Abstract  We report on the utilization of a novel nanoscaled cobalt phthalocyanine (NanoCoPc)-glucose oxidase (GOD) biocomposite colloid to create a highly responsive glucose biosensor. The biocomposite colloid is constructed under enzyme-friendly conditions by adsorbing GOD molecules on CoPc nanoparticles via electrostatic interactions. The glucose biosensor can be easily achieved by casting the biocomposite colloid on a pyrolytic graphite electrode (PGE) without any auxiliary matter. It has been found that GOD can be firmly immobilized on PGE surface and maintain its bioactivity after conjugating with NanoCoPc. NanoCoPc displays intrinsic electrocatalytic ability to the oxidation of the product of enzymatic reaction H2O2 and shows a higher catalytic activity than that of bulk CoPc. Under optimal conditions, the biosensor shows a wide linear response to glucose in the range of 0.02-18 mM, with a fast response (5s), high sensitivity (7.71 microA cm(-2) mM(-1)), as well as good thermostability and long-term life. The detection limit was 5 microM at 3 sigma. The general interferences coexisted in blood except ascorbic acid and L-cysteine do not affect glucose determination, and further coating Nafion film on the surface of the biosensor can effectively eliminate the interference from ascorbic acid and L-cysteine. The biosensor with Nafion film has been used for the determination of glucose in serum with an acceptable accuracy.

Abstract  The cost and performance of proton exchange membrane fuel cells strongly depend on the cathode electrode due to usage of expensive platinum (Pt) group metal catalyst and sluggish reaction kinetics. Development of low Pt content high performance cathodes requires comprehensive understanding of the electrode microstructure. In this study, a new approach is presented to characterize the detailed cathode electrode microstructure from nm to gm length scales by combining information from different experimental techniques. In this context, nano-scale X-ray computed tomography (nano-CT) is performed to extract the secondary pore space of the electrode. Transmission electron microscopy (TEM) is employed to determine primary C particle and Pt particle size distributions. X-ray scattering, with its ability to provide size distributions of orders of magnitude more particles than TEM, is used to confirm the TEM-determined size distributions. The number of primary pores that cannot be resolved by nano-CT is approximated using mercury intrusion porosimetry. An algorithm is developed to incorporate all these experimental data in one geometric representation. Upon validation of pore size distribution against gas adsorption and mercury intrusion porosimetry data, reconstructed ionomer size distribution is reported. In addition, transport related characteristics and effective properties are computed by performing simulations on the hybrid microstructure. Published by Elsevier B.V.

Abstract  Tin-doped zinc oxide nanoparticles (Sn/ZnO NPs) were prepared by a facile wet-chemical method using reducing agents in alkaline medium. The Sn/ZnO NPs were characterized by UV/vis, FT-IR, energy-dispersive X-ray spectroscopy (XEDS), X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The Sn/ZnO NPs were deposited onto a flat glassy carbon electrode (GCE) with conducting binders (5% nafion) to result in a sensor that has a fast response towards selected hydrazine compounds by electrochemical approaches. Features including ultra-sensitivity, lower-detection limit, reliability, reproducibility, ease of integration, long-term stability, selective, and enhanced electrochemical performances were investigated in detail. The calibration plot is linear over different concentration ranges (2.0 nM to 20.0 mM). The sensitivity and detection limit were calculated as 5.0108 mu A cm(-2) mu M-1 and 18.95 +/- 0.02 pM (at a signal-to-noise-ratio, SNR of 3) respectively. Finally, the efficiency of the proposed chemical sensors can be applied and effectively utilized for the detection of toxic hazardous chemicals for the safety of the green environment on a broad scale.

