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Carbon monoxide (CO) is a vital endogenous gaseous transmitter molecule involved in the regulation of various physiological and pathological processes in living biosystems. In order to investigate the biological function of CO, many technologies have been developed to monitor the level of endogenous CO in biosystems. Among them, the fluorescence detection technology based on the fluorescent probe has the advantages of high sensitivity, excellent selectivity, simple operation, especially non-invasive damage to biological samples, and the possibility of real-time in situ detection, etc., which is considered to be one of the most effective and applicable detection techniques. Therefore, in the last few years, a lot of work has been carried out on the design, synthesis and in vivo fluorescence imaging studies of CO fluorescent probes. Furthermore, using fluorescent probes to detect the changes in CO concentrations in living cells and tissues as well as in organisms has been one of the hot research topics in recent years. However, it is still a challenge to rationally design CO fluorescent probe with excellent optical performance, structural stability, low background interference, good biocompatibility, and excellent water solubility. Therefore, this review focuses on the research progress of CO fluorescent probes in the detection mechanism and biological applications in recent years. However, this popular and leading topic has rarely been summarized comprehensively to date. Thus, the research progress of CO fluorescent probes in recent years is reviewed in terms of their design concept, detection mechanism, and their biological applications. In addition, the relationship between the structure and performance of the probes was also discussed. More significantly, we hope that more excellent optical properties fluorescent probes for gaseous transmitter molecule CO detection and imaging will overcome the current problems of high biotoxicity and limited water solubility in future. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) is one of the important gaseous signalling molecules, which plays key roles in various critical biological processes. In this work, we report a novel two-photon near-infrared (TP-NIR) fluorescent probe (MNIR-H2S) for the sensing of mitochondrial H2S in living cells, tissues, zebrafish and nude mice. Using a xanthene dye as a TP-excitation (810 nm) NIR-emission (668 nm) fluorophore, a well-known H2S response moiety with a robust intramolecular charger transfer (ICT) effect can quickly respond to H2S and effectively quench the fluorescence intensity, and an oxonium cation structure serves as a mitochondria-targeting site. Notably, MNIR-H2S displays high sensitivity, high selectivity, low cytotoxicity, powerful mitochondrial localization ability, deep tissue penetration, and a very minimal imaging background. Biological imaging results show the biological application of MNIR-H2S as a robust new tool for use in H2S imaging in biological systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two fluorescent probes (CM-PhSH , CM-Ratio-PhSH) were constructed for PhSH detection. • CM-Ratio-PhSH becomes ratiometric probe by introducing a nitro group on CM-PhSH. • These two probes were successfully used for PhSH detection and imaging in the environment and food. Thiophenol (PhSH), a highly reactive aromatic thiol, plays an essential role as a common industrial raw material in food, pesticides, pharmaceuticals, and cosmetics. In this work, we designed and constructed two fluorescent probes CM-PhSH and CM-Ratio-PhSH by a rational strategy. Specifically, coumarin fluorophores with excellent optical properties were modified, and olefinic unsaturated bonds served as reaction sites for the detection of PhSH. Based on this, the introduction of the nitro group at specific positions of the CM-PhSH changed the fluorescence emission of the CM-Ratio-PhSH , eventually obtaining a novel ratiometric fluorescent probe CM-Ratio-PhSH for PhSH detection. Surprisingly, these two probes exhibited advantages such as high specificity and low limit of detection (LOD) for CM-PhSH 32.3 nM and CM-Ratio-PhSH 40.2 nM, respectively. Furthermore, subsequent experiments demonstrated CM-PhSH and CM-Ratio-PhSH could be successfully used for highly selective and rapid detection of PhSH in aqueous solutions, live cells, and complex food samples. [ABSTRACT FROM AUTHOR]

