Visual detection of silver(I) ions by a chromogenic reaction catalyzed by gold nanoparticles

We report on a novel method for visual detection silver(I) ion. It is based on the finding that Ag(I) ions are rapidly reduced by hydroquinone to form a shell of silver on the surface of gold nanoparticles (AuNPs) which act as catalysts for this reaction. This leads to a color change from red to yellow which can be seen with bare eyes. This scheme is sensitive and highly specific for Ag(I) ions. The detection limits are 5 μM for visual inspection and 1 μM for photometric readout, respectively. The method was successfully applied to the determination of Ag(I) ions in spiked lake water and soil.

Simple optical determination of silver ion in aqueous solutions using benzo crown-ether modified gold nanoparticles

We describe a method for the modification of gold nanoparticles (Au-NPs) with benzo-15-crown-5 that led to the development of a colorimetric assay for Ag(I) ion. The brown color of a solution of the modified Au-NPs turns to purple on addition of Ag(I) ion. The ratio of the UV–vis absorption at 600 nm and 525 nm is proportional to the concentration of Ag(I) ions in the range from 20 to 950 nM, and the detection limit is 12.5 nM. Other metal ions do not interfere if present in up to millimolar concentrations. The method enables a rapid determination of Ag(I) in lake and drinking water and is amenable to bare-eye readout.

Detection of silver(I) ion based on mixed surfactant-adsorbed CdS quantum dots

Mixed cationic and anionic surfactants were adsorbed on cadmium sulfide quantum dots (CdS QDs) capped with mercaptoacetic acid. The CdS QDs can be extracted into acetonitrile with 98 % efficiency in a single step. Phase separation only occurs at a molar ratio of 1:1.5 between cationic and anionic surfactants. The surfactant-adsorbed QDs in acetonitrile solution display stronger and more stable photoluminescence than in water solution. The method was applied for determination of silver(I) ion based on its luminescence enhancement of the QDs. Under the optimum conditions, the relative fluorescence intensity is linearly proportional to the concentration of silver(I) ion in the range between 50 pmol L^?1and 4 μmol L^?1, with a 20 pmol L^?1 detection limit. The relative standard deviation was 1.93 % for 9 replicate measurements of a 0.2 μmol L^?1 solution of Ag(I).

Anodic stripping voltammetric determination of silver ion at a carbon paste electrode modified with carbon nanotubes

A carbon paste electrode (CPE) was modified with multi-wall carbon nanotubes and successfully applied to the determination of silver ion by differential pulse anodic stripping voltammetry. Compared to a conventional CPE, a remarkably improved peak current response and sensitivity is observed. The analytical procedure consisted of an open circuit accumulation step for 2?min in ?0.4?V, this followed by an anodic potential scan between +0.2 and?+?0.6?V to obtain the voltammetric peak. The oxidation peak current is proportional to the concentration of silver ion in the range from 1.0?×?10^?8 to 1.0?×?10^?5?mol?L^?1, with a detection limit of 1.8?×?10^?9?mol?L^?1 after an accumulation time of 120?s. The relative standard deviation for 7 successive determinations of Ag(I) at 0.1???M concentration is 1.99%. The procedure was validated by determining Ag(I) in natural waters.

Determination of L-cysteine base on the reversion of fluorescence quenching of calcein by copper(II) ion

We report on a simple and sensitive method for the determination of L-cysteine (Cys). It is based on a redox reaction between the non-fluorescent Cu(II)-calcein complex and Cys which results in fluorescence recovery of calcein. When Cys is added to a solution of the Cu(II)-calcein complex, Cu(II) is reduced to Cu(I), and calcein is released to form a strongly fluorescent complex with Zn(II). The effect was used to develop a fluorescence enhancement method for the determination of Cys. Under the optimum conditions, the increase in signal intensity is linear in the range from 3.0?×?10^?7 to 1.2?×?10^?5?mol?L^?1, with a correlation coefficient (R) of 0.9978. The limit of detection (3σ) is 4.0?×?10^?8?mol?L^?1. The relative standard deviation (RSD) in the determination of 11 samples containing 5.0?×?10^?6?mol?L^?1 of Cys was 3.5%. There is little interference by common ions and other amino acids. The method, which is simple, rapid, and sensitive, was successfully applied to the determination of Cys in human serum samples.

