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Herein, we demonstrate the use of lysozyme (Lys) as a model to fabricate a protein carrier system based on gold nanoparticles (AuNPs) via the Layer-by-Layer (LbL) technology. Poly(ethyleneimine) (PEI) and poly(sodium 4-styrenesulfonate) (PSS) were used as cationic and anionic polymers respectively to grow oppositely charged layers. Mild aqueous conditions were utilized to avoid protein denaturation and activity instead of organic solvents that have been used in other encapsulation systems. Two different strategies were used: (A) lysozyme acting as a reducing and stabilizing agent in the formation of AuNPs at a temperature of 45 ± 2 °C followed by only two subsequent polymeric layers deposited by LbL, and (B) citrate acting as a reducing agent prior to stabilization of the AuNPs by mercaptoundecanoic acid. Dynamic light scattering, UV-vis spectroscopy, IR spectroscopy and transmission electron microscopy were used to characterize the nanoconjugates. Furthermore, the enzymatic activity of the resulting protein/nanoparticle conjugates was evaluated using the bacteria Micrococcus lysodeikticus as a substrate.

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We demonstrate the use of cysteine-modified polymer nanofibers for the rapid and efficient removal of Cr(III) from real tannery waste water samples. Various parameters such as pH, load of nanofibers and time of exposure were optimized to achieve maximum removal. The optimum parameters were found to be 0.1 mg of nanofibers per mL of tannery waste water with a pH of 5.5 and an exposure time of 45 min. Almost 99% Cr(III) was removed at these ideal conditions thus demonstrating the efficacy of our material. The maximum removal capacity at these ideal conditions was estimated to be approximately 1.75 g of chromium/gram of polymeric material. This is probably due to a variety of factors including the apparent high surface to volume ratio exhibited by these nanofibers and also due to the availability of numerous cysteine groups that are known to have high binding affinities with heavy metal ions. These nanoscale polymeric materials show great potential towards the removal of heavy metal cations from waste waters.

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We describe the synthesis of zinc oxide (ZnO) nanoparticles and demonstrate their attachment to multiwalled carbon tubes, resulting in a composite with a unique synergistic effect. Morphology and size of ZnO nanostructures were controlled using hydrothermal synthesis, varying the hydrothermal treatment temperature, prior to attachment to carboxylic acid functionalized multi-walled carbon nanotubes for sensing applications. A strong dependence of electrocatalytic activity on nanosized ZnO shape was shown. High activity for H2O2 reduction was achieved when nanocomposite precursors with a roughly semi-spherical morphology (no needle-like particles present) formed at 90 °C. A 2.4-fold increase in cyclic voltammetry current accompanied by decrease in overpotential from the composites made from the nanosized, needle-like-free ZnO shapes was observed as compared to those composites produced from needle-like shaped ZnO. Electrocatalytic activity varied with pH, maximizing at pH 7.4. A stable, linear response for H2O2 concentrations was observed in the 1-20 mM concentration range.

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This article reviews applications of nanoscale carbon-based materials in heavy metal sensing and detection. These materials, including single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon nanofibers among others, have unique and tunable properties enabling applications in various fields spanning from health, electronics and the environment sector. Specifically, we highlight the unique properties of these materials that enable their applications in the sorption and preconcentration of heavy metals ions prior to detection by spectroscopic, chromatographic and electrochemical techniques. We also discuss their distinct properties that enable them to be used as novel electrode materials in sensing and detection. The fabrication and modification of these electrodes is discussed in detail and their applications in various electrochemical techniques such as voltammetric stripping analysis, potentiometric stripping analysis, field effect transistor-based devices and electrical impedance are critically reviewed. Perspectives and futures trends in the use of these materials in heavy metal sensing and detection will also be highlighted.

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We report the electrochemical deposition of poly(pyrrolepropylic acid) nanowires, their covalent modification with antibodies and their conversion into potential functional sensor devices. The nanowires and the devices were characterised by optical microscopy, fluorescence microscopy, electron microscopy and electrical measurements. Fluorescence images, current-voltage (I-V) profiles and real-time sensing measurements demonstrated a rapid and highly sensitive and selective detection of human serum albumin (HSA), a substance that has been used to diagnose incipient renal disease. The detection is based on the selective binding of HSA onto anti-HSA that is covalently attached to the nanowires. The binding changes the electrical properties of the nanowires thus enabling the real-time detection. Whilst the utility of the research was demonstrated for protein binding/detection, the technology could easily be designed for the detection of other analytes by the modification of polymer nanowires with other analyte-specific molecules/biomolecules. Therefore, the technology has the potential to positively impact broad analytical applications in the biomedical, environmental and other sectors.

