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It is highly desirable to develop high-performance ratiometric fluorescent probes for SO2 derivative detection and realize their application in biological imaging. In this study, we report the rational design of a novel negative photochromic spiropyran derivative, spiro[azahomoadamantane-pyran] (MAHD-SP), with notable orange fluorescence in its stable ring-opened state without UV regulation. The unsaturated double bond of MAHD-SP underwent the Michael addition reaction of the SO2 derivative, making the fluorescence quenching of MAHD-SP obvious. Then, MAHD-SP, a fluorescent conjugated polymer PFO and a polymeric surfactant PEO113-b-PS49 were used to construct a ratiometric fluorescent polymeric nanoprobe (RFPN) via a coprecipitation method. The probe exhibited high sensitivity and selectivity for the ratiometric detection of SO2 derivatives in pure aqueous solutions. Moreover, the good biocompatibility of RFPN can be used to visualize exogenous and endogenous SO2 derivative generation in living cells. [ABSTRACT FROM AUTHOR]

Cysteine (Cys) is a critical biologically active sulfhydryl molecule that plays essential roles in anti-oxidation and maintains protein structure and function. In addition, Cys is also a vital nutrient in many foods. Therefore, the detection of Cys is highly required for food quality control and revealing the biological functions of Cys. Herein, we presented an effective fluorescent probe (denoted as DDP-C) for sensing Cys. The probe can produce a swift off–on fluorescence response to Cys and two other significant biothiols (homocysteine and glutathione) with emission in the deep-red to the near-infrared region (600–700 nm). The probe has a large Stokes shift (140 nm), as well as high selectivity and sensitivity. The linear range for Cys detection is 0.5–20 μM, and the detection limit is 37 nM. DDP-C can also realize the quantitative determination of Cys in milk samples and imaging of intracellular biothiols. Therefore, the probe can serve as a powerful tool for Cys sensing. [ABSTRACT FROM AUTHOR]

A simple and readily available fluorescent probe is needed for the real-time monitoring of endogenous cysteine (Cys) levels in living cells, as such a probe could be used to study the role of Cys in related diseases. Herein, we report the first fluorescent probe based on carbon dots (CDs-FITA) for the selective and ratiometric imaging of endogenous Cys in live cells. In this ratiometric fluorescent probe, a fluorescein derivative (FITA) that recognizes Cys is covalently linked to the surfaces of carbon dots (CDs); employing CDs greatly improves the water solubility of the probe. Acrylate on FITA is selectively cleaved by Cys in aqueous solution under mild conditions, leading to a dramatic increase in the fluorescence from fluorescein. The probe therefore allows the highly selective ratiometric fluorescent detection of Cys even in the presence of various interferents. The as-prepared CDs-FITA showed excellent performance when applied to detect Cys in blood serum. In addition, due to its negligible cytotoxicity, the CDs-FITA can also be utilized for the real-time monitoring of endogenous cysteine (Cys) levels in living cells.Illustration of the CD-based probe for Cys imaging in living cells [ABSTRACT FROM AUTHOR]

Imaging of hepatocellular nitric oxide (NO) in vivo is of great importance for understanding its roles in liver diseases, but such an imaging approach is still lacking. Herein, a hepatocyte-targeting fluorescent NO sensor has been fabricated. This sensor exhibits good water solubility, excellent selectivity, and high sensitivity (∼1.62 nM). The cells and in vivo imaging experiments reveal that Gal-RhB facilitates the visualization of hepatocellular NO in both HepG2 cells and zebrafish. These results demonstrate that Gal-RhB may be a promising tool for studying the function of NO in NO-associated liver diseases. [ABSTRACT FROM AUTHOR]

