Iron(III) selective molecular and supramolecular fluorescent probes

Pyrene-Phosphonate Conjugate: Aggregation-Induced Enhanced Emission, and Selective Fe3+ Ions Sensing Properties

A new pyrene-phosphonate colorimetric receptor 1 has been designed and synthesized in a one-step process via amide bond formation between pyrene butyric acid chloride and phosphonate-appended aniline. The pyrene-phosphonate receptor 1 showed aggregation-induced enhanced emission (AIEE) properties in water/acetonitrile (ACN) solutions. Dynamic light scattering (DLS) characterization revealed that the aggregates of receptor 1 at 80% water fraction have an average size of ≈142 nm. Field emission scanning electron microscopy (FE-SEM) analysis confirmed the formation of spherical aggregates upon solvent evaporation. The sensing properties of receptor 1 were investigated by UV-vis, fluorescence emission spectroscopy, and other optical methods. Among the tested metal ions, receptor 1 is capable of recognizing the Fe³⁺ ion selectively. The changes in spectral measurements were explained on the basis of complex formation. The composition of receptor 1 and Fe³⁺ ions was determined by using Job's plot and found to be 1:1. The receptor 1-Fe³⁺ complex showed a reversible UV-vis response in the presence of EDTA.

A New Polymer-Based Fluorescent Chemosensor Incorporating Propane-1,3-Dione and 2,5-Diethynylbenzene Moieties for Detection of Copper(II) and Iron(III)

A novel conjugated polymer (PDBDBM) was developed by the polymerization of 1,4-dioctyloxy-2,5-diethynylbenzene with 1,3-bis(4-bromophenyl)propane-1,3-dione based on Pd-catalyzed Sonogashira-coupling reaction. The obtained polymer PDBDBM exhibited bright green photoluminescence under UV irradiation. According to the metal ion titration experiments, PDBDBM showed high sensitivity and selectivity for detection of Cu2+ and Fe3+ over other metal ions. The fluorescent detection limits of PDBDBM were calculated to be 5 nM for Cu2+ and 0.4 μM for Fe3+ and the Stern⁻Volmer quenching constant for Cu2+ and Fe3+ were found to be 1.28 × 10⁸ M-1 and 2.40 × 10⁴ M-1, respectively. These results indicated that the polymer can be used as a potential probe for Cu2+ and Fe3+ detection.

A universal fluorogenic switch for Fe(ii) ion based on N-oxide chemistry permits the visualization of intracellular redox equilibrium shift towards labile iron in hypoxic tumor cells

Iron (Fe) species play a number of biologically and pathologically important roles. In particular, iron is a key element in oxygen sensing in living tissue where its metabolism is intimately linked with oxygen metabolism. Regulation of redox balance of labile iron species to prevent the generation of iron-catalyzed reactive oxygen species (ROS) is critical to survival. However, studies on the redox homeostasis of iron species are challenging because of a lack of a redox-state-specific detection method for iron, in particular, labile Fe2+. In this study, a universal fluorogenic switching system is established, which is responsive to Fe2+ ion based on a unique N-oxide chemistry in which dialkylarylamine N-oxide is selectively deoxygenized by Fe2+ to generate various fluorescent probes of Fe2+-CoNox-1 (blue), FluNox-1 (green), and SiRhoNox-1 (red). All the probes exhibited fluorescence enhancement against Fe2+ with high selectivity both in cuvette and in living cells. Among the probes, SiRhoNox-1 showed an excellent fluorescence response with respect to both reaction rate and off/on signal contrast. Imaging studies were performed showing the intracellular redox equilibrium shift towards labile iron in response to reduced oxygen tension in living cells and 3D tumor spheroids using SiRhoNox-1, and it was found that the hypoxia induction of labile Fe2+ is independent of iron uptake, hypoxia-induced signaling, and hypoxia-activated enzymes. The present studies demonstrate the feasibility of developing sensitive and specific fluorescent probes for Fe2+ with refined photophysical characteristics that enable their broad application in the study of iron in various physiological and pathological conditions.

