Search

The placement of polyoxometalates next to the surface of noble metallic nanoparticles has been found to enhance the surface-enhanced Raman scattering (SERS) effect. The enhancement is believed to stem from either charge (electrostatic attraction) or chemical effects. Anisotropic gold nanorods are recognized as useful nanostructures for SERS, mainly due to the high electric field enhancement at their ends. The presented work examines the use of a polyoxometalate encapsulated gold nanorod for SERS, to assess whether the two enhancement pathways would be synergetic. For this, a gold nanorod-polyoxometalate composite was synthesized by coating cetyltrimethylammonium bromide-stabilized gold nanorods with a silicotungstic Keggin anion through electrostatic attraction. The structure was characterized, confirming that the nanorods have been fully encapsulated by the polyoxometalate. The SERS performance of the composite was assessed in solution using crystal violet as a SERS indicator, finding an analytical enhancement factor of 1.8 × 10 4 in colloidal solution. The enhancement mechanism was examined first by comparison to gold nanorods stabilized by a cetyltriethylammonium bromide bilayer, cationic thiol bound polyoxometalate, and polyelectrolyte coating. Next, composites made using polyoxometalates of different atomic composition and charge were examined. It was concluded that the polyoxometalate charge had a noticeable effect on the enhancement while the atomic composition did not. Furthermore, high enhancement is observed mainly in cases where the nanorod monolayer allows the sequestration of the dye molecule into the nanoparticle's ligand layer. The proposed mechanism therefore involves the negative charge of the polyoxometalate attracting the positively charged dye, and facilitating the sequestration of the dye within the ligand bilayer, closer to the nanorod's surface., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Efficient removal of heavy metal pollutants from wastewater by ion-exchange sorbents requires knowledge and understanding of the interplay between the adsorption patterns of the different components. The present study elucidates the simultaneous adsorption characteristics of six toxic heavy metal cations (Cd 2+ , Cr 3+ , Cu 2+ , Ni 2+ , Pb 2+ , and Zn 2+ ) by two synthetic (13X and 4 A) and one natural (clinoptilolite) zeolite from solutions containing equimolar mixtures of the six metals. Equilibrium adsorption isotherms and equilibration dynamics were obtained by ICP-OES and complemented by EDXRF. An order of magnitude lower adsorption efficiency was exhibited by clinoptilolite (maximum of 0.12 mmol ions/g zeolite), relative to that obtained by the synthetic zeolites 13X and 4 A (a maximum of 2.9 and 1.65 mmol ions/g zeolite respectively). The strongest affinities to both zeolites were demonstrated by Pb 2+ and Cr 3+ (1.5 and 0.85 mmol/g zeolite respectively for 13X, and 0.8 and 0.4 mmol/g zeolite respectively for 4 A adsorbed from the highest solution concentration). The weakest affinities were observed by Cd 2+ (0.1 mmol/g for both zeolites), Ni 2+ (0.2 and 0.1 mmol/g for 13X and 4 A respectively), and Zn 2+ (0.1 mmol/g for both zeolites). Large differences were observed between the two synthetic zeolites in terms of their equilibration dynamics and adsorption isotherms. Pronounced maxima were displayed in the adsorption isotherms for zeolites 13X and 4 A. The decline in adsorption of the weaker adsorbing ions with the increase in total solution concentration was attributed to the thermodynamic equilibrium between the ions adsorbed on the zeolite surface and those in the solution. Regeneration by 3 M KCL eluting solution resulted in considerable reduction in adsorption capacities following each desorption cycle., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Chloride determination is of great importance, as chloride plays important roles in human health, pitting corrosion, environmental processes, and agriculture. However, chloride determination by inductively coupled plasma-optical emission spectroscopy (ICP-OES), one of the premier techniques used for elemental analysis, is currently limited to specific instrument types or requires the use of additional equipment. This work presents an argentometric method for the indirect measurement of chloride, applicable to any ICP-OES instrument. The initial Ag + concentration added to samples is of great importance, as it affects both the method's limit of quantification (LOQ) and the top limit of its working range. The developed method found 50 mg L -1 of Ag + to be the optimal concentration, providing a working range of 0.2-15 mg L -1 Cl - . The method was robust to changes in filtration time, temperature, and sample acidity. Using the argentometric method, chloride was determined in a variety of samples (spiked-purified water, seawater, wine, and urine). For validation, the results were compared to those obtained using ion chromatography and showed no statistical differences. Argentometric chloride determination by ICP-OES is therefore applicable to many types of samples and can be easily performed on any ICP-OES instrument.

