Novel colorimetric sensor for mercury (Ⅱ) based on layer-by-layer assembly of unmodified silver triangular nanoplates

A simple layer-by-layer deposition technique was used to fabricate the multilayer thin films of unmodified silver triangular nanoplates(AgTNPs).The multilayer of AgTNPs thin films were fabricated by alternate deposition of each anionic sodium citrate stabilized AgTNPs and cationic poly(diallyldimethylammonium chloride).All prepared AgTNPs multilayer thin films were exhibited a strong plasmon band at the wavelength of 667 nm,which confirmed the formation of AgTNPs onto the substrate.The characteristics of the multilayer thin films were investigated using contact angle measurement,UV-visible spectroscopy,X-ray diffraction analysis(XRD),atomic force microscope(AFM)and field emission scanning electron microscope(FESEM).As these films are to be used as a mercury(II)colorimetric sensor,the changes in optical properties of the films were evaluated for various mercury(Ⅱ)concentrations.AgTNPs assembled into thin films showed a strong color shift from blue to mauve and colorless when exposed to mercury(Ⅱ).The constructed multilayer thin films exhibited excellent color changes of mercury(II) with a linear range between 0.5 and 20 ppm.The limit of detection(LOD) and limit of quantitation(LOQ) were 0.45 ± 0.002 and 1.52 ± 0.002 ppm,respectively.The recovery values of AgTNPs multilayer thin films are satisfactory in the range of 100.1%-106.4%when applied to determining mercury(Ⅱ) in water samples.     

Natural pyrite as an electrochemical sensor for potentiometric titrations with EDTA, mercury(II) and silver(I)

The results obtained in potentiometric titrations of copper(II), mercury(II) and iron(III) with standard EDTA solutions are presented. The titration of copper(II) at pH values in the range from 8.11 to 10.99 (ammonia buffer) and the titration of mercury(II) and iron(III) at pH values from 3.59 to 5.65 (acetate buffer) were performed. The titration end-point (TEP) was detected with an indicator electrode made from natural crystalline pyrite as an electrochemical sensor. The results obtained in potentiometric titration with the pyrite electrode were compared with those obtained using a platinum electrode (Fe³⁺), a Cu ion selective electrode (Cu²⁺) and a Hg electrode (Hg²⁺). Accurate and reproducible results with good agreement were obtained, but higher potential changes at the TEP were obtained using the pyrite electrode. In the course of the titration the potential was established within less than 1 min, whereas at the TEP it was within about 2–3 min. The potential changes at the TEP were in the range from 60 to 200 mV per 0.1 ml EDTA, according to the stability constant of the complex formed. The highest potential changes, ranging from 160 to 200 mV, were obtained in the titration of iron(III) at pH 3.59. Reverse titration was also performed and accurate and reproducible results were obtained. Moreover, titration of halogenide and thiocyanate with standard mercury(II) solutions, as well as cyanide with silver(I) solution, were performed and accurate and reproducible results were again obtained. Received: 20 February 1998 / Accepted: 19 November 1999     

Target-triggered inhibiting oxidase-mimicking activity of platinum nanoparticles for ultrasensitive colorimetric detection of silver ion

The development of efficient methods for the detection of hazardous and toxic elements is extremely important for environmental security and public health. In this work, we developed a facile colorimetric assaying system for Ag⁺ detection in aqueous solution. Chitosan-stabilized platinum nanoparticles (Ch-PtNPs) were synthesized and severed as an artificial oxidase to catalyze the oxidation of the substrate 3,3′,5,5′-tetramethylbenzidine (TMB) and generate color signal. In the presence of Ag⁺, due to the strong metallophilic interactions between Ag⁺ and Pt²⁺ on the surface of Ch-PtNPs, Ag⁺ can weaken the affinity to the substrates and inactivate the catalytic activity of Ch-PtNPs, leading to decreased absorbance signal to varying degrees depending on Ag⁺ amount. Combing the specific binding between Ch-PtNPs and Ag⁺ with signal amplification procedure based on the Ch-PtNPs-catalyzed TMB oxidation, a sensitive, selective, simple, cost-effective, and rapid detection method for Ag⁺ can be realized. Ag⁺ ions in tap and lake waters have been successfully detected. We ensured that the proposed method can be a potential alternative for Ag⁺ determination in environmental samples.     

