We report the novel fabrication of a highly sensitive, selective, fast responding, and affordable amperometric glucose biosensor using exfoliated graphite nanoplatelets (xGnPs) decorated with Pt and Pd nanoparticles. Nafion was used to solublize metal-decorated graphite nanoplatelets, and a simple cast method with high content organic solvent (85 wt %) was used to prepare the biosensors. The addition of precious metal nanoparticles such as platinum (Pt) and palladium (Pd) to xGnP increased the electroactive area of the electrode and substantially decreased the overpotential in the detection of hydrogen peroxide. The Pt−xGnP glucose biosensor had a sensitivity of 61.5 ± 0.6 μA/(mM·cm2) and gave a linear response up to 20 mM. The response time and detection limit (S/N = 3) were determined to be 2 s and 1 μM, respectively. Therefore, this novel glucose biosensor based on the Pt nanoparticle coated xGnP is among the best reported to date in both sensing performance and production cost. In addition, the effects of metal nanoparticle loading and the particle size on the biosensor performance were systematically investigated.

Synthesis gas is readily obtained by gasifying coal, oil, biomass, or waste organics and represents an abundant, potentially inexpensive, feedstock for bioprocessing. The primary components of synthesis gas, carbon monoxide and hydrogen, can be converted into methane, organic acids, and alcohols via anaerobic fermentations. Bioconversion of synthesis gas is an attractive alternative to catalytic processing because the biological catalysts are highly specific and often more tolerant of sulfur contaminants than inorganic catalysts. However, because the aqueous solubilities of carbon monoxide and hydrogen are low, synthesis-gas fermentations are typically limited by the rate of gas-to-liquid mass transfer. Consequently, a major engineering challenge in commercial development of synthesis-gas fermentations is to provide sufficient gas mass transfer in an energy-efficient manner. This paper reviews recent progress in the development of synthesis-gas fermentations, with emphasis on efforts to increase the efficiency of gas mass transfer. Metabolic properties of several microbes able to ferment synthesis gas are described. Results of synthesis-gas fermentations conducted in various bioreactor configurations are summarized. Recent results showing enhancement of synthesis-gas fermentations using microbubble dispersions are presented, and studies of the mass-transfer and coalescence properties of microbubbles are described.

A novel and highly sensitive electroanalytical sensing nanocomposite material is reported for the development of a glucose biosensor. Exfoliated graphite nanoplatelets (xGnP) were tested to enhance the sensing capability. The xGnP has a diameter of 1 µm and a thickness of 10 nm, on average. The glucose biosensing interface was prepared by casting glucose oxidase and xGnP in a Nafion water–isopropyl-alcohol solution with a high concentrated organic solvent (85 wt%). The resulting biosensors showed rapid response time within 5 s, limits of detection of 10 µM glucose (S/N = 3), a linear detection range up to 6 mM, and high sensitivity of 14.17 µA/(mM·cm2) with an optimum glucose oxidase loading. The biosensors also showed good selectivity and long-term stability. These results indicate that xGnP can be an inexpensive alternative to carbon nanotubes for the fabrication of affordable high-performance biosensors.

Synthesis-gas fermentations have typically been gas-to-liquid mass-transfer-limited due to low solubilities of the gaseous substrates. A potential method to enhance mass-transfer rates is to sparge with microbubble dispersions. Mass-transfer coefficients for microbubble dispersions were measured in a bubble column. Oxygen microbubbles were formed in a dilute Tween 20 solution using a spinning disk apparatus. Axial dispersion coefficients measured for the bubble column ranged from 1.5 to 7.2 cm2/s and were essentially independent of flow rate. A laser-diffraction technique was used to determine the interfacial area per unit gas volume, a. The mass-transfer coefficient, KL, was determined by fitting a plug-flow model to the experimental, steady-state, liquid-phase oxygen-concentration profile. The KL values ranged from 2.9 x 10(-5) to 2.2 x 10(-4) m/s. Volumetric mass-transfer coefficients, KLa, for microbubbles with an average initial diameter of 60 microns ranged from 200 to 1800 h-1. Enhancement of mass transfer using microbubbles was demonstrated for a synthesis-gas fermentation. Butyribacterium methylotrophicum was grown in a continuous, stirred-tank reactor using a tangential filter for total cell recycle. The fermentation KLa values were 14 h-1 for conventional gas sparging through a stainless steel frit and 91 h-1 for microbubble sparging. The Power number of the microbubble generator was determined to be 0.036. Using this value, an incremental power-to-volume ratio to produce microbubbles for a B. methylotrophicum fermentation was estimated to be 0.01 kW/m3 of fermentation capacity.

BackgroundWith the increase in production and use of engineered nanoparticles (NP; ≤ 100 nm), safety concerns have risen about the potential health effects of occupational or environmental NP exposure. Results of animal toxicology studies suggest that inhalation of NP may cause pulmonary injury with subsequent acute or chronic inflammation. People with chronic respiratory diseases like asthma or allergic rhinitis may be even more susceptible to toxic effects of inhaled NP. Few studies, however, have investigated adverse effects of inhaled NP that may enhance the development of allergic airway disease.MethodsWe investigated the potential of polyethylene glycol coated amorphous silica NP (SNP; 90 nm diameter) to promote allergic airway disease when co-exposed during sensitization with an allergen. BALB/c mice were sensitized by intranasal instillation with 0.02% ovalbumin (OVA; allergen) or saline (control), and co-exposed to 0, 10, 100, or 400 μg of SNP. OVA-sensitized mice were then challenged intranasally with 0.5% OVA 14 and 15 days after sensitization, and all animals were sacrificed a day after the last OVA challenge. Blood and bronchoalveolar lavage fluid (BALF) were collected, and pulmonary tissue was processed for histopathology and biochemical and molecular analyses.ResultsCo-exposure to SNP during OVA sensitization caused a dose-dependent enhancement of allergic airway disease upon challenge with OVA alone. This adjuvant-like effect was manifested by significantly greater OVA-specific serum IgE, airway eosinophil infiltration, mucous cell metaplasia, and Th2 and Th17 cytokine gene and protein expression, as compared to mice that were sensitized to OVA without SNP. In saline controls, SNP exposure did cause a moderate increase in airway neutrophils at the highest doses.ConclusionsThese results suggest that airway exposure to engineered SNP could enhance allergen sensitization and foster greater manifestation of allergic airway disease upon secondary allergen exposures. Whereas SNP caused innate immune responses at high doses in non-allergic mice, the adjuvant effects of SNP were found at lower doses in allergic mice and were Th2/Th17 related. In conclusion, these findings in mice suggest that individuals exposed to SNP might be more prone to manifest allergic airway disease, due to adjuvant-like properties of SNP.