Two‐channel near‐infrared fluorescence Ag+ ion sensing of a new star‐shaped dendrimer

A new near‐infrared fluorescence sensor PDI‐PD for Ag⁺ ions was successfully prepared and its structure characterized by ¹H nuclear magnetic resonance (NMR), ¹³C NMR and high‐resolution mass spectrometry; matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (HRMS MALDI‐TOF). The probe exhibited rapid, sensitive, and selective two‐channel fluorescence responses towards Ag⁺ ions and protons. The probe has a marked high binding affinity and high sensitivity for Ag⁺, with a detection limit of 1.4 × 10^?6 M. An approximately five‐fold enhanced core emission at 784 nm was attributed to fluorescence resonance energy transfer (FRET). The enhanced core emission of the probe with Ag⁺ ions based on photo‐induced electron transfer and FRET is discussed. In addition, the probe presented a visible colour change. All experimental results demonstrated that PDI‐PD is an efficient tool for the selective, sensitive and rapid detection of Ag⁺ ions and protons using two‐channel fluorescence responses.     

A highly selective aggregation‐induced emission fluorogen for sensitive detection of Al3+ in living cells

A Schiff's base derivative was synthesized using a condensation reaction between 8‐formyl‐7‐hydroxy‐4‐methylcoumarin and furan‐2‐carbohydrazide that produced marked aggregation‐induced emission and had excellent ability to specifically recognize aluminium ions (Al³⁺). This compound displayed faint fluorescence in the benign solvent dimethyl formamide, and exhibited obvious green fluorescence following addition of specific amounts of water. Moreover, it exhibited strong blue fluorescence after combination with Al³⁺ even in the presence of other interfering ions. These experimental results demonstrated that this derivative could be used as a fluorescence probe for Al³⁺. The advantages, including significant fluorescence change, high selectivity and sensitivity, and fast response, meant that this probe could be used both to detect Al³⁺ in water samples and for fluorescence imaging in living cells.     

Selective sensing Ca2+ with a spiropyran‐based fluorometric probe

Spiropyran (SP) and its derivatives operate between their ring opening and closing forms as a versatile molecular platform for the fluorescence detection of cations and anions, using a colour change for signalling. A functionalized SP fluorescence probe, L , was prepared and characterized. Probe L can detect Ca²⁺ with a fluorescence ‘turn‐on’ response in ethanol solution. It selectively binds Ca²⁺ to form a 1:1 ligand/metal complex, which produced a new emission band centred at 604 nm. The sensing result was clearly observed by the solution colour change from colourless to pink under visible light, and from blue to red under ultraviolet light. The detection limit was calculated to be 4.53 × 10^?8 M for Ca²⁺. The probe provides another possibility that SP‐based derivatives could be used for the development and detection of metal ions in environmental and physiological systems.     

A coumarin‐based fluorescent probe for Hg2+ and its application in living cells and zebrafish

Mercury (Hg) is a heavy metal with high toxicity and easy migration; it can be enriched through the food chain, and cause serious threats to the natural environment and human health. So, the development of a method that can be used to detect mercury ions (Hg²⁺) in the environment, in cells, and in organisms is very important. Here, a new 7‐hydroxycoumarin‐derived carbonothioate‐based probe ( CC‐Hg ) was designed and synthesized for detection of Hg²⁺. After addition of Hg²⁺, a large fluorescence enhancement was observed due to the formation of 7‐hydroxyl, which reinforced the intramolecular charge transfer process. The CC‐Hg probe had good water solubility and selectivity. Moreover, the probe was able to detect Hg²⁺ quantitatively over the concentration range 0–2 μM and with a detection limit of 7.9 nM. Importantly, we successfully applied the probe to detect Hg²⁺ in water samples, in living cells, and in zebrafish. The experimental results demonstrated its potential value in practical applications.     

A carbonothioate‐based highly selective fluorescent probe with a large Stokes shift for detection of Hg2+

Mercury (Hg) is one of the heavy metal pollutants in the environment. Even a very small amount of mercury can cause serious harm to human beings. Herein, we reported a new carbonothioate‐based fluorescent probe for the detection of Hg²⁺ without interference from other metal ions. This probe possessed a very large Stokes shift (192 nm), which could improve the detection sensitivity by minimizing the interferences resulted from self‐absorption or auto‐fluorescence. With the addition of Hg²⁺ to the probe solution, considerable fluorescence enhancement was observed. Additionally, the Hg²⁺ concentration of 0–16 μM and fluorescence intensity showed a good linear relationship (y = 22106× + 53108, R² = 0.9955). Finally, the proposed probe was used to detect Hg²⁺ in real water samples, and its result was satisfactory. Therefore, our proposed probe would provide a promising method for the determination of Hg²⁺ in the environment.     

