Capillary systems are a promising technology for point-of-care microfluidics, since they are pre-programmable and self-powered. This work introduces “transistor valves” as a key building block for capillaric circuits, providing easy-to-use,...

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We report on a macroinitiator based smart hydrogel film applied on a microcantilever for sensing applications. The studied hydrogel features a comparatively wide dynamic range for changes in the electrolyte's ionic strength. Furthermore, it offers a simple spin coating process for thin film deposition as well as the capability to obtain high aspect ratio microstructures by reactive ion etching. This makes the hydrogel compatible to microelectromechanical system integration. As a proof of concept, we study the response of hydrogel functionalized cantilevers in aqueous sodium chloride solutions of varying ionic strength. In contrast to the majority of hydrogel materials reported in the literature, we found that our hydrogel still responds in high ionic strength environments. This may be of future interest for sensing e.g., in sea water or physiological environments like urine.

A novel capillary action microfluidic viscometer has been designed that can measure the relative viscosity of a sample compared to a control liquid. Using capillary action circuits, the viscosity of a sample is transformed into a microfluidic bar-graph format without the use of external instrumentation. The bars in this case are represented by the distance that a liquid has flown through a microfluidic channel, relative to another liquid in an identical channel. As the device does not require external instrumentation, its use is targeted at point-of-care (PoC) situations. This implementation is made practical through capillaric Field Effect Transistors, and the conditional flow paths they enable. In this paper, we report on the design, operation, and performance of a two-channel version viscometer device exclusively based on capillary action circuits. Using poly-ethylene glycol solutions as viscous samples, we demonstrate that the device can transduce the relative viscosity consistently to within 2%. Enabled by the flexibility of the capillary action circuits, we additionally present a modified device which can measure transparent liquids without the need to add colorants to the sample. The forms of the device presented in this work have applications in both medical care and scientific measurements—particularly for PoC measurements.