Synthetically simple, click-generated quinoline-based Fe3+ sensors

Simple quinoline-based fluorescent probes for Fe³⁺ have been efficiently synthesized through 'click' reaction. Both probes gave intense fluorescence compared to 8-hydroquinoline in various organic solvents due to the inhibition of the excited state intramolecular photon transfer process, while showing dramatically quenched and red-shifted fluorescence in an aqueous solution, which can be attributed to the hydrogen bond-induced intermolecular excited state proton transfer process. In the presence of Fe³⁺ or in an acidic condition (pH less than 4.0), both probes showed similar quenching of the emission and over 100 nm red-shifts of their emission maxima. The binding mode between the probes and Fe³⁺ has been found to be 1:1 based on Job's plot. A highly sensitive and selective response in their absorption and emission towards Fe³⁺ over many other metal ions, including Cr³⁺ and Cu²⁺, was observed and may be the result of the ground state metal to ligand charge transfer effect from Fe³⁺ to quinoline ligands.

A water-stable lanthanide metal-organic framework for fluorimetric detection of ferric ions and tryptophan

The preparation of a highly water stable and porous lanthanide metal-organic framework (MOF) nanoparticles (denoted SUMOF-7II; SU refers to Stockholm University) is described. SUMOF-7II was synthesized starting from the tritopic linker of 2,4,6-tri-p-carboxyphenyl pyridine (H3L2) and La(III) as metal clusters. SUMOF-7II forms a stable dispersion and displays high fluorescence emission with small variation over the pH range of 6 to 12. Its fluorescence is selectively quenched by Fe(III) ions compared to other metal ions. The intensity of the fluorescene emission drops drops linearly in 16.6-167 μM Fe(III) concentration range, and Stern-Volmer plots are linear. The limit of detection (LOD) is 16.6 μM (at an S/N ratio of >3). This indicator probe can also be used for selective detection of tryptophan among several amino acids. Compared to the free linker H3L2, SUMOF-7II offers improved sensitivity and selectivity of the investigated species. Graphical abstractA water-stable porous lanthanide metal-organic framework SUMOF-7II (La) has shown to be an excellent probe for the detection of ferric ions among other metal ions, and tryptophan among other amino acids in aqueous solution. The new probe displays high and stable fluorescence signal in a wide pH range (6-12).

Red Emissive Sulfur, Nitrogen Codoped Carbon Dots and Their Application in Ion Detection and Theraonostics

It is highly desirable and a great challenge for red light emission of carbon dots under long wavelength excitation. Here, we developed a facile route to synthesize carbon dots with red emission due to the doping effect of S and N elements, borrowing from the concept of the semiconductor. The maximum emission locates at 594 nm under 560 nm excitation. The absolute photoluminescence (PL) quantum yield (QY) is as high as 29% and 22% in ethanol and water, respectively. XPS and FTIR spectra illustrated that there exist -SCN and -COOH groups on the surface of the carbon dots. They endow the carbon dots with high sensitivity for ion detection of Fe³⁺. The quenched PL emission of Fe³⁺-S,N-CDs can be recovered by adding ascorbic acid to release the -COOH and -SCN group due to Fe²⁺ formation in the presence of ascorbic acid. High PL QY of red emission is beneficial to application in bioimaging. Doxorubicin was loaded onto carbon dots through π-π stacking to form a theranostic agent. When the CD-Dox was injected into the tumor site, a strong PL emission was observed. The PL intensity indicates the concentration of the theranostic agent. After 7 times injection, both the tumor size and weight clearly decrease. The results demonstrate that the S,N-CDs are a potentially excellent bioimaging component in the theranostic field.

Selective recognition of Cu (II) and Fe (III) using a pyrene based chemosensor

A pyrene-based colorimetric chemosensor 1-(pyren-1-yl)-N,N-bis-(pyridine-2-ylmethyl)methanamine (1) was synthesised for selective detection of Cu (II) and Fe (III) over the other metal cations Ni²⁺, Mg²⁺, Cd²⁺, Hg²⁺, Na⁺, K⁺, Ca²⁺, Co²⁺, Cr³⁺, Pb²⁺ and Zn²⁺. The significant changes in UV-vis absorption band of receptor 1 and the emergence of 660nm band in presence of Cu²⁺ ion indicates the selective binding of Cu²⁺ ion as compared to other metal cations which could easily be identified from the naked eye strong colour change. Job plots suggest a 1:1 and 2:1 stoichiometric binding of Cu²⁺ and Fe³⁺, respectively, which was evidenced by ESI-MS analysis. Chemosensor 1 explores a cost-effective and selective colorimetric sensor for naked eye detection of trace amount of Cu²⁺ and Fe³⁺ ions in presence of other metal cations.

