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.     

Electrochemical Aptasensor for the Determination of Cocaine Incorporating Gold Nanoparticles Modification

A novel electrochemical aptasensor incorporating a signal enhancement for the determination of cocaine was designed. Gold nanoparticles were self‐assembled onto the surface of a gold electrode through 1,6‐hexanedithiol. A bifunctional derivative of the 32‐base cocaine‐binding aptamer with a redox‐active ferrocene moiety and a thiol linker group at the termini of the strand was self‐assembled onto the surface of gold nanoparticles. The oxidation peak current is linearly related to the concentration of cocaine from 1.0 to 15.0 μM with a detection limit of 0.5 μM. It was found that the sensitivity of the aptasensor with gold nanoparticles modification was ca. 10‐fold higher than that of the aptasensor without gold nanoparticles modification. This work demonstrates that gold nanoparticles‐assembled gold electrode provides a promising platform for immobilizing aptamer and enhancing the sensitivity.     

Ultrasensitive Silicon Nanoparticle Ratiometric Fluorescence Determination of Mercury(II)

A novel ratiometric fluorescence sensing system for the ultrasensitive detection of Hg²⁺ was developed. It used aminofunctionalized silicon nanoparticles and rhodamine B, which exhibit two distinct fluorescence emission peaks at 449 and 581?nm, respectively, under a single excitation wavelength (350?nm). The fluorescence of the amino-functionalized silicon nanoparticles was selectively quenched by Hg²⁺, while that of rhodamine B was insensitive to Hg²⁺. The ratio of fluorescence intensities at 449–581?nm linearly decreased with increasing concentrations of Hg²⁺ from 0.005–0.1 and 0.1–7?µM within 0.5?min, and a detection limit as low as 3.3?nM was achieved. Moreover, the ratiometric fluorescence sensing system exhibited good selectivity toward Hg²⁺ over other metal ions with relatively low background interference, even in a complex matrix such as lake water. Most importantly, the practical use of this sensing system for Hg²⁺ detection in real water samples was also demonstrated.     

Fluorescence Determination of Merucury(II) Using a Thymine Aptamer

A label-free thymine-rich sequence and a molecular beacon were synthesized to construct a highly sensitive and selective fluorescence probe for the determination of mercury(II). The aptamer of the thymine-rich sequence selectively bonded with mercury(II) with an accompanying change in the fluorescence intensity of the molecular beacon due to the higher affinity of the aptamer with mercury(II). The limit of detection was 12.7 nanomolar, and a linear relationship was obtained between the fluorescence and mercury(II) concentrations up to 1 micromolar. The assay was highly selective for the mercury(II) and not significantly affected by other metal ions.     

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.     

Effect of Pulse Width of Square Potential to Remove Silver Interference in the Determination of Mercury(II)

A graphite electrode modified with silver (Ag‐CPE) has been applied to detect mercury(II) using differential pulse voltammetry (DPV). Under optimized conditions, the calibration curve is linear in the range from 5.0×10^?8 mol L^?1 to 1.0×10^?4 mol L^?1 of mercury(II). The detection limit was found to be 3.38×10^?8 mol L^?1 with a relative standard deviation (RSD) of 2.25 % (n=8). The proposed method was successfully applied for the detection of mercury(II) in leachate samples. The Ag‐CP composites were characterized using X‐ray diffraction (XRD), BET adsorption analysis and scanning electron microscopy (SEM).     