Sensor arrays use pattern recognition for the identification and quantification of analytes. In the presented work, a gold nanoparticle (GNP) based optical sensor array was employed to classify and quantify seven toxic metals (arsenic, barium, cadmium, cerium, chromium, lead, and mercury). The sensor array receptors were GNPs functionalized by mercaptoundecanoic acid, 2-mercaptoethanesulfonate, and a 1:1 mixture of the two ligands. The mixed-ligand particle responds to the same analytes as the mono-ligand particles but in a distinctive way. This behavior demonstrates the high potential of mixed-ligand particles in the fabrication of sensor array receptors. The responses of the GNPs to different concentrations of the seven metal ions were analyzed, and a unique "classification trajectory" was produced for every metal. Samples of different metal concentrations were then measured and identified using the "classification trajectories". Once sample composition has been identified, a PLSR model, produced from the concatenated sensor array spectra of four calibration samples for each nanoparticle, was used to determine the metal concentration., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Isotopic composition analysis of natural and depleted uranium by inductively coupled plasma optical emission spectrometry (ICP-OES) requires the use of a high-resolution instrument due to the very slight isotopic shifts between the atomic emission spectra of the 238 U and 235 U isotopes. In this work, we show that conventional ICP-OES (without high-resolution optics) can be used for highly accurate uranium isotopic analysis, on par with the results obtained by ICP-MS. Such accurate measurements are achieved by applying a preparatory mathematical procedure termed the optimal sensitivity position (OSP) procedure. In the OSP procedure, a theoretical spectrum for 238 U is constructed and subtracted from the measured spectra of calibration solutions encompassing various isotopic ratios. The resultant spectra are used to locate the optimal measurement positions for both major uranium isotopes ( 238 U and 235 U) and the background measurement position. Herein, the optimal measurement positions are revealed to be located not at each isotope's peak maximum but at 424.427, 424.409, and 424.390 nm for 238 U, 235 U, and the background position, respectively. These locations remained stationary during the period of this work, implying that the use of a routine mathematical procedure is not required before every analysis. The OSP procedure offers a direct and highly accurate approach for determining the isotopic ratio of uranium in a relatively cheap and simple fashion. Furthermore, this work also demonstrates the possibility of greatly enhancing ICP-OES capabilities using mathematical analysis of spectra.

The last two decades have seen great advancements in fundamental understanding and applications of metallic nanoparticles stabilized by mixed-ligand monolayers. Identifying and controlling the organization of multiple ligands in the nanoparticle monolayer has been studied, and its effect on particle properties has been examined. Mixed-ligand protected particles have shown advantages over monoligand protected particles in fields such as catalysis, self-assembly, imaging, and drug delivery. In this Review, the use of mixed-ligand monolayer protected nanoparticles for sensing applications will be examined. This is the first time this subject is examined as a whole. Mixed-ligand nanoparticle-based sensors are revealed to be divided into four groups, each of which will be discussed. The first group consists of ligands that work cooperatively to improve the sensors' properties. In the second group, multiple ligands are utilized for sensing multiple analytes. The third group combines ligands used for analyte recognition and signal production. In the final group, a sensitive, but unstable, functional ligand is combined with a stabilizing ligand. The Review will conclude by discussing future challenges and potential research directions for this promising subject.