Applications of vitamin B6 cofactor pyridoxal 5'-phosphate and pyridoxal 5'-phosphate crowned gold nanoparticles for optical sensing of metal ions

Vitamin B6 cofactor pyridoxal 5'-phosphate (PLP) and PLP crowned gold nanoparticles (PLP-AuNPs) was applied for the optical chemosensing of metal ions in aqueous medium. PLP showed a visually detectable colour change from colourless to yellow and 'turn-off' fluorescence in the presence of Fe³⁺. The fluorescence intensity of PLP at 433nm was also blue-shifted and enhanced at 395nm upon addition of Al³⁺. When the PLP was functionalized over AuNPs surface, the wine red colour of PLP-AuNPs was turned to purplish-blue and the SPR band at ~525nm was red-shifted upon addition of Al³⁺, Cd²⁺ and Pb²⁺ due to the complexation-induced aggregation of nanoparticles. The developed sensing systems exhibited good selectivity and specificity for the detected analytes (Fe³⁺, Al³⁺, Cd²⁺ and Pb²⁺).

A multifunctional Schiff base as a fluorescence sensor for Fe3+ and Zn2+ ions, and a colorimetric sensor for Cu2+ and applications

Chemosensors play important parts in the selective recognition of ions, which is widely applied in various fields of environment, industry and biological sciences. In this work, a chemosensor for multi-metal ions based on rhodamine B derivative was synthesized, which could selectively recognize various metal ions in different solvent system. The addition of Cu²⁺ caused the color change from colorless to pink in EtOH/H₂O (v/v=1:1) solvent system, which could be quickly identified by the naked eyes with a detection limit of 8.27×10^-8M. In ethanol solution system, the addition of Fe³⁺ and Zn²⁺ caused different fluorescence changes with the detection limit of 2.12×10^-7M and 6.64×10^-7M respectively. The binding ratios are 1:1 (1-Cu²⁺), 2:1 (1-Fe³⁺) and 1:1 (1-Zn²⁺), respectively. Meanwhile, the probe 1 was used to detect the trace metal ions in real water samples. Besides, the probe 1 showed sensitive fluorescence signals for Fe³⁺ in biological cells. The experimental results further verify the application value of the sensor.

Luminescent sensing and photocatalytic degradation properties of an uncommon (4,5,5)-connected 3D MOF based on 3,5-di(3′,5′-dicarboxylphenyl)benzoic acid

An uncommon microporous MOF 1 used as fluorescent chemosensor for NACs and as photocatalyst.

Expression of fluorescence properties by self-PET (photo-induced electron transfer) suppression both in solution and in the solid state

An-SO3H which is constructed from a PET (photo-induced electron transfer)-based structure expresses fluorescence properties due to the self-PET suppression both in the solution and in the solid-state.

Pillararene-based fluorescent chemosensors: recent advances and perspectives

This feature article summarizes recent research in the pillararene-based fluorescent chemosensor field in terms of ion sensing, small molecule recognition, biomolecule detection, fluorescent supramolecular aggregates, and biomedical imaging.

Schiff base derived Fe3+-selective fluorescence turn-off chemsensors based on triphenylamine and indole: synthesis, properties and application in living cells

A Schiff base with an AIE effect could act as a turn-off fluorescent chemosensor for Fe³⁺in living cells.

Highly sensitive and selective fluorescent probe for Fe3+ and hazardous phenol compounds based on a water-stable Zn-based metal–organic framework in aqueous media

A novel metal–organic framework (MOF), specifically a Zn-MOF, exhibited excellent performance in highly sensitive and selective sensing of Fe³⁺ and hazardous phenol compounds.

A rhodamine based fluorescent trivalent sensor (Fe3+, Al3+, Cr3+) with potential applications for live cell imaging and combinational logic circuits and memory devices

A novel sensor (HL5) recognizes sensitively and selectively trivalent metal ions M³⁺ (M = Al, Fe and Cr) with prominent enhancement in emission intensities with logic gate circuits and memory devices with living cell imaging application.

A supramolecular self-assembly host–guest system from cyclodextrin as an absolute water-soluble fluorescence sensor for aluminium ions: synthesis, characterization and sensing activity

In the study, an organic molecule derived from paeonol and anthraniloyl hydrazine (L) was synthesized via a Schiff-base reaction.

A 3D luminescent Zn(ii) MOF for the detection of high explosives and the degradation of organic dyes: an experimental and computational study

A 3D uncommon porous MOF 1 with a 4-c lonsdaleite (lon) topology based on binuclear Zn clusters behaves as a fluorescent chemosensor and a photocatalyst.

