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.     

Two new rhodamine‐based fluorescent chemosensors for Fe3+ in aqueous solution

Two new rhodamine‐based fluorescent probes were synthesized and characterized by NMR, high resolution mass spectrometer (HR‐MS) and IR. The probes displayed a high selectivity for Fe³⁺ among environmentally and biologically relevant metal ions in aqueous solution (CH₃OH–H₂O = 3 : 2, v/v). The significant changes in the fluorescence color could be used for naked‐eye detection. Job's plot, IR and ¹H NMR indicated the formation of 1: 1 complexes between sensor 1 and Fe³⁺. The reversibility establishes the potential of both probes as chemosensors for Fe³⁺ detection. The probe showed highly selectivity in aqueous solution and could be used over the pH range between 5 and 9. A simple paper test‐strip system for the rapid monitoring of Fe³⁺ was developed, indicating its convenient use in environmental samples. Copyright © 2014 John Wiley & Sons, Ltd.     

A novel optical probe based on d‐penicillamine‐functionalized graphene quantum dots: Preparation and application as signal amplification element to minoring of ions in human biofluid

In this study, d ‐penicillamine‐functionalized graphene quantum dots (DPA‐GQD) has been synthesized, which significantly increases the fluorescence intensity of GQD. We used this simple fluorescent probe for metal ions detection in human plasma samples. Designed DPA‐GQD respond to Hg²⁺, Cu²⁺, Au²⁺, Ag⁺, Co²⁺, Zn²⁺, and Pb²⁺ with high sensitivity. The fluorescence intensity of this probe decreased significantly in the presence of metal ions such as, Hg²⁺, Cu²⁺, Au²⁺, Ag⁺, Co²⁺, Zn²⁺, and Pb²⁺. In this work, a promising probe for ions monitoring was introduced. Moreover, DPA‐GQD probe has been tested in plasma samples. The functionalized DPA‐GQDs exhibits great promise as an alternative to previous fluorescent probes for bio‐labeling, sensing, and other biomedical applications in aqueous solution.     

Two new reversible naphthalimide‐based fluorescent chemosensors for Hg2+

Naphthalimide‐based fluorescent probes 1 and 2 were synthesized, and were designed to form probe–Hg complexes through Hg²⁺ ions coordinated to the amide group and imidazole group. They showed high sensitivity and were selective ‘naked‐eye’ chemosensors for Hg²⁺ in phosphate buffer. The fluorescence of compounds 1 and 2 could be quenched up to 90% by the addition of Hg²⁺. Reversible probes can detect Hg²⁺ ions over a wide pH range (7.0–10.0). Copyright © 2015 John Wiley & Sons, Ltd.     

Highly selective and sensitive coumarin–triazole‐based fluorometric ‘turn‐off’ sensor for detection of Pb2+ ions

Exposure to even very low concentrations of Pb²⁺ is known to cause cardiovascular, neurological, developmental, and reproductive disorders, and affects children in particular more severely. Consequently, much effort has been dedicated to the development of colorimetric and fluorescent sensors that can selectively detect Pb²⁺ ions. Here, we describe the development of a triazole‐based fluorescent sensor L5 for Pb²⁺ ion detection. The fluorescence intensity of chemosensor L5 was selectively quenched by Pb²⁺ ions and a clear color change from colorless to yellow could be observed by the naked eye. Chemosensor L5 exhibited high sensitivity and selectivity towards Pb²⁺ ions in phosphate‐buffered solution [20 mM, 1:9 DMSO/H₂O (v/v), pH 8.0] with a 1:1 binding stoichiometry, a detection limit of 1.9 nM and a 6.76 × 10⁶ M^?1 binding constant. Additionally, low‐cost and easy‐to‐prepare test strips impregnated with chemosensor L5 were also produced for efficient of Pb²⁺ detection and proved the practical use of this test.     

