A Novel Hg<Superscript>2+</Superscript> Selective Ratiometric Fluorescent Chemodosimeter Based on an Intramolecular FRET Mechanism

A irreversible Hg²⁺ selective ratiometric fluorescence probe FR, a fluorescein fluorophore linked to a rhodamine B hydrazide by a thiourea spacer, was designed and synthesized. The developed probe FR exhibited great ratiometric fluorescence enhancement and remarkable yellow-magenta color change toward Hg²⁺ with excellent selectivity in aqueous acetone solution, and the ratiometric fluorescence response to Hg²⁺ was not interfered by other metal cations including Fe³⁺, Co²⁺, Ni²⁺, Cr³⁺, Zn²⁺, Pb²⁺, Cd²⁺, Ca²⁺, Mg²⁺, Ba²⁺ and Mn²⁺. The linear range and the detection limit of this supposed ratiometric fluorescence method for Hg²⁺ were 0.0–10.0 × 10⁻⁶ and 5 × 10⁻⁸ M, respectively.     

A Fluorescent Chemodosimeter for Hg2+Based on a Spirolactam Ring-Opening Strategy and its Application Towards Mercury Determination in Aqueous and Cellular Media

A novel fluorescent chemosensor rhodamine B phenyl hydrazide (RBPH) for Hg²⁺ was designed and synthesized. This probe is highly sensitive, selective, and irreversible for Hg²⁺ and exhibits fluorescent response at 580 nm. RBPH also displayed detectable color change from colorless to pink upon treatment with Hg²⁺. This property has been utilized as naked eye detection for Hg²⁺ in various industrial samples. Fluorescence microscopic experiments demonstrated that this chemosensor is cell permeable and can be used for fluorescence imaging of Hg²⁺ in cellular media. This probe can detect Hg²⁺ with good linear relationships from 1 to 100 nM with r?=?0.99983 and the limit of detection were found to be 0.019 nM with?±?0.91 % RSD at 10 nM concentrations.     

A Fluorescence Turn-on Sensor for Hg<Superscript>2+</Superscript> with a Simple Receptor Available in Sulphide-Rich Environments

Detection of Hg²⁺ in complex natural environmental conditions is extremely challenging, and no entirely successful methods currently exist. Here we report an easy-to-prepare fluorescent sensor B3 with 2-aminophenol as Hg²⁺ receptor, which exhibits selective fluorescence enhancement toward Hg²⁺ over other metal ions. Especially, the fluorescence enhancement was unaffected by anions and cations existing in environment and organism. Moreover, B3 can detect Hg²⁺ in sulphide-rich environments without cysteine, S^2- or EDTA altering the fluorescence intensity. Consequently, B3 is capable of distinguishing between safe and toxic levels of Hg²⁺ in more complicated natural water systems with detection limit ≤2 ppb.     

<Emphasis Type="SmallCaps">l</Emphasis>-Tryptophan-capped carbon quantum dots for the sensitive and selective fluorescence detection of mercury ion in aqueous solution

l-Tryptophan-capped carbon quantum dots (l-CQDs) were facilely synthesized through “green” methodology, and the obtained material was utilized as a sensitive and selective fluorescence sensor for mercury ion (Hg²⁺) in pure aqueous solutions. Carboxyl-functionalized CQDs were first green synthesized by a one-step hydrothermal route, and l-tryptophan was then attached to CQDs via direct surface condensation reaction in aqueous solution at room temperature. The as-synthesized l-CQDs had an average size of ca. 5 nm with a good dispersity in water, and exhibited a favorable selectivity for Hg²⁺ ions over a range of other common metal cations in aqueous solution (10 mM PBS buffer, pH 6.0). Upon the addition of Hg²⁺, a complete fluorescence quenching (ON–OFF switching) of l-CQDs was evident from the fluorescence titration experiment, and the fluorescence detection limit of Hg²⁺ was calculated to be 11 nM, which indicated that the obtained environmentally friendly l-CQDs had sensitive detection capacity for Hg²⁺ in aqueous solution.     

A Dansyl-Rhodamine Ratiometric Fluorescent Probe for Hg<Superscript>2+</Superscript> Based on FRET Mechanism

Based on resonance energy transfer (FRET) from dansyl to rhodamine 101, a new fluorescent probe (compound 1) containing rhodamine 101 and a dansyl unit was synthesized for detecting Hg²⁺ through ratiometric sensing in DMSO aqueous solutions. This probe shows a fast, reversible and selective response toward Hg²⁺ in a wide pH range. Hg²⁺ induced ring-opening reactions of the spirolactam rhodamine moiety of 1, leading to the formation of fluorescent derivatives that can serve as the FRET acceptors. Very large stokes shift (220 nm) was observed in this case. About 97-fold increase in fluorescence intensity ratio was observed upon its binding with Hg²⁺.     

