Cholesteric Molecular Tweezer Artificial Receptor for Rapid and Highly Selective Detection of Ag+ in Food Samples

Chiral cholesteric molecular tweezer 7a was synthesized, and its recognition properties for Ag⁺, Al³⁺, Ca²⁺ etc., were investigated by UV and fluorescence spectra. The results showed that in ethanol/Tris (1/1, v/v, pH 7.0) buffer solution, the host molecular tweezer 7a had a specific recognition ability for Ag⁺, the detection limit was up to 1 × 10⁻⁶ mol/L, and other metal ions had little effect on Ag⁺ recognition. At the same time, the naked-eye detection of Ag⁺ was realized by the light red color of the complex solution. Furthermore, the mechanism of recognition of Ag⁺ by molecular tweezer 7a was studied by a nuclear magnetic titration test and computer molecular simulation, and a rapid detection method of Ag⁺ using host molecular tweezer 7a was established. Through the determination of Ag⁺ in milk powder, quinoa and other food samples, it was proved that this novel method had a good application prospect for the detection of Ag⁺ in food.     

Double-armed and tetra-armed cyclen-based cryptands

Double-armed and tetra-armed cyclen-based cryptands (1a–1d and 2) that bridge two aromatic rings by diethyleneoxy and triethyleneoxy units were prepared. The CSI-MS of 1:1 mixtures ([Ag⁺]/[ligand]) indicated that these new cryptands form 1:1 complexes with Ag⁺. The log K values for the interaction between Ag⁺ and 2 was greater than those of 1a–1d, double-armed cyclens (3a–3c and 4), and tetra-armed cyclen (5). The Ag⁺-ion-induced ¹H NMR spectral changes suggest that the Ag⁺–π interactions of the Ag⁺ complexes with the cryptands (1a–1d and 2) are stronger than those in Ag⁺/double-armed and tetra-armed cyclens. To visualise the Ag⁺?π interactions, the isosurfaces of the LUMO and HOMOs of the Ag⁺ complexes were calculated at the B3LYP/3–21G(*) theoretical level. The LUMO of the Ag⁺ ion is distorted by interaction with the HOMOs of the aromatic side arms. The calculations reveal Ag⁺?π interactions between the Ag⁺ ion and the aromatic side arms, and these are shown graphically.     

A borondipyrrolemethene-based turn-on fluorescent probe for silver ion with high sensitivity and selectivity and its application in water samples and living cells

A borondipyrrolemethene-based compound (1) is synthesized and used as a “turn-on” fluorescent probe for silver ions (Ag⁺). The probe displays highly sensitive fluorescence response toward Ag⁺ with a 40-fold fluorescence enhancement when 60 μM of Ag⁺ is added. The fluorescence intensity of the probe is linearly dependent on Ag⁺ concentration ranging from 0.05 to 60 μM. And the detection limit (LOD) can reach 0.02 μM, which complies with the standard of World Health Organization (WHO) for drinking water (0.9 μM). Moreover, the probe shows remarkable selectivity for Ag⁺ over other metal ions. Furthermore, the response behavior of 1 toward Ag⁺ is pH independent in the neutral range from 6.0 to 8.0. The response of 1 toward Ag⁺ is fast (response time is less than 2 min) and reversible chemically. What’s more, the sensing mechanism of probe 1 toward Ag⁺ is verified by mass spectra (MS) and density functional theory (DFT) calculations. In particular, the probe is applied for detection of Ag⁺ in water samples and living cells successfully.     

