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 Rhodamine Derivative Based Chemosensor with High Selectivity and Quick Respond to Cr<Superscript>3+</Superscript> in Aqueous Solution

In this paper, a new kind of colorimetric chemsensor aiming at detecting Cr³⁺ has been synthesized, and it is based on the “Off-On” effect of a rhodamine derivative. Comparing with other metal irons (Na⁺, K⁺, Ni²⁺, Hg²⁺, Fe³⁺, Mn²⁺, Co²⁺, Cd²⁺, Cu²⁺, Pb²⁺, Zn²⁺, Mg²⁺, Ba²⁺, Ag⁺, Fe²⁺, Ce³⁺), the chemsensor has a quick and accurate response to Cr³⁺ in H₂O-EtOH solution (4/1, v/v). There is an obvious change in color, from colorless to bright pink when Cr³⁺ is detected. According to the fitting curve based on Benesi-Hildebrand equation and working curve of absorption strength in UV-vis spectrum, the binding pattern of Cr³⁺ and the rhodamine derivative follows a 1:1 stoichiometry. The chemsensor shows great potential in monitoring Cr³⁺ in the aqueous medium with high efficiency, which is supposed to complete the recognition in the minimum as 5.2?×?10^?7 mol/L within 5 min.     

A New Reactive 1,8-Naphthalimide Derivative for Highly Selective and Sensitive Detection of Hg<Superscript>2+</Superscript>

A 1,8-naphthalimide derivative with a reactive aliphatic hydroxyl was designed and synthesized as a fluorescent probe. Its structure was characterized by IR, ¹H NMR, ¹³C NMR, LC-MS and HPLC. The probe showed high selectivity and sensitivity to Hg²⁺ over other metal ions such as Pb²⁺, Na⁺, K⁺, Cd²⁺, Cr³⁺, Zn²⁺, Cu²⁺, Ni²⁺, Ca²⁺, Fe³⁺, Fe²⁺, Co²⁺, Mn²⁺ and Mg²⁺ in MeCN/H₂O (15/85, v/v). The increase in fluorescence intensity was linearly proportional to the concentration of Hg²⁺ in the range of 18–40 μM with a detection limit of 1.38 × 10^?7 mol/L. The probe could work in a pH span of 4.3–9.0 and respond to Hg²⁺ quickly with strong anti-interference ability. Job’s plot suggested a 1:2 complex of the probe and Hg²⁺.     

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.     

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.     

Adsorption kinetics,isotherms, and thermodynamic studies for the adsorption of Pb<Superscript>2+</Superscript> and Hg<Superscript>2+</Superscript> metal ions from aqueous medium using Ti(IV) iodovanadate cation exchanger

In the current study, Ti(IV) iodovanadate cation exchanger (TIV) was synthesized and applied for the removal of Pb²⁺ and Hg²⁺ metal ions from the aqueous medium. The adsorption studies were performed by the batch techniques and adsorption parameters viz. contact time, pH, initial metal ion concentration, and temperature were also investigated. The optimum adsorption of Pb²⁺ (95 %) and Hg²⁺ (65 %) were observed at pH 6. The pseudo-second order equation represented the adsorption kinetics with high correlation coefficient. Langmuir model showed the best fitting to the isotherm equilibrium data, with a maximum adsorption capacity of 18.8 mg g^?1 for Pb²⁺ and 17.2 mg g^?1 for Hg²⁺. Furthermore, thermodynamic factors, i.e., ΔG, ΔH, and ΔS, indicated that adsorption of Pb²⁺ and Hg²⁺ onto TIV were spontaneous, endothermic, and feasible in the temperature range of 293–323 K.     

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.     

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.     

A New Sensitive and Selective Off-On Fluorescent Zn<Superscript>2+</Superscript> Chemosensor Based on 3,3′,5,5′-Tetraphenylsubstituted Dipyrromethene

3,3′,5,5′-Tetraphenyl-2,2′-dipyrromethene was described as a highly sensitive and selective Off-on fluorescent colorimetric chemosensor for Zn²⁺ based on the chelation-enhanced fluorescence (CHEF) effect. The reaction of dipyrromethene ligand with Zn²⁺ induces the formation of the [ZnL₂] complex, which exhibits the increasing fluorescence in 120 fold compared with ligand in the propanol-1/cyclohexane (1:30) binary mixture. The Zn²⁺ detection limit was 1.4 × 10^?7 М. The UV-Vis and fluorescence spectroscopic studies demonstrated that the dipyrromethene sensor was highly selective toward Zn²⁺ cations over other metal ions (Na⁺, Mg²⁺, Co²⁺, Ni²⁺, Fe³⁺, Cu²⁺, Mn²⁺, Cd²⁺ and Pb²⁺), excluding Hg²⁺.     

