An innovative fluorescent probe based on dicyanoisoflurone derivatives for differential detection of Hg2+ and Cu2+ and its applications in bacteria, cell imaging and food analysis.

BACKGROUND: Heavy metal pollution has become one of the world's most important environmental pollution, especially Hg2+ is enriched, it is easy to enter the human body through the food chain, bind to the sulfhydryl group in the protein, cause mercury poisoning. Traditional methods for detecting Hg2+ have obvious drawbacks, such as poor selectivity and long detection time. Fluorescence detection has attracted attention because of its good sensitivity and specificity detection ability. In previously reported probes for detecting Hg2+, Cu2+ often interferes. Therefore, it is of great practical significance to synthesize a fluorescent probe that can distinguish between Hg2+ and Cu2+. RESULTS: We have successfully synthesized the probe DFS, a fluorescent probe that can differentially detect Hg2+ and Cu2+, and the probe DFS has good selectivity and anti-interference ability for Hg2+ and Cu2+. The fluorescence intensity at 530 nm increased rapidly when Hg2+ was detected; during the Cu2+ detection, the fluorescence intensity at 636 nm gradually decreased, fluorescence quenching occurred, and the detection limits of Hg2+ and Cu2+ were 7.29 × 10-9 M and 2.13 × 10-9 M, respectively. Through biological experiments, it was found that probe DFS can complete the fluorescence imaging of Hg2+ and Cu2+ in Staphylococcus aureus and HUVEC cells, which has certain research value in the field of environmental monitoring and microbiology, and the probe DFS has low cytotoxicity, so it also has broad application prospects in the field of biological imaging. In addition, the probe DFS also has good applicability for Hg2+ and Cu2+ detection in actual samples. SIGNIFICANCE AND NOVELTY: This is a fluorescent probe that can distinguish between Hg2+ and Cu2+, the fluorescence emission peak appears at 530 nm when Hg2+ is detected; when detecting Cu2+, fluorescence quenching occurs at 636 nm, the fluorescence emission peak distance between Hg2+ and Cu2+ differs by 106 nm. This reduces mutual interference between Hg2+ and Cu2+ during detection, it provides a new idea for the detection of Hg2+ and Cu2+.

An innovative near-infrared fluorescent probe with FRET effect for the continuous detection of Zn2+ and PPi with high sensitivity and selectivity, and its application in bioimaging.

As the second most abundant transition metal element in the human body, zinc ions play an important role in the normal growth and development of the human body. We have successfully synthesized a near-infrared fluorescent probe with FRET effect for the detection of Zn2+. Probe DR6G has good selectivity and anti-interference ability for Zn2+. When Zn2+ is added to the probe DR6G solution, it responds completely within seconds, releasing red fluorescence with a detection limit of 2.02 × 10-8 M. As the main product of ATP hydrolysis, PPi is indispensable in various metabolic activities in cells and the human body. Due to the strong binding ability of Zn2+ and PPi, it is easy to form ZnPPi precipitation, so we added PPi to the solution to complete the Zn2+ detection, and realized the continuous detection of PPi, and the detection limit was 2.06 × 10-8 M. Since Zn2+ and PPi play an important role in vivo, it is of great practical significance to design and synthesize a fluorescent probe that can continuously detect Zn2+ and PPi. Biological experiments have shown that the probe DR6G has low cytotoxicity and can complete the detection of exogenous Zn2+ and PPi in cells and living mice in vitro. Bacterial experiments have shown that the DR6G probe also has certain research value in the field of environmental monitoring and microbiology. Due to the constant variation of the fluorescence signals of Zn2+ and PPi during detection, we designed the logic gate program. In practical applications, the probe DR6G can quantitatively detect Zn2+ in zinc-containing oral liquids and qualitatively detect PPi in toothpaste.

A novel "on-off-on" near-infrared fluorescent probe for Cu2+ and S2- continuous detection based on dicyanoisoflurone derivatives, and its application in bacterial imaging.

