Triangular silver nanoplates as a spectrophotometric reagent for the determination of mercury(II)

The applicability of triangular silver nanoplates (TNPs) as a spectrophotometric reagent for the determination of mercury(II) in an aqueous solution was estimated. The method is based on the oxidation of TNPs with a mean edge length of 52 nm and thickness of 4 nm by mercury(II) ions, which is accompanied by a decrease in the surface plasmon resonance of nanoparticles. The effect of reaction time, pH of solution, and TNP concentration on the sensitivity of mercury(II) determination was studied. The limit of mercury(II) detection under the selected conditions was 0.022 μg/mL.     

Silver nanoparticles capped with chalcon carboxylic acid as a probe for colorimetric determination of cadmium(II)

Microchimica Acta - The authors describe a selective and sensitive method for the colorimetric determination of Cd(II) by using silver nanoparticles capped with chalcone carboxylic acid (CCA) as an...     

Label-free colorimetric sensor for mercury(II) and DNA on the basis of mercury(II) switched-on the oxidase-mimicking activity of silver nanoclusters

In this paper, a novel colorimetric biosensor for Hg²⁺ and DNA molecules is presented based on Hg²⁺ stimulated oxidase-like activity of bovine serum albumin protected silver clusters (BSA-Ag NCs). Under mild conditions, Hg²⁺ activated BSA-Ag NCs to show high catalytic activity toward the oxidation of 3,3′,5, 5′-tetramethylbenzidine (TMB) using ambient dissolved oxygen as an oxidant. The oxidase-like activity of BSA-Ag NCs was “switched-on” selectively in the presence of Hg²⁺, which permitted a novel and facile colorimetric sensor for Hg²⁺. As low as 25 nmol L⁻¹ Hg²⁺ could be detected with a linear range from 80 nmol L⁻¹ to 50 mmol L⁻¹. In addition, the sensing strategy was also employed to detect DNA molecules. Hg²⁺ is known to bind very strongly and specifically with two DNA thymine bases (T) to form thymine–Hg²⁺–thymine (T–Hg²⁺–T) base pairs. The hairpin-structure was disrupted and Hg²⁺ ions were released after hybridization with the DNA target. By coupling the Hg²⁺ switched-on the oxidase-mimicking activity of BSA-Ag NCs, we developed a novel label-free strategy for facile and fast colorimetric detection of DNA molecules. More important, target DNA can be detected as low as 10 nmol L⁻¹ with a linear range from 30 to 225 nmol L⁻¹. Compared with other methods, this method presents several advantages such as the independence of hydrogen peroxide, high sensitivity and good selectivity, avoiding any modification or immobilization of DNA, which holds a great potential of metal NCs for clinical application in biosensing and biotechnology.     

Nanodiamonds conjugated to gold nanoparticles for colorimetric detection of clenbuterol and chromium(III) in urine

Nanodiamonds were modified such that they carry thiol groups (ND-thiol). Gold nanoparticles were reacted with ND-thiol to obtain a highly stable conjugate of the type ND@AuNPs. Both ND-thiol and the ND@AuNPs were characterized by SEM, TEM, AFM, DLS, zeta potential, XPS, XRD, UV-Vis, Raman, FTIR and cytotoxicity studies. Their biocompatibility was confirmed via an MTT assay with HeLa cells. At a pH value of 6, the ND@AuNPs represent a colorimetric probe that can be used to selectively detect the illegally used β-adrenergic drug clenbuterol (CLB) and the pollutant chromium(III). Detection can be performed visually by monitoring the color change from wine red to purple blue, or by colorimetric measurement of the so-called SPR peaks at 651 and 710 nm. The color changes are due to aggregation, and this is confirmed by TEM and DLS data. The involvement of surface functional groups that assist in analyte recognition was verified by FTIR. The detection limits are 0.49 nM for CLB, and 0.37 nM for Cr(III). The ND@AuNPs were successfully applied to the determination of Cr(III) and CLB in spiked human urine samples. Notably, the low interference by other ions in the detection of Cr(III) in tap and lake water is confirmed by ICP-MS analyses.

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Graphical abstract Nanodiamonds carrying thiol groups (ND-Thiol) were conjugated to gold nanoparticles, and the resulting ND@AuNPs are shown to be viable probes for the colorimetric detection of sub-nanomolar levels of clenbuterol (CLB) and Cr(III) ions, with demonstrated applicability to real water and urine samples.

     

Milligram level determination of mercury(II) and bismuth (III): p-mercaptoacetamidophenetidine as a gravimetric reagent

Summary The gravimetric estimation of mercury(II) and bismuth(III) has been carried out on a mg scale usingp-mercaptoacetamidophenetidine as the precipitant. The reagent has the required aqueous solubility and is superior to the commonly used analytical reagents of the mercaptan family. The complexes of the reagent with mercury(II) and bismuth(III) are obtained in pure state, definite in composition and stable in hot acid media.

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Zusammenfassung Die gravimetrische Bestimmung von Hg(II) und Bi(III) mit p-Mercaptoacetamidophenetidin als Fällungsmittel wurde ausgearbeitet. Dieses Reagens ist den üblicherweise verwendeten Merkaptanen überlegen. Die KomplexVerbindungen mit Hg und Bi erhält man rein und in definierter Zusammensetzung. Sie sind gegenüber heißer Säure beständig.