A naphthyridine based macrocyclic “switching on” fluorescent receptor for cadmium

A new macrocyclic receptor 1 having [1,8]-naphthyridine fluorophore is designed and synthesized for selective fluorescence sensing of Cd²⁺. Receptor 1 selectively responds to Cd²⁺ over other tested metal ions via a large enhancement of emission intensity due to the cation-induced CHEF (chelation enhanced fluorescence) effect. Receptor 1 although exhibits some affinity towards Zn²⁺, it selectively binds Cd²⁺ over Zn²⁺. Binding and selectivity were examined by ¹H-NMR, fluorescence, UV-vis, mass and IR-spectroscopic techniques.     

A Colorimetric and Fluorescent Indicator for Hg<Superscript>2+</Superscript> Detection Based on Cinnamamide Group-Containing Rhodamine Derivative

A colorimetric and fluorescent indicator based on cinnamamide group-containing rhodamine derivative was synthesized for the detection of Hg²⁺. The rhodamine B and cinnamamide were connected via ethylenediamine as a bridging molecule through a condensation reaction to obtain a colorimetric and fluorescent indicator for the detection of Hg²⁺ in H₂O-EtOH (4:1, v/v). The indicator was excellent in the selectivity of Hg²⁺ and was almost unaffected by other common ions such as Na⁺, K⁺, Mg²⁺, Fe³⁺, Cu²⁺, Zn²⁺, Cr³⁺. The Hg²⁺-containing aqueous solution turned from colorless to red within 7 min after the addition of the indicator, and had an absorption peak at 564 nm in UV-vis, which implies a significant colorimetric phenomenon. Their characteristic peaks varied with the Hg²⁺ content, and they reached a linear relationship at low concentrations. The binding stoichiometry proved to be 1:1. The lowest detection limit was 4.1?×?10^?7 mol/L, ranging from acidic to neutral.     

Interaction between 1-[p-(dimethylamino) benzoyl]-4′-phenyl-semicarbazide and Cu

A new compound, 1-[p-(dimethylamino)benzoyl]-4′-phenyl-semicarbazide (1) was synthesized and showed highly selective response to Cu²⁺ over other metal ions such as Pb²⁺, Mg²⁺, Fe²⁺, Co²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Ni²⁺, Ca²⁺, Ag⁺, Na⁺, K⁺, and Li⁺. The control compound, 1-[p-(dimethylamino)benzoyl]-4-phenyl-thiosemicarbazide (2), showed different fluorescence spectral response to Cu²⁺. A 1:1 complex between Cu²⁺ and 1 was formed while 1:1 and 1:2 complexes between Cu²⁺ and 2 were formed. The binding model between the receptor (1 or 2) and Cu²⁺ was supported by IR spectra, mass spectra, and computation model. 1 possessed higher selectivity towards Cu²⁺ compared with 2 owing to the difference of complexation ability between urea and thiourea groups.     

Highly selective fluorescent chemosensor for detecting Hg(II) in water based on pyrene functionalized core–shell structured mesoporous silica

Novel pyrene functionalized mesoporous core–shell structured silica (denoted as SiO₂@mSiO₂/Py-Si) was designed and synthesized as a highly selective fluorescent chemosensor for detecting Hg²⁺ in water. The core–shell structured silica was prepared by a simple sol–gel process through coating SiO₂ nanospheres with a layer of ordered mesoporous silica. The surface of outer mesoporous silica shell was then further functionalized by the fluorescent chromophore alkoxysilane modified pyrene (Py-Si). XRD data confirmed that the hexagonal ordered mesoporous structure was preserved after functionalization. The chemosensing material successfully exhibited a remarkable “turn on” response toward Hg²⁺ over miscellaneous metal ions. A good linear response towards Hg²⁺ in the concentration range of 10^?8–10^?4 M was constructed with R²=0.9913. Most importantly, a satisfactory detection limit of 3.4×10^?9 g mL^?1 (down to ppb level) was obtained, which is 100 times lower than our previous report of covalently grafted Py-OH to the bulk mesoporous silica SBA-15. These results indicated that SiO₂@mSiO₂/Py-Si can be used as a highly selective and sensitive fluorescence sensor for Hg²⁺.     

Radiative lifetimes of some excited states of Hg+ and Hg2+

A delayed-coincidence method with pulsed electron excitation was used to measure the radiative lifetimes of some 5d⁹6snl states of Hg⁺. Radiative lifetimes of five long lived 5d⁸6s² states of Hg²⁺ and some Hg²⁺ spectral line transition probabilities are also reported. The data are obtained for the first time.     