We have successfully synthesized a near-infrared fluorescent probe for the continuous detection of copper and sulfur ions. The probe has good selectivity and anti-interference ability against Cu2+ and S2-. The results show that after adding Cu2+ to the DL solution of the near-infrared fluorescent probe, Cu2+ forms a [DL + Cu2+] complex with the probe, which leads to fluorescence quenching due to the paramagnetism of Cu2+. The probe can be used for the quantitative detection of Cu2+ with a detection limit of 1.26 × 10-9 M. According to the Job's plot curve the binding stoichiometry between DL and Cu2+ is 1 : 1. Subsequently, S2- was added to the [DL + Cu2+] solution, because the precipitation dissolution equilibrium constant of CuS was Ksp = 1.27 × 10-36, so the binding capacity between Cu2+ and S2- was stronger, CuS precipitation was formed, and red fluorescence was re-released, and the quantitative detection of S2- was realized, and the detection limit was 3.50 × 10-8 M. Through bacterial imaging experiments, we found that the probe can accomplish the fluorescence imaging experiments of Staphylococcus aureus, indicating that the probe has good biopenetration and biocompatibility, and has application prospects in bioimaging and environmental monitoring. In addition, the probe DL has good suitability for Cu2+ and S2- detection in real samples.

Advances in electrospun nanofibrous membrane sensors for ion detection.

Harmful metal ions and toxic anions produced in industrial processes cause serious damage to the environment and human health. Chemical sensors are used as an efficient and convenient detection method for harmful ions. Electrospun fiber membranes are widely used in the field of solid-state chemical sensors due to high specific surface area, high porosity, and strong adsorption. This paper reviews the solid-state chemical sensors based on electrospinning technology for the detection of harmful heavy metal ions and toxic anions in water over the past decade. These electrospun fiber sensors have different preparation methods, sensing mechanisms, and sensing properties. The preparation method can be completed by physical doping, chemical modification, copolymerization, surface adsorption and self-assembly combined with electrospinning, and the material can also be combined with organic fluorescent molecules, biological matrix materials and precious metal materials. Sensing performance aspects can also be manifested as changes in color and fluorescence. By comparing the literature, we summarize the advantages and disadvantages of electrospinning technology in the field of ion sensing, and discuss the opportunities and challenges of electrospun fiber sensor research. We hope that this review can provide inspiration for the development of electrospun fiber sensors.

A novel fluorescent probe with aggregation induced emission (AIE) effect based on 1,4-dihydropyridine and its applications.

A fluorescent hydrazine hydrate probe (DMA) based on 1,4-dihydropyridine derivatives was designed and synthesized. The fluorescence emission peak of this probe is in the near-infrared region (667 nm), which has good selectivity to hydrazine hydrate and low detection limit (11 nM). Importantly, the probe exhibits aggregation-induced emission (AIE) characteristics. In addition, the probe is prepared with a portable test paper to realize the identification of hydrazine hydrate in the solution and the quantitative detection of hydrazine hydrate gas.

A novel Near-Infrared fluorescent probe for Zn2+ and CN- double detection based on dicyanoisfluorone derivatives with highly sensitive and selective, and its application in Bioimaging.

We have successfully synthesized NIRF as a near-infrared fluorescence probe for relay recognition of zinc and cyanide ions. The probe possesses well selectivity and anti-interference ability over common ions towards Zn2+ and CN-. The results showed that Zn2+ and the probe formed [NIRF-Zn2+] complex after added Zn2+ into the probe NIRF solution, which emited red fluorescence. The probe can be used for quantitative detection of Zn2+ with a detection limit of 4.61 × 10-8 M. It was determined that the binding stoichiometry between the NIRF and Zn2+ was 1:1 according to the job,s curve. Subsequently, CN- was added to the NIRF-Zn2+ solution, CN- combined with Zn2+ to generate [Zn(CN-)x]1-x due to the stronger binding ability between zinc ion and cyanogen, which lead to the red fluorescence disappeared. The quantitative detection of CN- was realized with a detection limit of 7.9 × 10*7 M. In addition, the probe has excellent specificity and selectivity for Zn2+ and CN-. And the probe can be stable in a wide range of pH. Through biological experiments, we found that it can complete cell imaging in macrophages and imaging of living mice, which has application prospects in Bioimaging. In addition, the probe NIRF has good applicability for Zn2+ and CN- detection in actual samples.

A novel mitochondrial-targeting fluorescent probe based on 1,4-dihydropyridine to visualize and monitor the viscosity of live cells and mice in vivo.