Colorimetric chiral fluorescent sensors for Eu3+ and sequential enantioselective sensing of malate anion

Novel phenanthroline Schiff base fluorescent sensors L1 , L2 , and D1 were designed and synthesized. The sensing abilities of the compounds in the presence of metal cations (Li⁺, Na⁺, K⁺, Ag⁺, Mg²⁺, Ba²⁺, Ca²⁺, Mn²⁺, Pb²⁺, Hg²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Co²⁺, Cu²⁺, Cr³⁺, Fe³⁺, Fe²⁺, Al³⁺, and Eu³⁺) were studied by UV‐vis and fluorescent spectroscopy. The compounds L1 , L2 , and D1 could act as Eu³⁺ ion turn‐off fluorescent sensors based on ligand‐to‐metal binding mechanism in DMSO‐H₂O solution (v/v = 1:1, 10 mM Tris, pH = 7.4). Additionally, the L1 –Eu³⁺ and D1 –Eu³⁺ complexes could be applied as turn‐on enantioselective sensors sensing of malate anion isomers with color changes. Furthermore, biological experiments using living PC‐12 cells demonstrated that L1 and D1 had excellent membrane permeability and could be used as effective fluorescent sensors for detecting Eu³⁺ and malate anion in living cells.     

A highly selective colorimetric and long‐wavelength fluorescent probe for the detection of Hg2+

Currently, the fluorescent probe is an important method for detecting heavy metal ions, especially mercury ion (Hg²⁺), which is harmful to the health of humans and the environment due to its toxicity and extensive use. In this paper, we designed and synthesized a colorimetric and long‐wavelength fluorescent probe Hg‐P with high sensitivity and excellent selectivity, which could detect Hg²⁺ by the changes of visual color, fluorescence and absorption spectroscopy. With the addition of Hg²⁺ to probe Hg‐P solution, its color changed from yellow to pink, and showed a 171 nm red‐shifted absorption spectrum. Probe Hg‐P was used in real water and soil solution samples to detect Hg²⁺, and the result is satisfactory. Therefore, this new probe shows great value and application in detecting Hg²⁺ in the environment.     

Three colorimetric and off–on fluorescent chemosensors for Fe3+ in aqueous media

Three Rhodamine B derivatives were synthesized and characterized by ESI‐MS, NMR, HR‐MS and IR. The probes exhibit high selectivity and sensitivity towards Fe³⁺ over other metal ions in CH₃CN–water. Upon the addition of Fe³⁺, the spirocyclic ring of the probe was opened and a significant enhancement of visible color and fluorescence within the range of 540–700 nm was observed. The colorimetric and fluorescent response to Fe³⁺ can be conveniently detected even by the naked eye, which provides a facile method for the visual detection of Fe³⁺. Job's plot, fluorescence titration and MS indicated the formation of 1:2 complexes between the probes and Fe³⁺. The reversibility of the reaction establishes the potential of these probes as chemosensors for Fe³⁺ detection. Copyright © 2013 John Wiley & Sons, Ltd.     

Naked eye sensing of toxic metal ions in aqueous medium using thiophene‐based ligands and its application in living cells

Thiophene‐based diimine (R1) and monoimine (R2) were synthesized in a single step, and their cation binding affinity was tested using colorimetric and UV–vis spectral studies. R1 selectively shows a colorimetric turn‐on response for Pb²⁺, Hg²⁺ ions and colorimetric turn‐off with Sn²⁺ ions, and R2 shows visual response for Cu²⁺ and Hg²⁺ over other examined metal ions in aqueous medium. R1 forms 1:1 complex with Pb²⁺, Hg²⁺, and Sn²⁺ and exhibits fluorescence quenching, whereas R2 shows 2:1 complex with Hg²⁺, Cu²⁺ and shows fluorescence enhancement. The structural and electronic properties of the sensors and their metal complexes were also investigated using Density Functional Theory calculations. R2 was also successfully demonstrated as a fluorescent probe for detecting Cu²⁺ ions in living cells. Copyright © 2014 John Wiley & Sons, Ltd.     