Eco‐friendly Sensors Developed by Herbal Based Silver Nanoparticles for Electrochemical Detection of Mercury (II) Ion

In our study, the single‐use & eco‐friendly electrochemical sensor platform based on herbal silver nanoparticles (AgNPs) was developed for detection of mercury (II) ion (Hg²⁺). For this purpose, the surface of pencil graphite electrode (PGE) was modified with AgNPs and folic acid (FA), respectively. The concentrations of AgNPs and FA were firstly optimized by differential pulse voltammetry (DPV) to obtain an effective surface modification of PGE. Each step at the surface modification process was characterized by using cyclic voltammetry (CV) and electrochemical impedence spectroscopy (EIS). The limit of detection (LOD) for Hg²⁺ was estimated and found to be 8.43 μM by CV technique. The sensor presented an excellent selectivity for Hg²⁺ against to other heavy metal ions such as Ca²⁺, Cd²⁺, Cr³⁺, Cu²⁺, Mg²⁺, Ni²⁺, Pb²⁺, Zn²⁺, Co²⁺ and Mn²⁺. Moreover, a rapid, selective and sensitive detection of Hg²⁺ was successfully performed in the samples of tap water within 1 min.     

Comparative Studies on the Quick Recognition of Melamine Using Unmodified Gold Nanoparticles and p‐Nitrobenzenesulfonic Grafted Silver Nanoparticles

Both unmodified gold nanoparticles (AuNPs) and p‐nitrobenzenesulfonic (p‐NBS) grafted silver nanoparticles (AgNPs) were prepared by chemical synthesis, respectively. They could be used for visual detection via the interaction with the twelve amide compounds including melamine. These color changes could be seen with the naked eye directly and monitored by ultraviolet visible (UV‐Vis) absorbance spectra. The recognition mechanism for both nanoparticles was comparatively investigated by the addition of glutathione (GSH) in the presence of melamine, respectively. The triple hydrogen bonding recognition and the attractive van der Waals interactions between melamine (0.5 mg/L) and AuNPs were responsible for the color change during its aggregation (red‐to‐purple or blue), whilst the electron donor‐acceptor interaction between melamine (0.2 mg/L) and p‐NBS modified on the surface of AgNPs resulted in the color changes (yellow‐to‐grey or dark green).     

Simultaneous Detection of Copper,Lead and Zinc on Tin Film/Gold Nanoparticles/Gold Microelectrode by Square Wave Stripping Voltammetry

In this work, three heavy metals (Cu(II), Pb(II) and Zn(II)) in wide potential window were simultaneously detected on tin film/gold nanoparticles/gold microelectrode (Sn/GNPs/gold microelectrode) by the method of square wave stripping voltammetry. The Sn/GNPs/gold microelectrode was fabricated by in situ plating of a Sn film on a gold nanoparticles (GNPs) modified gold microelectrode. The influence of hydrogen overflow on stripping of Zn(II) on the gold microelectrode was reduced by modification of GNPs, which made the stripping potential of target metals shift positively. The interference of sulfhydryl groups was reduced and the selectivity of the microelectrode was improved due to the addition of Sn in the detection solution. After accumulation at ?1.4 V for 300 s in acetate buffer solution (0.1 mol L^?1, pH 4.5), the Sn/GNPs/gold microelectrode revealed a good linear behavior in the examined concentration ranges from 5 to 500 µg L^?1 for Cu(II) and Pb(II), and from 10 to 500 µg L^?1 for Zn(II), with a limit of detection of 2 µg L^?1 for Cu(II), 3 µg L^?1 for Pb(II) and 5 µg L^?1 for Zn(II) (S/N=3). When compared with a Sb/GNPs/gold microelectrode and a Bi/GNPs/gold microelectrode, the Sn/GNPs/gold microelectrode showed the best stripping performance to Cu(II), Pb(II) and Zn(II). As a new type of environment‐friendly electrode, the Sn/GNPs/gold microelectrode has potential applications for detection of heavy metals.     

