Plasmon-based colorimetric assay using green synthesized gold nanoparticles for the detection of bisphenol A.

Herein, we report a green synthesized gold nanoparticle (AuNPs) based colorimetric detection of bisphenol A (BPA). The AuNPs were synthesized using khat leaf extract as a reducing agent by optimizing factors affecting the AuNPs synthesis, including gold precursor concentration (1 mM), and reaction temperature (60 °C). The AuNPs characterization was carried out using ultraviolet-visible spectrophotometry and transmission electron microscopy, and it was found spherical with an average particle size of 17.3 ± 3.7 nm. A colorimetric nanosensor was developed by conjugation of bio-inspired AuNPs with BPA-specific aptamer for a quick and easy detection of BPA in plastic bottled water. The colorimetric assay relies on the strong affinity of BPA for aptamer, which causes detachment of the aptamer from the AuNPs surface in the presence of BPA inducing AuNPs aggregation. To achieve the colorimetric detection of BPA, the concentrations of NaCl and aptamer were optimized. The detection of BPA was monitored visually using a naked eye, as well as quantitatively using an ultraviolet-visible spectrophotometer. The method visual limit of detection (LOD) was determined to be 0.1 ng/mL and reached 0.09 ng/mL using ultraviolet-visible spectrophotometer. The method demonstrated very good linearity (R2 = 0.9986) in the range of 0.1-100 ng/mL. The proposed method showed high sensitivity to BPA detection in plastic bottled water with 86.7-98.0%, recovery. Therefore, the proposed colorimetric nanosensor can be used for determination of BPA in plastic bottled waters with reliable performance at lower concentrations.

Self-assembly of supramolecular nanotubes/microtubes from 3,5-dimethyl-4-iodopyrazole for plasmonic nanoparticle organization.

Hierarchical super-architectures from small molecule self-assembly have interesting properties and play an indispensable role in many fields. In most cases, a self-assembly process refers to multiple intermolecular interactions among intricately designed building blocks. Here, a supramolecular assembly with a tubular morphology with dimensions ranging from nanometers to micrometers was prepared through self-assembly of 3,5-dimethyl-4-iodopyrazole (DMIP), a molecule with an unprecedented simple structure. As predicted by density functional theory (DFT) calculations, the hydrogen bond and halogen bond interaction energy between DMIP molecules can be up to 32.81 kJ mol-1, which effectively drives DMIP molecules to assemble into fibrils, sheets, and finally, tubular architectures. Intriguingly, the formed tubular structure can be easily removed by heating at 100 °C, enabling the material to function as a disposable template to guide linear organization of nanostructures. As a proof of concept, ordered Au or Ag nanochains with diameters ranging from 18 to 120 nm were facilely prepared in high yield.

Defect Sites in Ultrathin Pd Nanowires Facilitate the Highly Efficient Electrochemical Hydrodechlorination of Pollutants by H*ads.

Adsorbed atomic H (H*ads) facilitates indirect pathways playing a major role in the electrochemical removal of various priority pollutants. It is crucial to identify the atomic sites responsible for the provision of H*ads. Herein, through a systematic study of the distribution of H*ads on Pd nanocatalysts with different sizes and, more importantly, deliberately controlled relative abundance of surface defects, we uncovered the central role of defects in the provision of H*ads. Specifically, the H*ads generated on Pd in an electrochemical process increased markedly upon introducing defect sites by changing the morphology to ultrathin polycrystalline Pd nanowires (NWs), while dramatically reducing upon decreasing the number of surface defects through an annealing treatment. Benefiting from a proportion of H*ads up to 40% of the total H* species, the Pd NWs showed an electrochemical active surface area normalized rate constant of 13.8 ± 0.8 h-1 m-2, which is 8-9 times higher than its Pd/C counterparts. The pivotal role of defect sites for the generation of H*ads was further verified by blocking such sites with Rh and Pt atoms, while theoretical calculation also confirms that the adsorption energy of H*ads on these sites is much higher than that on the Pd{111} facet.

Facile fabrication of silver nanoparticle decorated α-Fe2O3 nanoflakes as ultrasensitive surface-enhanced Raman spectroscopy substrates.

Although great progress has been made on designing noble metal nanoparticle aggregates/assemblies as surface-enhanced Raman spectroscopy (SERS) substrates, an ever increasing research interest has focused on fabrication of hierarchical nanostructures for superior SERS performance. Here, we report effective decoration of silver nanoparticles (AgNPs) onto vertically and densely grown α-Fe2O3 nanoflakes (NFs) as SERS active substrates. The SERS substrate was prepared by thermally annealing Fe foil at 450 °C to grow α-Fe2O3 NFs and electroless deposition of AgNPs onto α-Fe2O3 NFs, with excellent ability to control the particle size and density. The AgNP-decorated α-Fe2O3 NFs offer high density hot spots and exhibited high SERS performance with enhancement factor of 8.1 × 106. Integration of α-Fe2O3 nanostructure functions as intrinsic internal standard and selective binder for specific analytes like the toxic arsenic. The substrate was successfully used for quantitative detection of arsenic with spatial uniformity (relative standard deviation, RSD, 8.8%) and good reproducibility (RSD, 9.7%). The Raman signal of α-Fe2O3 integrated to the SERS substrate was utilized as internal standard which significantly improves reproducibility. The substrate exhibited a high sensitivity for arsenic detection with a limit of detection down to 1.5 µg L-1, which is much lower than permissible limit (10 µg L-1) set by the WHO. Moreover, the SERS substrates showed excellent practicability and selectivity for determination of arsenic in environmental waters which is valuable for environmental and human health protection.

