BSA–AuNPs@Tb–AMP metal–organic frameworks for ratiometric fluorescence detection of DPA and Hg2+

An easy and effective strategy for synthesizing a ratiometric fluorescent nanosensor has been demonstrated in this work. Novel fluorescent BSA–AuNPs@Tb–AMP (BSA, bovine serum albumin; AMP, adenosine 5′‐monophosphate; AuNPs, Au nanoparticles) metal–organic framework (MOF) nanostructures were synthesized by encapsulating BSA–AuNPs into Tb–AMP MOFs for the detection of 2,6‐pyridinedicarboxylic acid (DPA) and Hg²⁺. DPA could strongly co‐ordinate with Tb³⁺ to replace water molecules from the Tb³⁺ center and accordingly enhanced the fluorescence of Tb–AMP MOFs. The fluorescence of BSA–AuNPs at 405 nm remained constant. While the fluorescence of BSA–AuNPs at 635 nm was quenched after Hg²⁺ was added, the fluorescence of Tb–AMP MOFs remained constant. Accordingly, a ratiometric fluorescence nanosensor was constructed for detection of DPA and Hg²⁺. The ratiometric nanosensor exhibited good selectivity to DPA over other substances. The F₅₄₅/F₄₀₅ linearly increased with increase of DPA concentration in the range of 50 nM to 10 μM with a detection limit as low as 17.4 nM. F₆₃₅/F₄₀₅ increased linearly with increase of Hg²⁺ concentration ranging from 50 nM to 1 μM with a detection limit as low as 20.9 nM. Additionally, the nanosensor could be successfully applied for the determination of DPA and Hg²⁺ in running water.     

A carbonothioate‐based highly selective fluorescent probe with a large Stokes shift for detection of Hg2+

Mercury (Hg) is one of the heavy metal pollutants in the environment. Even a very small amount of mercury can cause serious harm to human beings. Herein, we reported a new carbonothioate‐based fluorescent probe for the detection of Hg²⁺ without interference from other metal ions. This probe possessed a very large Stokes shift (192 nm), which could improve the detection sensitivity by minimizing the interferences resulted from self‐absorption or auto‐fluorescence. With the addition of Hg²⁺ to the probe solution, considerable fluorescence enhancement was observed. Additionally, the Hg²⁺ concentration of 0–16 μM and fluorescence intensity showed a good linear relationship (y = 22106× + 53108, R² = 0.9955). Finally, the proposed probe was used to detect Hg²⁺ in real water samples, and its result was satisfactory. Therefore, our proposed probe would provide a promising method for the determination of Hg²⁺ in the environment.     

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.     

Copper and mercury induced oxidative stresses and antioxidant responses of Spirodela polyrhiza (L.) Schleid

Duckweed is recognized as a phytoremediation aquatic plant due to the production of large biomass and a high level of tolerance in stressed conditions. A laboratory experiment was conducted to investigate antioxidant response and mechanism of copper and mercury tolerance of S. polyrhiza (L.) Schleid. To understand the changes in chlorophyll content, MDA, proline, and activities of ROS-scavenging enzymes (SOD, CAT, GPOD) during the accumulation of Cu⁺² and Hg⁺², S. polyrhiza were exposed to various concentrations of Cu⁺² (0.0–40 μM) and Hg⁺² (0.0–0.4 μM). antioxidant activity initially indicated enhancing trend with application of 10 μM Cu⁺²; 0.2 μM Hg⁺² (SOD), of 20 μM Cu⁺²; 0.2 μM Hg⁺² (CAT) and of 10 μM Cu⁺²;0.2 μM Hg⁺² (GPOD) and then decreased consistently up to 40 μM Cu⁺² and 0.4 μM Hg⁺². In the experiment chlorophyll and frond multiplication initially showed increasing tendency and decreased gradually with the application of increased metal concentration. Application of heavy metal has constantly enhanced proline and MDA content while the maximum increase was observed with the application of 40 μM Cu; 0.4 μM Hg for proline and MDA respectively. The upregulation of antioxidant enzymes and proline reveals that S. polyrhiza has strong biochemical strategies to deal with the heavy metal toxicity induced by the accumulation of Cu⁺² and Hg⁺².     