Cell viscosity is related to some diseases, such as diabetes, atherosclerosis, and Alzheimer's disease. These diseases can cause abnormal viscosity of the cell mitochondrial matrix. 1,4-Dihydropyridine (DHP) is an important organic compound with biological activity and is widely used in drug research. However, there are few studies on its optical properties, especially in the design of viscous fluorescent probes. In this study, a fluorescent probe for viscosity detection using 1,4-dihydropyridine as the fluorophore and indole iodide salt as the recognition group was designed and synthesized. The probe has the advantages of a deep-red emission, low cytotoxicity, good biocompatibility and excellent anti-interference ability. In addition, the probe also has the ability to target mitochondria and has been successfully applied to the detection of the viscosity response of HeLa cells and living mice, and has good clinical application potential.

A novel fluorescent probe based on a triphenylamine derivative for the detection of HSO3- with high sensitivity and selectivity.

A novel highly active fluorescence chemical sensor (TBQN) for HSO3- was synthesized by the Knoevenagel reaction based on triphenylamine-benzothiazole as a new fluorophore. The probe possessed good selectivity toward HSO3- and anti-interference ability with common ions. The fluorescence and UV-vis spectra of the TBQN probe were significantly changed after the addition of HSO3-. At the same time, the probe solution released obvious green fluorescence. Moreover, the limit of detection for HSO3- was calculated to be 3.19 × 10-8 M. The TBQN probe displayed a rapid response to HSO3- and it took about 3 min to complete the recognition. The detection mechanism is the nucleophilic addition reaction between HSO3- and -C[double bond, length as m-dash]C- in the probe molecule. The π-conjugation and ICT (intramolecular charge transfer) transition in the TBQN molecule were destroyed by this addition, which resulted in the change of the fluorescence before and after the addition of HSO3-. Then, the mechanism was verified by theoretical calculations, 1H NMR measurements and mass spectroscopy. In addition, the probe showed low cytotoxicity and could be used for biological imaging in RAW264.7 cells.

Development of a NIR fluorescent probe for highly selective and sensitive detection of cysteine in living cells and in vivo.

Cysteine (Cys) plays important physiological roles in the human body, and abnormal Cys concentrations can cause a variety of diseases. Thus, detecting Cys with high selectivity and sensitivity in vivo is important. Near-infrared (NIR) fluorescent probes are widely employed in biological detection because of their excellent optical properties such as minimal damage to biological samples, low background interference and high signal-to-noise ratio. However, few NIR fluorescent probes that can detect Cys over homocysteine (Hcy) and glutathione (GSH) have been reported because of their similar reactivity and structure. In this work, a highly water-soluble NIR probe (CYNA) for detecting Cys whose structure is similar to that of indocyanine green and is based on cyanine skeleton was synthesized and via aromatic nucleophilic substitution-rearrangement (SNAr-rearrangement) to specific recognize the cysteine. The probe showed high selectivity toward Cys and superior biosecurity, excellent biocompatibility and prolonged dynamic imaging. It also has long fluorescence emission wavelength (820 nm), low detection limit (14 nM) and was successfully applied for visualizing Cys in living cells and mice, which has great promise for applications in noninvasive vivo biological imaging and detection.

A novel 100% aqueous solution near-infrared ratiometric fluorescent CN- probe based on 1,4-dihydropyridines, with a large fluorescent emission peak shift.

1,4-Dihydropyridines are a class of drugs with a wide range of biological activities and pharmacological effects. However, there are few reports on its optical activity, especially its application on fluorescent CN- probe. In this experiment, we designed and synthesized a fluorescent probe based on 1,4-dihydropyridines to detect CN-. Interestingly, the probe exhibited outstanding properties such as 100% water soluble, near infrared, ratiometric, fast response, high selectivity and anti-interference ability for other ions. The color change indicated that the probe can be used for naked eye identification. In particular, the probe showed a super large fluorescent emission peak shift (260 nm). In addition, the reaction mechanism of the probe has been studied by 1H NMR titration, high resolution mass spectrometry and theoretical calculations.

A novel ratiometric fluorescent probe for differential detection of HSO3- and ClO- and application in cell imaging and tumor recognition.