Au@Pd Bimetallic Nanocatalyst for Carbon-Halogen Bond Cleavage: An Old Story with New Insight into How the Activity of Pd is Influenced by Au.

AuPd bimetallic nanocatalysts exhibit superior catalytic performance in the cleavage of carbon-halogen bonds (C-X) in the hazardous halogenated pollutants. A better understanding of how Au atoms promote the reactivity of Pd sites rather than vaguely interpreting as bimetallic effect and determining which type of Pd sites are necessary for these reactions are crucial factors for the design of atomically precise nanocatalysts that make full use of both the Pd and Au atoms. Herein, we systematically manipulated the coordination number of Pd-Pd, d-orbital occupation state, and the Au-Pd interface of the Pd reactive centers and studied the structure-activity relationship of Au-Pd in the catalyzed cleavage of C-X bonds. It is revealed that Au enhanced the activity of Pd atoms primarily by increasing the occupation state of Pd d-orbitals. Meanwhile, among the Pd sites formed on the Au surface, five to seven contiguous Pd atoms, three or four adjacent Pd atoms, and isolated Pd atoms were found to be the most active in the cleavage of C-Cl, C-Br, and C-I bonds, respectively. Besides, neighboring Au atoms directly contribute to the weakening of the C-Br/C-I bond. This work provides new insight into the rational design of bimetallic metal catalysts with specific catalytic properties.

Transformation and bioavailability of metal oxide nanoparticles in aquatic and terrestrial environments. A review.

Metal oxide nanoparticles (MeO-NPs) are among the most consumed NPs and also have wide applications in various areas which increased their release into the environmental system. Aquatic (water and sediments) and terrestrial compartments are predicted to be the destination of the released MeO-NPs. In these compartments, the particles are subjected to various dynamic processes such as physical, chemical and biological processes, and undergo transformations which drive them away from their pristine state. These transformation pathways can have strong implications for the fate, transport, persistence, bioavailability and toxic-effects of the NPs. In this critical review, we provide the state-of-the-knowledge on the transformation processes and bioavailability of MeO-NPs in the environment, which is the topic of interest to researchers. We also recommend future research directions in the area which will support future risk assessments by enhancing our knowledge of the transformation and bioavailability of MeO-NPs.

Use of Polycrystalline Ice for Assembly of Large Area Au Nanoparticle Superstructures as SERS Substrates.

It is still a great challenge to develop simple and low-cost methods for preparation of surface-enhanced Raman scattering (SERS) substrates with high sensitivity and reproducibility. Taking advantage of the microstructure of polycrystalline ice, we developed a new method to assemble large area gold nanoparticle (AuNP) superstructures as SERS substrates without external templating and aggregating agent. The assembly was conducted by freezing AuNP colloid at -20 °C, which concentrated AuNPs in the ice veins and produced an AuNP superstructure upon thawing the ice. The AuNP superstructures exhibited high SERS activity with enhancement factors on the order of 7.63 × 107 owing to the high-density hot spots throughout the superstructures. The SERS activity was found to increase with particle size and aggregate size of AuNP superstructures. Besides, the substrates showed good uniformity and reproducibility with relative standard deviations of 11.9% and 12.4%, respectively. The substrates showed long-term stability, maintaining SERS activity over a period of five months without noticeable change in morphology of the superstructures. The substrates was further used for label-free detection of trace Thiram on apple fruit with high sensitivity down to the concentration of 0.28 ng/cm2, offering great potential to monitor Thiram levels in foodstuffs and environmental samples.

Ionic liquid-based zinc oxide nanofluid for vortex assisted liquid liquid microextraction of inorganic mercury in environmental waters prior to cold vapor atomic fluorescence spectroscopic detection.

Zinc oxide nanofluid (ZnO-NF) based vortex assisted liquid liquid microextraction (ZnO-NF VA-LLME) was developed and employed in extraction of inorganic mercury (Hg(2+)) in environmental water samples, followed by cold vapor atomic fluorescence spectrometry (CV-AFS). Unlike other dispersive liquid liquid microextraction techniques, ZnO-NF VA-LLME is free of volatile organic solvents and dispersive solvent consumption. Analytical signals were obtained without back-extraction from the ZnO-NF phase prior to CV-AFS determination. Some essential parameters of the ZnO-NF VA-LLME and cold vapor generation such as composition and volume of the nanofluid, vortexing time, pH of the sample solution, amount of the chelating agent, ionic strength and matrix interferences have been studied. Under optimal conditions, efficient extraction of 1ng/mL of Hg(2+) in 10mL of sample solution was achieved using 50µL of ZnO-NF. The enrichment factor before dilution, detection limits and limits of quantification of the method were about 190, 0.019 and 0.064ng/mL, respectively. The intra and inter days relative standard deviations (n=8) were found to be 4.6% and 7.8%, respectively, at 1ng/mL spiking level. The accuracy of the current method was also evaluated by the analysis of certified reference materials, and the measured Hg(2+) concentration of GBW08603 (9.6ng/mL) and GBW(E)080392 (8.9ng/mL) agreed well with their certified value (10ng/mL). The method was applied to the analysis of Hg(2+) in effluent, influent, lake and river water samples, with recoveries in the range of 79.8-92.8% and 83.6-106.1% at 1ng/mL and 5ng/mL spiking levels, respectively. Overall, ZnO-NF VA-LLME is fast, simple, cost-effective and environmentally friendly and it can be employed for efficient enrichment of the analyte from various water samples.