Facile synthesis,cytotoxicity and bioimaging of Fe3+ selective fluorescent chemosensor

The designing and development of fluorescent chemosensors have recently been intensively explored for sensitive and specific detection of environmentally and biologically relevant metal ions in aqueous solution and living cells. Herein, we report the photophysical results of alanine substituted rhodamine B derivative 3 having specific binding affinity toward Fe³⁺ with micro molar concentration level. Through fluorescence titration at 599 nm, we were confirmed that ligand 3 exhibited ratiometric fluorescence response with remarkable enhancement in emission intensity by complexation between 3 and Fe³⁺ while it appeared no emission in case of the competitive ions (Sc³⁺, Yb³⁺, In³⁺, Ce³⁺, Sm³⁺, Cr³⁺, Sn²⁺, Pb²⁺, Ni²⁺, Co²⁺, Cu²⁺, Ba²⁺, Ca²⁺, Mg²⁺, Ag⁺, Cs⁺, Cu⁺, K⁺) in aqueous/methanol (60:40, v/v) at neutral pH. However, the fluorescence as well as colorimetric response of ligand–iron complex solution was quenched by addition of KCN which snatches the Fe³⁺ from complex and turn off the sensor confirming the recognition process was reversible. Furthermore, bioimaging studies against L-929 cells (mouse fibroblast cells) and BHK-21 (hamster kidney fibroblast), through confocal fluorescence microscopic experiment indicated that ligand showed good permeability and minimum toxicity against the tested cell lines.     

A new rhodamine‐based fluorescent chemodosimeter for mercuric ions in water media

A new rhodamine–ethylenediamine–nitrothiourea conjugate (RT) was synthesized and its sensing property as a fluorescent chemodosimeter toward metal ions was explored in water media. Analytical results from absorption and fluorescence spectra revealed that the addition of Hg²⁺ ions to the aqueous solution of the chemodosimeter RT caused a distinct fluorescence OFF–ON response with a remarkable visual color change from colorless to pink; however, no clear spectral and color changes were observed from other metal ions including: Zn²⁺, Cu²⁺, Cd²⁺, Pb²⁺, Ag⁺, Fe²⁺, Cr³⁺, Co³⁺, Ni²⁺, Ca²⁺, Mg²⁺, K⁺ and Na⁺. The sensing results and the molecular structure suggested that a Hg²⁺‐induced a desulfurization reaction and cyclic guanylation of the thiourea moiety followed by ring‐opening of the rhodamine spirolactam in RT are responsible for a distinct fluorescence turn‐on signal, indicating that RT is a remarkably sensitive and selective chemodosimeter for Hg²⁺ ions in aqueous solution. Hg²⁺ within a concentration range from 0.1 to 25 μM can be determined using RT as a chemodosimeter and a detection limit of 0.04 μM is achieved. Copyright © 2014 John Wiley & Sons, Ltd.     

A highly selective and sensitive turn‐on fluorescent probe for the detection of Al3+ and its bioimaging

A novel fluorescent sensor, 1‐((2‐hydroxynaphthalen‐1‐yl)methylene)urea (ocn) has been designed and applied as a highly selective and sensitive fluorescent probe for recognition of Al³⁺ in Tris–HCl (pH = 7.20) solution. The probe ocn exhibits an excellent selectivity to Al³⁺ over other examined metal ions, anions and amino acids with a prominent fluorescence ‘turn‐on’ at 438 nm. ocn binds to Al³⁺ with a 2:1 binding stoichiometry and the detection limit was 0.3 μM. Furthermore, its capability of biological application was evaluated and the results showed that the sensor could be used to detect Al³⁺ in living cells.     

The synthesis and modification of highly fluorescent carbon quantum dots for reversible detection of water‐soluble phosphonate‐1‐hydroxyethane‐1,1‐diphosphonic acid by fluorescence spectroscopy

Photoluminescent (PL) carbon quantum dots (CQDs) were prepared successfully using a facile and green procedure. They exhibited striking blue fluorescence and excellent optical properties, with a quantum yield as high as 61.44%. Due to the fluorescence quenching effect and the stronger complexing ability of the phosphoric acid group of 1‐hydroxyethane‐1,1‐diphosphonic acid (HEDP) to Fe³⁺ , CQDs doped with Fe³⁺ were adequately constructed as an efficient and sensitive fluorescent probe for HEDP‐specific sensing. The proposed fluorescent probe had a sensitive and rapid response in the range 5–70 μ M. Furthermore, quantitative molecular surface (QMS) analysis based on the Multiwfn program was applied to explore the complexation mode of HEDP and metal ions. The distribution of electrostatic potential (ESP), average local ionization energy (ALIE), the minimum value points and the position of the lone pair electrons on the surface of molecular van der Waals were further determined. More strikingly, this experiment achieved the quantitative detection of water‐soluble phosphonate‐HEDP, for the first time using fluorescence spectrometry. It has been proved to be an effective and intuitive sensing method for the detection of HEDP in real samples.     