Target-triggered inhibiting oxidase-mimicking activity of platinum nanoparticles for ultrasensitive colorimetric detection of silver ion

A facile colorimetric method for sensitive and selective detection of Ag⁺ is successfully developed based on the excellent oxidase-like activity of chitosan-stabilized platinum nanoparticles and the strong metallophilic Pt²⁺-Ag⁺ interactions.     

Gap site-specific rapid formation of fluorescent silver nanoclusters for label-free DNA nucleobase recognition

Silver nanoclusters (Ag NCs) templated with DNAs have attracted much attention as novel fluorophores because of their convenient emission tunability by the sequence and length of the template DNAs. However, the precise production of Ag NCs in a site-specific manner still remains a challenge to attain highly selective and label-free DNA recognition. Here we exploited the availability of a gap site in DNA duplexes as a new scaffold for the synthesis of Ag NCs. Compared to the commonly used DNA templates for the creation of Ag NCs, the gap site in DNA duplexes was found to facilitate the rapid formation of the fluorescent Ag NCs without sacrifice of their bright emission and excellent stability. We found that fluorescent Ag NCs were highly selectively formed when cytosine faced toward the gap site in DNA duplexes, and they were in situ utilized as readout by signal-on manner for the DNA mutation assays. This base-selective growth of the fluorescent Ag NCs at the gap site would find promising applications in practical detection of single nucleotide polymorphism (SNP) and construction of DNA-based functional sensors with label-free and cost-effective merits.     

Preparation,characterization and applications of polyurethane foam functionalized with resorcinol for quantitative separation and determination of silver(I) and mercury(II) from tap and wastewater

A stable chelating resin matrix was prepared by covalently linking resorcinol with polyurethane foam matrix through a –N=N– group. Preconcentration and determination of trace Ag⁺ and Hg²⁺ ions from samples of different origin, using Res-PUF, were studied. Various conditions influencing the sorption of these metal ions onto Res-PUF were optimized. The kinetics of sorption of the Ag⁺ and Hg²⁺ by Res-PUF were found to be fast, reached equilibrium in few minutes (5–10?min) and followed a first-order rate equation with an overall rate constant k in 0.102 and 0.267/min, respectively. Study of the variation of the sorption of the tested metal ions with temperature yielded average values for ΔG, ΔH and ΔS of ?3.94, ?22.02 and ?58.37, respectively. The mean free sorption energy (E) computed from the Dubinin–Radushkevich (D–R) isotherm was found to be equal to 8.91 kJ/mol, which reflects the chelation sorption process. The capacities of the foam material were 0.15 and 0.07?mmol/g for Ag⁺ and Hg²⁺, respectively. Preconcentration factors of?>?50 were achieved (RSD?≈?5.99). The proposed preconcentration procedure was applied successfully to the determination of trace metal ions in natural and wastewater samples.     

A selective, sensitive probe for mercury(II) ions based on oxazine-thione

A selective, sensitive probe for Hg(II) ions, 7-(diethylamino)-3-methyl-2H-benzo[b][1,4] oxazine-2-thione (1), is developed. Compound 1 behaves as a ratiometric probe, exhibiting a large blue shift of 100 nm in its absorption spectra upon exposure to Hg(II) ions. The dramatic color change of the solution made ‘naked-eye’ detection of Hg(II) ions possible. Emission spectra of 1 displayed a selective enhancement in intensity in the presence of Hg(II) ions. ESI⁺-MS analysis indicated that Hg²⁺-induced desulfurization caused the large absorption response.     

Development of a test strip based on DNA-functionalized gold nanoparticles for rapid detection of mercury(II) ions

A rapid,sensitive,selective and reliable strip assay based on DNA-functionalized gold nanoparticles for Hg²⁺ detection has been developed,with a detection limit 5 nmol/L.The measurement principle was based on thymine-Hg²⁺-thymine(T-Hg²⁺-T) coordination chemistry and streptavidin-biotin interaction.The major advantages of this assay are that results can be read visually without any instrument in less than 10 min and that it does not require any sample pretreatment.     