Paper test strip for silver ions detection in drinking water samples based on combined fluorometric and colorimetric methods

In this study, a portable silver ion (Ag⁺) sensor was fabricated based on a dual signal output system using black phosphorus quantum dots (BPQDs) as probes. It is the first work for Ag⁺ detection using paper test strip based on BPQDs. The color change of BPQDs paper sensor for the determination of Ag⁺ was easily identified by naked eye. BPQDs were synthesized from bulk black phosphorus (BP) by mechanical exfoliation combined with a solvothermal method. BPQDs exhibited blue fluorescence with a quantum yield of 8.82 %. The fluorescence of BPQDs can be quenched by Ag⁺, and the absorbance of BPQDs is increased with increasing Ag⁺ concentration. The mechanism of the interaction between BPQDs and Ag⁺ involving fluorescence quenching and bonding was investigated by experimental and computational methods. The detection limit of Ag⁺ was 1.56 μg/mL and 0.19 μg/mL using fluorometry and colorimetry methods, respectively. A portable visual sensor based on paper test strip was constructed for Ag⁺ detection using the colorimetric approach. The strategy was employed to determine Ag⁺ successfully in drinking water samples. Therefore, the proposed portable Ag⁺ sensor can be potentially utilized for the lab-free analysis of drinking water and even dietary samples.     

The electrode modified with Langmuir–Blodgett film of p-tert-butylcalix[4]arene derivatives with sulfur-containing functionalities for the determination of silver

A new voltammetric sensor, based on a new p-tert-butylcalix[4]arene derivative (TCAD) modified glassy carbon electrode (GCE) using Langmuir–Blodgett (LB) technique, was designed successfully and used for recognition and determination of Ag⁺. The π?-?A isotherms suggested that the monolayer of TCAD can coordinate with Ag⁺ at the air–water surface. Under the optimum experimental conditions, this voltammetric sensor shows a linear voltammetric response for Ag⁺ in the range of 1.0?×?10^?8?～?6.0?×?10^?6?mol?L^?1 with detection limit 5.0?×?10^?9?mol?L^?1. The high sensitivity, selectivity, and stability of this LB film modified electrode also demonstrate its practical application for a simple, rapid and economical determination of Ag⁺ in water sample.     

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.     

Characterization of [peptide+(Ag)n]+ complexes using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Silver ion complexes of peptides [M + (Ag)_n]⁺, M = angiotensin I or substance P where n = 1–8 and 17–23 for angiotensin I and n = 1–5 for substance P, are identified and characterized using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS). The Ag⁺ coordination number exceeds the number of available amino acid residues in angiotensin I whereas the number of observed complexes in substance P is less than the number of amino acid residues in it. The larger coordination number of angiotensin I with Ag⁺ indicates the simultaneous binding of several Ag⁺ ions to the amino acid residue present in it. The lower number of observed complexes in substance P suggests the binding of two or more residues to one Ag⁺ ion. The presence of trifluoroacetic acid in the peptide samples reduces the Ag⁺ coordination ability in both the peptides which indicates that the basic residues in it are already protonated and do not participate in the Ag⁺‐binding process. The Ag⁺ ion also forms a complex with the α‐cyano‐4‐hydroxycinnamic acid (CHCA) matrix and is observed in the MALDI mass spectra and the formation of [CHCA + Ag]⁺, [CHCA + AgNO₃]⁺ and [(CHCA)₂ + Ag]⁺ ions is due to the high binding affinity of Ag⁺ to the CN group of CHCA. Copyright © 2010 John Wiley & Sons, Ltd.     

A Reusable DNA Single‐Walled Carbon‐Nanotube‐Based Fluorescent Sensor for Highly Sensitive and Selective Detection of Ag+ and Cysteine in Aqueous Solutions