Ratiometric fluorescent detection of Cu2+ based on dual‐emission ZIF‐8@rhodamine‐B nanocomposites

Zeolitic imidazolate framework‐8 (ZIF‐8) loading rhodamine‐B (ZIF‐8@rhodamine‐B) nanocomposites was proposed and used as ratiometric fluorescent sensor to detect copper(II) ion (Cu²⁺). Scanning electron microscopy, Fourier transform infrared spectroscopy, X‐ray powder diffraction, nitrogen adsorption/desorption isotherms and fluorescence emission spectroscopy were employed to characterize the ZIF‐8@rhodamine‐B nanocomposites. The results showed the rhodamine‐B was successfully assembled on ZIF‐8 based on the π‐π interaction and the hydrogen bond between the nitrogen atom of ZIF‐8 and –COOH of rhodamine‐B. The as‐obtained ZIF‐8@rhodamine‐B nanocomposites were octahedron with size about 150–200 nm, had good water dispersion, and exhibited the characteristic fluorescence emission of ZIF‐8 at 335 nm and rhodamine‐B at 575 nm. The Cu²⁺ could quench fluorescence of ZIF‐8 rather than rhodamine‐B. The ZIF‐8 not only acted as the template to assemble rhodamine‐B, but also was employed as the signal fluorescence together with the fluorescence of rhodamine‐B as the reference to construct a novel ratiometric fluorescent sensor to detect Cu²⁺. The resulted ZIF‐8@rhodamine‐B nanocomposite fluorescence probe showed good linear range (68.4 nM to 125 μM) with a low detection limit (22.8 nM) for Cu²⁺ combined with good sensitivity and selectivity. The work also provides a better way to design ratiometric fluorescent sensors from ZIF‐8 and other fluorescent molecules.     

A ratiometric fluorescence sensor based on carbon quantum dots realized the quantitative and visual detection of Hg2+

In this paper, based on the fluorescence of carbon quantum dots (CQDs) quenched by mercury ions (Hg²⁺) and the nonresponse of Hg²⁺ to rhodamine B fluorescence, a dual emission ratio fluorescence sensor was constructed to realize the quantitative detection of Hg²⁺. Under excitation at 365 nm, the fluorescence spectrum showed double emission peaks at 437 nm and 590 nm, corresponding to the fluorescence emissions of CQDs and rhodamine B, respectively. This method quantitatively detected Hg²⁺ based on the linear relationship between the ratio of the intensities of the two emission peaks F₄₃₇/F₅₉₀ and the concentration of Hg²⁺. The detection range was 10–70 nM, and the limit of detection (S/N = 3) was 3.3 nM. In addition, this method could also realize the qualitative and semiquantitative detection of Hg²⁺ according to the fluorescence colour change of the probe under ultraviolet light. After various evaluations, the method could be successfully applied to the quantitative and visual detection of Hg²⁺ in tap water, and demonstrated excellent selectivity, anti-interference performance, and repeatability of the method.     

An integrated system of pyrene and rhodamine-6G for selective colorimetric and fluorometric sensing of mercury(II)

A pyrene and rhodamine-6G functionalized simple chemosensor L is studied toward sensing of metal ions in solution extensively. L shows selective color change from colorless to pink in the presence of Hg²⁺ in acetonitrile and the UV-Vis study shows peak at 525 nm with a ε value of 5.2 × 10⁴ M⁻¹ cm⁻¹ due to selective ring opening of rhodamine spirolactam moiety. The selective sensing of Hg²⁺ by L in the presence of other metal ions and reversible nature of “OFF-ON-OFF” functionality of L by Hg²⁺ and EDTA, respectively, are also established. The fluorescence study of L in the presence of Hg²⁺ shows emission at 550 nm when excited at 525 nm (ring opened rhodamine wavelength) or 340 nm (pyrene wavelength) in dry CH₃CN. Thus L acts as a selective colorimetric and fluorometric probe (dual probe) for the Hg²⁺ in solution. Metal ion sensing ability of L is also carried out in water as well as in aqueous Hepes buffer. These studies suggest that the fluorescence output of L in presence of Hg²⁺ in aqueous environment is apparently due to the generation of acid upon addition of Hg²⁺ salt in water.     

