A dual-response NIR fluorescent probe for separately and continuously recognizing H2S and Cys with different fluorescence signals and its applications.

Given the significant interactions between hydrogen sulfide (H2S) and cysteine (Cys) in organisms, a dual-site multi-purpose fluorescent probe (Cy-NP) for H2S and Cys was synthesized. Cy-NP is composed of two fluorophores: naphthalimide that emits in the visible region of 500-600 nm, and cyanine dye that emits in the NIR region of 700-800 nm. Cy-NP showed admirable sensitivity and selectivity for identifying H2S and Cys by fluorescent signals with limits of detection as low as 0.15 µM and 1.4 µM, respectively. Furthermore, other biological thiols (especially GSH and Hcy) showed no positive response to Cy-NP compared with H2S and Cys. The chemical mechanism of Cy-NP with H2S and Cys in DMF/PBS (1/1, v/v, pH = 7.4) solution was verified by HRMS and DFT calculations. Further, Cy-NP was successfully applied to monitor H2S released in raw meat and adapted to detect H2S and Cys in MCF-7 cells independently and continuously.

A "Turn-on" Fluorescent Probe Based on Phenothiazine for Selectively Recognizing ClO- and its Practical Applications.

Hypochlorous acid (HClO), a highly reactive oxygen species, has important effects on human health. High selectivity and sensitivity remain challenges of fluorescent probes for detection of ClO- with a large Stokes shift. This work designed and synthesized a novel phenothiazine-based fluorescent probe TF which can detect ClO- by colorimetric and fluorescent dual signals. TF displayed turn-on fluorescence effect toward ClO- with high selectivity (≥ 28-folds) and sensitivity (LOD = 0.472 µM), fast response time (< 1 min) and large Stokes shift (150 nm) in PBS (pH = 7.4, 40% DMSO). Meanwhile, TF can visualize ClO- on the mung bean sprouts model and apply as testing strips for portable and rapid detecting ClO- by the naked eyes. A phenothiazine-based fluorescent probe with large Stokes shift was synthesized and its responding rapidly ability to detect ClO- was studied.

A Highly Selective Hg2+ Fluorescent Chemosensor Based On Photochromic Diarylethene With Quinoline Unit.

A novel diarylethene-based fluorescent chemosensor containing a quinoline unit (1o) had been designed and synthesized. 1o showed good photochromic ability and fluorescence switching properties by alternating UV/vis light irradiation. The chemosensor showed high "Turn-off" fluorescent selectivity for Hg2+ by competitive tests of the fluorescence reaction in the presence other ions in acetonitrile solution. The stoichiometry between the compound 1o and Hg2+ was 1:1 by Job's plot curve and HRMS analysis. In addition, the LOD for Hg2+ was calculated as 60 nM. The fluorescence emission can be back to the "Turn-on" state by adding EDTA. Based on these facts, a molecular logic gate that including four input signals (UV/vis and Hg2+/EDTA) and one output signal (fluorescent intensity at 491 nm) was designed.

A novel full symmetric diarylethene-based ratiometric fluorescent sensor for lysine and the application for a logic circuit.

A novel diarylethene-based ratiometric fluorescent sensor with full symmetric structure, 1o, was designed and synthesized successfully. 1o could identify lysine (Lys) with high selectivity and sensitivity and the fluorescence emission peak was red shifted 85 nm upon addition of Lys, which could realize ratio recognition. It exhibited excellent anti-interference performance in the presence of various amino acids in CH3 CN/H2 O (7/3, v/v) solution. Moreover, the limit of detection of 1o to Lys could reach 0.019 µM based on a good linear range of 0-40 µM. In addition, the fluorescence emission intensity of 1o could be turned off/on by ultraviolet/visible light due to the special structure of diarylethene. A logic circuit was designed with three inputs. The ratiometric fluorescent sensor 1o could be as a new tool and provide a new method for detection of Lys.

Hg2+ -selective ratiometric and colorimetric probe based on dansyl-rhodamine and its staining function in cell imaging.

A new ratiometric probe composed of a dansyl-rhodamine dyad for the detection of Hg2+ via fluorescence resonance energy transfer was designed and synthesized. Rhodamine, dansyl chloride, and hydrazide were selected as the acceptor, donor, and reaction site, respectively. It displayed high selectivity and sensitivity to Hg2+ with obvious colour change and fluorescence change due to Hg2+ -assisted hydrolysis of rhodamine hydrazide. A good linear relationship ranging from 0 to 16 µM and 0-28 µM for the Hg2+ concentration was found based on absorbance and fluorescence assay, respectively. Detection limits of absorbance and fluorescence for Hg2+ were calculated to be 1.22 µM and 9.10 µM, respectively.