Here we report a reusable DNA single‐walled carbon nanotube (SWNT)‐based fluorescent sensor for highly sensitive and selective detection of Ag⁺ and cysteine (Cys) in aqueous solution. SWNTs can effectively quench the fluorescence of dye‐labeled single‐stranded DNA due to their strong π–π stacking interactions. However, upon incubation with Ag⁺, Ag⁺ can induce stable duplex formation mediated by C–Ag⁺–C (C=cytosine) coordination chemistry, which has been further confirmed by DNA melting studies. This weakens the interactions between DNA and SWNTs, and thus activates the sensor fluorescence. On the other hand, because Cys is a strong Ag⁺ binder, it can remove Ag⁺ from C–Ag⁺–C base pairs and deactivates the sensor fluorescence by rewrapping the dye‐labeled oligonucleotides around the SWNT. In this way, the fluorescence signal‐on and signal‐off of a DNA/SWNT sensor can be used to detect aqueous Ag⁺ and Cys, respectively. This sensing platform exhibits high sensitivity and selectivity toward Ag⁺ and Cys versus other metal ions and the other 19 natural amino acids, with a limit of detection of 1 nM for Ag⁺ and 9.5 nM for Cys. Based on these results, we have constructed a reusable fluorescent sensor by using the covalent‐linked SWNT–DNA conjugates according to the same sensing mechanism. There is no report on the use of SWNT–DNA assays for the detection of Ag⁺ and Cys. This assay is simple, effective, and reusable, and can in principle be used to detect other metal ions by substituting C–C base pairs with other native or artificial bases that selectively bind to other metal ions.     

Kinetics of Ag+ contained polymeric complex membranes for facilitated olefin transport

The reactions of silver ion complexes with polyethylene-graft-poly(acrylic acid) (PE-g-AA) and the olefin reversible coordinates with the PE-g-AA–Ag⁺ complex membranes were studied. Infrared and nuclear magnetic resonance spectra confirmed the complex formation between the carboxylic acid of the PE-g-AA and the Ag⁺ ion. Also, the Ag⁺ ion in PE-g-AA-Ag⁺ membrane was assumed to be a fixed carrier that adsorbs and transports olefin, thereby causing a selective olefin/paraffin separation. A theoretical model of the PE-g-AA-Ag⁺ (olefin) complex was proposed. The coordination number of Ag⁺ ion binding to the carboxylic acid of PE-g-AA is about 1.6 in glycerol solution. The coordination number of olefin binding to the Ag⁺ in the PE-g-AA–Ag⁺ complex membrane is 1. Moreover, the kinetics of olefin binding to the PE-g-AA–Ag⁺ complex membranes were studied. The equilibrium, association, and dissociation constants were also presented. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 909–917, 1997     

Fluorescent detection of silver(I) and cysteine using SYBR Green I and a silver(I)-specific oligonucleotide

We report on a novel method for the determination of silver ion (Ag⁺) and cysteine (Cys) by using the probe SYBR Green I (SGI) and an Ag+-specific cytosine-rich oligonucleotide (C-DNA). The fluorescence of SGI is very weak in the absence or presence of randomly coiled C-DNA. If, however, C-DNA interacts with Ag⁺ through the formation of cytosine-Ag⁺-cytosine (C-Ag⁺-C) base pairs, the randomly coiled C-DNA undergoes a structural changes to form a hairpin-like structure, thereby increasing the fluorescence of SGI. This fluorescence turn-on process allows the detection of Ag⁺ in the 10–600?nM concentration range, with a detection limit of 4.3?nM. Upon the reaction of Ag⁺ with Cys, Cys specifically removes Ag⁺ from the C-Ag⁺-C base pairs and destroys the hairpin-like structure. This, in turn, results in a decrease in fluorescence intensity. This fluorescence turn-off process enables the determination of Cys in the 8–550?nM concentration range, with a detection limit of 4.5?nM. The method reported here for the determination of either Ag⁺ or Cys is simple, sensitive, and affordable, and may be applied to other detection systems if appropriately selected DNA sequences are available.