Abstract  Cytochrome P450-3A4 (CYP3A4) is a monooxygenase enzyme that plays a major role in the detoxification of bioactive compounds and hydrophobic xenobiotics ( e. g. medicines, drugs, environmental pollutants, food supplements and steroids). Physiologically the monooxygenation reactions of this class II, microsomal, b-type heme enzyme, usually requires cytochrome P450 reductase, NADPH. A novel CYP3A4 biosensor system that essentially simplified the enzymatic redox processes by allowing electron transfer between the electrode and the enzyme redox centre to occur, without any need for the physiological redox partners, was developed for the detection of 2,4-dichlorophenol (2,4-DCP), a priority environmental pollutant and an endocrine disruptor. The biosensor, GC/Naf-Co(Sep)(3+)/CYP3A4/Naf, was constructed by encapsulating CYP3A4 in a Nafion-cobalt (III) sepulchrate (Naf-Co(Sep)(3+)) composite film on a glassy carbon (GC) electrode. The responses of the biosensor to 2,4-dichlorophenol, erythromycin (CYP3A4 native substrate) and ketoconazole (CYP 3A4 natural inhibitor) were studied by cyclic and square wave voltammetric techniques. The detection limit (DL) of the biosensor for 2,4-dichlorophenol was 0.043 mu gL(-1), which is by an order of magnitude lower than the EU limit (0.3 mu gL(-1)) for any pesticide compound in ground water. The biosensor's DL is lower than the U. S. Environmental Protection Agency's drinking water equivalent level (DWEL) value for 2,4-DCP, which is 2 mu gL(-1). (C) 2008 Elsevier Ltd. All rights reserved.

Abstract  The chemical amplification (PERCA) method has been widely used for measuring peroxy radical concentrations in the troposphere. The accuracy and sensitivity of the method is critically dependent on the chain length (CL)-that is, the number of radical amplification cycles. However, CL decreases strongly with higher relative humidity (RH). So far, there does not appear to be a method to overcome this impact. Here we report the development of a Nafion dryer based dual-channel PERCA instrument. The large diameter Nafion dryer efficiently removes water vapor in milliseconds and minimally affects the sample. The low losses of peroxy radicals on the Nafion membrane make it an attractive tool for raising the CL, and thereby the measurement accuracy and sensitivity of PERCA systems. The reported instrument demonstrates this promising and simple method to minimize water vapor interference.

Abstract  Pathogenic bacterial detection is needful in disease diagnosis as well as in the prevention of bacterial infections. This work proposes the electrochemical detection of pathogenic bacterial cells of Staphylococcus aureus (S. aureus) in a simple and cost-effective manner. We have developed a surface imprinted matrix on silver (Ag) decorated Manganese dioxide (MnO2) thin film coated Fluorine doped Tin oxide (FTO) electrode. The pulsed electrodeposition technique has been employed to develop the Ag decorated MnO2 thin films. The surface imprintation was done by using S. aureus as a model bacterial template, Polyethyleneimine (PEI) as a molecular recognizer and nafion as an additive to stick the imprinted PEI to the surface of the film. In order to find the binding probabilities, docking studies were done between PEI with the bacterial cell wall components. From cyclic voltammetry (CV) analysis, we found the presence and absence of the bacterial cells lead to the variability in the redox peaks corresponds to the redox activity of [Fe(CN)(6)](3-)/[Fe(CN)(6)](4-) has been found. Based on this, Differential Pulse Voltammetry (DPV) analysis was performed with different bacterial concentrations resulted in the detection range of 10(3) to 10(7) CFU/ml. (C) 2019 The Electrochemical Society.

Abstract  Typically Pt is alloyed with metals such as Ru, Sn, or Mo to provide a more CO-tolerant, high-performance proton exchange membrane fuel cell (PEMFC) anode. In this work, a layer of carbon-supported Ru is placed between the Pt catalyst and the anode flow field to form a filter. When oxygen is added to the fuel stream, it was predicted that the slow H-2 kinetics of Ru in this filter would become an advantage compared to Pt and Pt: Ru alloy anodes, allowing a greater percentage of O-2 to oxidize adsorbed CO to CO2. With an anode feed of H-2,2% O-2, and up to 100 ppm CO, the Pt 1 Ru filter anode performed better at 70degrees C than the Pt: Ru alloy. The oxygen in the anode feed stream was found to form a hydroxyl species within the filter. The reaction of these hydroxyl groups with adsorbed CO was the primary means of CO oxidation within the filter. Because of the resulting proton formation, the Ru filter must be placed in front of and adjacent to the Pt anode and must contain Nafion in order to provide the ionic pathways for proton conduction, and hence achieve the maximum benefit of the filter. (C) 2002 The Electrochemical Society.