A Highly Sensitive and Selective Fluorescent Chemodosimeter for Hg<Superscript>2+</Superscript> in Neutral Aqueous Solution

A fluorescent assay of Hg²⁺ in neutral aqueous solution was developed using N-[p-(dimethylamino)benzamido]-N′-phenylthiourea (1). 1’s fluorogenic chemodosimetric behaviors towards various metal ions were studied and a high sensitivity as well as selectivity was achieved for Hg²⁺. It was because of a strongly fluorescent 1,3,4-oxadiazoles which was produced by the Hg²⁺ promoted desulfurization reaction. The spectra of ESI mass and IR provided evidences for this reaction. According to fluorescence titration, a good linear relationship ranging from 1.0 × 10⁻⁷ to 2.0 × 10⁻⁵ mol l⁻¹ was obtained with the limit of detection as 3.1 × 10⁻⁸ mol l⁻¹. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Analytical Evaluation of Cu<Superscript>2+</Superscript> Selective Behavior of calix[4]arene Derivative

The present article describes the solvatochromic effect including solvent system selection, time study and a detailed complexation study along with exploration of extraction properties of 5,11,17,23-tetrakis[(diethylamino)methyl]-25,26,27,28-tetrahydroxycalix[4]arene (4) that bears nitrogen atom as a donor group available for chelating metal ions. Complexation properties of 4 toward selected transition metal ions have been investigated by UV-visible and fluorescence spectroscopies. The% efficiency of 4 toward selected transition metal ions was found in order Cu²⁺> Ni²⁺> Hg²⁺> Zn²⁺> Co²⁺> Cd²⁺> Pb²⁺. It has been noticed that 4 is not only proved to be an efficient Cu²⁺ selective chromoionophore but also possesses an effective extraction property for transferring Cu²⁺ ions from an aqueous to dichloromethane layer. The FT-IR spectroscopic method has also been applied for further confirmation of the complexation phenomenon of 4 with Cu²⁺ ion and found adequate.     

Sensing of Zn2+ion by N-Furfurylsalicylaldimine Based on CHEF Process†

The recognition ability of N-Furfurylsalicylaldimine (HL) toward various cations (Pb²⁺, Hg²⁺, Ba²⁺, Cd²⁺, Ag⁺, Zn²⁺, Cu²⁺, Ni²⁺, Co²⁺, K⁺, Sr²⁺, and Na⁺) has been studied by UV–Vis and fluorescence spectroscopy. The compound showed highly selective fluorescence signaling behaviour for Zn²⁺ ions in methanol-water medium based on CHEF process and is capable of distinguishing Zn²⁺ from Cd²⁺ ion. From single crystal X-ray analysis it is revealed that a Zn²⁺ ion binds two ligand molecules through imine nitrogen and phenolate oxygen atom.

Highly Selective and Anions Controlled Fluorescent Sensor for Hg<Superscript>2+</Superscript> in Aqueous Environment

A highly selective PET fluorescent sensor B1 for Hg²⁺ containing a BODIPY fluorophore and a NS₂O₂ penta-chelating receptor has been synthesized and characterized. Its absorption maximum wavelength (498 nm) and emission maximum wavelength (512 nm) are both in the visible range. The fluorescence quantum yields of the B1 and Hg²⁺-bound states of BHg1 are 0.008 and 0.58 in 70% aqueous ethanol solution, respectively. The pKa of 1.97 is the lowest in metal ions PET chemo sensors reported up till now as we know. Thus, B1 can detect the Hg²⁺ in a wide pH span, which indicates that it has more potential and further practical applications for biology and toxicology. Furthermore, BHg1 also displays response to some anions such as Cl⁻(Br⁻), , SCN⁻ and CH₃COO⁻, which is attributed to the significant coordinating ability of these anions to Hg²⁺.     

Synthesis and Analytical Application of a Novel Fluorescent Hg2+ Probe 3′, 6′-Bis(Diethylamino)-2-((2,4-Dimethoxybenzylidene)Amino)Spiro[Isoindoline-1,9′-Xanthene]-3-Thione

A novel probe, 3′,6′ - bis(diethylamino) -2- ((2,4-dimethoxybenzylidene)amino) spiro [isoindoline-1,9′-xanthene]-3-thione (RBS), was designed and synthesized. Its structure was characterized with elemental analysis, IR spectra and ¹H NMR. The probe displayed highly selective and sensitive recognition of Hg²⁺. Reacting with mercury ions in aqueous solution, its fluorescence intensity was enhanced significantly, while its color was changed from colorless to pink. So, a new fluorescence method of detection of Hg²⁺ was proposed. Its dynamic response concentration range and detection limit for Hg²⁺ were 5.00?×?10^?9 M to 1.00?×?10^?6 M detected and 1.83?×?10^?9 M, respectively. Satisfying results were obtained when the probe was applied to detect spiked Hg²⁺ in samples.     