A colorimetric fluorescent probe for rapid and specific detection of nitrite

The method of fluorescent probes has been an important technique for detection of nitrite (NO₂^?). As an important inorganic salt, excessive nitrite would threaten humans and the environment. In this paper, a colorimetric fluorescent probe P‐N (1,2‐diaminoanthraquinone) with rapid response and high selectivity, which could detect NO₂^? by visual colour changes and fluorescence spectroscopy is presented. The probe P‐N solution (pH 1) changed from pink to colourless with the addition of NO₂^? and fluorescence intensity at 639 nm clearly decreased. Good linear exists between fluorescence intensities and NO₂^? concentrations for the range 0–16 μM, and the detection limit was 54 nM (based on a 3σ/slope). Moreover, probe P‐N could also detect NO₂^? in real water samples, and results were all satisfactory. Probe P‐N shows great practical application value for detecting NO₂^? in the environment.     

Studies of the effect of halide ions on the fluorescence of quinine sulfate

The effect of halide ions (Cl^?, Br^? and I^?) on the fluorescence of quinine sulfate in dilute sulfuric acid solution was studied by fluorescence spectra, ultraviolet‐visible (UV‐visible) absorption spectra and fluorescence decay technique. The results exhibited that halide ions with heavier atomic mass could significantly reduce the fluorescence intensity of quinine sulfate, as a result, the order of fluorescence quenching caused by halide ions is Cl^? < Br^? < I^?. Therefore, halide ions with high concentration could seriously quench the fluorescence of quinine sulfate. The UV‐visible absorption spectra and fluorescence decay technique revealed that the fluorescence quenching of quinine sulfate caused by halide ions was attributed to dynamic quenching, static quenching process, self‐quenching fluorescence effect and electronic transfer.     

Rapid and visual detection for hypochlorite of an AIE enhanced fluorescence probe

In this paper, a new ‘turn‐on' fluorescence probe for the rapid, sensitive, and visual detection of hypochlorite is reported. The push–pull type trianiline–tricyanofuran‐based fluorescent probe was prepared using a condensation reaction between tricyanofuran and the thiophene–trianiline derivative that had high quantum yields and showed aggregation‐induced emission enhanced properties. Upon exposure to hypochlorite, prominent fluorescence enhancement of the probe was observed via the release of the fluorophore from the probe. The probe showed a ratiometric absorption change at 315 nm and 575 nm. Importantly, the probe showed an excellent detection limit for hypochlorite at 1.2 × 10^?7 M in solution and it was successfully applied for monitoring hypochlorite in waste water by test strip. This work reports a new fluorescence analytical sensing method for hypochlorite that has potential practical value in environmental monitoring and biological discrimination.     

Rhodamine-based ‘turn-on’ fluorescent probe for Cu(II) and its fluorescence imaging in living cells

A novel rhodamine spirolactam derivative 3′,6′-Bis(diethylamino)-2-(2-hydroxyethylamino) spiro[isoindoline-1,9′-xanthen]-3-one (RO1) was synthesized, and characterized by high-resolution mass spectrometry (HRMS), X-ray crystallography, Infrared spectroscopy (IR), and ¹H NMR and ¹³C NMR spectroscopy. RO1 exhibited highly sensitive and exclusively selective fluorescence response toward Cu²⁺ over other metal ions with a detection limit of 0.56 ppb in mixed aqueous solution. The fluorescence was pH-independent in the wide range pH 3.1–11.6. The turn-on fluorescence enhancement of the probe is based on Cu²⁺ induced ring-opening mechanism of the rhodamine spirolactam. Moreover, by means of fluorescence microscopy experiments, it was demonstrated that RO1 could monitor trace Cu²⁺ changes by live cell imaging.     

Nitrogen‐doped carbon dots as a fluorescent probe for the highly sensitive detection of Ag+ and cell imaging

An easy hydrothermal synthesis strategy was applied to synthesize green‐yellow emitting nitrogen‐doped carbon dots (N‐CDs) using 1,2‐diaminobenzene as the carbon source, and dicyandiamide as the dopant. The nitrogen‐doped CDs resulted in improvement in the electronic characteristics and surface chemical activities. N‐CDs exhibited bright fluorescence emission and could response to Ag⁺ selectively and sensitively. Other ions produced nearly no interference. A N‐CDs based fluorescent probe was then applied to sensitively determine Ag⁺ with a detection limit of 5 × 10^?8 mol/L. The method was applied to the determination of Ag⁺ dissolved in water. Finally, negligibly cytotoxic, excellently biocompatibile, and highly fluorescent carbon dots were applied for HepG2 cell imaging and the quenched fluorescence by adding Ag⁺, which indicated its potential applications.     

