Ratiometric Zn2+ sensor and strategy for Hg2+ selective recognition by central metal ion replacement

Strategies of both self-assembly and metal ion replacement were adopted in the development of new metal ion sensors for Zn2+ and Hg2+. Ligand BPBA, phenylene-bridged bis(pyrrol-2-ylmethyleneamine), could self-assemble to form a molecular square in the presence of Zn2+, which showed strong emission in solution. The fluorescent emission of formed BPBA-Zn2+ dropped with the addition of Hg2+. BPBA could be a good Zn2+ sensor candidate and BPBA-Zn2+ could be a good Hg2+ sensor candidate based on the mechanisms of the chelation-enhanced fluorescence effect and the replacement of central metal ion induced chelation-enhanced fluorescence quenching effect, respectively.     

A highly selective and sensitive fluorescent chemosensor for Zn^2＋

A new selective Zn^2＋ fluorescent chemosensor, o-vanillin-4-ethoxybenzoylhydrazone （1）, was designed and prepared. Free 1 mainly displayed very weak fluorescence at 480 nm upon excitation at 403 nm. It displayed high selectivity for Zn^2＋ and had a 518- fold fluorescent enhancement upon binding of Zn^2＋, while the other cation ions had only little influence on the fluorescence of 1. Mechanism of enhancement of l＇s fluorescence by Zn^2＋ was briefly discussed.     

Metal-chelating nanoparticles as selective fluorescent sensor for Cu2+

A fluorescent sensor for Cu(2+) at the nanomolar level in water has been designed by associating a BODIPY fluorophore and a selective ligand (cyclam) in ultrafine polymer nanoparticles.     

Highly selective and sensitive fluorescent sensing of oxalate in water

Effective fluorescent sensing of oxalate in water is significant but still remains a challenge. By using indicator-displacement assays, a readily available macrocyclic copper(II) complex was found to show a sensitive off-on fluorescent sensing for oxalate with high selectivity and high binding affinity (>10(7) M(-1)) in water at neutral pH.     

A benzimidazole-based fluorescent sensor for Cu2+ and its complex with a phosphate anion formed through a Cu2+ displacement approach

A benzimidazole-based imine linked receptor was synthesized for fluorescent recognition of Cu²⁺ in a CH₃CN/H₂O (8:2, v/v) solvent system. The receptor offers an opportunity for the selective estimation of Cu²⁺ in the presence of another metal ion at equimolar concentration. The Cu²⁺ complex with the receptor acted as a sensor for a phosphate anion, and the phosphate recognition event restored the fluorescence intensity of the receptor.     

"Turn-on" fluorescent sensor for Hg2+ via displacement approach

A new Cu2+ compound Cu- NB, (where H2 NB is bis(2-hydroxyl-naphthalene-carboxaldehyde) benzil dihydrazone) was synthesized as a highly selective fluorescence chemosensor for the detection of Hg2+ in aqueous media through a displacement "turn-on" signaling strategy. Whereas the coordination of Cu2+ resulted in a considerable quenching of the typical luminescence of the naphthol rings in Cu-NB, the addition of Hg2+ ion led to a dramatic increase in the emission intensity of Cu-NB at about 530 nm (excitation at 430 nm). The competitive fluorescent experiments showed that alkali, alkaline earth metal ions, the group 12 metals Zn2+, Cd2+, the first-row transition-metal ions such as Mn2+, Fe2+, Co2+, and Ni2+, as well as Pb2+ could not inhibit the Hg2+-binding fluorescent enhancement. It is postulated that the existence of Cu2+ in the luminescent probe Cu-NB could turn away the interferences of other metal cations from Hg2+ detection. The optical responses of the free ligand upon addition of Cu2+ ion, and of the Hg-H2NB compound upon the addition of Cu2+ were also investigated for comparisons.     

Coumarin-derived transformable fluorescent sensor for Zn2+

We report a coumarin-derived fluorescent sensor for Zn(2+) termed CTS. CTS shows excellent binding selectivity for Zn(2+) over competing metal ions due to the transformable ability of CTS, that is the displacement of other metal ions by Zn(2+), which induces transformation of chelation from an amide to an imidic acid tautomeric form.     

