We report gas and water flow measurements through microfabricated membranes in which aligned carbon nanotubes with diameters of less than 2 nanometers serve as pores. The measured gas flow exceeds predictions of the Knudsen diffusion model by more than an order of magnitude. The measured water flow exceeds values calculated from continuum hydrodynamics models by more than three orders of magnitude and is comparable to flow rates extrapolated from molecular dynamics simulations. The gas and water permeabilities of these nanotube-based membranes are several orders of magnitude higher than those of commercial polycarbonate membranes, despite having pore sizes an order of magnitude smaller. These membranes enable fundamental studies of mass transport in confined environments, as well as more energy-efficient nanoscale filtration.

Carbon nanotubes have been featured prominently in the nanotechnology research for some time, yet robust strategies for noncovalent chemical modification of the nanotube surface are still missing. Such strategies are essential for the creation of functional device architectures. Here, we present a new general procedure for carbon nanotube modification based on polyelectrolyte layer-by-layer assembly. We have built multilayer structures around individual carbon nanotube bridges by first modifying the nanotube surface with a pyrene derivative followed by layer-by-layer deposition of polyelectrolyte macroions on the nanotube. Transmission electron microscopy and scanning confocal fluorescence microscopy images confirm the formation of nanometer-thick amorphous polymer nanoshells around the nanotubes. These multilayer polyelectrolyte shells on individual carbon nanotubes introduce nearly unlimited opportunities for the incorporation of various functionalities into nanotube devices, which, in turn, opens up the possibility of building more complex multicomponent structures.

Background: Ascarosides play central roles regulating C. elegans behavior and development. Results: L1 larvae produce starvation-dependent ascarosides based on succinylated octopamine. Conclusion: Succinylation is an important pathway for metabolism of biogenic amines in C. elegans. Significance: Octopamine ascarosides connect neurotransmitter and ascaroside signaling in C. elegans.

We have investigated growth kinetics of multiwall carbon nanotube (MWCNT) arrays produced by catalytic thermal decomposition of ethylene gas in hydrogen, water, and argon mixture. The MWCNT growth rate exhibits a nonmonotonic dependence on total pressure and reaches a maximum at approximately 750 Torr of total pressure. Water concentrations in excess of 3000 ppm lead to the decrease in the observed growth rate. Optimal pressure and water concentration combination results in a reliable growth of well-aligned MWCNT arrays at a maximum growth rate of approximately 30 microm/min. These MWCNT arrays can reach heights of up to 1 mm with typical standard deviations for the array height of less than 8% over a large number of process runs spread over the time of 8 months. Nanotube growth rate in this optimal growth region remains essentially constant until growth reaches an abrupt and irreversible termination. We present a quantitative model that shows how accumulation of the amorphous carbon patches at the catalyst particle surface and the carbon diffusion to the growing nanotube perimeter causes this abrupt growth cessation. The influence of the partial pressures of ethylene and hydrogen on the ethylene decomposition driving force explains the nonlinear behavior of the growth rate as a function of total process pressure.

Peroxisomal β-oxidation (pβo) is a highly conserved fat metabolism pathway involved in the biosynthesis of diverse signaling molecules in animals and plants. In Caenorhabditis elegans, pβo is required for the biosynthesis of the ascarosides, signaling molecules that control development, lifespan, and behavior in this model organism. Via comparative mass spectrometric analysis of pβo mutants and wildtype, we show that pβo in C. elegans and the satellite model P. pacificus contributes to life stage-specific biosynthesis of several hundred previously unknown metabolites. The pβo-dependent portion of the metabolome is unexpectedly diverse, e.g., intersecting with nucleoside and neurotransmitter metabolism. Cell type-specific restoration of pβo in pβo-defective mutants further revealed that pβo-dependent submetabolomes differ between tissues. These results suggest that interactions of fat, nucleoside, and other primary metabolism pathways can generate structural diversity reminiscent of that arising from combinatorial strategies in microbial natural product biosynthesis.

Carbon nanotube transistors are a promising platform for the next generation of nonoptical biosensors. However, the exact nature of the biomolecule interactions with nanotubes in these devices remains unknown, creating one of the major obstacles to their practical use. We assembled alternating layers of oppositely charged polyelectrolytes on the carbon nanotube transistors to mimic gating of these devices by charged molecules. The devices showed reproducible oscillations of the transistor threshold voltage depending on the polarity of the outer polymer layer in the multilayer film. This behavior shows excellent agreement with the predictions of a simple electrostatic model. Finally, we demonstrate that complex interactions of adsorbed species with the device substrate and the surrounding electrolyte can produce significant and sometimes unexpected effects on the device characteristics.

We describe a new type of collective behavior in C. elegans nematodes, aggregation of starved L1 larvae. Shortly after hatching in the absence of food, L1 larvae arrest their development and disperse in search for food. In contrast, after two or more days without food, the worms change their behavior—they start to aggregate. The aggregation requires a small amount of ethanol or acetate in the environment. In the case of ethanol, it has to be metabolized, which requires functional alcohol dehydrogenase sodh-1. The resulting acetate is used in de novo fatty acid synthesis, and some of the newly made fatty acids are then derivatized to glycerophosphoethanolamides and released into the surrounding medium. We examined several other Caenorhabditis species and found an apparent correlation between propensity of starved L1s to aggregate and density dependence of their survival in starvation. Aggregation locally concentrates worms and may help the larvae to survive long starvation. This work demonstrates how presence of ethanol or acetate, relatively abundant small molecules in the environment, induces collective behavior in C. elegans associated with different survival strategies.

Excreted small-molecule signals can bias developmental trajectories and physiology in diverse animal species. However, the chemical identity of these signals remains largely obscure. Here we report identification of an unusual N -acylated glutamine derivative, nacq#1, that accelerates reproductive development and shortens lifespan in C. elegans . Produced predominantly by C. elegans males, nacq#1 hastens onset of sexual maturity in hermaphrodites by promoting exit from the larval dauer diapause and by accelerating late larval development. Even at picomolar concentrations, nacq#1 shortens hermaphrodite lifespan, suggesting a trade-off between reproductive investment and longevity. Acceleration of development by nacq#1 requires chemosensation and depends on three homologs of vertebrate steroid hormone receptors. Unlike ascaroside pheromones, which are restricted to nematodes, fatty acylated amino acid derivatives similar to nacq#1 have been reported from humans and invertebrates, suggesting that related compounds may serve signaling functions throughout Metazoa.