Analytical Chemistry

Capillaric - Field Effect Transistors



Controling fluid flow in capillaric circuits is a key requirement to increase their uptake for assay applications. Capillary action off-valves provide such functionality by pushing an occluding bubble into the channel using a difference in capillary pressure. Previously, we utilised the binary switching mode of this structure to develop a powerful set of fundamental fluidic valving operations. In this work we provide evidence that these structures are in fact functionally complementary to electronic Junction Field Effect Transistors and thus warrant the use of the new term of capillaric- Field Effect Transistor to describe these types of valves. To support this conclusion, we present a theoretical description, experimental characterisation, and practical application of analog flow resistance control. In addition, we demonstrate that the valves can also be re-opened. These are two key capabilities previously missing for a full analogy to electronic transistors. We show modulation of the flow resistance from fully open to pinch-off, determine the flow rate – trigger channel volume relationship and demonstrate that the latter can be modelled using Shockley’s equation for electronic transistors. Finally, we provide a first example of how the valves can be opened and closed repeatedly.

Version notes

Added Supplementary Videos


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Supplementary material

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Supplementary Information
Supplementary Information contains additional experimental detail, CAD files, and modelling resources.
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Supplementary Video 1
Movie V1: “Analog resistance modes of the cFET” contains video results of two experiments used to determine the Shockley equation equivalent for capillaric-FETs
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Supplementary Video 2
Movie V2: “Off-valve/cFET reopening and closing” contains the video results showing the reversible operation of an off-valve/cFET.

Supplementary weblinks

cFET Jupyter otebook
A Jupyter notebook iPython notebook file which shows the fluid flow model. This code models the closing behaviour of the cFET device.