A New Turbidimetric Method for Determination of Melamine Based on its Reaction with Mercury(II)

A turbidimetric technique based on a reaction between Hg(II) and melamine is described for the measurement of melamine content of wastewater of a petrochemical company. The present technique is rapid and simple, uses a small amount of reagent and is set up with low‐cost equipment, making this system economically viable. The experimental conditions such as volume of reagent, pH of buffer, stirring time, stirring speed, ionic strength, etc. were optimized and used in plotting the calibration curve. The linear dynamic range was 1–70 mg/L with a limit of detection of 0.3 mg/L. Repeatability of the proposed method is good, and the relative standard deviation (RSD%) is less than 1.5%. Interferences studies showed that the common compounds existing in wastewater have no negative effect on the efficiency of the method at relatively high concentrations. Finally, the proposed method has been successfully used in determination of melamine in wastewater of Urmia Petrochemical Company.     

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.     

复合SERS基底的构建及性质

通过自组装方法以对巯基苯胺(PATP)为偶联分子, 在石英基片上构筑了多种形貌的银钠米粒子单层结构和三明治结构. 研究了组装膜在不同激发线下表面增强拉曼散射(SERS)的增强差异. 研究结果表明, 单层基底和三明治基底中偶联分子的SERS信号因银纳米粒子间的电磁场耦合而显著增强, 且在三明治结构中增强更加明显. 对复合SERS基底增强因子进行计算可知, 复合SERS基底的表面等离子体共振(SPR)峰与激发线的匹配程度越好, 其增强因子越大. 在三明治结构中更易发生PATP分子转变为对巯基偶氮苯(DMAB)分子的激光诱导催化偶联反应. 另外, 该激光诱导催化偶联反应与激发波长密切相关.     

Gold Nanoparticle Modified Electrodes Show a Reduced Interference by Cu(II) in the Detection of As(III) Using Anodic Stripping Voltammetry

Interference by Cu(II) causes serious problems in the detection of As(III) using anodic stripping voltammetry at gold electrodes. The behavior of Cu(II) and As(III) were examined at both a gold macro electrode and two kinds of gold nanoparticle modified electrodes, one where gold particles are deposited on glassy carbon (GC) and the other where basal plane pyrolytic graphite (BPPG) is the substrate. The sensitivity of As(III) detection was higher on gold nanoparticle modified electrodes than those on a macro gold electrode by up to an order of magnitude. In addition, the stripping peak of As(III) was narrower and more symmetric on a gold nanoparticle‐modified GC electrode, leading to analytical data with a lower limit of detection. At a macro gold electrode, the peak currents of Cu(II) were higher than those on gold nanoparticle modified electrodes. Accordingly, through the use of gold nanoparticle modified electrodes, the effect of copper interference to the arsenic detection can be reduced.     

Anodic Stripping Voltammetric Determination of Iron(II) at a Carbon Paste Electrode Modified with Dithiodianiline (DTDA) and Gold Nanoparticles (GNP)

A differential pulse anodic stripping voltammetric procedure was developed for the determination of trace amounts of iron(II) in the presence of iron(III) at a carbon paste electrode (CPE) modified with dithiodianiline and gold nanoparticle. At the pH working of 3.0, a wide concentration range from 0.1 nM to 100 nM was observed with the detection limit of 0.05 nM. The relative standard deviation for a solution containing 50 nM of iron(II) was found to be 3.11 % (n=9). Possible interferences from the coexisting ions were also investigated. The validity of the method and applicability of the sensor were successfully tested by determining of iron(II) in lentil, wheat seed and barley seed samples.     

Electrochemical Sensor Based on Gold Nanoparticles Stabilized in Poly(Allylamine hydrochloride) for Determination of Vanillin

Gold nanoparticles stabilized in poly(allylamine hydrochloride) (AuNP‐PAH) were synthesized, characterized and applied in the development of a new sensor for the determination of vanillin by square‐wave voltammetry. Under optimized conditions, the calibration curve showed a linear range for vanillin of 0.90 to 15.0 µmol L^?1, with a limit of detection of 55 nmol L^?1. The sensor demonstrated acceptable selectivity and stability, as well as good intra‐day and inter‐day repeatability and electrode‐to‐electrode repeatability (with relative standard deviations of 3.5, 4.5 and 3.9 %, respectively). The sensor was successfully applied in the determination of vanillin in different commercial samples.     