Protein-stabilized fluorescent nanocrystals consisting of a gold core and a silver shell for detecting the total amount of cysteine and homocysteine

We report on a simple and sensitive method for the determination of the total amount of cysteine (Cys) and homocysteine (hCys), [Cys plus hCys], by exploiting the effect of Cys and hCys on the photoluminescence of human serum albumin-stabilized gold-core silver-shell nanocrystals (NCs). If Cys (or hCys) are added to these NCs, Cys (or hCys) will be adsorbed on the surface due to ligand exchange with human serum albumin, and this results in the quenching of the luminescence of the NCs. The addition of mixtures of Cys and hCys in different molar ratios also induces a decrease in luminescence whose intensity is linearly related to the concentration of [Cys plus hCys] in the range from 0.1 – 5.0 μM, with a correlation coefficient (R ²) of 0.9953 and a detection limit of 15 nM. The method is highly selective and sensitive over other α-amino acids, water-soluble thiols, and biomolecules. It has been successfully applied to the determination of the concentration of [Cys plus hCys] in spiked solutions of biomolecules and in real biological samples.

Water-soluble homo-oligonucleotide stabilized fluorescent silver nanoclusters as fluorescent probes for mercury ion

Water–soluble fluorescent silver nanoclusters (Ag NCs) were prepared with the assistance of commercially available polyinosinic acid (PI) or polycytidylic acid (PC). The fluorescence of the Ag NCs is effectively quenched by trace mercury(II) ions, which can be applied for their detection. The response of the Ag NCs prepared with PI to Hg(II) ion is linear in the Hg(II) concentration range from 0.05 to 1.0 μM (R²?=?0.9873), and from 0.5 to 10 μM of Hg(II) (R²?=?0.9971) for Ag NCs prepared with PC. The detection limits are 3.0 nM and 9.0 nM (at an S/N of 3), respectively. The method is simple, sensitive and fairly selective.

Experimental and DFT study on the complexation of the silver cation with calix[4]arene-bis(t-octylbenzo-18-crown-6)

From extraction experiments and γ-activity measurements, the exchange extraction constant corresponding to the equilibrium Ag⁺ (aq) + 1·Cs⁺(org) ? 1·Ag⁺ (org) + Cs⁺ (aq) taking place in the two-phase water–phenyltrifluoromethyl sulfone (FS 13) system (1 = calix[4]arene-bis(t-octylbenzo-18-crown-6); aq = aqueous phase, org = FS 13 phase) was evaluated as logK _ex (Ag⁺, 1·Cs⁺) = ?1.5 ± 0.1. Further, the stability constant of the 1·Ag⁺ complex in FS 13 saturated with water was calculated for a temperature of 25 °C: log β _org(1·Ag⁺) = 10.1 ± 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structure of the cationic complex species 1·Ag⁺ was derived. In the resulting 1·Ag⁺ complex, the “central” cation Ag⁺ is bound by eight bond interactions to six oxygen atoms from the respective 18-crown-6 moiety and to two carbons of the corresponding two benzene rings of the parent ligand 1 via cation-π interaction.     

Shell correction study of fission of doubly charged silver clusters

Fission of doubly charged silver clusters is investigated by the method of shell corrections. The following fission events are considered: Ag ₂₂ ²⁺ → Ag _n ⁺ + Ag _{22 ?n} ⁺ , (n=11, 10, 9, 8); Ag ₂₁ ²⁺ → Ag _n ⁺ + Ag _{21 ?n} ⁺ , (n=10, 9, 8, 7); Ag ₁₈ ²⁺ → Ag _n ⁺ + Ag _{18 ?n} ⁺ , (n=9, 8, 7, 6). It is found that the shell correction energy is comparable to or larger than the deformation energy of the liquid drop. Threshold energies for the fission events are calculated and compared with the experimental abundance spectra obtained by Katakuse et al. (1990). Correspondence between the calculated threshold energies with the shell corrections and the experimental abundance is very good, showing products from lower threshold fission channels yield more abundance. The threshold energies without the shell corrections are almost constant irrespective of the fission channels and cannot explain the experimental abundance. Abundance of some products are too small to be accounted for only by the threshold energies. The low abundance of those products may be explained by the presence of competing fission channels that have similar minimal energy paths. It is found in fission of Ag ₁₈ ²⁺ that the shell correction overwhelms the Coulomb energy and the fission channel to Ag₈ + Ag ₁₀ ²⁺ is preferred over the fission channel to Ag ₈ ⁺ + Ag ₁₀ ⁺ .     