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Environmental security is one of the fundamental requirements of our well being. However, it still remains a major global challenge. Therefore, in addition to reducing and/or eliminating the amounts of toxic discharges into the environment, there is need to develop techniques that can detect and monitor these environmental pollutants in a sensitive and selective manner to enable effective remediation. Because of their integrated nature, biosensors are ideal for environmental monitoring and detection as they can be portable and provide selective and sensitive rapid responses in real time. In this review we discuss the main concepts behind the development of biosensors that have most relevant applications in the field of environmental monitoring and detection. We also review and document recent trends and challenges in biosensor research and development particularly in the detection of species of environmental significance such as organophosphate nerve agents, heavy metals, organic contaminants, pathogenic microorganisms and their toxins. Special focus will be given to the trends that have the most promising applications in environmental security. We conclude by highlighting the directions towards which future biosensors research in environmental security sector might proceed.

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This paper describes a new approach for the preparation of polyamic acid (PAA) composites containing Ag and Au nanoparticles. The composite film of PAA and metal particles were obtained upon electrodeposition of a PAA solution containing gold or silver salts with subsequent thermal treatment, while imidization to polyimide is prevented. The structural characterization of the films is provided by 1H NMR and Fourier transform infrared spectroscopy (FTIR), while the presence of metallic nanoparticles within the polymeric matrix was confirmed by scanning electron microscopy (SEM), cyclic voltammetry (CV), energy-dispersive X-ray analysis (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). This approach utilizes the unique reactivity of PAA by preventing the cyclization of the reactive soluble intermediate into polyimides at low temperature to design polymer-assisted nanostructured materials. The ability to prevent the cyclization process should enable the design of a new class of electrode materials by use of thermal reduction and/or electrodeposition.

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The need for rapid and accurate detection systems is expanding and the utilization of cross-reactive sensor arrays to detect chemical warfare agents in conjunction with novel computational techniques may prove to be a potential solution to this challenge. We have investigated the detection, prediction, and classification of various organophosphate (OP) nerve agent simulants using sensor arrays with a novel learning scheme known as support vector machines (SVMs). The OPs tested include parathion, malathion, dichlorvos, trichlorfon, paraoxon, and diazinon. A new data reduction software program was written in MATLAB V. 6.1 to extract steady-state and kinetic data from the sensor arrays. The program also creates training sets by mixing and randomly sorting any combination of data categories into both positive and negative cases. The resulting signals were fed into SVM software for "pairwise" and "one" vs all classification. Experimental results for this new paradigm show a significant increase in classification accuracy when compared to artificial neural networks (ANNs). Three kernels, the S2000, the polynomial, and the Gaussian radial basis function (RBF), were tested and compared to the ANN. The following measures of performance were considered in the pairwise classification: receiver operating curve (ROC) Az indices, specificities, and positive predictive values (PPVs). The ROC Az) values, specifities, and PPVs increases ranged from 5% to 25%, 108% to 204%, and 13% to 54%, respectively, in all OP pairs studied when compared to the ANN baseline. Dichlorvos, trichlorfon, and paraoxon were perfectly predicted. Positive prediction for malathion was 95%.

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This work describes a novel technique for the digestion of metals in solid matrices. The technique is called pressure assisted chelating extraction (PACE). In a typical procedure, a solid sample is placed in a stainless steel cell and is mixed with appropriate chelating agents. Using a programmed sequence of temperature, static time, pressure and thermal equilibration available in ASE 200, the metal is removed under moderate temperature (up to 200 degrees C) and pressure (up to 3000 psi). PACE achieves metal recovery that is equivalent to that of wet digestion techniques and also provides for a clean and safe operation by substituting the strong acids commonly used during wet digestion with chelating agents. It uses less solvents and significantly less time (minutes vs. hours) for metal digestion. PACE has been validated using certified standard reference materials (SRMs) including industrial sludge, buffalo river sediments and coal fly ash. The total time required to remove metals was approximately 20 min. Results show that the PACE system provides an ideal platform for efficient, rapid, and safe metal digestion. Good agreement between measured and reference values for Pb, Mn, and Cu were found with recoveries averaging between 80 and 101% and a relative standard deviation of less than 5%. This approach may provide an alternative digestion technique for environmental samples, alloys, biological materials and samples of geological importance. The potential advantage offered lies in non-destruction of the sample, automation and the exclusion of concentrated mineral acids during the digestion procedure.

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