Self-driven capillaric viscometer for direct or cascaded bar graph read-out of relative sample viscosity

The viscosity of samples is a key property, where differences can indicate variation or abnormalities. A biological example is that high blood viscosity is a predictor of cardiovascular events. However, viscosity is difficult to measure in a simple and affordable way, such as for Point-of-Care applications. Thus, we developed a simple to use platform that eliminates external effects like temperature by measuring the sample viscosity relative to a control. The platform employs a novel capillaric driven circuit, including the recently developed capillaric field effect transistors and a single integrated capillaric pump, to apply an identical pressure to parallel sample and control channels simultaneously. This induces flow in the parallel channels relative to the viscosity, which presents as a difference in the distance travelled along the bar graph read-out section of the device. Using poly-ethylene glycol solutions as exemplars, we demonstrate that the device can visualize relative viscosity of colored samples and control consistently within 2%. Additionally, the design of the capillaric circuitry inherently accounts for viscosity variation due to temperature, improving the applicability of the device to less-controlled environments. Finally, we demonstrate how the design can be cascaded to read-out translucent samples via colored indicator liquid and how, based on blood mimicking liquids, it can be used to compare blood viscosity.