A rhodamine‐triazole fluorescent chemodosimeter for Cu2+ detection and its application in bioimaging

A rhodamine‐based fluorescent chemodosimeter rhodamine hydrazide‐triazole (RHT) tethered with a triazole moiety was developed for Cu²⁺ detection. In aqueous medium, the RHT probe exhibited high selectivity and sensitivity toward Cu²⁺ among other metal ions. The addition of Cu²⁺ triggered a fluorescence emission of RHT by 384‐fold (Φ = 0.33) based on a ring‐opening process and a subsequent hydrolysis reaction. Moreover, RHT also showed a selective colorimetric response toward Cu²⁺ from colorless solution to pink, readily observed with the naked eye. The limit of detection of RHT for Cu²⁺ was calculated to be 1 nM (0.06 ppb). RHT was successfully demonstrated to detect Cu²⁺ in Chang liver cells by confocal fluorescence microscopy.     

Water‐soluble polymeric chemosensor for selective detection of Hg2+ in aqueous solution using rhodamine‐based modified poly(acrylamide–acrylic acid)

We report the fabrication of a novel easily available turn‐on fluorescent water‐soluble polymeric chemosensor for Hg²⁺ ions that was simply prepared by micellar free radical polymerization of a water‐insoluble organic rhodamine‐based Hg²⁺‐recognizing monomer (GR6GH), with hydrophilic monomers acrylamide (AM) and acrylic acid (AA). The chemical structure of the polymeric sensor was characterized by FT‐IR and ¹H NMR spectroscopy. The apparent viscosity average molecular weight M_η of poly(acrylamide–acrylic acid) [poly(AM–NaAA)] and the water‐soluble polymeric chemosensor poly(AM–NaAA–GR6GH) were 1.76 × 10⁶ and 6.84 × 10⁴ g/mol, respectively. Because of its amphiphilic property, the water‐soluble polymeric chemosensor can be used as a chemosensor in aqueous media. Upon addition of Hg²⁺ ions to an aqueous solution of poly(AM–NaAA–GR6GH), fluorescence enhancements were observed instantly. Moreover, other metal ions did not induce obvious changes to the fluorescence spectra. This approach may provide an easily measurable and inherently sensitive method for Hg²⁺ ion detection in environmental and biological applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Multifunctional peptide‐based fluorescent chemosensor for detection of Hg2+, Cu2+ and S2− ions

A novel multifunctional fluorescent peptide sensor based on pentapeptide dansyl‐Gly‐His‐Gly‐Gly‐Trp‐COOH (D‐P5) was designed and synthesized efficiently using Fmoc solid‐phase peptide synthesis (SPPS). This fluorescent peptide sensor shows selective and sensitive responses to Hg²⁺ and Cu²⁺ among 17 metal ions and six anions studied in N‐2‐hydroxyethylpiperazine‐N‐2‐ethane sulfonic acid (HEPES) buffer solution. The peptide probe differentiates Hg²⁺ and Cu²⁺ ions by a ‘turn‐on’ response to Hg²⁺ and a ‘turn‐off’ response to Cu²⁺. Upon addition of Hg²⁺ or Cu²⁺ ions, the sensor displayed an apparent color change that was visible under an ultraviolet lamp to the naked eye. The limits of detection (LOD) of DP‐5 were 25.0 nM for Hg²⁺ and 85.0 nM for Cu²⁺; the detection limits for Cu²⁺ were much lower than the drinking water maximum contaminant levels set out by the United States Environmental Protection Agency (USEPA). It is noteworthy that both D‐P5‐Hg and D‐P5‐Cu systems were also used to detect S^2? successfully based on the formation of ternary complexes. The LODs of D‐P5‐Hg and D‐P5‐Cu systems for S^2? were 217.0 nM and 380.0 nM, respectively. Furthermore, the binding stoichiometry, binding affinity and pH sensitivity of the probe for Hg²⁺ and Cu²⁺ were investigated. This study gives new possibilities for using a short fluorescent peptide sensor for multifunctional detection, especially for anions.     

Luminescent sensor for Cd2+, Hg2+ and Ag+ in water based on a sulphur‐containing receptor: quantitative binding–softness relationship