An ever-growing demand for uranium in various industries raises concern for human health of both occupationally exposed personnel and the general population. Toxicological effects related to uranium (natural, enriched, or depleted uranium) intake involve renal, pulmonary, neurological, skeletal, and hepatic damage. Absorbed uranium is filtered by the kidneys and excreted in the urine, thus making uranium detection in urine a primary indication for exposure and body burden assessment. Therefore, the detection of uranium contamination in bio-samples (urine, blood, saliva, etc.,) is of crucial importance in the field of occupational exposure and human health-related applications, as well as in nuclear forensics. However, the direct determination of uranium in bio-samples is challenging because of "ultra-low" concentrations of uranium, inherent matrix complexity, and sample diversity, which pose a great analytical challenge to existing detection methods. Here, we report on the direct, real-time, sensitive, and selective detection of uranyl ions in unprocessed and undiluted urine samples using a uranyl-binding aptamer-modified silicon nanowire-based field-effect transistor (SiNW-FET) biosensor, with a detection limit in the picomolar concentration range. The aptamer-modified SiNW-FET presented in this work enables the simple and sensitive detection of uranyl in urine samples. The experimental approach has a straight-forward implementation to other metals and toxic elements, given the availability of target-specific aptamers. Combining the high surface-to-volume ratio of SiNWs, the high affinity and selectivity of the uranyl-binding aptamer, and the distinctive sensing methodology gives rise to a practical platform, offering simple and straightforward sensing of uranyl levels in urine, suitable for field deployment and point-of-care applications.

This article presents a new method for the simpler and faster determination of tin in beverages using EDXRF. Absorption coefficients for aqueous calibration samples were calculated and shown to be nearly identical to those of the beverage samples, thus permitting the use of aqueous standard solutions for external calibration. Beverage samples could then be measured directly using the external calibration. Determination of tin using this method takes 4 min. The LOD and LOQ were 4 mg L -1 and 15 mg L -1 respectively, and the precision was 3.89%. Different canned beverages (cold coffee, various fruit juices) were measured and the results compared to the concentrations obtained using ICP-OES after digestion. The two methods showed good compatibility, thus establishing the newly developed method as a rapid, simple, and accurate method for the determination of tin in beverages., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The controlled assembly of gold nanoparticles (AuNPs) with the size of quantum dots into predictable structures is extremely challenging as it requires the quantitatively and topologically precise placement of anisotropic domains on their small, approximately spherical surfaces. We herein address this problem by using polyoxometalate leaving groups to transform 2 nm diameter gold cores into reactive building blocks with hydrophilic and hydrophobic surface domains whose relative sizes can be precisely tuned to give dimers, clusters, and larger micelle-like organizations. Using cryo-TEM imaging and 1 H DOSY NMR spectroscopy, we then provide an unprecedented "solution-state" picture of how the micelle-like structures respond to hydrophobic guests by encapsulating them within 250 nm diameter vesicles whose walls are comprised of amphiphilic AuNP membranes. These findings provide a versatile new option for transforming very small AuNPs into precisely tailored building blocks for the rational design of functional water-soluble assemblies., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The uptake of molecular guests, a hallmark of the supramolecular chemistry of cages and containers, has yet to be documented for soluble assemblies of metal nanoparticles. Here we demonstrate that gold nanoparticle-based supraspheres serve as a host for the hydrophobic uptake, transport and subsequent release of over two million organic guests, exceeding by five orders of magnitude the capacities of individual supramolecular cages or containers and rivalling those of zeolites and metal-organic frameworks on a mass-per-volume basis. The supraspheres are prepared in water by adding hexanethiol to polyoxometalate-protected 4 nm gold nanoparticles. Each 200 nm assembly contains hydrophobic cavities between the estimated 27,400 gold building blocks that are connected to one another by nanometre-sized pores. This gives a percolated network that effectively absorbs large numbers of molecules from water, including 600,000, 2,100,000 and 2,600,000 molecules (35, 190 and 234 g l -1 ) of para-dichorobenzene, bisphenol A and trinitrotoluene, respectively.

