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.

Nanoenabled Enhancement of Plant Tolerance to Heat and Drought Stress on Molecular Response.

Global warming has posed significant pressure on agricultural productivity. The resulting abiotic stresses from high temperatures and drought have become serious threats to plants and subsequent global food security. Applying nanomaterials in agriculture can balance the plant's oxidant level and can also regulate phytohormone levels and thus maintain normal plant growth under heat and drought stresses. Nanomaterials can activate and regulate specific stress-related genes, which in turn increase the activity of heat shock protein and aquaporin to enable plants' resistance against abiotic stresses. This review aims to provide a current understanding of nanotechnology-enhanced plant tolerance to heat and drought stress. Molecular mechanisms are explored to see how nanomaterials can alleviate abiotic stresses on plants. In comparison with organic molecules, nanomaterials offer the advantages of targeted transportation and slow release. These advantages help the nanomaterials in mitigating drought and heat stress in plants.

Contents and health risk assessments of selected heavy metals in vegetables produced through irrigation with effluent-impacted river.

The widely consumed vegetables, khat, lettuce, and Swiss chard, in Hirna town, West Hararghe, Ethiopia, are extensively cultivated through irrigation with an effluent-impacted river that flows through the town which denotes that monitoring the safety of the vegetables is crucial. Herein, the contents of Pb, Zn, Cu, Cr, and Cd in vegetables, water, and soils were determined by flame atomic absorption spectrometry after a wet digestion procedure based on a mixture of HNO3 and HClO4 at 200 °C. pH and electrical conductivity of the water and soil, and health risks associated with vegetable consumption were determined. The pH of the water (6.64) and soil (6.67) was slightly acidic, and electrical conductivity values were 0.416 and 0.024 mS/cm, respectively, indicating both are in good condition. The metal concentrations were in the range of ND-3.12, 3.43-9.22, and 0.15-10.6 mg/L in the water, soil, and vegetables, respectively, and the contents followed a trend of Cu > Zn > Cr > Pb > Cd. The irrigation water contained all metals above the guidelines except Cd, and the soil contained safe levels except Cd which is above the guideline. The obtained metal levels in the vegetables were below the safe limits. Estimated daily intakes and the total target cancer risks were below the guidelines, and the target hazard quotient and the hazard index were below 1 indicating that the vegetables are safe for consumption. In general, the obtained results suggest that the vegetables are safe for consumption. However, continuous monitoring and policy development are required to mitigate contamination of the river.

Compound-specific isotopic analysis to characterize the photocatalytic reaction of TiO2 nanoparticles with diethyl phthalate.

In this study compound-specific isotope analysis (CSIA) has been used to explore the degradation mechanism of nano titanium dioxide (TiO2) catalyzes photodegradation of diethyl phthalate (DEP). TiO2 is a popular photosensitizer with potential in waste water treatment and application in advanced oxidation processes. The degradation process of DEP can be described with a first-order kinetics in the applied concentration ranges. The larger degradation rate constant has been found at neutral conditions. The 13C and 2H isotope fractionation associated with the nano TiO2 catalyzes photodegradation of DEP at pH 3, 7 and 11 yield normal isotope effects. In the TiO2/UV/DEP and TiO2/H2O2/UV/DEP systems, the correlation of 13C and 2H fractionation (Λ) were calculated to be 2.7 ± 0.2, 2.8 ± 0.2 at pH 3, 2.2 ± 0.4, 2.5 ± 0.2, 2.3 ± 0.6 at pH 7 and 2.6 ± 0.3, 2.2 ± 0.3, 2.7 ± 0.2 and 2.3 ± 0.3 at pH11, respectively. The dominant free radical species in studied systems were explored by combining free radical quenching method and electron paramagnetic resonance analysis. The hydroxyl radicals have been found as the main radical species at all pH conditions studied. Furthermore, the 13C and 2H fractionation suggested that the addition of •OH on the benzene ring of DEP is the main conversion pathway. Therefore, CSIA is a promising technology for the identification of reaction pathways of DEP for example in water treatment systems.

A robust biocatalyst based on laccase immobilized superparamagnetic Fe3O4@SiO2-NH2 nanoparticles and its application for degradation of chlorophenols.

The presence of chlorophenols in water and wastewater is considered a serious environmental issue. To eliminate these micropollutants, biodegradation of chlorophenols using enzyme-nanoparticle conjugated biocatalyst, is proposed as an economical and eco-friendly method. Herein, amino-functionalized superparamagnetic Fe3O4@SiO2-NH2 nanoparticles with core-shell structure were constructed as a promising carrier for immobilization of laccase from Trametes versicolor. Compared with free laccase, Fe3O4@SiO2-NH2-Laccase displayed remarkable outcomes in all major areas such as temperature and storage stabilities, and tolerance to organic solvents and metal ions. The biocatalytic performance and reusability of Fe3O4@SiO2-NH2-Laccase were evaluated for the degradation of 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) in repeated cycles. Even after 10 successive reuses, the degradation rate of 2,4-DCP and 2,4,6-TCP were found to be 54.9% and 68.7%, respectively. The influences of solution pH, initial chlorophenol concentration, and temperature on the degradation rate of these two chlorophenols were evaluated. The degradation intermediate products including dimers, trimers, and tetramers of 2,4-DCP and 2,4,6-TCP were identified. Release of chloride ions was observed during the enzymatic degradation of these two chlorophenols. Based on the determination of intermediate products and released chloride ions, the degradation pathway that was involved in dehydrogenation, reactive radical intermediates formation, dechlorination, self-coupling and oligomers/polymers formation was proposed. The toxicity of these two chlorophenols and their intermediates was substantially reduced during the enzymatic degradation. The results of this study might present an alternative clean biotechnology for the remediation of 2,4-DCP and 2,4,6-TCP contaminated water matrices.