Pyrazolone as a recognition site: Rhodamine 6G‐based fluorescent probe for the selective recognition of Fe3+ in acetonitrile–aqueous solution

Two novel Rhodamine–pyrazolone‐based colorimetric off–on fluorescent chemosensors for Fe³⁺ ions were designed and synthesized using pyrazolone as the recognition moiety and Rhodamine 6G as the signalling moiety. The photophysical properties and Fe³⁺‐binding properties of sensors L¹ and L² in acetonitrile–aqueous solution were also investigated. Both sensors successfully exhibit a remarkably ‘turn‐on’ response, toward Fe³⁺, which was attributed to 1: 2 complex formation between Fe³⁺ and L¹/L². The fluorescent and colorimetric response to Fe³⁺ can be detected by the naked eye, which provides a facile method for the visual detection of Fe³⁺. Copyright © 2014 John Wiley & Sons, Ltd.     

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.     

Carbazole–azine based fluorescence ‘off–on’ sensor for selective detection of Cu2+ and its live cell imaging

A new carbazole–azine based fluorescent sensor was synthesized and characterized. The selectivity of the sensor for Cu²⁺ over other counter ions in a dimethyl sulfoxide/H₂O mixture was shown through enhancement in fluorescence – an off to on transformation. The specificity of the probe towards Cu²⁺ was evident in ultraviolet/visible, fluorescence, Fourier transform infrared and mass studies. Application of the probe in the cell imaging and cytotoxicity of living cells is illustrated.     

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.     

A new fluorescent chemosensor for Hg2+ in aqueous solution

We prepared an aminothiourea‐derived Schiff base (DA) as a fluorescent chemosensor for Hg²⁺ ions. Addition of 1 equiv of Hg²⁺ ions to the aqueous solution of DA gave rise to an obvious fluorescence enhancement and the subsequent addition of more Hg²⁺ induced gradual fluorescence quenching. Other competing ions, including Pb²⁺, Cd²⁺, Cr³⁺, Zn²⁺, Fe²⁺, Co³⁺, Ni²⁺, Ca²⁺, Mg²⁺, K⁺ and Na⁺, did not induce any distinct fluorescence changes, indicating that DA can selectively detect Hg²⁺ ions in aqueous solution. Copyright © 2012 John Wiley & Sons, Ltd.     

Rhodamine-based “turn-on” fluorescent probe with high selectivity for Fe imaging in living cells

A rhodamine-based “turn-on” fluorescent probe 1 was synthesized with high yield. The recognizing behavior displays high selectivity of 1 toward Fe²⁺ with a 2:1 complex, and 1 exhibits a stable response for Fe²⁺ over a concentration range from 2 μM to 24 μM. Most importantly, probe is hardly interfered by other transition metal ions. Their fluorescent enhancement is observed in the presence of Fe²⁺ because of the ring-open interactions of spirocyclic. All measurements are made in PBS buffer environments simulating biological conditions to make them suitable candidates for fluorescent labeling of biological systems. Confocal laser scanning microscopy experiments have proven that probe can be used to monitor Fe²⁺ in living cells.     

A simply synthesized biphenyl substituted piperidin‐4‐one for the fluorescence chemosensing of Cd2+

Ion‐induced change in fluorescence is a straight‐forward method for detection of toxic metal ions showing immediate response. Cadmium ions are toxic to the environment. We report in this paper a piperidine‐4‐one‐based fluorescent chemosensor of Cd²⁺ ions, designed and synthesized by a simple method. The compound is characterized using infra‐red (IR) and ¹H–NMR spectral techniques. The chemosensor showed Cd²⁺ ion selectivity and sensitivity in aqueous solution. The stoichiometry and the binding constants were determined using fluorescence spectroscopy. Piperidine‐4‐one shows a 1:1 stoichiometric binding to Cd²⁺. The limit of detection of Cd²⁺ was reported.