A highly Sensitive Turn-on Fluorescent Sensor for Ba<Superscript>2+</Superscript> Based on G-Quadruplexes

A G-quadruplex-based fluorescent biosensor for highly sensitive detection of barium ion (Ba²⁺) was constructed for the first time. In the absence of Ba²⁺, the G-quadruplex-specific fluorescence ligand N-methyl mesoporphyrin IX (NMM) remained weakly fluorescent when coexisted with a single-stranded G-quadruplex sequence AGRO100. Upon addition of Ba²⁺, AGRO100 was folded into G-quadruplex structures with the aid of Ba²⁺, which bound with NMM by stacking forces and significantly enhanced its fluorescence. The maximum fluorescence intensity of NMM was increased by ca. 22-fold in response to 1 μM Ba²⁺. This simple method exhibites a good linear relationship in the range of 0–600 nM with the detection limit of 4 nM. The detection method is turn-on, fast, economic, high in signal-to-noise ratio and free of participation of toxic organic solvents, demonstrating its great potential for on-site and real-time Ba²⁺ detection.     

A New Fluorescent Chemosensor Detecting Co<Superscript>2+</Superscript> and K<Superscript>+</Superscript> in DMF Buffered Solution

A new fluorescent chemosensor 2-(2-thiophene)imidazo [4,5,f]-1,10-phenanthroline (L) was prepared and characterized. By adding univalent or divalent metal ions such as Na⁺, K⁺, Mg²⁺, Ba²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Zn²⁺, Cd²⁺ and Hg²⁺ ions into the solution of L in DMF under buffered conditions with the working pH ranging from 7.0 to 8.0, we found that L could be used to detect K⁺ ratiometricly and it could also be applied to sense Co²⁺ with the phenomenon of fluorescence quenching of L. While the response behavior of L was not discernibly affected by other examined metal ions.     

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.     

Fluorescence Sensors for Selective Detection of Hg2+ Ion Using a Water-Soluble Poly(vinyl alcohol) Bearing Rhodamine B Moieties

The novel water-soluble poly(vinyl alcohol) with pendant rhodamine B moiety as colorimetric and fluorescene chemosensor for Hg²⁺ ions was prepared by grafting poly(vinyl alcohol) using rhodamine B hydrazide and hexamethylenediisocyanate as fluorescent dye and coupling agent, respectively. Because of their good water-solubility, the polymers binding rhodamine B can be used as chemosensors in aqueous media. With the addition of Hg²⁺ ions into the aqueous solution, visual color changes and fluorescence enhancements were detected. In addition, we also noticed that other metal ions such as Ag⁺, Cd²⁺, Co²⁺, Cu²⁺, K⁺, Mg²⁺, Ba²⁺, Fe²⁺, Ni²⁺, Pb²⁺, Cr³⁺, Fe³⁺ and Zn²⁺ cannot induce obvious changes to the fluorescence spectra of the polymer chemosensors. The combination of water solubility and positive fluorescence response as well as color change are hence particularly promising for the practical utility of the sensors.     

A Highly Selective Turn on Fluorescence Sensor for Hg2+ Based on Rhodamine Derivative

A novel fluorescent rhodamine based chemosensor (E)-3′,6′-bis(diethylamino)-2-((2-(pyridin-2-ylmethoxy)benzylidene)amino)spiro[isoindoline-1,9′-xanthen]-3-one, RSP, had been successfully developed and well characterized by NMR, FT-IR and Mass spectroscopy. The chemosensor exhibits high selectivity for Hg²⁺ over other ions (Ag⁺, Pb²⁺, Cu²⁺, Ni²⁺, Fe³⁺, Co²⁺, Zn²⁺ and Cd²⁺) with fluorescence enhancement in ethanol solution. More over the detection limit of the sensor is in the 10^?6 M level. The binding ratio of RSP-Hg²⁺ complex was determined to be 1:1 according to the Job plot. Test strips based on RSP were fabricated, which showed the application of the sensor for detection of mercuric ions in water by naked eyes.     