Nano-selenium functionalized zinc oxide nanorods: A superadsorbent for mercury (II) removal from waters.

In this study, nano selenium functionalized zinc oxide nanorods, NanoSe@ZnO-NR, was prepared, characterized and investigated for Hg(II) removal from waters of different types. The study results revealed that the material showed a superior adsorption capacity (qm, 1110 mg g-1) and excellent distribution coefficient (Kd, 9.11 × 108 mL g-1) which is two or more orders above most of the adsorbents reported in the literature. It should be also known that, 30 mg of the adsorbent can quickly reduce 10 mg L-1 Hg(II) to undetectable level from 10 mL of sample solution. The adsorption data were well explained with the pseudo-second order kinetic model and Langmuir adsorption isotherm model. Besides, the capturing capability of the material is independent on the pH change (2-12), selective against interfering cations, and exhibited fast kinetics (equilibrium time, ∼1 min). The NanoSe@ZnO-NR performance was also tested on real samples from different origin, surface waters (tap, lake and river) and wastewaters (effluent and influent), and complete removal and ≥99.2% removal efficiency was observed at 0.01 and 10 mg L-1 spiking levels, respectively. Therefore, NanoSe@ZnO-NR can be considered as a potential adsorbent in advancing the wastewater treatment technology.

Separation and size characterization of zinc oxide nanoparticles in environmental waters using asymmetrical flow field-flow fractionation.

There are few studies on separation and size characterization of zinc oxide nanoparticles (ZnO-NPs), which have wide applications in several science and technology areas, in the environment. In this work, we report a method for the separation and size characterization of ZnO-NPs by asymmetrical flow field-flow fractionation (AF4) coupled to UV-vis detector. Experimental conditions such as composition of the carrier solution, focus time, crossflow, detector flow rate and injection volume were systematically studied in terms of NPs separation, recovery, and repeatability. Size characterization was achieved using polystyrene nanoparticles as a size standard and a mixture of < 35 nm (NP-A) and < 100 nm (NP-B) ZnO-NPs were separated and size characterized posterior preconcentration using ultracentrifugation. The method was also employed to characterize the size of homemade ZnO-NPs, and the results were in concordance with dynamic light scattering (DLS) analysis and thus, the method can be used as an alternate method. Upon application on environmental water samples, the two ZnO-NPs, NP-A and NP-B, have been separated and size characterized. The estimated hydrodynamic sizes of the NP-A and NP-B were found to be in the range of 83-97 nm and 188-202 nm, respectively, with good precision (RSD, <11%), suggesting that the current method can satisfactorily separate and generate information about sizes of the NPs in samples with a complex matrix. Therefore, the developed technique can be used as a baseline to investigate size related environmental processes of the NPs in environmental water samples.

Level of selected heavy metals in surface dust collected from electronic and electrical material maintenance shops in selected Western Oromia towns, Ethiopia.

Surface dusts from electronic and electrical material maintenance workshops may present significant environmental contamination. The aim of this study was to determine levels of selected heavy metals (Cu, Ni, Co, Cd, Cr, Pb, Zn, and Fe) in surface dust samples collected from electronic and electrical device maintenance workshops located in Ambo, Gedo, and Nekemte towns in Ethiopia. An optimized wet digestion procedure (acid mixture, 3 mL HNO3, 2 mL HClO4, and H2O2; digestion time, 2 h; digestion temperature, 200 °C) was employed prior to the metals determination by flame atomic absorption spectroscopy. The average amounts of the metals were found to be in the ranges of 73,970-58,980, 59,290-51,120, 8570-5778, 1273-1126, 708.9-261.6, 111.7-101.0, 114.9-89.50, and 12.30-9.620 mg/kg for Pb, Fe, Cu, Cr, Zn, Co, Ni, and Cd, respectively. The results showed that the investigated surface dust samples contained significant levels of the analyzed heavy metals compared to soil samples collected from the corresponding control sites. The heavy metal concentrations in the investigated samples from the three towns followed a decreasing order Pb > Fe >> Cu >> Cr > Zn > Co > Ni > Cd, indicating the presence of elevated amount of Pb in the surface dust samples. The significantly high levels of heavy metals detected in all surface dust samples from electronic and electrical device maintenance shops could be inferred to the seepage of these metals from electronic materials during the maintenance procedures. Based on the result obtained, we strongly recommend a strict monitoring and disposal (policy issue) of wastes generated from electronic and electrical device maintenance shops.

