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A tyrosinase-activatable fluorescent probe with endoplasmic reticulum targetability was developed for the first time. It can ratiometrically fluoresce and hence be used to monitor refluxed tyrosinase into the endoplasmic reticulum. [ABSTRACT FROM AUTHOR]

Nitrogen-enriched carbon dots (NCDs) with green fluorescence were prepared with an average diameter of 4.8 nm by a room temperature self-polymerization method using catechol and ethylenediamine as precursors. It was found that the green fluorescence of NCDs can be quenched directly by uric acid (UA). A facile and fast fluorescent enzyme-free sensor has been developed for the detection of UA in the linear concentration range of 0–30 μM, with a limit of detection of 0.22 μM. High sensitivity, stability and selectivity can also be achieved for the detection of UA. In addition, the mechanism of fluorescence quenching of NCDs induced by UA was the dynamic quenching type according to the linearity of the Stern–Volmer equation and the change of the lifetime of NCDs after adding UA. Furthermore, UA in saliva samples was successfully detected using this established fluorimetric method, showing the feasible detection of UA in complicated body fluid samples. This NCD-based fluorimetric non-invasive method can be used for the highly selective determination of UA in the clinical laboratory. [ABSTRACT FROM AUTHOR]

Hypochlorous acid (HOCl) was crucial for maintaining the homeostasis in cells and plays vital roles in many physiological and pathological processes. In this work, a highly selective fluorescent probe for hypochlorous acid in living cells was constructed and prepared based on a naphthalene derivative. A naphthalene derivative was utilized as the fluorescent group, and N,N-dimethylthiocarbamate was applied as the selective recognition site for HOCl. Before adding HOCl, the fluorescent probe exhibited weak fluorescence. Upon adding HOCl, the fluorescent probe displayed remarkable fluorescence enhancement. The fluorescence intensity at 502 nm showed a linear response to the concentration of HOCl from 3.0 × 10−7 to 1.0 × 10−5 mol·L−1. The detection limit was estimated to be 1.5 × 10−7 mol·L−1 for HOCl. The fluorescent probe showed fast response and outstanding selectivity toward HOCl. It owned good biocompatibility and had also been successfully applied in the confocal imaging of exogenous and endogenous HOCl in living cells. [ABSTRACT FROM AUTHOR]

Hydrogen polysulfide (H 2 S n , n≥2), as a kind of active sulfur species (RSS), has become a hot topic in RSS. It can regulate the biological activity of many proteins through S-sulfhydrylation of cysteine residues (protein Cys-SSH), and has a protective effect on cells. Although there have been some studies on hydrogen polysulfide, its production, degradation pathway and regulation mechanism still need further be researched. In presented study, an original lysosome-localized fluorescent probe for determining H 2 S n was developed utilizing rhodamine as the fluorogen. The probe used morpholine as the locating unit of lysosomes and chose 2-fluoro-5-nitrobenzoate as the recognizing group. Before adding H 2 S n , the proposed probe displayed a spironolactone structure and emitted very weak fluorescence. After adding H 2 S n , a conjugated xanthene was formed and the probe demonstrated green fluorescence. When the H 2 S n concentration was varied from 6.0×10−7 mol·L−1 to 10.0×10−5 mol·L−1, the fluorescence intensity of the probe was linearly dependent on the H 2 S n concentration. And the detection limit was 1.5×10−7 mol·L−1. The presented probe owned a fast response speed, good selectivity, excellent sensitivity and broad pH work scope. In addition, the probe had been well utilized to sense endogenic and exogenic H 2 S n in lysosomes. [Display omitted] • A lysosome-targetable fluorescent probe for H 2 S n has been reported. • The probe displays high sensitivity and high selectivity for H 2 S n. • The probe can be utilized for determination of H 2 S n within the lysosomes. [ABSTRACT FROM AUTHOR]

Lysosomes, important acidic organelles, under hypoxia status are closely associated with many diseases. The development of a molecular tool for the precise monitoring of lysosomal hypoxia is of great significance but remains challenging. Herein, we present a novel fluorescence probe HPFR, which is consisted of anthocyanidin fluorophore incorporated with quenching and hypoxia-sensitive azobenzene group, pH-switchable spirolactam moiety, and morpholine as lysosome targetable unit. Due to its hypoxia and acid dual-activatable characteristics, the proposed probe displays a highly sensitive and selective fluorescence response to azoreductase under a lysosomal pH environment but remains silent under neutral or alkaline conditions. Furthermore, it is confirmed to be biocompatible and could be employed to accurately visualize the hypoxia level of acidic lysosomes, offering a promising imaging tool for investigating hypoxic lysosome-related physiopathology. • A hypoxia-sensitive and pH-switchable fluorescence probe was developed. • The probe can specifically detect hypoxia-related azoreductase under acidic solution. • The probe enables to precisely monitor lysosome-confined hypoxia level. [ABSTRACT FROM AUTHOR]