Fluorescent nanoprobes for carbon monoxide (CO) imaging emerged as an excellent tool for cancer diagnosis, but they are activated by single-biomarker. Herein, we developed a dual-locking fluorescent nanoprobe (HA-DMC) for HAase-triggered carbon monoxide imaging in the mitochondrion of the cancer cells. The fluorescent nanoprobes have "double locks" structures made of acetyl hyaluronic acid chains (hyaluronidase-triggered, first lock) as a barrier to form nanoparticles and the nitro group (CO-triggered, second lock) as intramolecular charge transfer (ICT) groups to quench the fluorescence of coumarin-pyridine derivative dyes. When the "locks" were only unlocked in sequence (from hyaluronidase to CO), a strong green fluorescence appeared for achieving cancer imaging. Meanwhile, the HA-DMC exhibited some satisfactory properties, such as mitochondria-targeting properties, excellent selectivity and sensitivity (24-fold), good water dispersibility, low detection limit (225 nM), and low cytotoxicity. Such features ensured that the HA-DMC could be successfully utilized for fluorescently imaging exogenous CO in the mitochondrion of living cells. In addition, the HA-DMC was successfully used to monitor exogenous and endogenous CO in vivo. We thus envision that HA-DMC is a promising platform for CO imaging in the mitochondrion of cancer cells and would promote the progress of fluorescent nanoprobes. [Display omitted] • A dual-locking fluorescent nanoprobe (HA-DMC) for CO imaging was well developed. • HA-DMC was used for HAase-triggered mitochondrial CO imaging in cancer cells. • This work provides the first dual-locking probe for HAase and CO in tumor cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A near-infrared ratiometric fluorescent probe (DCPBCl 2 -Hz) was developed. • DCPBCl 2 -Hz exhibited excellent sensitivity and selectivity for hydrazine. • The probe can monitor gaseous hydrazine with a content down to 1 ppm (mg/m3). • The probe was applied for detecting hydrazine in solid and in live cells. Hydrazine (N 2 H 4) is a widely used raw material in the chemical industry, but at the same time hydrazine has extremely high toxicity. Therefore, the development of efficient detection methods is crucial for monitoring hydrazine in the environment and evaluating the biological toxicity of hydrazine. This study reports a near-infrared ratiometric fluorescent probe (DCPBCl 2 -Hz) for the detection of hydrazine by coupling a chlorine-substituted D-π-A fluorophore (DCPBCl 2) to the recognition group acetyl. Due to the halogen effect of chlorine substitution, the fluorophore has an elevated fluorescence efficiency and a lowered pKa value and is suitable for physiological pH conditions. Hydrazine can specifically react with the acetyl group of the fluorescent probe to release the fluorophore DCPBCl 2 , so the fluorescence emission of the probe system significantly shifted from 490 nm to 660 nm. The fluorescent probe has many advantages, such as good selectivity, high sensitivity, large Stokes shift, and wide applicable pH range. The probe-loaded silica plates can realize convenient sensing gaseous hydrazine with content down to 1 ppm (mg/m3). Subsequently, DCPBCl 2 -Hz was successfully applied to detect hydrazine in soils. In addition, the probe can also penetrate living cells and allow the visualization of intracellular hydrazine. It can be anticipated that probe DCPBCl 2 -Hz will be a useful tool for sensing hydrazine in biological and environmental applications. [ABSTRACT FROM AUTHOR]

Illustration of the nanoprobe for imaging of HAase and PDT of tumor. [Display omitted] • A dual-targeting and tumor microenvironment-response nanoassembly was developed for imaging of HAase and PDT of tumor. • The HA-Mito TPP exhibits desirable selectivity and excellent anti-interference for HAase analysis. • The first report on HA-based stimuli-response nanoassembly for simultaneous dual targeting and activated tumor imaging and photodynamic therapy. A nanotheranostic system integrating activatable photoactivity and dual targeting modalities is significant for bioimaging and biomedicine. In this study, a dual-targeting and tumor microenvironment responsive nanoassembly for imaging of HAase and PDT of tumor was developed. The synthesized water-soluble cationic porphyrin act as both the mitochondrion targeting photosensitizer and crosslinking agent to trigger the formation of HA-Mito TPP nanoparticle via the electrostatic interaction with hyaluronic acid. The nanoassembly could be efficiently endocytosed into targeted tumor cells and activated both fluorescence signal and enhanced PDT effect by highly expressed HAase. In vitro experiments suggested that the reported assay had desirable selectivity and excellent anti-interference for HAase quantitative analysis. The live cell studies showed the HA-Mito TPP had obviously enhanced PDT efficiency and caused mitochondria damage. Therefore, the developed dual-targeting nanotheranostic system provide a promising platform for bioanalysis and imaging guided photodynamic therapy. [ABSTRACT FROM AUTHOR]