Tracking the Transformation of Nanoparticulate and Ionic Silver at Environmentally Relevant Concentration Levels by Hollow Fiber Flow Field-Flow Fractionation Coupled to ICPMS.

It is a great challenge to monitor the physical and chemical transformation of nanoparticles at environmentally relevant concentration levels, mainly because the commonly used techniques like dynamic light scattering and transmission electron microscopy are unable to characterize and quantify trace level nanoparticles in complex matrices. Herein, we demonstrate the on-line coupled system of hollow fiber flow field-flow fractionation (HF5), minicolumn concentration, and inductively coupled plasma mass spectrometry (ICPMS) detection as an efficient approach to study the aggregation and chemical transformation of silver nanoparticles (AgNPs) and ionic Ag species in the aqueous environment at ng/mL levels. Taking advantage of the in-line dialysis of HF5, the selective capture of Ag(I) species by the resin in minicolumn, and the high selectivity and sensitivity of ICPMS detection, we recorded the aggregation of 10 ng/mL AgNPs in complex matrices (e.g., NOM, Na+/Ca2+), revealing an interesting tiny AgNPs formation process of photoreduction of trace level Ag(I) that is different from larger AgNPs generated at high concentration of Ag(I) by accurate characterization and respectively identifying and quantifying new thiol-complexed Ag(I) and residual Ag(I) in the intertransformation of Ag(I) and AgNPs in domestic wastewater by simultaneously detecting the S and Ag signals via ICPMS.

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.

Development of reusable magnetic chitosan microspheres adsorbent for selective extraction of trace level silver nanoparticles in environmental waters prior to ICP-MS analysis.

Solid-phase extraction (SPE) based on reusable magnetic chitosan microspheres was coupled with ICP-MS for separation and quantification of silver nanoparticles (AgNPs) in the presence of silver ions in environmental water samples. The monodisperse magnetic chitosan microspheres with an average size of 2µm were engineered using suspension cross-linking technique, and characterized and investigated for its application as SPE adsorbent. Parameters affecting the SPE were optimized, and the best performance was achieved by extracting a 20mL sample (pH 4.5) with 10mg adsorbent for 90min, followed by elution with 1mL 1% (w/v) thiourea in 10% (v/v) nitric acid for 10min. The detection limit, calculated as 3s (s, standard deviation for 11 blank readings), for three AgNPs coated with polyvinyl pyrrolidone (PVP), citrate and polyvinyl alcohol (PVA) and sizes of 31, 40, 46nm, respectively, were in the range of 0.016‒0.023µg/L. The repeatability and reproducibility (RSD, n=7) at a spiking level of 0.1µg/L AgNPs were 4.2% and 8.1%, respectively. The developed method has been applied in the analysis of AgNPs in river, lake and wastewater samples, with excellent extraction efficiencies (84.9‒98.8%) for AgNPs at spiking levels of 0.86 and 8.70µg/L. The cationic chitosan microspheres showed good species selectivity and reusability for extraction of AgNPs in the presence of Ag+, and hence the proposed method is simple, cost effective and environmentally friendly.

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.

Environmental Application, Fate, Effects, and Concerns of Ionic Liquids: A Review.

Ionic liquids (ILs) comprise mostly of organic salts with negligible vapor pressure and low flammability that are proposed as replacements for volatile solvents. ILs have been promoted as "green" solvents and widely investigated for their various applications. Although the utility of these chemicals is unquestionable, their toxic effects have attracted great attention. In order to manage their potential hazards and design environmentally benign ILs, understanding their environmental behavior, fate and effects is important. In this review, environmentally relevant issues of ILs, including their environmental application, environmental behavior and toxicity are addressed. In addition, also presented are the influence of ILs on the environmental fate and toxicity of other coexisting contaminants, important routes for designing nontoxic ILs and the techniques that might be adopted for the removal of ILs.

Nanofluid of zinc oxide nanoparticles in ionic liquid for single drop liquid microextraction of fungicides in environmental waters prior to high performance liquid chromatographic analysis.

Using a nanofluid obtained by dispersing ZnO nanoparticles (ZnO NPs) in 1-hexyl-3-methylimidazolium hexafluorophosphate, new single drop microextraction method was developed for simultaneous extraction of three fungicides (chlorothalonil, kresoxim-methyl and famoxadone) in water samples prior to their analysis by high performance liquid chromatography (HPLC-VWD). The parameters affecting the extraction efficiency such as amount of ZnO NPs in the nanofluid, solvent volume, extraction time, stirring rate, pH and ionic strength of the sample solution were optimized. Under the optimized conditions, the limits of detection were in the range of 0.13-0.19ng/mL, the precision of the method assessed with intra-day and inter-day relative standard deviations were <4.82% and <7.04%, respectively. The proposed method was successfully applied to determine the three fungicides in real water samples including lake water, river water, as well as effluent and influent of wastewater treatment plant, with recoveries in the range of 74.94-96.11% at 5ng/mL spiking level. Besides to being environmental friendly, the high enrichment factor and the data quality obtained with the proposed method demonstrated its potential for application in multi residue analysis of fungicides in actual water samples.