A water‐soluble, high‐output fluorescent sensor, based on a lumazine ligand with a thiophene substituent for Cd²⁺, Hg²⁺ and Ag⁺ metal ions, is reported. The sensor displays fluorescence enhancement upon Cd²⁺ binding (log  β = 2.79 ± 0.08) and fluorescence quenching by chelating with Ag⁺ and Hg²⁺ (log β = 4.31 ± 0.15 and 5.42 ± 0.1, respectively). The mechanism of quenching is static and occurs by formation of a ground‐state non‐fluorescent complex followed by rapid intersystem crossing. The value of the Stern–Volmer quenching rate constant (k_q) by Ag⁺ ions is close to 6.71 × 10¹² mol/L/s at 298 K. The thermodynamic parameters (ΔG, ΔH and ΔS) were also evaluated and indicated that the complexation process is spontaneous, exothermic and entropically favourable. The quantitative linear relationship between the softness values of Klopman (σ_K) or Ahrland (σ_A) and the experimental binding constants (β) being in the order of Hg²⁺ > Ag⁺ > Cd²⁺ suggests that soft–soft interactions are the key for the observed sensitivity and selectivity in the presence of other metal ions, such as: Pb²⁺, Ni²⁺, Mn²⁺, Cu²⁺, Co²⁺, Zn²⁺ and Mg²⁺ ions. Copyright © 2008 John Wiley & Sons, Ltd.     

Terbium (III) coordination polymer–copper (II) compound as fluorescent probe for time‐resolved fluorescence ‘turn‐on’ detection of hydrogen sulfide

With recognition of the biological importance of hydrogen sulfide (H₂S), we present a simple and effective fluorescent probe for H₂S using a Tb³⁺ coordination polymer–Cu²⁺ compound (DPA/Tb/G–Cu²⁺). Dipicolinic acid (DPA) and guanosine (G) can coordinate with Tb³⁺ to form a macromolecular coordination polymer (DPA/Tb/G). DPA/Tb/G specifically binds to Cu²⁺ in the presence of coexisting cations, and obvious fluorescence quenching is observed. The quenched fluorescence can be exclusively recovered upon the addition of sulfide, which is measured in the mode of time‐resolved fluorescence. The fluorescence intensities of the DPA/Tb/G–Cu²⁺ compound enhance linearly with increasing sulfide concentrations from 1 to 30 μM. The detection limit for sulfide in aqueous solution is estimated to be 0.3 μM (at 3σ). The DPA/Tb/G–Cu²⁺ compound was successfully applied to sense H₂S in human serum samples and exhibited a satisfactory result. It displays some desirable properties, such as fast detection procedure, high selectivity and excellent sensitivity. This method is very promising to be utilized for practical detection of H₂S in biological and environmental samples.     

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.     

The human xenobiotic-metabolizing enzyme arylamine N-acetyltransferase 1 (NAT1) is irreversibly inhibited by inorganic (Hg) and organic mercury (CH3Hg): Mechanism and kinetics

Human arylamine N-acetyltransferase 1 (NAT1) is a xenobiotic-metabolizing enzyme that biotransforms aromatic amine chemicals. We show here that biologically-relevant concentrations of inorganic (Hg²⁺) and organic (CH₃Hg⁺) mercury inhibit the biotransformation functions of NAT1. Both compounds react irreversibly with the active-site cysteine of NAT1 (half-maximal inhibitory concentration (IC₅₀) = 250 nM and k_inact = 1.4 × 10⁴ M⁻¹ s⁻¹ for Hg²⁺ and IC₅₀ = 1.4 μM and k_inact = 2 × 10² M⁻¹ s⁻¹ for CH₃Hg⁺). Exposure of lung epithelial cells led to the inhibition of cellular NAT1 (IC₅₀ = 3 and 20 μM for Hg²⁺ and CH₃Hg⁺, respectively). Our data suggest that exposure to mercury may affect the biotransformation of aromatic amines by NAT1.     

A triazole‐based fluorescence probe for detecting Hg2+ ions and its biological application

A new compound, ethyl 5‐phenyl‐2‐(p‐tolyl)‐2H‐1,2,3‐triazole‐4‐carboxylate was successfully introduced and synthesized as a novel rhodamine B derivative named REPPC, and characterized by ¹H nuclear magnetic resonance (NMR), ¹³C NMR, and high resolution mass spectrometry (HRMS). It showed an obvious fluorescence and UV–visible light absorption enhancement towards Hg²⁺ ion without interference from common metal ions in N,N‐dimethylformamide–H₂O (pH 7.4). The spirolactam ring moiety of rhodamine in REPPC was converted to the open‐ring form generating a 1:1 complex with the intervention of a mercury ion, verified by electrospray ionization‐mass spectroscopy testing and density functional theory calculation. REPPC was used to visualize the level of mercury ions in living HeLa cells with encouraging results.     