一种基于硫杂杯[4]芳烃的高效银离子载体

合成了基于下缘含有酰肼基团的硫杂杯芳烃衍生物的银离子载体1,其核磁研究证实硫杂杯芳烃以1,3-交替构象存在,并且通过非竞争萃取实验和竞争萃取实验研究了它对碱金属和过渡金属离子（Li⁺, Na⁺, K⁺, Cs⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Ag⁺）的键合能力和选择性。实验结果表明：将酰肼基团引入1,3-交替构象的硫杂杯芳烃骨架的下缘可以提高其对Ag⁺的键合能力和选择性,同时,对Cu²⁺的萃取能力较弱,对碱金属离子和其它的重金属离子几乎没有萃取能力。进一步的核磁滴定和电喷雾质谱实验显示化合物1与银离子形成配合物的配合计量比为1：1,由此推断主要由“N-Ag⁺”配位键以及硫杂杯芳烃骨架的协同作用构成了化合物1与银离子的配合模式。     

Gas‐phase copper and silver complexes with phosphorothioate and phosphorodithioate pesticides investigated using electrospray ionization mass spectrometry

Efforts to improve agricultural productivity have led to a growing dependency on organophosphorus pesticides. Phosphorothioate and phosphorodithioate pesticides are organophosphorus pesticide subclasses with widespread application for the control of insects feeding on vegetables and fruits. However, even low doses of these pesticides can cause neurological problems in humans; thus, their determination and monitoring in agricultural foodstuffs is important for human health. Phosphorothioate and phosphorodithioate pesticides may be poorly ionized during electrospray, adversely affecting limits of detection. These pesticides can form complexes with Cu²⁺ and Ag⁺, however, potentially improving ionization. In the present work, we used electrospray ionization/mass spectrometry (ESI/MS) to study fenitrothion, parathion, diazinon, and malathion coordination complexes with silver and copper ions. Stable 1 : 1 and 1 : 2 metal/pesticide complexes were detected. Mass spectra acquired from pesticide solutions containing Ag⁺ or Cu²⁺ showed a significant increase in signal‐to‐background ratio over those acquired from solutions containing only the pesticides, with Ag⁺ improving detection more effectively than Cu²⁺. Addition of Ag⁺ to a pesticide solution improved the limit of detection by ten times. The relative affinity of each pesticide for Ag⁺ was related to complex stability, following the order diazinon > malathion > fenitrothion > parathion. The formation of Ag⁺–pesticide complexes can significantly improve the detection of phosphorothioate and phosphorodithioate pesticides using ESI/MS. The technique could potentially be used in reactive desorption electrospray ionization/mass spectrometry to detect phosphorothioate and phosphorodithioate pesticides on fruit and vegetable skins. Copyright © 2015 John Wiley & Sons, Ltd.     

Organoselenide as a Novel Ionophore for a Silver-Selective Membrane Electrode

Abstract

Three selenium-containing compounds, diphenyl selenide, benzyl phenyl selenide and dibenzyl selenide were used as neutral carriers to make a Ag⁺-selective membrane electrode. All three compounds exhibited higher sensitivity to Ag⁺ than the corresponding sulfides and ethers. The highest sensitivity was obtained by dibenzyl selenide and an electrode constructed using this carrier and bis(l-butylpentyl) adipate as a membrane solvent in a poly(vinyl chloride) membrane matrix exhibited a near-Nernstian response to Ag⁺ in the concentration range from 1 x 10^?5 to 1 x 10^?2 M with a slope of 52 mV per concentration decade. The lower limit of detection was around 1 μM. The ion selectivity of this electrode for Ag⁺ was over 10⁴ times that for other metal cations. Dibenzyl selenide and Ag⁺ interactions were examined by ¹H-NMR spectroscopy.     

The Ag+-G interaction inhibits the electrocatalytic oxidation of guanine--a novel mechanism for Ag+ detection

The heavy metal ions-nucleobases interaction is an important research topic in environmental and biochemical analysis. The presence of the silver ion (Ag⁺) may influence the formation of oxidation intermediate and the electrocatalytic oxidation activity of guanine (G), since Ag⁺ can interact with guanine at the binding sites which are involved in the electrocatalytic oxidation reaction of guanine. According to this principle, a new electrochemical sensor for indirectly detecting Ag⁺ based on the interaction of Ag⁺ with isolated guanine base using differential pulse voltammetry (DPV) was constructed. Among the heavy metal ions examined, only Ag⁺ showed the strongest inhibitory effect on the electrocatalytic oxidation of guanine at the multi-walled carbon nanotubes modified glassy carbon electrode (CNTs/GC). And the quantitative study of Ag⁺ based on Ag⁺-G sensing system gave a linear range from 100 nM to 2.5 μM with a detection limit of 30 nM. In addition, this modified electrode had very good reproducibility and stability. The developed electrochemical method is an ideal tool for Ag⁺ detection with some merits including remarkable simplicity, low-cost, and no requirement for probe preparation.     