Iron Oxide Nanoparticles Labeled with an Excited-State Intramolecular Proton Transfer Dye

Excited-state intramolecular proton transfer (ESIPT) is a particularly well known reaction that has been very little studied in magnetic environments. In this work, we report on the photophysical behavior of a known ESIPT dye of the benzothiazole class, when in solution with uncoated superparamagnetic iron oxide nanoparticles, and when grafted to silica-coated iron oxide nanoparticles. Uncoated iron oxide nanoparticles promoted the fluorescence quenching of the ESIPT dye, resulting from collisions during the lifetime of the excited state. The assembly of iron oxide nanoparticles with a shell of silica provided recovery of the ESIPT emission, due to the isolation promoted by the silica shell. The silica network gives protection against the fluorescence quenching of the dye, allowing the nanoparticles to act as a bimodal (optical and magnetic) imaging contrast agent with a large Stokes shift.

Sensing behavior and logic operation of a colorimetric fluorescence sensor for Hg(2+)/Cu(2+) ions

A BODIPY-based 1 as a colorimetric fluorescence sensor was synthesized, and its metal sensing property was investigated. 1 displayed high selectivity and sensitivity towards Hg(2+) and Cu(2+) ions among 15 different metal cations. The addition of Hg(2+) and Cu(2+) ions into 1 in CH3CN resulted in a significant bathochromic shift of the UV absorption spectra from 533nm to 560nm and 593nm, respectively, changing the corresponding colors from pink to purple and blue. When excited at 530nm, the fluorescence intensity of 1 was quenched over 75% upon addition of Hg(2+) ions, while 1 with Cu(2+) ions exhibited significant fluorescence enhancement with a 23nm red-shift. Based on these results, three logic gates (OR, IMPLICATION, and INHIBIT) were obtained by controlling the chemical inputs.

Fluorescent Sensing of both Fe(III) and pH Based on 4-Phenyl-2-(2-Pyridyl)Thiazole and Construction of OR Logic Function

In the presented paper we investigated a 2-pyridylthiazole derivative, 4-phenyl-2-(2-pyridyl)thiazole (2-PTP), as the molecular fluorescent switches. It was firstly found that 2-PTP could perform a "turn-on" fluorescent sensing for Fe(III) with selectivity and reversibility. A 2:1 stoichiometry between 2-PTP and Fe(III) was determined according to the molar ratio method. The binding constant was evaluated as (1.90 ± 0.05) × 10(5) (L/mol)(2). The detection limit was found as 2.2 × 10(-7) M (S/N = 3). Secondly, 2-PTP also exhibited a pH-dependent dual-emission. The pK a(2-PTP-H(+)/2-PTP) value was then estimated as 2.0. To explain the identical emission at 479 nm of both the Fe(III) coordinated form and the protonated form of the ligand, we proposed a "locked" conformation. Finally, combining the two external stimuli as inputs, an OR logic gate was constructed using the fluorescent emission at 479 nm as the output channel.

A Fluorescent Sensor for Al(III) and Colorimetric Sensor for Fe(III) and Fe(II) Based on a Novel 8-Hydroxyquinoline Derivative

A novel 8-hydroxyquinoline-based fluorescent and colorimetric chemosensor was designed, synthesized and fully characterized. The sensor showed high selectivity and sensitivity toward Al(3+) over other tested cations in EtOH/H2O (1:99, v/v) medium. The increase in fluorescence intensity was linearly proportional to the concentration of Al(3+) with a detection limit of 7.38 × 10(-6) M. Moreover, the sensor exhibited an obvious color change from yellow to black in the presence of Fe(2+) and Fe(3+) in EtOH/THF (99:1, v/v) solution. The absorbance changes showed a linear response to iron ions with the detection limits of 4.24 × 10(-7) M and 5.60 × 10(-7) M for Fe(2+) and Fe(3+), respectively. Thus, this chemosensor provides a novel approach for selectively recognition of Al(3+), Fe(3+) and Fe(2+) among environmentally relevant metal ions.

Fluorescent aliphatic hyperbranched polyether: chromophore-free and without any N and P atoms

The strong fluorescence, in both the solution and the bulk state, of a chromophore-free aliphatic hyperbranched polyether which does not contain N and P atoms was reported for the first time. Effects of concentration and solvent solubility were measured. Its ethanol solution shows a strong blue-green fluorescence (Yu = 0.11-0.39), and its fluorescence shows a strong selective quenching with respect to Fe(3+).