Anodic stripping voltammetry of silver(I) using a carbon paste electrode modified with multi-walled carbon nanotubes

We describe a silver(I)-selective carbon paste electrode modified with multi-walled carbon nanotubes and a silver-chelating Schiff base, and its electrochemical response to Ag(I). Effects of reduction potential and time, accumulation time, pH of the solution and the stripping medium were studied by differential pulse anodic stripping voltammetry and optimized. The findings resulted in a method for the determination of silver over a linear response range (from 0.5 to 235 ng?mL^?1) and with a detection limit as low as 0.08 ng?mL^?1. The sensor displays good repeatability (with the RSD of ±?2.75 % for 7 replicates) and was applied to the determination of Ag(I) in water samples and X-ray photographic films.

A New Phosphorescent Cyclometalated Iridium(III) Complex for the Selective Detection of Silver(I) Ion

A new cyclometalated iridium(III) complex, Ir(ppz)₂(dtp) (Ir1) (ppzH = 4-phenylphthalazinone, dtp = diethyl dithiophosphate), has been synthesized and characterized by single-crystal X-ray diffraction. The photoluminescence spectrum of Ir1 shows an emission maximum at 597 nm and its quantum yield is ca. 0.072. Complex Ir1 exhibits a strong and fast decrease of emission upon addition of Ag⁺ in aqueous media. The ratio of Ir1 responding to Ag⁺ was determined to be 1:1 by UV?CVis absorption and phosphorescent emission measurements. Complex Ir1 is a highly selective chemosensor for Ag⁺ over other transition metal ions.     

Fluorescent sensing of nitrite at nanomolar level using functionalized mesoporous silica

Aminopyrene was covalently anchored onto mesoporous silica through serial post-grafting to obtain a fluorescent solid that can be used as a sensing material for the determination of nitrite. The latter, in acidic medium, reacts with the secondary amino groups on the material to form a non-fluorescent nitroso derivative. Based on the fluorescence quenching caused by this specific reaction, a method was developed for the determination of nitrite at nanomolar levels. The range for detection of nitrite in 1.5?mol.L^?1 HCl is linear between 1.50?nM to 0.45???M and 0.45???M to 2.22???M, the detection limit being 1.10?nM and 0.307???M respectively at an S/N of 3.

Green biosynthesis of silver nanoparticles and nanomolar detection of p-nitrophenol

Green biosynthesis of nanoparticles and their applications in sensor field is of great interest to the researchers. We report herein a simple green approach for the synthesis of silver nanoparticles (Ag-NPs) using Acacia nilotica Willd twig bark and its application for the detection of 4-nitro phenol (4-NP). The synthesized Ag-NPs were characterized by Transmission electron microscopy, X-ray diffraction and elemental analysis. The size of synthesized Ag-NPs was in the range of 10–50 nm. The Ag-NPs modified electrode shows a high sensitivity and selectivity towards the sensing of 4-NP. The fabricated modified electrode shows a low detection limit of 15 nM on the wider linear response range from 100 nM to 350 μM with the sensitivity of 2.58?±?0.05 μAμM^?1 cm^?2. In addition, the fabricated sensor shows good repeatability and reproducibility.

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.

Ligation-triggered fluorescent silver nanoclusters system for the detection of nicotinamide adenine dinucleotide

Herein, we demonstrate a novel silver nanocluster-based fluorescent system for the detection of nicotinamide adenine dinucleotide (NAD⁺), an important biological small molecule involved in a wide range of biological processes. A single-stranded dumbbell DNA probe was designed and used for the assay, which contained a nick in the stem, a poly-cytosine nucleotide loop close to 5′ end as the template for the formation of highly fluorescent silver nanoclusters (Ag NCs) and another loop close to 3′ end. Only in the presence of NAD⁺, the probe was linked at 5′ and 3′ ends by Escherichia coli DNA ligase, which blocked the DNA polymerase-based extension reaction, ensuring the formation of fluorescent Ag NCs. This technique provided a logarithmic linear relationship in the range of 1 pM–500 nM with a detection limit of as low as 1 pM NAD⁺, and exhibited high selectivity against its analogues, and was then successfully used for the detection of NAD⁺ level in four kinds of cell homogenates. In addition, this new approach was conducted in an isothermal and homogeneous condition without the need of any thermal cycling, washing, and separation steps, making it very simple. Overall, this label-free protocol offers a promising alternative for the detection of NAD⁺, taking advantage of specificity, sensitivity, cost-efficiency, and simplicity.