Rapidly responsive and highly selective NIR fluorescent probe for detecting hydrogen sulfide in food samples and living cells.

Hydrogen sulfide (H2S) is a pungent gas that is one of the key mediators of signal transduction in biological systems, and its presence is related to the freshness of some protein foods. Using phenothiazine derivatives as fluorophores and 2, 4-dinitrobenzene sulfonate (DNBS) fragments as reaction groups, a near-infrared (NIR) probe WX-HS for H2S identification was designed. With the addition of H2S, WX-HS appeared a strong fluorescence signal at 660 nm with short reaction time (90 s) and high sensitivity, and fluorescence state change from non-fluorescent to orange-red. In addition, WX-HS could effectively detect H2S produced during food oxidation. Based on its low cytotoxicity, the WX-HS probe further enabled the detection and imaging of H2S in A549 cells.

A mitochondrial targeted dual ratiometric near-infrared fluorescent probe based on ICT effect for the detection of SO2 derivative and its bioimaging.

SO2 derivatives play an important role in many metabolic processes, excessive ingestion of them can lead to serious complications of various diseases. In this work, a novel dual ratiometric NIR fluorescent probe XT-CHO based on ICT effect was synthesized for detecting SO2 derivative. In the design of the probe, the α, ß-unsaturated bond formed between benzopyran and coumarin was used as the reaction site for SO2, meanwhile, the extended π-conjugate system promoted maximum emission wavelength of the probe up to 708 nm. Notably, the probe exhibited high selectivity and sensitivity for detecting SO2, the limit of detection reached 2.13 nM and 58.5 nM in fluorescence spectra and UV-Vis absorption spectra, respectively. The reaction mechanism of SO2 and XT-CHO had been verified by 1H NMR, ESI-MS spectra and DFT calculation. Moreover, the probe was successfully applied in detecting endogenous and exogenous SO2 in living cells and proved possessed the mitochondrial targeted ability.

A turn-off xanthene-based fluorescent probe for detection of cysteine and its practical application in bioimaging and food samples.

BACKGROUND: Cys, as an essential amino acid that can be ingested from daily food, plays an important role in maintaining the oxidative balance in cells. Abnormal Cys levels in organisms will lead to various diseases. Therefore, it is of great significance to construct a fluorescent probe that can detect Cys levels in food and biological systems. RESULTS: Here, a turn-off type probe TA had been successfully synthesized, which attached diethylamine as the strong electron donor, acrylate as the weak electron donor, and xanthene as the π-bridge. TA showed wonderful selectivity, low detection limit, good photostability and well live-cell compatibility for Cys by reducing acrylate group to hydroxyl group of TAOH. The reaction mechanism was demonstrated by 1H NMR, ESI-MS spectra, pH-dependent response experiments, and DFT calculations. Importantly, the reason why TAOH exhibited no fluorescence was the disappearance of the ICT effect in the molecule due to the dominant existence of spirocyclic state of TAOH. In addition, the probe can be used not only for the imaging detection of Cys in A549 cells and zebrafish, but also for the detection of Cys levels in food samples. SIGNIFICANCE: This work provides a new idea for the design of Cys fluorescent probe, which may be beneficial to the comprehension of the potential mechanism of novel fluorescent probe.

A novel diarylethene-based fluorescence sensor for Zn2+ detection and its application.

A series of fluorometric sensors of Zn2+ have been synthesized due to the significant function of Zn2+ in the human body and environment. However, most of probes reported for detecting Zn2+ have high detection limit or low sensitivity. In this paper, an original Zn2+ sensor, namely 1o, was synthesized by diarylethene and 2-aminobenzamide. When Zn2+ was added, the fluorescence intensity of 1o increased by 11 times within 10 s, along with a fluorescence color change from dark to bright blue, and the detection limit (LOD) was calculated to be 0.329 µM. According to Job's plot curves, the binding mode of 1o and Zn2+ was measured as 1:1, which was further proved by 1H NMR spectra, HRMS and FT-IR spectra. The logic circuit was designed to take advantage of the fact that the fluorescence intensity of 1o can be controlled by Zn2+, EDTA, UV and Vis. In addition, Zn2+ in actual water samples were tested, in which the recovery rate of Zn2+ was between 96.5 % and 109 %. Furthermore, 1o was successfully made into a fluorescent test strip, which could be used to detect Zn2+ in the environment economically and conveniently.

Rational design of a FRET-based ratiometric fluorescent probe with large Pseudo-Stokes shift for detecting Hg2+ in living cells based on rhodamine and anthracene fluorophores.