An OFF–ON–OFF type fluorescent probe based on a naphthalene derivative for Al3+ and F− ions and its biological application

A novel fluorescent probe‐based naphthalene Schiff, 1‐(C2‐glucosyl‐ylimino‐methyl)‐naphthalene‐2‐ol (L) was synthesized by coupling d ‐glucosamine hydrochloride with 2‐hydroxy‐1‐naphthaldehyde. It exhibited excellent selectivity and highly sensitivity for Al³⁺ in ethanol with a strong fluorescence response, while other common metal ions such as Pb²⁺, Mg²⁺, Cu²⁺, Co²⁺, Ni²⁺, Cd²⁺, Fe²⁺, Mn²⁺, Hg²⁺, Li⁺, Na⁺, K⁺, Fe³⁺, Cr³⁺, Zn²⁺, Ag⁺, Ba²⁺ and Ca²⁺ did not cause the same fluorescence response. The probe selectively bound Al³⁺ with a binding constant (K_a) of 5.748 × 10³ M^?1 and a lowest detection limit (LOD) of 4.08 nM. Moreover, the study found that the fluorescence of the L ? Al³⁺ complex could be quenched after addition of F^? in the same medium, while other anions, including Cl^?, Br^?, I^?, NO₂^?, NO₃^?, ClO₄^?, CO₃^2?, HCO₃^?, SO₄^2?, HSO₄^?, CH₃COO^?, PO₄^3?, HPO₄^2?, S^2? and S₂O₃^2? had nearly no influence on probe behaviour. Binding of the [L ? Al³⁺] complex to a F^? anion was established by different fluorescence titration studies, with a detection limit of 3.2 nM in ethanol. The fluorescent probe was also successfully applied in the imaging detection of Al³⁺ and F^? in living cells.     

Synthesis and application of a “turn on” fluorescent probe for glutathione based on a copper complex of coumarin hydrazide Schiff base derivative

Discrimination and quantification of intracellular biothiols, such as cysteine (Cys), homocysteine (Hcy), glutathione (GSH) under physiological conditions is significant for academic research and disease diagnosis. A new fluorescent probe (complex 1-Cu²⁺) for discriminate detection of GSH was prepared by copper ions coordinate with coumarin carbohydrazide Schiff base derivative 1. In suitable buffer solution (CH₃CN: HEPES = 3:2, v/v) and under appropriate pH condition (pH = 7.2–7.4), the UV–vis spectroscopy experiments showed that compound 1 and copper ion exhibited a 1:1 ratio binding mode and moderate binding ability. Fluorescence quenching of compound 1 was observed when it complexed with Cu²⁺ ions. An obviously fluorescence restoration appeared after addition of GSH to the solution of probe, which also exhibited a highly selectivity relative to cysteine (Cys) and homocysteine (Hcy) in the amino acid competitive experiments. The minimum detection limit was calculated to 0.12 μM by fluorescent method, which was distinctly below the physiological concentration of GSH in live cells. Its biological application to detect the endogenous GSH was further proved by the HepG2 cell fluorescence image test.     

Construction of a novel turn‐on–off fluorescence sensor used for highly selective detection of thiamine via its quenching effect on o‐phen‐Zn2+ complex

In this work, a simple and selective fluorescence sensor approach called ‘turn‐on–off’ for the determination of thiamine (TM) has been developed. As known, the o‐phenanthroline (o‐phen) has inner fluorescence, though when reacted with zinc ions to form the o‐phen–Zn²⁺ complex the fluorescence intensity was enhanced effectively, while upon addition of TM into the o‐phen–Zn²⁺ complex solution, the intensity of the system was gently quenched, which was termed the ‘turn‐on–off’ probe. Notably, the method possessed highly selective, sensitive determination for TM with a detection limit of 0.25 μmol L^?1 and the reduced fluorescence intensity was proportional to the concentration of TM in the range 0.84–80.0 μmol L^?1. Besides, the proposed mechanism was also investigated through exploring the Fourier transform infrared (FT‐IR), nuclear magnetic resonance (NMR) spectroscopy. Furthermore, this manner was successfully applied into practical samples for TM detection with satisfactory results.     

