A sensor under development by researchers at the Eindhoven University of Technology in the Netherlands takes inspiration from how plants draw water out of the earth. Designed to take medically useful readings from patient sweat, the sensor doesn't require any form of external power.

Analyzing a person's sweat can tell you a lot about their health. For example, acidity levels can provide key information about skin diseases, while saline concentration in the liquid can tell doctors about cystic fibrosis cases. However, for sweat to be analytically useful, the readings must be kept fresh by constantly passing the liquid through a sensor, rather than taking static samples.

Working to that goal, the Eindhoven University researchers looked to nature for inspiration, using the method by which trees draw water out of the ground as a basis for their device. Constructed from a flexible plastic foil, the sensor incorporates a micro-channel with a porous structure at one end and a paper at the other.

The paper soaks up the sweat, which is then drawn through the micro-channel and excreted through the porous outlet. The design allows for a constant flow without a single moving part – just the same as in plants and trees.

Once the constant flow of sweat was achieved, the researchers added a microchip into the sensor, with electrodes inserted into the channel. As the liquid flows through, the sensor can continuously analyze it. The team successfully tested a prototype that was able to measure acidity level.

Looking forward, the researchers plan to continue developing the sensor, looking more closely at eventual real-world applications, in both medical and sporting fields. The team believes that the plastic build of the device will keep the cost low, and it's currently working to integrate a solution for wireless transmission of the recorded data.

The findings of the study are published online in the journal Sensors and Actuators B: Chemical.