By connecting 1,8-naphthalimide and indole sulfonate, a ratio fluorescent probe capable of differential detection of hydrogen sulfite and hypochlorite was synthesized for the first time. It was able to achieve the qualitative detection of HSO3- and ClO- with high sensitivity and selectivity, respectively. It provides a multi-purpose probe and is based on different emission channels without mutual interference. The probe has the advantages of larger Stokes shift (ClO-: 115 nm, HSO3-: 88 nm), longer λem (ClO-: 515 nm, HSO3-: 548 nm) and better water solubility (DMF/PBS = 1:99, v/v). In addition, the probe is a ratio fluorescence probe, which can detect fluorescence intensity with two different emission waves. It provides internal self-calibration, reduces interference from the background and increases detection accuracy. In vitro cytotoxicity and imaging experiments show that the probe can effectively perform the detection of exogenous HSO3- and ClO- in cells. It can also achieve the detection of HSO3- and ClO- in the plasma environment. Because the probe can detect endogenous ClO-, it also has a good prospect for biological application in identifying tumor cells. Graphical abstract.

Near-infrared turn-on fluorescent probe for discriminative detection of Cys and application in in vivo imaging.

Near-infrared (NIR) fluorescent probes are widely employed in biological detection because of their lower damage to biological samples, low background interference, and high signal-to-noise ratio. Herein, a highly water-soluble NIR probe (NIRHA) based on a hemicyanine skeleton and bearing an acrylate moiety was synthesized. The probe showed high selectivity toward cysteine (Cys) over homocysteine (Hcy) and glutathione (GSH). The probe also had low cytotoxicity and was successfully applied in HeLa cells and mouse experiments. Results of bioimaging experiments indicated that the probe was effective for visualizing endogenous Cys in vitro and in vivo.

Preparation of prolinamide with adamantane for aldol reaction catalysis in brine and separation using a poly(AN-MA-ß-CD) nanofibrous film via host-guest interaction.

Prolinamides with double-H potential were prepared and employed as organocatalysts in asymmetric aldol reactions. The catalyst with adamantane showed improved catalytic activity, which was further enhanced by using brine as the solvent. A series of aldol reactions in brine at 0 °C provided good yields (up to 98%) with high diastereoselectivities (>99 : 1) and enantioselectivities (>99%). The prepared catalyst was adsorbed by a nanofibrous film of poly(AN-MA-ß-CD) via host-guest interaction in the reaction system. The catalyst was separated from the film by applying ultrasound, with a total recovery of 96.2%. The catalyst was reused up to five times without a significant change in diastereoselectivity and enantioselectivity.

A novel "turn-on" thiooxofluorescein-based colorimetric and fluorescent sensor for Hg2+ and its application in living cells.

A novel water-soluble fluorescent probe FLS2 based on the thiooxofluorescein derivative has been firstly designed and synthesized. UV-vis absorption and fluorescence spectra studies showed that the FLS2 as a colorimetric and ratiometric fluorescent probe exhibited high selectivity and sensitivity towards Hg2+, which was mainly attributed to the special binding with the receptor unit accompanied with the spirolactam ring-opening progress. In addition, the probe FLS2 could be used as a naked-eye indicator for Hg2+ with reversible response. It displayed approximate 37-fold fluorescent enhancement at 529nm in the presence of only 2.0 equiv. Hg2+ and the detection limit was calculated at about 39nM. What's more, cellular imaging experiment revealed that the sensor had excellent biocompatibility and low cytotoxicity that could be utilized for monitoring Hg2+ in living cells.

Significant and sustaining elevation of blood oxygen induced by Chinese cupping therapy as assessed by near-infrared spectroscopy.

Cupping therapy has been used in traditional Chinese medicine for thousands of years to relieve muscle pain/tendency/fatigue and to cure or reduce symbols of other diseases. However, its therapeutic effect is sparsely interpreted in the language of modern physiology. To objectively evaluate its therapeutic effect, we focused on dry cupping treatment and utilized near-infrared spectroscopy (NIRS) to assess the concentration change in oxy-hemoglobin ([HbO2]), deoxy-hemoglobin ([Hb]), and blood volume in the course of cupping therapy over 13 volunteers on the infraspinatus muscle, where is usually applied for shoulder pains. Both a prominent drop in [Hb] and a significant elevation in [HbO2] in the tissue surrounding the cupping site were observed during both cupping and post-treatment, manifesting the enhancement of oxygen uptake. This resulting promotion indicates potential positive therapeutic effect of cupping therapy in hemodynamics for facilitating muscular functions.

A novel reaction-based colorimetric and ratiometric fluorescent sensor for cyanide anion with a large emission shift and high selectivity.