Cadmium (Cd), a widespread and highly toxic environmental contaminant, has seriously impacted the growth of rice and the quality of its products. Hence, it is crucial to monitor and employ robust means to reduce Cd levels in rice, and selenium (Se) has been proven to chelate cadmium ion (Cd2+) in rice with rational use. Herein, for the first time, the reported selenocysteine (Sec) probe NN-Sec and the newly designed Cd2+ probe SCP were chosen as visualization tools to monitor Sec-inhibited Cd2+ uptake in rice. Specifically, reduced fluorescence of rice precultured with Cd2+ was observed by SCP after Se application, while similarly decreased fluorescence of rice pretreated with Se was observed by NN-Sec after Cd2+ addition. The diminished fluorescence indicated the formation of Cd-Se complexes reduced the Cd2+ content in rice. Additionally, it was Cd2+ and Se that entered the rice causing the fluorescence generation, as demonstrated by inductively coupled plasma mass spectrometry (ICP-MS). To conclude, the two probes successfully visualized Se inhibited Cd2+ uptake in rice, which could provide a robust tool for supporting the development of novel organic fertilizers and reagents to reduce Cd2+ content in rice and the environment. [Display omitted] • Fluorescent probes for visualizing selenium inhibition of cadmium uptake in rice. • A Cd2+ fluorescent probe and a Sec fluorescent probe for rice imaging. • The content of Cd2+ in Se treated rice was decreased. [ABSTRACT FROM AUTHOR]

Fluorescence imaging plays an increasingly important role in biomedicine field due to its superior sensitivity and selectivity along with dynamic, real-time, in situ monitoring the occurrence and development of biological events. Therefore, it is crucial to construct a near-infrared (NIR) fluorescent molecule with excellent optical properties. Herein a NIR robust out mitochondria-targeting dye NN has been designed, synthesized and characterized, whose fluorescence properties are easily adjusted by changing the substitution position of the nitro group at the benzene ring in this fluorescent dye. NN was a unique fluorescence-enhanced nitro dye with high fluorescence quantum yields∼0.17, a large Stokes shift∼120 nm and stable chemical structure. Encouraged by this, a novel fluorescent probe NN - Sec based on intramolecular charge transfer (ICT) was constructed by grafting NN with a selenocysteine (Sec) recognition group 2,4-dinitrobenzenesulfonyl (DNBS), and it exhibited a targeted ability with great sensitivity and selectivity. Subsequently, the probe was used for NIR imaging in living cells and mice, and deep imaging results further illustrate its potential application in biosystems. The successful design of NN and NN - Sec offer a valuable theoretical basis and technical support for investigating the occurrence and development of Sec-related diseases. • A novel NIR fluorescent dye NN bearing nitro was reported with an enhanced fluorescence quantum yields. • The recognition group 2,4-dinitrobenzenesulfonyl of Sec was grafted with dye NN to synthesize fluorescent probe NN-Sec. • ANN-Sec can detect Sec in live cells and mice by high sensitivity and selectivity, accompanied by bright NIR emission. [ABSTRACT FROM AUTHOR]

To understand the entangled relationship between reactive oxygen species (ROS) and arthritis, it is of great interest to urgently need an effective bioanalytical method to detect biomarker peroxynitrite (ONOO-) of arthritis in vivo. In contrast to the previously reported ONOO- fluorescent probes, multicolor fluorescent probe could be applied to complex environments for multi-component analysis and provide multichannel imaging results. However, multicolor fluorescent probes for ONOO- detecting have not been reported so far. Herein, an ONOO--activated multicolor fluorescent probe (MULTI-ONOO) based on FRET was developed for quantitative detecting and visualization of ONOO- levels in arthritis. This probe mainly contained an acceptor (near-infrared xanthane fluorophore) and a donor (naphthalimide fluorophore). In the presence of ONOO-, the oxonium ion undergoes a strong nucleophilic response between ONOO- and xanthane to generate coumarin (CM) and naphthimide (NP) fluorophores with multicolor signal output. Impressively, MULTI-ONOO has a rapid response time (~20 s) and outstanding detection limits as low as 11.6 nM. Finally, this probe was successfully adopted to detect endogenous ONOO- in living cells, arthritis tissues and rat model. Thus, this ONOO--activated multicolor probe could provide a robust tool for investigating the role of ONOO- between in different inflamed diseases. [Display omitted] • A biomarker-activated multicolor probe MULTI-ONOO was constructed for arthritis detecting. • MULTI-ONOO contained a NIR xanthane fluorophore and a naphthalimide fluorophore. • MULTI-ONOO has a rapid response time (~20 s) and outstanding LOD as low as 11.6 nM. • MULTI-ONOO was successfully adopted to detect endogenous ONOO in arthritis rat model. [ABSTRACT FROM AUTHOR]