Abstract  An electrochemical device for the reduction of CO2 back to liquid fuels is here presented. The key of this novel electrocatalytic approach is the design and development of the gas diffusion membrane (GDM), which is obtained by assembling (i) a proton selective membrane (Nafion), (ii) a nanocomposite electrocatalyst based on metal-doped conjugated microporous polymer (CMP) and (iii) a C-based support working as the gas diffusion layer. CMP is a very attractive material able to adsorb CO2 selectively with respect to other gases (such as H-2, O-2, N-2, etc.), also in mild conditions (r.t. and atmospheric pressure). Particularly, tetrakis-phenylethene conjugated microporous polymer (TPE-CMP) was synthesized through Yamamoto homo-coupling reaction. TPE-CMP was modified by depositing noble (Pt) and non-noble (Fe) metal nanoparticles to create the active catalytic sites for the process of CO2 reduction directly on the polymer surface where CO2 is adsorbed. The metal-doped TPE-CMP electrocatalysts were fully characterized by infrared spectroscopy (IR), thermo-gravimetric analysis (TGA) and transmission electron microscopy (TEM). Then, the as-assembled GDM was tested in our homemade semi-continuous three-electrode electrochemical cell working in gas phase at 60 A degrees C, coupled with a cold trap for the accumulation of the liquid products. Results showed the better performances of the metal-doped TPE-CMP in terms of total productivity (C1-C8 oxygenates) with respect to other kinds of materials that do not show high CO2 adsorption capacity.

Abstract  A screen-printed three-electrode amperometric biosensor based on urease and the nicotinamide adenine dinucleotide hydrogen (NADH)-glutamic dehydrogenase system was developed and applied to the screening of heavy metals in environmental samples. The development of an amperometric sensor for the monitoring of urease activity was feasible by coupling the urea breakdown reaction catalysed by urease to the reductive ammination of ketoglutarate catalysed by glutamic dehydrogenase (GLDH). The ammonia provided by the urea conversion is required for the conversion of ketoglutarate to glutamate with the concomitant oxidation of the NADH cofactor. NADH oxidation is monitored amperometrically at 0.3 V (vs. Ag/AgCl) after urease immobilization onto the screen-printed three-electrode configuration. Immobilization of urease on the surface of screen-printed electrodes was performed by entrapment in alginate gel and adsorption on the electrode in a nafion film. Low sensitivity to inactivation by metals was recorded after urease entrapment in alginate gel with detection limits of 2.9 and 29.8 mg L(-1) for Hg(II) and Cu(II), respectively. The use of the negatively charged nafion film created a more concentrated environment of cations in proximity to the enzyme, thus enhancing the urease inhibition when compared to gel entrapment. The calculated detection limits were 63.6 and 55.3 microg L(-1) for Hg(II) and Cu(II), respectively, and 4.3 mg L(-1) for Cd(II). A significant urease inactivation was recorded in the presence of trace amounts of metals (microg L(-1)) when the enzyme was used free in solution. Analysis of water and soil samples with the developed nafion-based sensor produced inhibition on urease activity according to their metal contents. The obtained results were in agreement with the standard methods employed for sample analysis. Nevertheless, the use of the amperometric assay (with free urease) proved more feasible for the screening of trace amounts of metals in polluted samples.

Abstract  ZnO nanoparticles (nanoZnO) were decorated on multiwalled carbon nanotubes (MWCNTs) and then the prepared nano-hybrids, nanoZnO-MWCNTs, were immobilized on the surface of a glassy carbon electrode (GCE) to fabricate nanoZnO-MWCNTs modified GCE. The prepared electrode, GCE/nanoZnO-MWCNTs, showed excellent electrocatalytic activity towards luminol electrochemiluminescence (ECL) reaction. The electrode was then further modified with lactate oxidase and Nafion to fabricate a highly sensitive ECL lactate biosensor. Two linear dynamic ranges of 0.01-10 μmol L(-1) and 10-200 μmol L(-1) were obtained for lactate with the correlation coefficient better than 0.9996. The detection limit (S/N=3) was 4 nmol L(-1) lactate. The relative standard deviation for repetitive measurements (n=6) of 10 μmol L(-1) lactate was 1.5%. The fabrication reproducibility for five biosensors prepared and used in different days was 7.4%. The proposed ECL lactate biosensor was used for determination of lactate in human blood plasma samples with satisfactory results.