Novel Screen-Printed Gold Nano Film Electrode for Trace Mercury(II) Determination Using Anodic Stripping Voltammetry

Integrating the screen printing technique with the vacuum evaporation method, we developed a novel and disposable screen-printed gold film electrode (SPGFE) in the present work. First, a conductive silver layer, a connection graphite-carbon layer, and an insulating polymer layer were successively printed onto a flexible polyethylene terephthalate (PET) substrate. Then, a gold thin film was achieved on the scheduled vacant site by use of the vacuum evaporation method. In order to enhance the electroanalytical performance of the SPGFE, the thickness of the gold film was controlled in the range of 70–80 nm under optimum conditions. The fabricated SPGFE was applied to detect trace mercury(II) based on the square-wave anodic stripping voltammetry (SWASV). The results indicated that the proposed SPGFE exhibited higher sensitivity to trace mercury(II) than the gold disc electrode. The stripping current was linearly related to the concentration of mercury(II) in the range of 16–280 µg/L (R² = 0.9919) and 1.2–8.0 µg/L (R² = 0.9977), with a detection limit of 0.8 µg/L (S/N = 3) under 180 s accumulation. The SPGFE was further used to detect mercury in real samples, and the obtained results revealed a good agreement with those of inductively coupled plasma atomic emission spectrometry (ICP-AES) and atomic absorption spectroscopy (AAS). The highly sensitive and environmental friendly electrode, as another type of “mercury-free” electrode, holds great promise in stripping measurements.     

Synthesis and characterization of gold nanoparticles stabilized by palladium(II) phosphine thiol

This work is focused on the synthesis of innovative hybrids made by linking gold nanoparticles to protected organometallic Pd(II) thiolate. The organometallic protected Pd(II) thiolate, i.e. trans-thioacetate-ethynylphenyl-bis(tributylphosphine)palladium(II) has been synthesized, in situ deprotected and linked to Au nanoparticles. In this way new hybrid, with a direct link between Pd(II) and Au nanoparticles through a single S bridge, has been isolated. The combination of the organometallic Pd(II) thiol with gold nanoparticles allows the enhancement and tailoring of electronic and optical properties of the new organic-inorganic nano-compound. Single-crystal gold nanoparticles, uniform in shape and size were obtained by applying a modified two-phase method (improved Brust-Schiffrin reaction). In addition, the chemical environment of the Au nanoparticles was investigated and a covalent bonding between Au nanoparticles and the organometallic thiols was observed.     

A New Sensor with Increased Lifetime Based on a Mixed Diazonium Thick Film/Gold Nanoparticles Interface for Hg(II) Trace Detection

This work describes a novel strategy for surface functionalization, the aim of which is to significantly increase the lifetime of an electrochemical sensor dedicated to Hg(II) trace determination. In order to tailor stable mixed organic/inorganic interfaces, gold nanoparticles were electrodeposited onto a glassy carbon electrode previously functionalized by a thick 4‐thiophenol diazonium film, which affords a good anchoring to the nanoparticles. AFM and FEG‐SEM were used to characterize the film thickness and the nanoparticles average size and density, respectively. By using square wave anodic stripping voltammetry, the sensor exhibited a linear response between 1 and 10 nM Hg(II) and a normalized sensitivity 0.03 μA nM^?1 min^?1. Compared to previous works, the storage lifetime of the interface was at least three times longer, being more than three weeks.     

Gravimetric Determination of Mercury(II) and Vanadium(IV) with Benzoylacetanilide

Abstract

Gravimetric methods for the determinations of mercury(II) and vanadium(IV) with benzoylacetanilide have been described. These metals have been separated from commonly associated ions and a procedure for the determination of vanadium content of steel has been developed. By these methods, 14 to 50 mg. of mercury and 5 to 20 mg. of vanadium have been estimated with relative standard deviations of 0.18% and 0.10%, respectively.