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⁺.     

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.     

A Novel Naphthalene-Immobilized Nanoporous SBA-15 as a Highly Selective Optical Sensor for Detection of Fe<Superscript>3+</Superscript> in Water

A novel organic-inorganic hybrid optical sensor (SBA-NCO) was designed and synthesized through immobilization of isocyanatopropyl-triethoxysilane and 1-amino-naphthalene onto the surface of SBA-15 by post-grafting method. The characterization of materials using XRD, TEM, N₂ adsorption-desorption, and FT-IR techniques confirmed the successful attachment of organic moieties and preserving original structure of SBA-15 after modification step. Fluorescence experiments demonstrated that SBA-NCO was a highly selective optical sensor for the detection of Fe³⁺ directly in water over a wide range of metal cations including Na⁺, Mg²⁺, Al³⁺, K⁺, Ca²⁺, Cr³⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺ in a wide pH values.     

A Novel Ratiometric Fluorescent Mercury Probe Based on Deprotonation-ICT Mechanism

A new NBD-rhodamine dye (1) was developed as a colorimetric and ratiometric fluorescent chemosensor for Hg²⁺ with good selectivity in aqueous ethanol solutions under neutral to basic conditions. Sensor 1 showed absorption at 468 nm and a weak emission at 529 nm (? _F ?=?0.063) in ethanol/aqueous tris buffer (9:1, v/v) of pH 9.17 solution. Bathochromic shifts in both absorption (492 nm) and fluorescence spectra (569 nm, ? _F ?=?0.129), respectively upon addition of 2 equiv. of Hg²⁺ were observed. The ring-opening reaction of the spirolactam form to the corresponding xanthene form was not found. The interaction of Hg²⁺ with chemosensor 1 resulted in the deprotonation of the secondary amine conjugated to the NBD component so that the electron-donating ability of the N atom was enhanced. Deprotonation-ICT mechanism of secondary amines was suggested for the ratiometric fluorescent chemosensing for Hg²⁺.     

Fluorescent carbon dots: facile synthesis at room temperature and its application for Fe<Superscript>2+</Superscript> sensing

A new route for one-pot preparation of carbon dots (CDs) was developed at room temperature using PEG400 as both the carbon source and passitive agent. The new method possesses the advantages of facile, rapid, energy-saving, without any external stimulus and environment friendly. By changing the content of NaOH, the PEG400-CDs with blue-emitting, yellow-emitting, orange red-emitting and red-emitting were obtained, and the formation mechanism were carefully investigated. In addition, a sensitive fluorescence sensor were developed for Fe²⁺ detection based on PEG400-CDs since the fluorescence of PEG400-CDs could be enhanced by Fe²⁺. It was found that there is a good linear relationship between the enhanced fluorescence and Fe²⁺ concentration in the range of 0.5 to 2.0 μmol·L^?1 with the detection limit of 6.0 × 10^?8 mol·L^?1, and Fe²⁺ in water samples was also determined with high accuracy and repeatability.     

A Novel Fluorimetric Bulk Optode Membrane Based on NOS Tridentate Schiff Base for Selective Optical Sensing of Al<Superscript>3+</Superscript> Ions

A novel fluorimetric optode has been developed for the highly selective and sensitive for the determination of ultra trace amounts of Al³⁺ ions. The proposed fluorescent optode is based on the incorporation of a simple and effective fluorescent sensor tridentate NOS Schiff base N-(2-hydroxynaphthylidene)-2-aminothiophenol (H₂L) in a plasticized PVC containing KTpClPB as a lipophilic anionic additive. H₂L was synthesized by a facile one-step Schiff base reaction. The plasticized PVC-membrane displays a calibration response for Al³⁺ ions over a wide concentration range from 1.0 × 10^?9 to 4.4 × 10^?3 mol/L. The fluorescence signal of the optode membrane can be easily recovered by immersion in 0.01 M EDTA. In addition to high stability and reproducibility, the sensor shows a unique selectivity towards Al³⁺ ion with respect to common co-existing cations, particularly Ga³⁺and In³⁺. The proposed optode was applied successfully for determination of Al³⁺ in some real samples, including bottled drinking waters, bottled mineral waters and soft drinks.