An anticancer-active imidazole analogue as a fluorescent sensor: sensitive and selective detection of Cu2+ ions

Transition Metal Chemistry - A highly sensitive and selective imidazole-based fluorescent “on–off” probe, (2-(4,5-bis((E)-4-methoxystyryl)-1H-imidazol-2-yl) phenol) (BMIP), is...     

Highly selective and sensitive detection of Cu2+ with lysine enhancing bovine serum albumin modified-carbon dots fluorescent probe

Based on the ability of lysine (Lys) to enhance the fluorescence intensity of bovine serum albumin modified-carbon dots (CDs-BSA) to decrease surface defects and quench fluorescence of the CDs-BSA-Lys system in the presence of Cu(2+) under conditions of phosphate buffer (PBS, pH = 5.0) at 45 °C for 10 min, a sensitive Lys enhancing CDs-BSA fluorescent probe was designed. The environment-friendly, simple, rapid, selective and sensitive fluorescent probe has been utilized to detect Cu(2+) in hair and tap water samples and it achieved consistent results with those obtained by inductively coupled plasma mass spectroscopy (ICP-MS). The mechanism of the proposed assay for the detection of Cu(2+) is discussed.     

Highly sensitive and selective cyanide detection via Cu2+ complex ligand exchange

A new type of fluorescent probe (1) with two triazole groups that are conjugated with a carbazole moiety was synthesized by a Cu(I)-catalyzed alkyne-azide click reaction for the selective and sensitive detection of cyanide via fluorescence enhancement by ligand exchange and metal ion removal.     

Highly selective fluorescent sensor for homocysteine and cysteine

A new fluorescent sensor (1) based on a coumarin was synthesized for the selective detection of homocysteine (Hcy) and cysteine (Cys). The chemosensor has shown a selective response to Hcy or Cys over other various amino acids via a ring formation of thiazinane or thiazolidine. When Hcy or Cys was added, the fluorescent intensity of 1 was completely quenched through a photo-induced electron transfer with the sensitivity of sub-millimolar concentration.     

Highly selective fluorescent recognition of Zn2+ based on naphthalene macrocyclic derivative

A new macrocyclic chemosensor containing two naphthalene fluorophores has been synthesized. The fluorescent properties of this receptor has been studied in the presence of various metal ions such as Na⁺, Ag⁺, Cr³⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺. When increasing concentrations of Zn²⁺ ions were introduced, the emission of L was drastically increased (EFE = 4.34). This special change was not observed when other metal ions were used; such highly selective fluorescent response indicates that this receptor can easily discriminate Zn²⁺ ions from other similar species. Model calculations at DFT level further suggest the possible interaction mode, and relatively steric position between the host and guest also influence the optical response.     

Highly sensitive and selective optical chemosensor for determination of Cu2+ in aqueous solution

A highly selective and sensitive rhodamine-based colorimetric chemosensor (1) for quantification of divalent copper in aqueous solution has been investigated in this work. It was designed using salicylaldehyde hydrazone and rhodamine 6G as copper-chelating and signal-reporting groups, respectively. In environmentally friendly media (50% (v/v) water/ethanol and 10 mM NaAc–HAc neutral buffer (pH 7.0)), the sensor exhibited selective absorbance enhancement to Cu²⁺ over other metal ions at 529 nm, with a dynamic working range of 0.05–5.00 μM and a detection limit of 10 nM Cu²⁺, respectively. To achieve fluorometric determination of Cu²⁺, the Cu²⁺-induced absorbance enhancement of 1 was efficiently converted to fluorescence quenching by fluorescence inner filter effects using rhodamine B (RB) as a fluorophore. The selectivity and sensitivity of fluorescence analysis were similar to those of absorptiometric measurement. Both absorptiometric and fluorometric methods were successfully applied to the detection of Cu²⁺ in three water samples.     

