An integrated flex-microfluidic-Si chip device towards sweat sensing applications

In this work, we introduce a flexible microfluidic device with an integrated silicon sensor chip, which may in the future be developed towards a wearable device for continuous and prolonged sweat sensing. The device is made by the lamination of three thin layers of polyethylene terephthalate (PET), in which fluidic structures are created using laser microfabrication. The main fluidic structures are an inlet, a microchannel, a sensing cavity, and a porous structure as an outlet. When placed on a surface such as the skin, a filter integrated in the inlet absorbs any liquid present on the surface. Then, the liquid fills the microchannel and the sensing cavity by capillarity; specially designed filter paper structures prevent any liquid pinning or air inclusions to form during this process. Finally, when the liquid reaches the porous outlet, it evaporates via the pores, which generates a continuous flow through the device and over the sensor chip. The latter contains electrodes for electrochemical pH monitoring, and is mounted within the sensing cavity via screen-printed electrical connections. We show a proof-of-principle of the integrated device by demonstrating continuous monitoring of pH changes of liquids that are sequentially fed into the device inlet.