Cytidine-stabilized gold nanocluster as a fluorescence turn-on and turn-off probe for dual functional detection of Ag and Hg

In this study, we have developed a label-free, dual functional detection strategy for highly selective and sensitive determination of aqueous Ag⁺ and Hg²⁺ by using cytidine stabilized Au NCs and AuAg NCs as fluorescent turn-on and turn off probes, respectively. The Au NCs and AuAg NCs showed a remarkably rapid response and high selectivity for Ag⁺ and Hg²⁺ over other metal ions, and relevant detection limit of Ag⁺ and Hg²⁺ is ca. 10 nM and 30 nM, respectively. Importantly, the fluorescence enhanced Au NCs by doping Ag⁺ can be conveniently reusable for the detection of Hg²⁺ based on the corresponding fluorescence quenching. The sensing mechanism was based on the high-affinity metallophilic Hg²⁺–Ag⁺ interaction, which effectively quenched the fluorescence of AuAg NCs. Furthermore, these fluorescent nanoprobes could be readily applied to Ag⁺ and Hg²⁺ detection in environmental water samples, indicating their possibility to be utilized as a convenient, dual functional, rapid response, and label-free fluorescence sensor for related environmental and health monitoring.     

Surface plasmon resonance detection of silver ions and cysteine using DNA intercalator-based amplification

We report the development of a surface plasmon resonance sensor based on the silver ion (Ag⁺)-induced conformational change of a cytosine-rich, single-stranded DNA for the detection of Ag⁺ and cysteine (Cys) in aqueous solutions. In the free state, single-stranded oligonucleotides fold into double-helical structures through the addition of Ag⁺ to cytosine–cytosine (C–C) mismatches. However, in the presence of Cys, which competitively binds to Ag⁺, the formation of the C–Ag⁺–C assembly is inhibited, resulting in free-state, single-stranded oligonucleotides. To enhance sensitivity, the DNA intercalator, daunorubicin, was employed to achieve signal enhancement. The detection limit for Ag⁺ was 10 nM with a measurement range of 50–2,000 nM, and the detection limit for Cys was 50 nM with a measurement range of 50–2,000 nM. This simple assay was also used to individually determine the spiked Ag⁺ concentration in water samples and Cys concentrations in biological fluid samples.     

A H+/Ag+ Dual‐Target Responsive Label‐Free Light‐Up Probe Based on a DNA Triplex

We developed a dual‐target responsive sensor for label‐free light‐up fluorescent detection of protons (H⁺) and silver ions (Ag⁺) using an “OR′′ logic gate. Berberine, a cost‐effective and non‐toxic indicator, partially intercalates the formed triplex DNA in the presence of H⁺ or Ag⁺, generating enhanced fluorescence. The designed Ag⁺ probe has high selectivity and desirable sensitivity, which is necessary for practical use. The robust ”OR“ logic gate is capable of a rapid and reversible response to the H⁺ and/or Ag⁺ inputs.     