8-Hydroxyquinoline Functionalized Graphene Oxide: an Efficient Fluorescent Nanosensor for Zn<Superscript>2+</Superscript> in Aqueous Media

A nanosensor, based on 8-hydroxyquinoline functionalized graphene oxide, was developed for the fluorescence detection of Zn²⁺. It showed high selectivity and sensitivity for Zn²⁺ion in aqueous solution over other metal ions such as Li⁺, Na⁺, Ca²⁺, Mg²⁺, Al³⁺, Cd²⁺, Co²⁺, Cu²⁺, Hg²⁺, Ni²⁺, Pb²⁺, Fe²⁺, Fe³⁺and Cr³⁺. Due to the linearity of the emission intensity toward Zn²⁺ concentration, fluorescent technique could be used for the detection of Zn²⁺ ion even at very low concentrations.     

Highly Sensitive Visualization of Inorganic Mercury in Mouse Neurons Using a Fluorescent Probe

In the present study, we used the previously developed fluorescence probe, EPNP, to generate the first image of the distribution of mercuric ion in primary mouse neuron cultures. At postnatal day 1 (P1), the mice were intraperitoneally (IP) injected with mercuric chloride in doses ranging from 0.05 to 0.6 μg/g body weight. After 1, 2, 3, and 4 days exposure, primary nervous cell cultures and frozen brain and spinal tissue sections were prepared and dyed using EPNP. On the third day of repeated injections, Hg²⁺ was visualized in primary cerebral neuron cultures as an increase of Hg²⁺-induced fluorescence at the doses?≥?0.1 μg/g. A similar accumulation of Hg²⁺ was observed in frozen hippocampus tissue sections. In contrast, no Hg²⁺ was observed in spinal cord neurons and spinal tissue sections. The detection of a low dose of IP injected mercury in mouse cerebral neurons facilitated the evaluation of the exposure risk to low-dose Hg²⁺ in immature organisms. Moreover, the highly sensitive EPNP revealed Hg²⁺ in the cerebral neurons of mice younger than P4, while the presence of Hg²⁺ was not detected until?≥?P11 in previous reports. Thus, this technology and the results obtained herein are of interest for neurotoxicology.     

Both “Naked-Eye” and Fluorescent Sensor for Hg2+ Based upon 8-Hydroxyquinoline

A chemosensor, 2,2′-(1,4-phenylenedivinylene)bis-8-acetoxyquinoline (1), its fluorescent sensing behavior toward representative alkali ions (Na⁺, K⁺), alkaline earth ions (Mg²⁺, Ca²⁺), and transition-metal ions (Ni²⁺, Cu²⁺, Zn²⁺, Hg²⁺, Pb²⁺, Cd²⁺) was intensively investigated. The compound (1) exhibited pronounced Hg²⁺ selective on–off-type fluoroionophoric properties among the representative ions in DMF/ethanol (1:9, v/v) solution. Moreover, the highly Hg²⁺-selective fluorescence quenching property in conjunction with a visible colorimetric change from colorless to light yellow can be observed, leading to potential fabrication of both “naked-eye” and fluorescent detection of Hg²⁺.     

Condensation Product of Phenylalanine and Salicylaldehyde: Fluorescent Sensor for Zn<Superscript>2+</Superscript>

The condensation product of phenylalanine and salicylaldehyde (L) was synthesised and characterised which was found to be selective fluorescent “off-on” sensor for Zn²⁺ ion with the detection limit 10^?5 M. The sensor is free of interferences from metal ions - Na⁺, K⁺, Al³⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Pb²⁺, Cd²⁺ and Hg²⁺. The Fluorescence and the UV/visible spectral data reveals a 1:1 interaction between the sensor and Zn²⁺ ion with binding constant 10⁸. The DFT and TDDFT calculations confirm the structures of the sensor and the sensor-Zn²⁺ complex.     

Synthesis and Characterization of New Light Emitter Symmetrical Phenoxazinium Salt and Its Potential Application as Sensor for Assessment of Hg2+

The sensitization of the excited triplet state of a novel symmetrical Bis(dialkylamino)phenoxazinium salt was developed in the presence of Hg²⁺. This effect was used to determine the concentration of Hg²⁺ in different water samples. The phenoxazinium salt sensor was characterized by different spectroscopic tools such as: UV, FTIR, NMR and fluorescence spectra. The sensor has an emission band at 347 nm in DMSO. Hg²⁺ in DMSO at pH 5.6 can remarkably quench the fluorescence intensity of the sensor at 347 nm and a new band was appeared at 436 nm due to the strong complex formation between Hg²⁺ and sensor. The quenching of the band intensity at 347 and the enhancement of the intensity of the new band at 436 were used to determine the Hg²⁺ in different waste water samples. The dynamic range found for the determination of Hg²⁺ concentration is 8.7?×?10^-10 – 1.4?×?10^-6 mol L^?1 with a detection limit of 5.8?×?10^?10 mol L^?1 and quantification detection limit of 1.8?×?10^-9 mol L^-1.