Design and synthesis of a new fluorescent probe for cascade detection of Zn2+ and H2PO4− in water and targeted imaging of living cells

Design and synthesis of new fluorescence probes with good water‐solubility is of great importance to better understanding the significant role of ions which are related to biology and the environment. As important ions, zinc ion (Zn²⁺) and dihydrogen phosphate ion (H₂PO₄^?) display essential roles in living systems, and quantitative detection of these ions in water is still a challenge. In order to consider the significant role of the galactose moiety in the design of a water‐soluble fluorescence sensor, herein, we have developed a novel probe, Gal‐AQTF, for the cascade detection of Zn²⁺ and H₂PO₄^? with excellent selectivity in water. Through the introduction of the galactose moiety onto the sensor AQTF, which has been reported earlier by us, the water‐solubility, cell compatibility and targeting ability were enhanced. Gal‐AQTF has been successfully applied in the imaging of the living cells of HepG2 and A549, and illustrated good selectivity for the HepG2 cells which overly express the asialoglycoprotein (ASGP) receptor.     

Fluorescent sensors based on quinoline‐containing styrylcyanine: determination of ferric ions,hydrogen peroxide,and glucose,pH‐sensitive properties and bioimaging

A novel styrylcyanine‐based fluorescent probe 1 was designed and synthesized via facile methods. Ferric ions quenched the fluorescence of probe 1, whereas the addition of ferrous ions led to only small changes in the fluorescence signal. When hydrogen peroxide was introduced into the solution containing probe 1 and Fe²⁺, Fe²⁺ was oxidized to Fe³⁺, resulting in the quenching of the fluorescence. The probe 1/Fe²⁺ solution fluorescence could also be quenched by H₂O₂ released from glucose oxidation by glucose oxidase (GOD), which means that probe 1/Fe²⁺ platform could be used to detect glucose. Probe 1 is fluorescent in basic and neutral media but almost non‐fluorescent in strong acidic environments. Such behaviour enables it to work as a fluorescent pH sensor in both the solution and solid states and as a chemosensor for detecting volatile organic compounds with high acidity and basicity. Subsequently, the fluorescence microscopic images of probe 1 in live cells and in zebrafish were achieved successfully, suggesting that the probe has good cell membrane permeability and a potential application for imaging in living cells and living organisms. Copyright © 2014 John Wiley & Sons, Ltd.     

A novel fluorescent probe based on rhodamine hydrazone derivatives bearing a thiophene group for Al3+

In the present work, a novel 5‐methyl‐thiophene‐carbaldehyde‐functionalized rhodamine 6G Schiff base (RA) was designed and easily prepared as an Al³⁺ fluorescent and colorimetric probe, which could selectively and sensitively detect Al³⁺ by showing enhanced fluorescence emission. Meanwhile distinct color variation from colorless to pink also provided ‘naked eye’ detection of Al³⁺, due to the ring spirolactam opening of the rhodamine derivative. Other metal ions (including K⁺, Mg²⁺, Na⁺, Ba²⁺, Mn²⁺, Cd²⁺, Fe²⁺, Ni²⁺, Pb²⁺, Zn²⁺, Hg²⁺, Co²⁺, Li⁺, Sr²⁺ and Cu²⁺) could only induce limited interference. The detection limit of the fluorescent probe was estimated to be 4.17 × 10^?6 M, the binding constant of the RA–Al³⁺ complex was 1.4 × 10⁶ M^?1. Moreover, this fluorescent probe RA possessed high reversibility. As aluminum is a ubiquitous metal in nature and plays vital roles in many biological processes, this chemosensor could be explored for biological study applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Electrophoresis–chemiluminescence detection of phenols catalyzed by hemin

Based on the catalytic activity of hemin, an efficient biocatalyst, an indirect capillary electrophoresis–chemiluminescence (CE‐CL) detection method for phenols using a hemin–luminol–hydrogen peroxide system was developed. Through a series of static injection experiments, hemin was found to perform best in a neutral solution rather than an acidic or alkaline medium. Although halide ions such as Br^? and F^? could further enhance the CL signal catalyzed by hemin, it is difficult to apply these conditions to this CE‐CL detection system because of the self‐polymerization of hemin, as it hinders the CE process. The addition of concentrated ammonium hydroxide to an aqueous/dimethyl sulfoxide solution of hemin–luminol afforded a stable CE‐CL baseline. The indirect CE‐CL detection of five phenols using this method gave the following limits of detections: 4.8 × 10^?8 mol/L (o‐sec‐butylphenol), 4.9 × 10^?8 mol/L (o‐cresol), 5.4 × 10^?8 mol/L (m‐cresol), 5.3 × 10^?8 mol/L (2,4‐dichlorophenol) and 7.1 × 10^?8 mol/L (phenol). Copyright © 2013 John Wiley & Sons, Ltd.     

