Metallic copper, which is normally considered as a contaminant in the growth of single-walled carbon nanotubes (SWNTs), was found to be an efficient catalyst to grow SWNTs under suitable conditions. It showed very high catalytic activity for the growth of both random SWNT networks and horizontally aligned SWNT arrays. Especially, high-quality SWNT arrays were obtained when monodispersed copper nanoparticles were used. The catalytic behavior of copper for the growth of SWNTs was discussed. The weaker interaction between the copper and silica surfaces plays an important role in the growth of high-quality horizontally aligned SWNT arrays. This new synthesis process of SWNTs with a non-ferromagnetic catalyst brings more convenience to the study of magnetic properties of SWNTs and gives more insight in structure-controlled synthesis of SWNTs.

This paper describes a droplet-based microfluidic chip with pneumatic valves for measuring millisecond enzyme kinetics using amperometric detection method. Aqueous streams containing reactants were injected to an oil flow to form droplets, and each droplet represented one microreactor. Pneumatic valves were used to control the moving distance and in turn the reaction time of the droplets. The reaction time was also fine-tuned by varying the flow rate of the droplets in microchannels. A complete Michaelis-Menten kinetics of catalase was successfully measured by amperometric method in a single-run experiment, and the total consumption of reagents was less than 50 microL. In the current experiment, the best time resolution was about 0.05 s, and the reaction time measured was from 0.05 to 25 s. This microfluidic system is applicable to many biochemical reactions, as long as one of the reactants or products is electrochemically active. With appropriate quenching method at the outlet, various detection methods can be integrated into the microfluidic system, further extending the application of the combination of pneumatic valves and droplets in microchannels.

This paper describes a poly(dimethylsiloxane) (PDMS) microfluidic device for measuring the viscosity of Newtonian fluids. The viscometer utilized the high solubility and permeability of air in PDMS to generate Poiseuille flow in the degassed PDMS microfluidic device. By measuring the distance the fluids traveled and the flow velocity in the PDMS microchannel, the ratio of the viscosity of the sample fluid to the viscosity of a reference fluid was determined, and the viscosity of the sample fluid was then obtained. Only 5 µL or less volume was consumed for the viscosity measurement. For most of the tested fluids, the results were in good agreement with the results from Ubbelohde viscometers, and the coefficients of variance were 3% or better. The wettability of the fluids on PDMS did not affect the measurement as the capillary forces were cancelled out in the data analysis. The PDMS viscometer was found applicable to a broad range of fluids, including aqueous solutions, non-PDMS-swelling organic solvents, fluorinated oil and blood plasma.

Engineered peptide ligands with exceptionally high affinity for metal can self-assemble with nanoparticles in biological fluids. A high-affinity dendrimeric peptide ligand for CdSe-ZnS quantum dots (QDs) exhibited very fast association kinetics with QDs and reached equilibrium within 2 s. Here, we have combined a droplet-based microfluidic device with fluorescence detection based on Förster resonance energy transfer (FRET) to provide subsecond resolution in dissecting this fast self-assembly kinetics in solution. This work represents the first application of microfluidic devices to ligand-particle assembly for the measurement of fast assembly kinetics in solution.

Droplets containing RNA and Mg(2+) were generated in microfluidic channels. By integrating a group of pneumatic valves and phase separation channels in the microfluidic system, the rapid RNA-Mg(2+) binding kinetics was studied by measuring the Mg(2+) ion concentration using an ion-selective electrode.

Phase behavior captures an essential feature of classic thermodynamics. Because of the greater molecular size, polymer phase behavior possess unique aspects that make it significantly different from that of smaller molecules 1 and hence impressively enriches and extends the thermodynamic study. 2,3 Polymer phase diagrams, showing conditions under which polymer multiple phases can coexist at equilibrium, not only provide a basis to advance modern thermodynamics but also play an important role in polymer science and engineering, including, for instance, in the process of polymer preparation, purification, fractionation, and characterization. 1,4,5 Despite the widespread use of polymer phase diagrams, their construction in bulk scales has been restricted by two problems: the difficulty of obtaining narrowly distributed polymer samples in large quantity, and the long time required for the conventional phase transition measurement. Microfluidic systems provide an attractive platform to address these two problems by significantly reducing the consumption of reagents and the time for reaching thermal equilibrium. Previously, Mao et al. employed a linear temperature gradient to

This paper describes a poly(dimethylsiloxane) (PDMS) microfluidic device for measuring the viscosity of power law fluids. The viscometer utilized the high solubility and permeability of air in PDMS to generate vacuum and drive the Poiseuille flow in the degassed PDMS microchannels. Wide ranges of shear rates in PDMS microchannels were generated by controlling the chamber sizes of the PDMS viscometer. By measuring the distance the fluids traveled and the flow velocity in the PDMS microchannel, the flow behavior index n was determined and the viscosity profile of the sample fluid under a range of shear rates was obtained. Only 5 µL or less volume was consumed for the viscosity measurement. Viscosities of poly(ethylene oxide) solutions and blood control standard were successfully measured under shear rates varying from 10 to 500 s−1, and the results were consistent with those from conventional cone–plate rheometers. The PDMS viscometer was applicable to a broad range of power law fluids, such as diluted polymeric solutions and colloidal suspensions.

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