Fluorescence detection of mercury(II) and lead(II) ions using aptamer/reporter conjugates

We have developed a fluorescence technique for the detection of Hg²⁺ and Pb²⁺ ions using polythymine (T₃₃)/benzothiazolium-4-quinolinium dimer derivative (TOTO-3) and polyguanine (G₃₃)/terbium ions (Tb³⁺) conjugates, respectively. Hg²⁺ ions induce T₃₃ to form folded structures, leading to increased fluorescence of the T₃₃/TOTO-3 conjugates. Because Pb²⁺ ions compete with Tb³⁺ ions to form complexes with G₃₃, the extent of formation of the G₃₃-Tb³⁺ complexes decreases upon increasing the Pb²⁺ concentration, leading to decreased fluorescence at 545 nm when excited at 290 nm. To minimize interference from Hg²⁺ ions during the detection of Pb²⁺ ions, we conducted two-step fluorescence measurements; prior to addition of the G₃₃/Tb³⁺ probe, we recorded the fluorescence of a mixture of the T₃₃/TOTO-3 conjugates and Hg²⁺ ions. The fluorescence signal obtained was linear with respect to the Hg²⁺ concentration over the range 25.0-500 nM (R² = 0.99); for Pb²⁺ ions, it was linear over the range 3.0-50 nM (R² = 0.98). The limits of detection (at a signal-to-noise ratio of 3) for Hg²⁺ and Pb²⁺ ions were 10.0 and 1.0 nM, respectively. Relative to other techniques for the detection of Hg²⁺ and Pb²⁺ ions in soil and water samples, our present approach is simpler, faster, and more cost-effective.     

p-Dimethylaminobenzaldehyde thiosemicarbazone: a simple novel selective and sensitive fluorescent sensor for mercury(II) in aqueous solution

A novel and simple fluorophore, p-dimethylaminobenzaldehyde thiosemicarbazone (DMABTS), was prepared in order to find available fluorescent chemosensor for mercuric ion in aquesous solution. DMABTS emitted fluorescence at 448 nm in aqueous solution and its fluorescence intensity was completely quenched upon interaction with Hg²⁺ ions, which should be attributed to the 1:1 complex formation between DMABTS and Hg²⁺. The binding constant of the complex was determined as 7.48 × 10⁶ mol l⁻¹. The linear range of quantitative detection of 0 to 5.77 × 10⁻⁶ mol l⁻¹ and the detection limit of 7.7 × 10⁻⁷ mol l⁻¹ for Hg²⁺ in the 6.3 × 10⁻⁶ mol l⁻¹ DMABTS aqueous solution were obtained from a calibration curve. The coexistence of several transition metal ions and anions did interfere the fluorometric titration of Hg²⁺ ion by less than 4% in the emission change.     

Specific mercury(II) adsorption by thymine-based sorbent

A new kind of polymer sorbent based on the specific interaction of Hg(II) with nucleic acid base, thymine, is described for the selective adsorption of Hg(II) from aqueous solution. Two types of sorbents immobilized with thymine were prepared by one-step swelling and polymerization and graft polymerization, respectively. The maximum static adsorption capacity of the new polymer sorbents for Hg(II) is proportional to the density of thymine on their surface, up to 200 mg/g. Moreover, the new kind polymer sorbent shows excellent selectivity for Hg(II) over other interfering ions, such as Cu(II), Cd(II), Zn(II), Co(II), Ca(II) and Mg(II), exhibits very fast kinetics for Hg(II) adsorption from aqueous solution, and can be easily regenerated by 1.0 M HCl. It also has been successfully used for the selective adsorption of spiked Hg(II) from real tap water samples. This new thymine polymer sorbent holds a great promise in laboratory and industrial applications such as separation, on-line enrichment, solid-phase extraction, and removal of Hg(II) from pharmaceutical, food and environmental samples.     

Multiparametric optimization of a new high-sensitive and disposable mercury (II) electrochemical sensor

An electrochemical sensor for mercury (II) determination was developed by modifying the surface of a commercial screen-printed carbon electrode (SPCE) with a polystyrene sulfonate-NiO-carbon nanopowder composite material. Mercury measurements were performed by differential pulse anodic stripping voltammetry (DPASV). Sensor composition and measurement conditions were optimized using a multivariate experiment design. A screening experiment by using a Plackett-Burman design was first performed in order to determine the main contributing factors to the electrochemical response. The most important factors were employed to establish the interactions between different experimental variables and get the best conditions for mercury determination. For this purpose, a five level central composite design and a response surface methodology were used. The optimized method using the developed NiO-PSS-SPCE sensor presents a very low limit of detection of 0.021 μg L⁻¹ and a linear response over two concentration ranges with two different slopes, from 0.05 to 2.0 μg L⁻¹ and between 2.0 and 75 μg L⁻¹. The sensor was successfully applied to mercury determination in water samples.     