Unraveling Geometrical Site Confinement in Highly Efficient Iron‐Doped Electrocatalysts toward Oxygen Evolution Reaction

Introduction of iron in various catalytic systems has served a crucial function to significantly enhance the catalytic activity toward oxygen evolution reaction (OER), but the relationship between material properties and catalysis is still elusive. In this study, by regulating the distinctive geometric sites in spinel, Fe occupies the octahedral sites (Fe³⁺_(Oh)) and confines Co to the tetrahedral site (Co²⁺_(Td)), resulting in a strikingly high activity (η_{j = 10 mA cm}^?2 = 229 mV and η_{j = 100 mA cm}^?2 = 281 mV). Further enrichment of Fe ions would occupy the tetrahedral sites to decline the amount of Co²⁺_(Td) and deteriorate the OER activity. It is also found that similar tafel slope and peak frequency in Bode plot of electrochemical impedance spectroscopy indicate that Co²⁺_(Td) ions are primarily in charge of water oxidation catalytic center. By means of electrochemical techniques and in situ X‐ray absorption spectroscopy, it is proposed that Fe³⁺_(Oh) ions mainly confine cobalt ions to the tetrahedral site to restrain the multipath transfer of cobalt ions during the dynamic structural transformation between spinel and oxyhydroxide, continuously activating the catalytic behavior of Co²⁺_(Td) ions. This material‐related insight provides an indication for the design of highly efficient OER electrocatalysts.     

Phenothiazine–rhodamine‐based colorimetric and fluorogenic ‘turn‐on' sensor for Zn2+ and bioimaging studies in live cells

A phenothiazine–rhodamine (PTRH) fluorescent dyad was synthesized and its ability to selectively sense Zn²⁺ ions in solution and in in vitro cell lines was tested using various techniques. When compared with other competing metal ions, the PTRH probe showed the high selectivity for Zn²⁺ ions that was supported by electronic and emission spectral analyses. The emission band at 528 nm for the PTRH probe indicated the ring closed form of PTRH, as for Zn²⁺ ion binding to PTRH, the λ_em get shift to 608 nm was accompanied by a pale yellow to pink colour (under visible light) and green to pinkish red fluorescence emission (under UV light) due to ring opening of the spirolactam moiety in the PTRH ligand. Spectral overlap of the donor emission band and the absorption band of the ring opened form of the acceptor moiety contributed towards the fluorescence resonance energy transfer ON mechanism for Zn²⁺ ion detection. The PTRH sensor had the lowest detection limit for Zn²⁺, found to be 2.89 × 10^?8 M. The sensor also demonstrated good sensing application with minimum toxicity for in vitro analyses using HeLa cells.     

A selective and sensitive turn-on chemosensor for detection of Fe3+ in aqueous solution and its cell imaging in dorsal root ganglia neurons and MKN-45 cells

A new turn-on fluorescent chemosensor (RBTM) for Fe³⁺ was designed based on Rhodamine B and a thiocarbonylimidazole moiety. The spectroscopic probe used for characterization of the synthesized system showed 300-fold fluorescence enhancement for the detection of Fe³⁺ with a 1:1 stoichiometry in EtOH/H₂O solution (2:1, v/v, HEPES buffer, 1 mM, pH 7.30). Upon addition of Fe³⁺ in aqueous ethanol, the probe displayed a significant fluorescence enhancement and a distinct color change (colorless to pink) that can be detected by the naked eye. The binding constant between the probe and Fe³⁺ was determined to be 1.16 × 10⁴ M⁻¹ and the corresponding detection limit was calculated to be 0.256 µM. In addition, the energy gaps between the HOMO and LUMO in RBTM and RBTM-Fe³⁺ were calculated using DFT calculations to be 92.93 kcal/mol and 37.49 kcal/mol, respectively. The results indicate that binding of Fe³⁺ to RBTM lowered the HOMO–LUMO energy gap of the complex and stabilized the system. Fluorescence imaging experiments demonstrated that RBTM can be used as a fluorescent probe to detect Fe³⁺ in MKN-45 cells and dorsal root ganglia, thus revealing that RBTM could be used for biological applications.