Polyoxometalate (POM) cluster anions are shown to serve as covalently coordinated ligands for anatase-TiO2 nanocrystals, giving isolable assemblies uniquely positioned between molecular macroanions and traditional colloidal nanoparticles. Na(+) salts of the water-soluble polyanionic structures are obtained by reacting amorphous TiO2 with the 1 nm lacunary ion, Na7 [α-XW11 O39 ] (X=P(5+) ), at 170 °C, after which an average of 55 α-PW11 O39 (7-) clusters are found as pentadentate ligands for Ti(IV) ions covalently linked to 6 nm single-crystal anatase cores. The attached POMs are reversible electron acceptors, the reduction potentials of which shift in a predictable fashion by changing the central heteroatom, X, directly influencing a model catalytic reaction. Just as POM cluster anions control the reactivities of metal centers in molecular complexes, directly coordinated POM ligands with tunable redox potentials now provide new options for rationally controlling the reactions of semiconductor nanocrystals., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Electrostatically stabilized monolayer shells of metal-oxide cluster anions (polyoxometalates, or POMs) on the surfaces of ca. 8 nm tetrahedral and octahedral gold nanocrystals regioselectively direct water-soluble alkanethiolate ligands to the corners and edges of the gold polyhedra.

Cryogenic transmission electron microscopy of polyoxometalate-protected gold nanoparticles reveals that the Preyssler ion, [NaP(5)W(30)O(110)](14-), lies "face down" with its C(5) axis perpendicular to the gold surface, while the Finke-Droege ion, [P(4)W(30)Zn(4)(H(2)O)(2)O(112)](16-), is "tilted", with its long axis close to 60° from the normal to the surface.

Polyoxometalate (POM)-monolayer stability constants, K, for three POM anions vary with the cation size, in the same order as that for increasing ion-pair formation with α-SiW(11)O(39)(8-) (1) in the early nucleation phase of monolayer self-assembly: Li(+) < Na(+) < K(+) < Cs(+). Cryo-TEM images demonstrating the use of the cation size to rationally control monolayer formation provide definitive evidence that the POM monolayers are electrostatically stabilized (ionic) shells, analogous in that respect to the monolayer walls of "hollow" POM-macroanion vesicles.

The metal oxide cluster α-AlW(11)O(39)(9-) (1), readily imaged by cryogenic transmission electron microscopy (cryo-TEM), is used as a diagnostic protecting anion to investigate the self-assembly of alkanethiolate monolayers on electrostatically stabilized gold nanoparticles in water. Monolayers of 1 on 13.8 ± 0.9 nm diameter gold nanoparticles are displaced from the gold surface by mercaptoundecacarboxylate, HS(CH(2))(10)CO(2)(-) (11-MU). During this process, no aggregation is observed by UV-vis spectroscopy, and the intermediate ligand-shell organizations of 1 in cryo-TEM images indicate the presence of growing hydrophobic domains, or "islands", of alkanethiolates. UV-vis spectroscopic "titrations", based on changes in the surface plasmon resonance upon exchange of 1 by thiol, reveal that the 330 ± 30 molecules of 1 initially present on each gold nanoparticle are eventually replaced by 2800 ± 30 molecules of 11-MU. UV-vis kinetic data for 11-MU-monolayer formation reveal a slow phase, followed by rapid self-assembly. The Johnson, Mehl, Avrami, and Kolmogorov model gives an Avrami parameter of 2.9, indicating continuous nucleation and two-dimensional island growth. During nucleation, incoming 11-MU ligands irreversibly displace 1 from the Au-NP surface via an associative mechanism, with k(nucleation) = (6.1 ± 0.4) × 10(2) M(-1) s(-1), and 19 ± 8 nuclei, each comprised of ca. 8 alkanethiolates, appear on the gold-nanoparticle surface before rapid growth becomes kinetically dominant. Island growth is also first-order in [11-MU], and its larger rate constant, k(growth), (2.3 ± 0.2) × 10(4) M(-1) s(-1), is consistent with destabilization of molecules of 1 at the boundaries between the hydrophobic (alkanethiolate) and the electrostatically stabilized (inorganic) domains., (© 2011 American Chemical Society)