Fabrication of Microfluidic Devices for the study of Ion transport through Single-Walled Carbon Nanotubes
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Fabrication of Microfluidic Devices for the study of Ion transport through Single-Walled Carbon Nanotubes Khadija Yazda1, Sophie Roman1, Saïd Tahir1, François Henn1, Vincent Jourdain1,* Laboratoire Charles Coulomb UMR 5221, CNRS-Université de Montpellier, F-34095, France * Contact: [email protected]
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ABSTRACT Studying the transport of ions through single-walled carbon nanotubes (SWCNTs) necessitate the fabrication of a fluidic setup integrating carbon nanotubes. In this article, we report on the development of a simple fabrication protocol of SWCNTs fluidic devices. This protocol allows an excellent control of the system features and of the experimental conditions compared with previously published protocols. Our protocol based on the use of the popular SU8, the preferred photoresist for the fabrication of high-aspect-ratio patterns, allows one to prepare sealed microfluidic devices incorporating one or several tens of individual carbon nanotubes of length between 20 and 80 μm. INTRODUCTION Due to their high symmetry, their sp2 carbon walls and their large aspect ratio, SWCNTs are expected to display new and exciting transport regimes distinct from these encountered in other nanopore systems. However, the main challenge to appropriately study the transport of liquids and solutes through SWCNTs is the fabrication of nanotube-integrating fluidic devices which are well-controlled, robust and allow investigations in a large range of experimental parameters by complementary techniques. The fabrication of carbon nanotube (CNT) fluidic systems was demonstrated by several groups which established different approaches for preparing such fluidic platforms. It must be noted that the developed platforms differed greatly in terms of barrier materials and of CNT number, length, orientation, synthesis and opening methods. The first successful CNT-fluidic platforms were reported by the Crooks [1] and Hinds groups [2]. These platforms were based on vertically-aligned multi-walled CNTs (MWCNTs) of inner diameters of ~7 nm embedded in an epoxy polymer membrane. Later fabrication approaches focused on the use of single-walled CNTs, which generally have diameters (typically less than 3 nm) much smaller than MWCNTs. The use of sub-2 nm SWCNTs in nanofluidic setups was first reported by the Noy and Bakajin group [3,4]. This group prepared silicon nitride (SiNx) membranes incorporating forests of vertically aligned SWCNTs (with a diameter distribution of 1.3 - 2.0 nm) opened at both ends using a plasma treatment. Similarly, the Hinds group [5] developed CNT/epoxy composites using SWCNTs (diameters of 0.7 - 1.4 nm) incorporated in a 5-μm thick epoxy resin. For further understanding of the transport properties of ions through SWCNTs, studies later focused on fabricating experimental platforms incorporating a single nanotube. The Lindsay group [6,7] was the pioneer in developing nanofluidic platforms incorporating a single SWCNT: the studied SWCNTs were 2-10 μm long with diameters between 0.8 and 4 nm and were deposited on a
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