Schiff base stabilized silver nanoparticles as potential sensor for Hg(II) detection,and anticancer and antibacterial agent

This study reports a facile synthesis of silver nanoparticles (C3-AgNPs) by chemical route, using C3; 2,2′-((1E,1′E)-(propane-1,3-diylbis(azanylylidene))bis(methanylylidene))diphenol (3) and silver nitrate. The formation of nanoparticles was monitored using UV–Vis spectroscopy by the appearance of typical surface plasmon absorption maxima. The synthesized C3-AgNPs were characterized using Fourier-Transform-infrared (FTIR) and atomic force microscopy (AFM) techniques. In addition, the effect of concentration, temperature, time, pH, and stability in salts solution on C3-AgNPs was determined. From AFM, C3-AgNPs were found polydispersed with average size of 29.93 nm. Furthermore, the study reports C3-AgNPs as sensitive protocol for the detection of toxic metal; Hg(II) in tap water. From ten salts tested, C3-AgNPs demonstrated a sensitive and selective spectrophotometric signal and aggregation induced decrease of surface plasmon resonance (SPR) band. The nanosensor probe displayed a sensitive response to Hg(II) in a wide range of concentrations and pH. In addition, the decrease in SPR band of C3-AgNPs due to Hg(II) was not affected by tap water samples. C3-AgNPs also exhibited a redox catalytic potential in dyes degradation. In biological application, C3-AgNPs exhibited significant anticancer and antibacterial potential of 65 to 94% at 24–72 h, and inhibition zone of 7–18 mm, respectively. Hence, the synthesized C3-AgNPs could have promising application in environmental and pharmacological remediation.     

Preparation and Spectral Investigation of Bis[N(2-methyl-phenyl) 4-Nitro-thiobenzamidato] mercury(II), Bis[N(2-methoxy-phenyl) 4-Nitro-thiobenzamidato]mercury(II), and Bis[N(2-chloro-phenyl) 4-Nitro-thiobenzamidato]mercury(II) Complexes

Several preparative routes to bis[N(substituted-phenyl) 4-nitro-thiobenzamidato] mercury(II) complexes are presented, including the reaction of mercury(II) oxide, fluoride, chloride, bromide, cyanide, acetate, and nitrate with N(substituted-phenyl) 4-nitro-thiobenzamide derivatives. ¹ H-NMR, Raman, and IR measurements confirmed the complexation of mercury to sulphur.     

Some neutral three-coordinate complexes of mercury(II) halides and pseudohalides with N-methylnicotinamide

Coordination compounds of mercury(II) chloride, bromide, cyanide and thiocyanate with N-methylnicotinamide, a potentially bidentate ligand, have been prepared. The complexesisolated have 1∶1 (metal:ligand)stoichiometry. Molecular weight measurements in molten camphor indicate that the mercury (II) chloride and bromide complexes are monomeric. Based on conductance values, molecular weight determinations and infrared spectral data, it is inferred that in the solid state in all these complexes the metal ion has a coordination number three and is bonded to the N-methylnicotinamide via its pyridine ring nitrogen, and is terminally bonded to the halogen/pseudohalogens.     

Synthesis,crystal structure,DNA/BSA interaction and in vitro antitumor activity of N-heterocycle Cu(II) and Co(II) complexes

Investigation of N-heterocycle transition metal complexes has led to the discovery of metal-based antitumor agents. Herein, two binuclear complexes, [Cu(p-4-bmb)(Ac)₂]₂ (1) and [Co(p-4-bmp)Cl₂]₂ (2), were prepared and characterized. The interactions of 1 and 2 with calf thymus (CT)-DNA and bovine serum albumin (BSA) were detected by absorbance and emission spectroscopy. The complexes bind to CT-DNA via an intercalative mode and show moderate affinity to BSA. Both complexes exhibited remarkable DNA cleavage activity. The MTT assay demonstrated that 1 exhibited higher cytotoxicity against three human alimentary system carcinoma cell lines compared to 2. Further, a cellular uptake assay demonstrated that 1 can accumulate in the nucleus and mitochondria of SMMC7721 cells to induce DNA damage and mitochondrial dysfunction. Fluorescence staining and flow cytometry analyses revealed that 1 can induce cell death by apoptosis. These findings should promote the development of benzimidazole-based transition metal complexes as novel chemotherapy agents with fewer side effects than conventional antitumor drugs.     

