High throughput production of single-wall carbon nanotube fibres independent of sulfur-source.

Floating catalyst chemical vapor deposition (FC-CVD) methods offer a highly scalable strategy for single-step synthesis and assembly of carbon nanotubes (CNTs) into macroscopic textiles. However, the non-uniform axial temperature profile of a typical reactor, and differing precursor breakdown temperatures, result in a broad distribution of catalyst particle sizes. Spun CNT fibres therefore contain nanotubes with varying diameters and wall numbers. Herein, we describe a general FC-CVD approach to obtain relatively large yields of predominantly single-wall CNT fibres, irrespective of the growth promoter (usually a sulfur compound). By increasing carrier gas (hydrogen) flow rate beyond a threshold whilst maintaining a constant C : H2 mole ratio, CNTs with narrower diameters, a high degree of graphitization (G : D ratio ∼100) and a large throughput are produced, provided S : Fe ratio is sufficiently low. Analysis of the intense Raman radial breathing modes and asymmetric G bands, and a shift in the main nanotube population from thermogravimetric data, show that with increasing flow rate, the fibres are enriched with small diameter, metallic CNTs. Transmission electron microscopy corraborates our primary observation from Raman spectroscopy that with high total flow rates, the fibres produced consist of predominantly small diameter SWCNTs.

Microfluidics device for single cell gene expression analysis in Saccharomyces cerevisiae.

We have measured single-cell gene expression over time using a microfluidics-based flow cell which physically traps individual yeast using microm-sized structures (yeast jails). Our goal was to determine variability of gene expression within a cell over time, as well as variability between individual cells. In our flow cell system, yeast jails are fabricated out of PDMS and gene expression is visualized using fluorescently-tagged proteins of interest. Previously, single-cell yeast work has been done using micromanipulation on agar, or FACS. In the present device agar is eliminated, resulting in a superior optical system. The flow of media through the flow cell washes daughter cells away, eliminating the need for micromanipulation. Unlike FACS, the described device can track individual yeast over a time course of many hours. The flow cells are compatible with the needs of quantitative fluorescence microscopy, and allow simultaneous measurements to be done on a large number of individual yeast. We used these flow cells to determine the expression of HSP104-GFPand RAS2-YFP, genes known to affect yeast life span. The results demonstrate inter-cell variation in expression of both genes that could not have been detected without this single-cell analysis.