissive adduct with a marked fluorescence in the green channel (535 nm). In vitro studies showed a remarkable selectivity of photoactivated Ly-NT-MR to SO2 with a limit of detection as low as 4.7 μM. MTT viability assays demonstrated that the Ly-NT-SP is nontoxic to HeLa cells and can be used to detect SO2 in lysosomes. Taking advantage of this, the sensor is successfully applied to image increasing SO2 values in lysosomes during heat shock for the first time. Moreover, we also confirmed that the increased SO2 can protect the small intestine against damage induced by heat shock through regulating oxidative stress in cells and mice.

Heat Stroke in Cell Tissues Related to Sulfur Dioxide Level Is Precisely Monitored by Light-Controlled Fluorescent Probes.

In recent years, it has become a trend to employ organic molecular fluorescent probes with multireaction sites for the distinguishable detection and biological imaging of similar substances. However, the introduction of multireaction sites brought great challenges to organic synthesis, and at the same time, often destroyed the conjugated structure of the molecules, leading to an unsatisfactory fluorescence emission wavelength not conducive to practical application. As the eternal theme of life, metabolism goes on all the time. Metabolism is a series of ordered chemical reactions that occurs in the organism to maintain life. Chemical reactions in metabolism can be summarized as metabolic pathways. Simultaneous monitoring of different metabolic pathways of the same substance poses a lofty challenge to the probe. Here, we developed a new strategy: to construct new sites through the preliminary reactions between probes and some targets, which can be used to further distinguish among targets or detect their metabolites, so as to realize the simultaneous visualization tracer of multiple metabolic pathways. By intravenous injection, it revealed that the probe containing benzopyrylium ion can target tumors efficiently, and thiols are highly expressed in tumors compared to other tissues (heart, lung, kidney, liver, etc.). The consumption of thiols by the probe could not prevent tumor growth, suggesting that the tumor cure was not correlated with thiol concentration. The construction of new sites in the reaction process is a novel idea in the pursuit of multiple reaction sites, which will provide more effective tools for solving practical problems.

A New Strategy: Distinguishable Multi-substance Detection, Multiple Pathway Tracing Based on a New Site Constructed by the Reaction Process and Its Tumor Targeting

The reactive oxygen species (ROS) including hypochlorous acid (HOCl), on the one hand they can regulate physiological function in our living organisms, on the other hand abnormal concentration of ROS would induce a series of biomacromolecules damage and further endanger virtually all aspects of human health. Especially it can be directly related to cancer. Thus to elucidate and visualize their concentration is very imminent. Before many fluorescent probes were used to detect HOCl. In recent years, near-infrared or ratiometric fluorescent developed prosperously. The strategy of combining near-infrared and ratiometric fluorescent probe is overwhelming in the design of fluorescent probes. In this work, we successfully designed and obtained a near-infrared and ratiometric fluorescent probe with large stokes by reacting isophorone with coumarin, which can monitor HOCl high efficiently with quick response and low detection limit. In addition, cell imaging experiments show that the probe can identify endogenous and exogenous ClO− successfully, and nude mouse imaging experiments show that the probe can detect exogenous ClO−. It is possible that the probe can be applied in early clinical diagnosis.

A near-infrared ratiometric fluorescent probe with large stokes based on isophorone for rapid detection of ClO− and its bioimaging in cell and mice

Ratiometric fluorescent probes for ClO− and in vivo applications

Hydrazine (N2H4), a well-known reagent, was widely used in many chemical industries. However, it was a kind of highly toxic to the environment and biosome. Therefore, it was necessary to design a sensitive method for the detection of hydrazine. In this work, a new type of ratiometric fluorescent probe based on novel cyclization mechanism for detecting hydrazine in PBS buffer (7.4) solution was designed. The response time of probe for detecting hydrazine was within 7 min, and the detection limit was 31 μM. The novel recognition mechanism was proved by ESI–MS analysis and NMR spectroscopic analysis. In addition, the application of probe was proved by bioimaging in living cell.

Jianbin Chao

Papers

Heat Stroke in Cell Tissues Related to Sulfur Dioxide Level Is Precisely Monitored by Light-Controlled Fluorescent Probes.

A New Strategy: Distinguishable Multi-substance Detection, Multiple Pathway Tracing Based on a New Site Constructed by the Reaction Process and Its Tumor Targeting

A near-infrared ratiometric fluorescent probe with large stokes based on isophorone for rapid detection of ClO− and its bioimaging in cell and mice

Ratiometric fluorescent probes for ClO− and in vivo applications

A ratiometric fluorescent probe for hydrazine based on novel cyclization mechanism and its application in living cells