Highly sensitive fluorescent probe for selective detection of Hg2+ in DMF aqueous media

A highly sensitive fluorescent probe 1 for selective detection of Hg ion in mixed N,N-dimethylformamide aqueous media was designed and prepared by incorporating the well-known Rhodamine 6G fluorophore and a carbohydrazone binding unit into one molecule. The fluorescent probe 1 can detect the parts per billion level of HgII in a mixed aqueous environment and displays a highly selective response of fluorescence enhancement toward HgII.     

Highly sensitive and selective turn-on fluorescent and chromogenic probe for Cu2+ and ClO- based on a N-picolinyl rhodamine B-hydrazide derivative

A new rhodamine B-based dual-function chromo- and fluorogenic probe for Cu(2+) and ClO(-) has been designed, synthesized, and characterized. The probe comprises a spectroscopic unit of rhodamine B and a Cu(2+)-specific chelating unit of pyridinecarboxamide as well as a ClO(-)-specific reactive moiety of diacylhydrazine, and is a highly selective and extremely sensitive fluorescent and colorimetric sensor for Cu(2+) and ClO(-) in different pH conditions. Compared with the reported probes for Cu(2+) or ClO(-), this is the first chemosensor based on a small molecule that can detect both Cu(2+) and ClO(-), respectively, at 1 nM level.     

A new highly selective fluorescent K+ sensor

We describe the synthesis, properties, and application of a new fluorescent potassium chemosensor, KS2, for K(+) sensing and imaging in live cells. By virtue of a strong electron-withdrawing group, 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF), with a triazacryptand ligand, the new sensor can respond to K(+) up to 1.6 M. This is the first highly selective intracellular sensor suitable for sensing K(+) over a broad and high concentration range. Confocal fluorescence microscopy has established the utility of KS2 for live-cell K(+) detection. The application of KS2 combined with other sensors will be of great benefit for investigating cellular metabolism, detecting and diagnosing diseases including cancer, and monitoring responses to therapy.     

A highly selective and sensitive BODIPY-based colourimetric and turn-on fluorescent sensor for Hg2+ ions

A series of monostyryl boron dipyrromethenes appended with an NO(4), NO(2)S(2), N(3)O(4), or N(3)O(2)S(2)-type ligand have been prepared and characterised. While the UV-Vis spectra of the former three compounds in CH(3)CN/H(2)O (2?:?3 v/v) do not respond towards a wide range of metal ions, the derivative with an N(3)O(2)S(2)-ligand exhibits a highly selective and sensitive spectral response towards Hg(2+) ions. The absorption band is blue-shifted by 40 nm due to inhibition of the intramolecular charge transfer process upon metal complexation. The fluorescence is also turned on giving a strong emission band at 572 nm. The colour changes can be easily detected by the naked eye. The results suggest that this compound serves as a promising colourimetric and fluorescent sensor for Hg(2+) ions in this mixed aqueous medium.     

A highly selective visual and fluorescent sensor for Pb2+ and Zn2+ and crystal structure of Cu2+ complex based-on a novel single-armed Salamo-type bisoxime

A novel single-armed Salamo-type bisoximes (H₄L) has been designed and synthesised. An obvious colour change from yellow (H₄L) to pale pink (HL-Pb²⁺) which can be visually observed by the naked eye in visible light. H₄L can act as a fluorescent sensor for ratiometric recognition of Zn²⁺ with high selectivity and sensitivity. Crystallographic data of the [Cu(HL)(μ-OAc)Cu] reveals that the two Cu²⁺ ions are both penta-coordinated with square pyramidal geometries, and forms a 2D supramolecular plane structure by hydrogen bonding interactions.     

Highly sensitive and selective colorimetric and off-on fluorescent probe for Cu(2+) based on rhodamine derivative

A new probe for Cu(2+) based on the Cu(2+)- induced reversible ring-opening mechanism of the rhodamine spirolactam was described. It displayed a highly selective and sensitive "turn-on" fluorescent and colorimetric response toward Cu(2+).