A Combined Experimental and Theoretical Study on the Complexation of Ag<Superscript>+</Superscript> with a Hexaarylbenzene-Based Receptor

From extraction experiments and γ-activity measurements, the exchange extraction constant corresponding to the equilibrium Ag⁺(aq) + 1⋅Cs⁺(nb) ⇆ 1⋅Ag⁺(nb) + Cs⁺(aq) taking part in the two-phase water–nitrobenzene system (where 1 = hexaarylbenzene-based receptor; aq = aqueous phase, nb = nitrobenzene phase) was evaluated to be log ₁₀ K _ex(Ag⁺, 1⋅Cs⁺) = −1.0±0.1. Further, the stability constant of the hexaarylbenzene-based receptor⋅Ag⁺ complex (abbreviation 1⋅Ag⁺) in nitrobenzene saturated with water, was calculated at a temperature of 25 °C: log ₁₀ β _nb(1⋅Ag⁺) = 5.5±0.2. By using quantum mechanical DFT calculations, the most probable structure of the 1⋅Ag⁺ complex species was solved. In this complex having C₃ symmetry, the cation Ag⁺ synergistically interacts with the polar ethereal oxygen fence and with the central hydrophobic benzene ring via cation–π interaction.     

Mo3S132− Intercalated Layered Double Hydroxide: Highly Selective Removal of Heavy Metals and Simultaneous Reduction of Ag+ Ions to Metallic Ag0 Ribbons

We demonstrate a new material by intercalating Mo₃S₁₃^2? into Mg/Al layered double hydroxide (abbr. Mo₃S₁₃-LDH), exhibiting excellent capture capability for toxic Hg²⁺ and noble metal silver (Ag). The as-prepared Mo₃S₁₃-LDH displays ultra-high selectivity of Ag⁺, Hg²⁺ and Cu²⁺ in the presence of various competitive ions, with the order of Ag⁺>Hg²⁺>Cu²⁺>Pb²⁺≥Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺. For Ag⁺ and Hg²⁺, extremely fast adsorption rates (≈90 % within 10 min, >99 % in 1 h) are observed. Much high selectivity is present for Ag⁺ and Cu²⁺, especially for trace amounts of Ag⁺ (≈1 ppm), achieving a large separation factor (SF_Ag/Cu) of ≈8000 at the large Cu/Ag ratio of 520. The overwhelming adsorption capacities for Ag⁺ (q_m^Ag=1073 mg g^?1) and Hg²⁺ (q_m^Hg=594 mg g^?1) place the Mo₃S₁₃-LDH at the top of performing sorbent materials. Most importantly, Mo₃S₁₃-LDH captures Ag⁺ via two paths: a) formation of Ag₂S due to Ag-S complexation and precipitation, and b) reduction of Ag⁺ to metallic silver (Ag⁰). The Mo₃S₁₃-LDH is a promising material to extract low-grade silver from copper-rich minerals and trap highly toxic Hg²⁺ from polluted water.     

Eight‐Electron Silver and Mixed Gold/Silver Nanoclusters Stabilized by Selenium Donor Ligands

The first atomically and structurally precise silver‐nanoclusters stabilized by Se‐donor ligands, [Ag₂₀{Se₂P(OⁱPr)₂}₁₂] ( 3 ) and [Ag₂₁{Se₂P(OEt)₂}₁₂]⁺( 4 ), were isolated by ligand replacement reaction of [Ag₂₀{S₂P(Oⁱ Pr)₂}₁₂] ( 1 ) and [Ag₂₁{S₂P(Oⁱ Pr)₂}₁₂]⁺ ( 2 ), respectively. Furthermore, doping reactions of 4 with Au(PPh₃)Cl resulted in the formation of [AuAg₂₀{Se₂P(OEt)₂}₁₂]⁺ ( 5 ). Structures of 3 , 4 , and 5 were determined by single‐crystal X‐ray diffraction. The anatomy of cluster 3 with an Ag₂₀ core having C ₃ symmetry is very similar to that of its dithiophosphate analogue 1 . Clusters 4 and 5 exhibit an Ag₂₁ and Au@Ag₂₀ core of O_h symmetry composed of eight silver capping atoms in a cubic arrangement and encapsulating an Ag₁₃ and Au@Ag₁₂ centered icosahedron, respectively. Both ligand exchange and heteroatom doping result in significant changes in optical and emissive properties for chalcogen‐passivated silver nanoparticles, which have been theoretically confirmed as 8‐electron superatoms.