A hybrid carbazole-hemicyanine dye (Cac) has been developed as a novel colorimetric and ratiometric fluorescent sensor for cyanide detection. Upon treatment with cyanide, Cac displayed a remarkable fluorescence ratiometric response, with the emission wavelength displaying a very large emission shift (214 nm). The detection of cyanide was performed via the nucleophilic addition of cyanide anion to the indolium group of the sensor, which resulted in the blocking of the intramolecular charge transfer (ICT) process in the sensor, inducing a ratiometric fluorescence change and simultaneously an obvious color change. Furthermore, competitive anions did not showed any significant changes both in color and emission intensity ratio (I381/I595), indicating the high selectivity of the sensor to CN(-).

Colorimetric magnetic microspheres as chemosensor for Cu(2+) prepared from adamantane-modified rhodamine and ß-cyclodextrin-modified Fe3O4@SiO2 via host-guest interaction.

Adamantane-modified salicylrhodamine B and ß-cyclodextrin-modified Fe3O4@SiO2 were assemblied by host-guest interactions which induced novel inclusion complex magnetic nanoparticles (SFIC MNPs) colorimetric sensitive for Cu(2+) being prepared. The MNPs exhibit a clear color change from colorless to pink selectively and sensitively with the addition of Cu(2+) in the experiments of UV-visible spectra, and the detection limit measures up to 5.99×10(-6)M in solutions of CH3CN-H2O =1:10. The SFIC magnetic nanoparticles are superparamagnetic according to magnetic measurements and can be separated and collected easily with a commercial magnet in nine seconds. In addition, the microspheres have also showed good ability of separating for other ions from aqueous solutions due to a large number of hydroxyl groups on the surface.

Regenerable fluorescent nanosensors for monitoring and recovering metal ions based on photoactivatable monolayer self-assembly and host-guest interactions.

Efficient detection, removal, and recovery of heavy metal ions from aqueous environments represents a technologically challenging and ecologically urgent question in the face of increasing metal-related pollution and poisoning across the globe. Although small-molecule and entrapment-based nanoparticle sensors have been extensively explored for metal detection, neither of these extant strategies satisfies the critical needs for high-performance sensors that are inexpensive, efficient, and recyclable. Here we first report the development of a regenerable fluorescent nanosensor system for the selective and sensitive detection of multiple heavy metal ions, based on light-switchable monolayer self-assembly and host-guest interactions. The system exploits photocontrolled inclusion and exclusion responses of an α-cyclodextrin (CD)-containing surface conjugated with photoisomerizable azobenzene as a supramolecular system that undergoes reversible assembly and disassembly. The metal nanosensors can be facilely fabricated and photochemically switched between three chemically distinct entities, each having an excellent capacity for selective detecting specific metal ions (namely, Cu(2+), Fe(3+), Hg(2+)) in a chemical system and in assays on actual water samples with interfering contaminants.

A new fluorescent and colorimetric sensor for hydrazine and its application in biological systems.

Hydrazine is a very important industrial chemical and exhibits high toxicity to human beings. Here we have constructed a novel ICT-based fluorescence sensor with a high selectivity and sensitivity, rapid detection, and huge color-change. We used the sensor for hydrazine determination in live cells and also in live fish, and manufactured dipsticks using our sensor. The sensing mechanism is well rationalized with the aid of TD-DFT (time-dependent density functional theory) calculations.

Fluorescent and colorimetric magnetic microspheres as nanosensors for Hg2+ in aqueous solution prepared by a sol-gel grafting reaction and host-guest interaction.

Fluorescent sensing TSRh6G-ß-cyclodextrin fluorophore/adamantane-modified inclusion complex magnetic nanoparticles (TFIC MNPs) have been synthesized via the cooperation of a host-guest interaction and sol-gel grafting reaction. Powder X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and UV-visible absorption and emission spectroscopy have been employed to characterize the material. Fluorescence and UV-visible spectra have shown that the resultant multifunctional nanoparticle sensors exhibit selective 'turn-on' type fluorescent enhancements and a clear color change from light brown to pink with Hg(2+). Owing to a larger surface area and high permeability, TFIC MNPs exhibit remarkable selectivity and sensitivity for Hg(2+), and its detection limit measures up to the micromolar level in aqueous solution. Most importantly, magnetic measurements have shown that TFIC magnetic nanoparticles are superparamagnetic and they can be separated and collected easily using a commercial magnet. These results not only solve the limitations in practical sensing applications of nanosensors, but also enable the fabrication of other multifunctional nanostructure-based hybrid nanomaterials.