Mass transfer in Nanofluidic Devices embedded in a Microfluidic Channel

Liza Rassaei 

MESA Institute for Nanotechnology, University of Twente (MESA), PO Box 217, Enschede 7500AE, Netherlands

Abstract

Electrochemical nanofluidic devices have been introduced at 2008 []. These tiny devices feature two planar microelectrodes (~ 5-10 µm) separated by a thin layer of fluid (with a desired thickness, less than 300 nm) was fabricated on a chip. The fabrication of these channels involves photolithographic patterning in a way that the nanofluidic device is encapsulated in silicon dioxide with two access holes. Access holes are created to reach the metal and etching solution is introduced to remove the metal, leaving behind a nanoscale cavity.  Redox active molecules can freely diffuse in and out of the channel and undergo electrochemical redox cycling at both suitably biased potentials. Since these molecules are capable of repetitively undergoing oxidation and reduction, each molecule can transfer, on average, thousands of electrons by repeatedly traveling between the electrodes before escaping back out into the bulk. This leads to a corresponding boost in sensitivity and selectivity. This design offer experimentalists many potential applications in designing new sensors with the option of integration on a chip. The substantial current amplifications provide researchers the opportunity to access lower detection limits. The devices are so far operated under conditions of diffusion controlled mass transport.

Here, we examine the electrochemical response of a nanofluidic device placed inside a rectangular microfluidic cell. Solution was pumped to the cell under laminar flow conditions.  In this arrangement, we expect that the material is brought to the device via both diffusion and convection in a microchannel. However, we show that the mass transfer inside nanofluidic device is not affected by the rate of flow in the microchannel. We validate our experimental data with those obtained theoretically with COMSOL multiphysics.

[1]  B. Wolfrum, M. A. G. Zevenbergen and S. G. Lemay, Analytical Chemistry 80, 972 – 977 (2008).

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Presentation: Poster at SMCBS'2011 International Workshop, by Liza Rassaei
See On-line Journal of SMCBS'2011 International Workshop

Submitted: 2011-08-31 16:43
Revised:   2011-10-27 13:24
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