The development of fluorescent dyes has been a continuing attractive research topic in the field of fluorescence sensing and bioimaging technologies, most of them were subject to a single signal change. In this work, a novel colorimetric and ratiometric fluorescent probe 1 based on rhodamine and anthracene groups was designed and synthesized via the fluorescence resonance energy transfer (FRET) mechanism. Probe 1 showed excellent selectivity, higher sensitivity and ratiometric response to Hg2+ in the CH3CN/H2O (1/1, v/v) system, with a fast response time (less than 30 s); The fluorescent color changed from purple to orange and the solution visible to the naked-eye changed from colorless to pink. The Pseudo-Stokes shift was 174 nm upon addition of Hg2+. The limit of detection (LOD) was calculated to be 0.81 µM and 0.38 µM according to fluorescence and UV/vis measurements, respectively. Furthermore, a possible mechanism for the detection of Hg2+ by probe 1 was verified by using 1H NMR, ESI-MS, and HPLC spectra. Meanwhile, probe 1 was successfully used for cell imaging for the detection of Hg2+ in living cells.

pH-responsive UV crosslinkable chitosan hydrogel via "thiol-ene" click chemistry for active modulating opposite drug release behaviors.

Numbers of UV crosslinkable chitosan hydrogels through chemical modification had drawn increasing attention, however most of these chitosan hydrogels lost the pH-responsive performance because plenty of amino groups (‒NH2) in chitosan were consumed by reacting with other functional groups. To construct a pH-responsive UV-crosslinkable chitosan hydrogel for active modulating drug release with desired behavior, C6-OH selectively modified chitosan via protection/deprotection strategy to amino groups was synthesized, the allyl groups on C6 site and amino groups on C2 site endowed chitosan with UV crosslinking capability and pH responsiveness, respectively. Rapid UV crosslinking gelation (30 s) with low-dose UV irradiation (4 mW/cm2) via "thiol-ene" click chemistry were demonstrated for the patterned microgel and in-situ formed hydrogel in vivo. The swelling and shrinkage of hydrogel could active modulate the opposite release behaviors of doxorubicin (DOX) and bovine serum albumin (BSA) in different pH medium. The smart UV-crosslinkable chitosan hydrogel via click chemistry might provide a new drug carrier for active modulating opposite drug release behaviors.

Nonswelling injectable chitosan hydrogel via UV crosslinking induced hydrophobic effect for minimally invasive tissue engineering.

Injectable chitosan hydrogels exhibit excellent biological properties for application in biomedical engineering, however most of these hydrogels have limited applicability because "Swelling" can induce volume expansion of conventional hydrogels implanted in the body damages the surrounding tissues. Here, we report a new "Nonswelling" pentenyl chitosan (PTL-CS) hydrogel via N‒acylation reaction to graft an UV crosslinkable short hydrophobic alkyl chain (n‒pentenyl groups). The incorporated pentenyl groups can be crosslinked by UV irradiation to form hydrophobic chains via combination termination, which generate strong hydrophobic effect to extrude the excess water in hydrogel, resulting in a "Nonswelling" state at biological temperature. Furthermore, the PTL-CS solution showed no cytotoxicity in vitro and minimally invasive treatment in vivo demonstrated the PTL-CS hydrogel no adverse effects in a rat model. The nonswelling injectable and UV crosslinkable chitosan hydrogel hold potential applications in smart biomaterials and biological engineering as well as providing a new natural hydrogel in minimally invasive tissue engineering..

Decoupled pH- and Thermo-Responsive Injectable Chitosan/PNIPAM Hydrogel via Thiol-Ene Click Chemistry for Potential Applications in Tissue Engineering.

Stimuli-responsive chitosan (CS) hydrogels exhibit great potential for drug delivery and tissue engineering; however, the structure of these stimuli-responsive CS hydrogels, such as dual pH- and thermo-responsive hydrogels, is difficult to control or needs additional crosslinking agents. Here, a new dual pH- and thermo-responsive hydrogel system is developed by combining pH-responsive C6 -OH allyl-modified CS (OAL-CS) with thermo-responsive poly(N-isopropylacrylamide) (PNIPAM). The thiol groups in PNIPAM and the allyl groups in OAL-CS can rapidly form crosslinking hydrogel network by "thiol-ene" click chemistry under UV irradiation. As expected, the swelling ratio of the OAL-CS/PNIPAM hydrogel can be controlled by changing pH and temperature. Moreover, the hydrogel displays non-cytotoxic nature toward human bone marrow mesenchymal stem cells, and the histological analyses reveal the subcutaneous tissue with no signs of inflammation after 5 days of injection in vivo. The results indicate that the new OAL-CS/PNIPAM hydrogel has potential to serve as a smart injectable platform for application in drug delivery and tissue engineering.