Fluorescent probe for copper(II) ion based on a rhodamine spirolactame derivative, and its application to fluorescent imaging in living cells

A fluorescent probe for Cu(II) ion is presented. It is based on the rhodamine fluorophore and exhibits high selectivity and sensitivity for Cu(II) ion in aqueous methanol (2:8, v/v) at pH 7.0. The response is based on a ring opening reaction and formation of a strongly fluorescent 1:1 complex. The response is reversible and linear in the range between 50?nM and 900?nM, with a detection limit of 7.0?nM. The probe was successfully applied to fluorescent imaging of Cu(II) ions in HeLa cells.

Sensitive immunoassay for porcine pseudorabies antibody based on fluorescence signal amplification induced by cation exchange in CdSe nanocrystals

We report on a novel immunoassay for porcine pseudorabies virus (PRV) antibody that is based on fluorescence signal amplification induced by silver(I) ion exchange in CdSe nanocrystals. An antigen-antibody-secondary antibody sandwich structure was first formed from PRV, PRV antibody, and CdSe-labeled rabbit anti-pig antibody. Then, the Cd(II) ions in the CdSe labels were released by a cation exchange reaction with Ag(I). Released Cd(II) was finally quantified using the sensitive fluorescent probe Rhodamine 5 N. Due to this signal amplification, the sensitivity and linear range of the immunoassay were largely improved (compared to the traditional ELISA) in having a limit of detection as low as 1.2 ng?mL^?1 of PRV antibody and a linear range from 2.44 to 312 ng?mL^?1. The successful determination of PRV antibody in pig serum samples is proof for the utility of the method.

Anodic stripping voltammetric determination of arsenic(III) using a glassy carbon electrode modified with gold-palladium bimetallic nanoparticles

We have developed a method for the determination of the three catecholamines (CAs) epinephrine (EP), norepinephrine (NE), and dopamine (DA) at sub-nanomolar levels. It is found that the luminescence of the complexes formed between the CAs and Tb³⁺ ion is strongly enhanced in the presence of colloidal silver nanoparticles (Ag-NPs). The Ag-NPs cause a transfer of the resonance energy to the fluorophores through the interaction of the excited-state fluorophores and surface plasmon electrons in the Ag-NPs. Under the optimized condition, the luminescence intensity of the system is linearly related to the concentration of the CAs. Linearity is observed in the concentration ranges of 2.5–110?nM for EP, 2.8–240?nM for NE, and 2.4–140?nM for DA, with limits of detection as low as 0.25?nM, 0.64?nM and 0.42?nM, respectively. Relative standard deviations were determined at 10?nM concentrations (for n?=?10) and gave values of 0.98%, 1.05% and 0.96% for EP, NE and DA, respectively. Catecholamines were successfully determined in pharmaceutical preparations, and successful recovery experiments are demonstrated for urine and serum samples.

A Surface Enhanced Raman Scattering (SERS) microdroplet detector for trace levels of crystal violet

We report on a microfluidic platform that integrates a winding microdroplet chip and a surface-enhanced Raman scattering (SERS) detection system for trace determination of crystal violet (CV). Colloidal silver was applied to generate SERS. Compared to the continuous flow microfluidic system, the microdroplet based detection described here effectively eliminates any memory effects. Effects of flow pattern, droplet size, surfactant, and position of detection were optimized. Under optimal conditions, there is a linear correlation between signal and the concentration of CV in the 10 nM to 800 nM range, with a correlation coefficient (R²) of 0.9967. The limit of detection in water is 3.6 nM.

Differential pulse anodic stripping voltammetric determination of traces of tin using a glassy carbon electrode modified with bismuth and a film of poly(bromophenol blue)

We report on an anodic stripping voltammetric method for the determination of tin using a glassy carbon electrode modified with bismuth and poly(bromophenol blue). After an accumulation time of 60?s at ?1.20?V (vs. SCE), the response of the electrode to tin in 1.0?M HCl is linear in the concentration ranges from 20 nM to 1.0?μM, and from 1.0?μM to 20?μM, with a detection limit of 7.0 nM (at an SNR of 3) and with relative standard deviations in the order of 3.0–3.8%. The method was validated by comparing the results with those obtained by AAS and successfully applied to the determination of tin in canned food.