Recently, using nanomaterials to enhance the endocytosis capability and sensitivity of probes for RNA imaging in living cells has gotten the attention of many researchers. Nanomaterials, as a reliable alternative to transfection reagents, could prevent nucleic acid probes from being degraded by DNase, and bring them into sub-cellular locations for efficient internalization. Therefore, nanomaterial-based fluorescent probes (NFPs) provide a promising sensing platform to realize in situ RNA detection and imaging, which can reveal the expression of RNA at single cell level and provide large amount of information about RNA spatial localization. Meanwhile, many RNAs are in low abundance in living cells, resulting in difficulty in sensitive detection. Thus, the incorporation of NFPs and signal amplification strategy offers a broader prospect for the detection of RNAs, that have been proven as predominant therapeutic targets or diagnostic biomarkers. Herein, the purpose of our review is to first introduce the general procedure of NFPs used for in situ RNA imaging and how nanomaterials deliver these probes into living cells. Further, we focused on different kinds of nanomaterials that are mainly used for sensitive detection of RNAs and those in low abundance, through different signal read-out modes. Nanomaterial-based fluorescent probe (NFP) provides a promising sensing platform to realize effectively cellular endocytosis and intracellular RNA Imaging in situ. In our review, we try to basically introduce the whole progress of NFPs used for in situ RNA imaging, particularly focusing on the endocytic pathways that nanomaterials deliver these probes into living cells, as well as different kinds of nanomaterials that are mainly used for sensitive signal detection of RNAs, especially for those in low abundance. [Display omitted] • Monitoring the level of RNA expression, can assist our understanding of the progression, diagnosis and further treatment of tumor. • NFPs has high internalization efficiency and excellent biocompatibility to achieve cellular uptake and RNA imaging in situ. • Different kinds of nanomaterials for detection of RNAs, especially for those in low abundance, are summarized. [ABSTRACT FROM AUTHOR]

Water-soluble non-conjugated polymer dots (PDs) have been synthesized using hyperbranched polyethyleneimine (PEI) and dihydroxybenzaldehyde (DHB) for the first time via the Schiff base reaction at room temperature. The yielded non-conjugated PDs of PEI-DHB could display the well-defined spheric structure and good water solubility. In contrast to the common PDs otherwise showing blue emission, the PEI-DHB PDs could give out strong green fluorescence in aqueous media. Especially, the fluorescence of the PEI-DHB PDs could be specifically quenched by MnO 2 nanosheets through the inner filter effects and further restored by the thiocholine that could reduce MnO 2 nanosheets into Mn2+. Herein, thiocholine could be produced in hydrolysis reaction of acetylthiocholine catalyzed by the acetylcholinesterase (AChE), of which the catalytic activity could be irreversibly inhibitted by the introduction of organophosphates. A highly selective fluorimetric method was thereby been developed for the detection of organophosphorus pesticides using dimethyl-dichloro-vinyl phosphate as a model. The linear concentrations ranges from 0.050 to 2.5 μM. Importantly, the non-conjugated PDs probes with strong green fluorescence and high water solubility may promise the extensive applications in the environmental, food, and clinical analysis fields. [Display omitted] • Water-soluble non-conjugated polymer dots (PDs) were made by Schiff base reaction. • The PDs can display the well-defined structure and strong green fluorescence in water. • MnO 2 -quenched PDs fluorescence is restored by AChE-catalyzed hydrolysis. • The detection of pesticides is performed via the AChE catalysis inhibition. [ABSTRACT FROM AUTHOR]

Nanozymes are more stable, economical, and easier to produce than natural enzymes; however, their low activity in non-acidic environments and lack of substrate selectivity severely limit the applications of nanozymes. In this study, we developed Co- and N-doped carbon dot nanozymes (CoNCDs) that specifically exhibited peroxidase-like activity toward o-phenylenediamine in a non-acidic environment. Based on the peroxidase-like activity and fluorescence property of CoNCDs in a neutral environment, a one-pot multi-mode sensing platform (colorimetric and ratiometric fluorescence imaging) was developed to detect cholesterol and xanthine in solution and human serum samples. This platform was simple to operate, and the CoNCDs demonstrated a reduced detection time and an improved analytical performance compared to most of the reported nanozymes. Moreover, the improved peroxidase activity at neutral pH, good biocompatibility, and photostability of CoNCDs facilitated their use for monitoring endogenous H 2 O 2 levels in vivo. This study not only provides a novel approach for developing an acid pH-independent and substrate selectivity nanozyme but also demonstrates the application of ratiometric fluorescence imaging using the developed CoNCDs both in vitro and in vivo. [Display omitted] • CoNCDs showed the peroxidase-like activity at neutral and alkaline pH. • CoNCDs showed the substrate selectivity toward OPD, but no activity toward TMB and ABTS. • The one-pot multi-mode sensing platform for cholesterol and xanthine were developed. • CoNCDs was firstly applied to monitor H 2 O 2 in vitro and in vivo. [ABSTRACT FROM AUTHOR]