New N-heterocyclic carbene mercury(II) and silver(I) complexes

The complexes [1-(9-anthracenylmethyl)-3-octylimy]₂Hg[HgCl₄] (2a) (imy = imidazol-2-ylidene) and [1-(9-anthracenylmethyl)-3-butylbimy]₂AgPF₆ (2b) (bimy = benzimidazol-2-ylidene) have been prepared and characterized. Crystal packing of complex 2a revealed that 1D polymeric chains are formed by [1-(9-anthracenylmethyl)-3-octylimy]Hg and [HgCl₄]²⁻ through weak Hg…Cl bonds. The packing diagram of 2b showed that 1D supramolecular chains are formed by both benzimidazole ring head to tail π–π stacking interactions and anthracene ring face-to-face π–π stacking interactions.     

Sensitive pseudobienzyme electrocatalytic DNA biosensor for mercury(II) ion by using the autonomously assembled hemin/G-quadruplex DNAzyme nanowires for signal amplification

Herein, a novel sensitive pseudobienzyme electrocatalytic DNA biosensor was proposed for mercury ion (Hg²⁺) detection by using autonomously assembled hemin/G-quadruplex DNAzyme nanowires for signal amplification. Thiol functionalized capture DNA was firstly immobilized on a nano-Au modified glass carbon electrode (GCE). In presence of Hg²⁺, the specific coordination between Hg²⁺ and T could result in the assembly of primer DNA on the electrode, which successfully triggered the HCR to form the hemin/G-quadruplex DNAzyme nanowires with substantial redox probe thionine (Thi). In the electrolyte of PBS containing NADH, the hemin/G-quadruplex nanowires firstly acted as an NADH oxidase to assist the concomitant formation of H₂O₂ in the presence of dissolved O₂. Then, with the redox probe Thi as electron mediator, the hemin/G-quadruplex nanowires acted as an HRP-mimicking DNAzyme that quickly bioelectrocatalyzed the reduction of produced H₂O₂, which finally led to a dramatically amplified electrochemical signal. This method has demonstrated a high sensitivity of Hg²⁺ detection with the dynamic concentration range spanning from 1.0 ng L⁻¹ to 10 mg L⁻¹ Hg²⁺ and a detection limit of 0.5 ng L⁻¹ (2.5 pM) at the 3S_blank level, and it also demonstrated excellent selectivity against other interferential metal ions.     

A PVC-based pentathia-15-crown-5 membrane potentiometric sensor for mercury(II)

Poly(vinyl chloride) (PVC)-based membrane of pentathia-15-crown-5 exhibits good potentiometric response for Hg²⁺ over a wide concentration range (2.51 × 10⁻⁵ to 1.00 × 10⁻¹ mol dm⁻³) with a slope of 32.1 mV per decade of Hg²⁺ concentration. The response time of the sensor is as fast as 20 s. The electrode has been used for a period of six weeks and exhibits fairly good discriminating ability towards Hg²⁺ in comparison to alkali, alkaline and some heavy metal ions. The electrode can be used in the pH range from 2.7 to 5.0.     

Control of the Fluorescence of DNA‐templated Silver Nanoclusters by Adenosine Triphosphate and Mercury(II)

Several DNA templates with the sequence 5′‐T _n TAACCCCTAACCCCT ‐3′ (n = 0, 15, 30, and 45) were used to prepare DNA template–silver nanoclusters (DNA –Ag NCs ). The T _n sequence acts as a recognition element for Hg²⁺, while the rest of the sequence acts as a template for DNA –Ag NCs . At pH 3.0, the fluorescence intensity of DNA –Ag NCs is enhanced by ATP , and the enhanced fluorescence is quenched by Hg²⁺. The length of polyT shows a slight effect on the sensitivity for the detection of Hg²⁺ but almost no effect on the optical properties of DNA –Ag NCs . The fluorescence response of DNA –Ag NCs (T₁₅‐DNA –Ag NCs ) vs. Hg²⁺ concentration shows two linear ranges over 10–100 and 100–1000 nM , mainly because of the fluorescence quenching due to DNA conformational changes through T–Hg²⁺–T coordination and the formation of an amalgam with Ag NCs , respectively. The sensitivity of the T₁₅‐DNA –Ag NC probe was validated through the analysis of Hg²⁺ in spiked pond water. Based on the switch‐on and switch‐off fluorescence properties of T₁₅‐DNA –Ag NCs , an IMPLICATION logic gate was fabricated using the concentrations of ATP and Hg²⁺ as inputs and the fluorescence intensity at 585 nm as output.