     

Selective colorimetric sensing of mercury(II) using turn off-turn on mechanism from riboflavin stabilized silver nanoparticles in aqueous medium

A simple Hg(2+) sensor has been developed using the vitamin B2 (riboflavin) stabilized Ag nanoparticle via a "turn off"-"turn on" mechanism; both the colour and photoluminescence properties of the riboflavin solution are used as sensitizing tools showing a sensitivity up to 5 nM Hg(2+) concentration.     

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.     

Cation-exchange separation and determination of silver in admixture with mercury(II)

Cation-exchange separation of silver from mercury(II), copper(II), cobalt(II), nickel and zinc, based on the differences in the stability constants of the complexes formed by these elements with EDTA at pH 4.6, is described. Silver is eluted with 16% nitric acid and is determined by Volhard's method.     

Enzyme-free colorimetric assay for mercury(II) using DNA conjugated to gold nanoparticles and strand displacement amplification

The authors describe a colorimetric method for the determination of Hg(II) ion. It is based on the color change from red to colorless as displayed by gold nanoparticle (AuNP) modified with thymine - rich DNA. Signal amplification is accomplished by free strand displacement recycling. In this strategy, Hg(II) unfolds the arch-trigger duplex due to the high affinity between Hg(II) and the thymines to form T-Hg(II)-T structures, thereby causing the release of trigger. The liberated trigger unfolds the hairpin structure of H1, and unfolded H1 further unfolds with H2. As a result, the H2 hairpin displaces trigger, and the released trigger unfolds another H1. This results in strong and enzyme-free strand displacement recycling amplification. The aggregation of DNA-AuNPs occurs in the presence of the duplex formed by hairpins H2 and H1. This results in a color change from red to colorless that can be visually observed. Under optimal conditions, the assay has a detection range over 4 orders of magnitude and a 3.4 nM detection limit. The assay is selective, sensitive, rapid and cost-effective. In our perception, it represents a useful platform for determination of Hg(II).

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Graphical abstract Schematic presentation of the  simple, rapid, low cost colorimetric detection of mercury(II) based on enzyme-free strand displacement amplification along with DNA-labeled AuNP.

     

A colorimetric method for the determination of lead(II) ions using gold nanoparticles and a guanine-rich oligonucleotide

We have developed a colorimetric method for the determination of Pb(II) ions. It is based on the use of gold nanoparticles and a guanine-rich synthetic oligonucleotide. On addition of Pb(II), the color of the solution turns from red to blue. The ratio of the UV-vis absorption at 630?nm and 525?nm is proportional to the concentration of Pb(II) ions in the range from 10 to 100?nM, and the detection limit is 20?nM. Other metal ions do not interfere if present in up to a 10-fold molar excess. The method was successfully applied to the detection of Pb(II) in lake water and urine. The recovery in case of spiked samples is 92%. The results show that this method is sensitive, simple and fast.

Refreshable mercury film silver based electrode for determination of chromium(VI) using catalytic adsorptive stripping voltammetry

The refreshable mercury film silver based electrode Hg(Ag)FE applied for determination of Cr(VI) traces using catalytic adsorptive striping voltammetry (CAdSV) will be presented. The film electrode is characterized by its very good surface reproducibility (not less than 2%) and long-term stability (1500–2000 measurement cycles). The mechanical refreshing of mercury film is realized in the specially constructed device, in a time shorter than 1–2 s.

In the paper, it will be proved that a mechanically weak hanging mercury drop electrode (HMDE) may be substituted by mercury film Hg(Ag)FE electrode with a surface area adjustable from 1.5 to 12 mm². For the electrode surface 4 mm² the detection limit obtained for Cr(VI) was 0.19 nM, while the linearity range measured for a 20 s accumulation time was between 0.5 and 50 nM. The relative standard deviation (R.S.D.) in determination of Cr(VI) varied from 1 to 5%. The influence of the excess of Cr(III) on determination of Cr(VI) was analyzed using samples from the Dobczyce reservoir spiked with known amounts of Cr(VI) and Cr(III).     

Rapid and ultrasensitive colorimetric detection of mercury(II) by chemically initiated aggregation of gold nanoparticles

The article describes a method for rapid and visual determination of Hg(II) ion using unmodified gold nanoparticles (Au-NPs). It involves the addition of Au-NPs to a solution containing Hg(II) ions which, however, does not induce a color change. Next, a solution of lysine is added which induces the aggregation of the Au-NPs and causes the color of the solution to change from wine-red to purple. The whole on-site detection process can be executed in less than 15 min. Other amines (ethylenediamine, arginine, and melamine) were also investigated with respect to their capability to induce aggregation. Notably, only amines containing more than one amino group were found to be effective, but a 0.4 μM and pH 8 solution of lysine was found to give the best results. The detection limits for Hg (II) are 8.4 pM (for instrumental read-out) and 10 pM (for visual read-out). To the best of our knowledge, this LOD is better than those reported for any other existing rapid screening methods. The assay is not interfered by the presence of other common metal ions even if present in 1000-fold excess over Hg(II) concentration. It was successfully applied to the determination of Hg(II) in spiked tap water samples. We perceive that this method provides an excellent tool for rapid and ultrasensitive on-site determination of Hg(II) ions at low cost, with relative ease and minimal operation.

Rapid and ultrasensitive detection of mercury ions using gold nanoparticle based label-free colorimetric method with excellent sensitivity, easy operation and low cost.

     

Cyclopentadienyl mesityl complexes of chromium(II) and chromium(III)

Chromium(III) mesityl complexes were synthesized by protonolysis of chromocene with 1,3-diisopropylimidazolium chloride or DBU hydrochloride, salt metathesis with MesMgBr, and single electron oxidation with iodine.