Pathogenic bacteria such as Escherichia coli O157, Salmonella and Campylobacter are the main causes for food and waterborne illnesses. Lysis of these bacteria is an important component of the sample preparation for molecular identification of these pathogens. The pathogenicity of these bacteria is so high that they cause illness at very low concentrations (1–10 CFU/100 mL). Hence, there is a need to develop methods to collect a small number of such bacterial cells from a large sample volume and process them in an automated reagent-free manner. An electrical method to concentrate the bacteria and lyse them has been chosen here as it is reagent free and hence more conducive for online and automated sample preparation. We use commercially available nanoporous membranes sandwiched between two microfluidic channels to create thousands of parallel nanopore traps for bacteria, electrophoretically accumulate and then lyse them. The nanopores produce a high local electric field for lysis at moderate applied voltages, which could simplify instrumentation and enables lysis of the bacteria as it approaches them under an appropriate range of electric field (>1000 V/cm). Accumulation and lysis of bacteria on the nanoporous membrane is demonstrated by using the LIVE/DEAD BacLight Bacterial Viability Kit and quantified by fluorescence intensity measurements. The efficiency of the device was determined through bacterial culture of the lysate and was found to be 90% when a potential of 300 V was applied for 3 min.
A series of novel organic-inorganic hybrid membranes have been prepared employing Nafion and acid-functionalized meso-structured molecular sieves (MMS) with varying structures and surface area. Acid-functionalized silica nanopowder of surface area 60 m 2 /g, silica meso-structured cellular foam (MSU-F) of surface area 470 m 2 /g and silica meso-structured hexagonal frame network (MCM-41) of surface area 900 m 2 /g have been employed as potential filler materials to form hybrid membranes with Nafion framework. The structural behavior, water uptake, proton conductivity and methanol permeability of these hybrid membranes have been investigated. DMFCs employing Nafion-silica MSU-F and Nafion-silica MCM-41 hybrid membranes deliver peak-power densities of 127 mW/cm 2 and 100 mW/cm 2 , respectively; while a peak-power density of only 48 mW/cm 2 is obtained with the DMFC employing pristine recast Nafion membrane under identical operating conditions. The aforesaid characteristics of the hybrid membranes could be exclusively attributed to the presence of pendant sulfonic acid groups in the filler, which provide fairly continuous proton-conducting pathways between filler and matrix in the hybrid membranes facilitating proton transport without any trade-off between its proton conductivity and methanol crossover.
In situ polymerization of 3,4-ethylenedioxythiophene with sol-gel-derived mesoporous carbon ͑MC͒ leading to a new composite and its subsequent impregnation with Pt nanoparticles for application in polymer electrolyte fuel cells ͑PEFCs͒ is reported. The composite exhibits good dispersion and utilization of platinum nanoparticles akin to other commonly used microporous carbon materials, such as carbon black. Pt-supported MC-poly͑3,4-ethylenedioxythiophene͒ ͑PEDOT͒ composite also exhibits promising electrocatalytic activity toward oxygen reduction reaction, which is central to PEFCs. The PEFC with Pt-loaded MC-PEDOT support exhibits 75% of enhancement in its power density in relation to the PEFC with Pt-loaded pristine MC support while operating under identical conditions. It is conjectured that Pt-supported MC-PEDOT composite ameliorates PEFC performance/ durability on repetitive potential cycling. © 2010 The Electrochemical Society. ͓DOI: 10.1149/1.3486172͔ All rights reserved. Commercial viability of the polymer electrolyte fuel cells ͑PEFCs͒ requires almost an order of magnitude reduction in Pt usage with improved performance and durability.1-5 The U.S. Department of Energy has set targets for electrocatalyst performance for the year 2010 at a mass activity of 0.44 A/mg ͑Pt͒ as compared against the current value of 0.28 A/mg ͑Pt͒ and an electrochemical surface area ͑ESA͒ Ͻ40% after accelerated aging. In the literature, 6-16 efforts are being expended to improve the performance and durability of electrocatalysts in PEFCs by alloying Pt with transition metals, such as Ru, Ir, Co, Ti, Zr, Sn, etc., heat-treatment of Pt-based alloys, preparation of core-shell catalysts, dealloying Pt metal alloys, and adapting conducting polymers for developing a durable porous catalyst support with a suitable surface area.A fuel cell catalyst support should have a large surface area with adequate surface functionalities for finely dispersing catalytic metal particles, high electrical conductivity for providing electrical pathways, and highly developed mesoporosity to facilitate diffusion of reactants and products in conjunction with high electrochemical stability during long-term operation. 17,18 Carbon supports, such as carbon black and activated carbon that are being currently used, usually exhibit a large surface area but their pore structures are primarily microporous 19 with pore sizes Ͻ2 nm, which makes the microporous structures incompatible for transporting the reactants; besides, catalyst particles get buried in the micropores making them inaccessible to fuel 20,21 and hence to the overall electrochemical process. Furthermore, these carbon supports, being prone to corrosion caused by electrochemical oxidation during repetitive PEFC cycling, limit its operational life. [22][23][24]
Mesoporous carbon (MC)-Poly (3,4-ethylenedioxythiophene) (PEDOT) composites are synthesized using structure-directing agents and explored as catalyst supports for polymer electrolyte fuel cell (PEFC) electrodes. To this end, platinum nanoparticles are deposited onto the composite supports as also on Vulcan XC-72 carbon black from platinum salts by formaldehyde reduction. The morphologies and crystallinity of Pt=Vulcan XC-72 and various Pt=PEDOT-MC are characterized using powder X-ray dif-fraction and transmission electron microscopy, which suggest Pt nanoparticles to be uniformly dispersed onto the supports. The durability of MC-PEDOT-supported catalysts in PEFCs is attributed to enhanced corrosion-resistance of MC. Indeed, the non-de-structive functionalization of MC with conducting polymer makes them promising catalyst-supports for PEFCs. VC 2011 The Electrochemical Society. [DOI: 10.1149/1.3568004] All rights reserved. Manuscript submitted January 19, 2011; revised manuscript received February 21, 2011. Published April 7, 2011. It is now established that to make the polymer electrolyte fuel cells (PEFCs) commercially attractive, it would be mandatory to make them both cost effective and durable. Factors that affect the durability of PEFCs are platinum-particle dissolution and sintering, carbon-support corrosion and membrane thinning.1 Among these, carbon-support corrosion changes the structure and stability of th
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