A ratiometric and colorimetric probe for detecting Hg2+ based on naphthalimide-rhodamine and its staining function in cell imaging.

In this work, a rhodamine derivative was developed as a colorimetric and ratiometric fluorescent probe for Hg2+. It exhibited a highly sensitive fluorescence response toward Hg2+. Importantly, studies revealed that the probe could be used for ratiometric detection of Hg2+, with a low detection limit of 0.679 µM. The mechanism of Hg2+ detection using compound 1 was confirmed by ESI-MS, 1H NMR, and HPLC. Upon the addition of Hg2+, the rhodamine receptor was induced to be in the ring-opening form via an Hg2+-promoted hydrolysis of rhodamine hydrazide to rhodamine acid. In addition to Hg2+ detection, the naphthalimide-rhodamine compound was proven to be effective in cell imaging.

A colorimetric and ratiometric fluorescent sensor for sequentially detecting Cu2+ and arginine based on a coumarin-rhodamine B derivative and its application for bioimaging.

In this work, a colorimetric and ratiometric fluorescent sensor based on a coumarin-rhodamine B hybrid for the sequential recognition of Cu2+ and arginine (Arg) via the FRET mechanism was designed and synthesized. With the addition of Cu2+, the solution displayed a colorimetric change from pale yellow to pink which is discernible by the naked eye. Additionally, the fluorescence intensities of the sensor exhibited ratiometric changes for the detection of Cu2+ at 490 and 615 nm under a single excitation wavelength of 350 nm, which corresponded to the emissions of coumarin and rhodamine B moieties, respectively. The fluorescence color change could be visualized from blue to pink. The limits of detection were determined to be as low as 0.50 and 0.47 µM for UV-vis and fluorescence measurements, respectively. More importantly, the sensor not only can recognize Cu2+ and form a sensor-Cu2+ complex but can also sequentially detect Arg with the resulting complex. The detection limits for Arg were as low as 0.60 µM (UV-vis measurement) and 0.33 µM (fluorescence measurement), respectively. A fluorescence imaging experiment in living cells demonstrated that the fabricated sensor could be utilized in ratiometric fluorescence imaging towards intracellular Cu2+, which is promising for the detection of low-level Cu2+ and Arg with potentially practical significance.

A solvent-dependent chemosensor for fluorimetric detection of Hg2+ and colorimetric detection of Cu2+ based on a new diarylethene with a rhodamine B unit.

A novel solvent-dependent chemosensor 1o based on a diarylethene containing a rhodamine B unit has been designed. It could be used as a dual-functional chemosensor for selective detection of Hg2+ and Cu2+ by monitoring the changes in the fluorescence and UV-vis spectral in different solvents. A striking fluorescence enhancement at 617 nm was observed in DMSO upon the addition of Hg2+. However, 1o showed a remarkable absorption band appeared with maximum absorption at 555 nm after the addition of Cu2+ in THF. The results of ESI-MS spectra and Job's plot confirmed a 1 : 1 binding stoichiometry between 1o and the two ions. The limits of detection of Hg2+ and Cu2+ were determined to be 0.14 µM and 0.51 µM, respectively. A 1 : 2 demultiplexer circuit was constructed by using UV light as data input, Cu2+ as the address input, and the absorbance at 555 nm and the absorbance ratio of (A 603/A 274) as the dual data outputs.

An ''off-on-off'' sensor for sequential detection of Cu2+ and hydrogen sulfide based on a naphthalimide-rhodamine B derivative and its application in dual-channel cell imaging.

A novel colorimetric and fluorometric sensor with unique dual-channel emission to sequentially detect Cu2+ and hydrogen sulfide (H2S) was synthesized from naphthalimide-rhodamine B through the PET and FRET mechanism. The sensor showed a selective "off-on" fluorescence response with a 120-fold increase toward Cu2+, and its limits of detection were 0.26 µM and 0.17 µM for UV-vis and fluorescence measurements, respectively. In addition, 1-Cu2+ was an efficient "on-off" sensor to detect H2S with detection limits of 0.40 µM (UV-vis measurement) and 0.23 µM (fluorescence measurement), respectively. Furthermore, the sensor can also be used for biological imaging of intracellular staining in living cells. Therefore, the sensor should be highly promising for the detection of low level Cu2+ and H2S with great potential in many practical applications.