Technical updates to the bacterial method for nitrate isotopic analyses

The bacterial conversion of aqueous nitrate (NO(3)(-)) to nitrous oxide (N(2)O) for isotopic analysis has found widespread use since its introduction (Sigman, D. M.; Casciotti, K. L.; Andreani, M.; Galanter, M.; Bo?hlke, J. K. Anal. Chem.2001, 73, 4145-4153; Casciotti, K. L.; Sigman, D. M.; Galanter Hastings, M.; Bo?hlke, J. K.; Hilkert, A. Anal. Chem.2002, 74, 4905-4912). The bacterial strain Pseudomonas aureofaciens (ATTC no. 13985) was shown to convert NO(3)(-) to N(2)O while retaining both N and O isotopic signatures, and automation of the isotopic analysis of N(2)O greatly increased the throughput of the method (Casciotti, K. L.; Sigman, D. M.; Galanter Hastings, M.; Bo?hlke, J. K.; Hilkert, A. Anal. Chem.2002, 74, 4905-4912). Continued development of the denitrifier method has led to increased precision and throughput of NO(3)(-) isotopic analysis. Presented here are several recent procedural modifications and the demonstration of their effectiveness.     

Ag nanotubes and Ag/AgCl electrodes in nanoporous membranes

Miniaturization of the entire experimental setup is a key requirement for widespread application of nanodevices. For nanopore biosensing, integrating electrodes onto the nanopore membrane and controlling the pore length is important for reducing the complexity and improving the sensitivity of the system. Here we present a method to achieve these goals, which relies on electroless plating to produce Ag nanotubes in track-etched polymer nanopore templates. By plating from one side only, we create a conductive nanotube that does not span the full length of the pore, and thus can act as a nanoelectrode located inside the nanopore. To give optimal electrochemical behavior for sensing, we coat the Ag nanotube with a layer of AgCl. We characterize the behavior of this nanoelectrode by measuring its current-voltage response and find that, in most cases, the response is asymmetric. The plated nanopores have initial diameters between 100 and 300?nm, thus a range suitable for detection of viruses.     

Double helical laser beams based on interfering first-order Bessel beams

We demonstrate the generation of a nondiffracting double helical beam using axicons and ±1 vortex phase plates in a common-path interferometric system. Using linear diffraction theory, a simple analytical expression describing beam propagation is shown to agree with both experiments and Fresnel-diffraction-based simulations. Experiments are performed using continuous laser light in addition to ultrafast pulses, demonstrating that the common-path arrangement and the diffraction theory work equally well for both cases.     

Chemical alignment of DNA origami to block copolymer patterned arrays of 5 nm gold nanoparticles

We have used block copolymer patterned arrays of 5 nm gold nanoparticles (AuNPs) for chemically aligned surface attachment of DNA origami. Addition of single-stranded DNA-thiol to AuNPs allowed a base paired attachment of sticky end modified DNA origami. Results indicate a stable, selective attachment between the DNA origami and ssDNA modified AuNPs. Yield data showed 74% of AuNP binding sites forming an attachment with a DNA origami rectangle, and control surfaces showed less than 0.5% nonspecific adsorption.     

Electric-field-induced wetting and dewetting in single hydrophobic nanopores

The behaviour of water in nanopores is very different from that of bulk water. Close to hydrophobic surfaces, the water density has been found to be lower than in the bulk, and if confined in a sufficiently narrow hydrophobic nanopore, water can spontaneously evaporate. Molecular dynamics simulations have suggested that a nanopore can be switched between dry and wet states by applying an electric potential across the nanopore membrane. Nanopores with hydrophobic walls could therefore create a gate system for water, and also for ionic and neutral species. Here, we show that single hydrophobic nanopores can undergo reversible wetting and dewetting due to condensation and evaporation of water inside the pores. The reversible process is observed as fluctuations between conducting and non-conducting ionic states and can be regulated by a transmembrane electric potential.     

Tourism as tragedy? Common problems with water in post-revolutionary Nicaragua

This paper examines the increased demand placed on limited water resources by a rapidly growing tourism sector in Playa Gigante, Nicaragua. Results from field campaigns suggest that recharge of the local aquifer may not meet burgeoning tourism demands for water. This paper also points to initial conflicts over water between locals and tourism operations, which are further complicated by ineffective implementation of national water policies and the common pool nature of groundwater. The conclusion discusses the need for more extensive research and better implementation of water policy through community governance and collaboration.     

Dialysis patients treated with Epoetin α show improved exercise tolerance and physical function: A new analysis of the Canadian Erythropoietin Study Group trial

The risks/benefits of anemia treatment in dialysis patients have been redefined in the US Epoetin α label. This analysis was carried out to determine if increasing hemoglobin (Hb) levels improve exercise tolerance and physical function in anemic dialysis patients. This is a new analysis of the Canadian Erythropoietin Study Group trial, a double‐blind, randomized, placebo‐controlled trial in dialysis patients. Subjects were 18 to 75 years old, on hemodialysis for >3 months, and had a baseline Hb <9.0 g/dL. Patients with a history of diabetes mellitus, ischemic heart disease, or severe/uncontrolled hypertension were excluded. Patients were randomized to receive Epoetin α to a target Hb of 9.5 to 11.0 g/dL (n=40) or a target of 11.5 to 13.0 g/dL (n=38), or receive placebo (n=40). Results from patients in the Epoetin‐α–treated arms were combined for this analysis. Hb level, exercise tolerance (Treadmill Stress Test and 6‐Minute Walk Test) and patient‐reported physical function measures (Physical Summary domain from the Kidney Disease Questionnaire, and 4 domains from the Sickness Impact Profile) were reported at baseline and months 2, 4, and 6. Differences in measures were statistically significant for exercise tolerance (Treadmill Stress, P=0.0001) and patient‐reported physical function (Kidney Disease Questionnaire Physical, P=0.0001; Sickness Impact Profile Physical, P=0.0015) across all time points for Epoetin‐α–treated patients compared with placebo. Improvements were seen at 2 months and were maintained through months 4 and 6. Dialysis patients receiving Epoetin α showed improved exercise tolerance and physical function. These findings should be considered as physicians weigh the risks and benefits of treatment.