A highly efficient and selective turn‐on fluorescent sensor for Hg2+, Ag+ and Ag nanoparticles based on a coumarin dithioate derivative

Based on chelation‐enhanced fluorescence, a new fluorescent coumarin derivative probe 3(1‐(7‐hydroxy‐4‐methylcoumarin)ethylidene)hydrazinecarbodithioate for Hg²⁺, Ag⁺ and Ag nanoparticles is reported. Fluorescent probe acts as a rapid and highly selective “off–on” fluorescent probe and fluorescence enhancement by factors 5 to12 times was observed upon selective complexation with Hg²⁺, Ag⁺ and Ag nanoparticles. The molar ratio plots indicated the formation of 1:1 complexes between Hg²⁺ and Ag⁺ with the probe. The linear response range covers a concentration range 0.1 × 10^–5–1.9 × 10^–5 mol/L, 0.1 × 10^–5–2.3 × 10^–5 mol/L and 0.146 × 10^–12–2.63 × 10^–12 mol/L for Hg²⁺, Ag⁺ and Ag nanoparticles, respectively. The interference effect of some anions and cations was also tested. Copyright © 2013 John Wiley & Sons, Ltd.     

Optimization of ASE and SPE conditions for the HPLC‐FLD detection of piperazine in chicken tissues and pork

Accelerated solvent extraction (ASE) and solid‐phase extraction (SPE) conditions were optimized by a high‐performance liquid chromatography‐fluorescence detector (HPLC‐FLD) method for the detection of piperazine in chicken tissues and pork. Piperazine residues were determined by precolumn derivatization with trimethylamine and dansyl chloride. Samples were extracted with 2% formic acid in acetonitrile using an ASE apparatus and purified using a Strata‐X‐C SPE column. The monosubstituted product of the reaction of piperazine with dansyl chloride was 1‐dansyl piperazine (1‐DNS‐piperazine). Chromatographic separations were performed on an Athena C₁₈ column (250 × 4.6 mm, id: 5 μm) with gradient elution using ultrapure water and acetonitrile (5:95, V/V) as the mobile phase. The calibration curves showed good linearity over a concentration range of LOQ‐200.0 μg/kg with a coefficient of determination (R²) ≥ .9992. The recoveries and relative standard deviations (RSD values) ranged from 78.49% to 97.56% and 1.19% to 5.32%, respectively, across the limit of quantification (LOQ) and 0.5, 1, and 2.0 times the maximum residue limit (MRL; μg/kg). The limits of detection (LODs) and LOQs were 0.96 to 1.85 μg/kg and 3.20 to 5.50 μg/kg, respectively. The method was successfully applied for the validation of animal products in the laboratory.     

A sugar-aza-crown ether-based fluorescent sensor for Hg and Cu

A fluorescent sensor, 5, based upon the sugar-aza-crown ether structure with two anthracenetriazolymethyl groups was prepared and its fluoroionophoric properties toward transition metal ions were investigated. In methanol, the sensor exhibits highly selective recognition of Cu²⁺ and Hg²⁺ ions among a series of tested metal ions. The association constant for 5·Cu²⁺ and 5·Hg²⁺ in methanol was calculated to be 4.0 × 10⁵ M⁻¹ and 1.1 × 10⁵ M⁻¹, respectively. The detection limits for the sensing of Cu²⁺ and Hg²⁺ ions were 1.39 × 10⁻⁶ M and 1.39 × 10⁻⁵ M, respectively.     

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.     

Naphthalimide-based fluorescent probe for Hg2+ detection and imaging in living cells and zebrafish

A simple naphthalimide-based fluorescent probe was designed and synthesized for the determination of mercury ion (Hg²⁺). The probe showed a noticeable fluorescence quenching response for Hg²⁺. When added with Hg²⁺, the fluorescence intensity of the probe at 560 nm was remarkably decreased with the color changed from yellow to colorless under ultraviolet (UV) light. The probe had a notable selectivity and sensitivity for Hg²⁺ and displayed an excellent sensing performance when detecting Hg²⁺ at low concentration (19.5 nM). The binding phenomenon between the probe and Hg²⁺ was identified by Job's method and high-resolution mass spectrometry (HRMS). Moreover, the probe was not only utilized to identify Hg²⁺ in real samples with satisfactory results (92.00%–110.00%) but also was successfully used for bioimaging in cells and zebrafish. The recognition mechanism has been verified by transmission electron microscopy (TEM) for the first time. All the results showed that the probe could be used as a potent useful tool for detection of Hg²⁺.