Nobody likes having blood samples taken, which is why we've seen a number of devices that gather sweat from the skin and then analyze it. An inexpensive new bandage-like biosensor simplifies that concept, as it doesn't incorporate any electronic components.

Developed by scientists from China and the US, the device consists of an adhesive-backed flexible polyester film that's coated with a super-hydrophobic (water-repelling) silica suspension. Etched into that coating are four tiny super-hydrophilic (water-attracting) wells.

When the biosensor is applied to a patient's skin like a bandage, their perspiration gets channeled into those microwells, where it collects. Dyes applied to the bottom of each well subsequently change color according to the sweat's pH level, and its concentrations of chloride, glucose and calcium.

A smartphone camera and app are then used to assess the color of the wells, providing users with a readout of the four parameters – although the data is obtained from sweat, it corresponds to levels within the patient's body. When tested on a volunteer who was perspiring as they exercised, the device/app determined that their sweat had a pH level of 6.5 to 7.0, a chloride concentration of about 100 mM (nanomolars), and trace amounts of calcium and glucose.

The scientists – from the University of Science and Technology Beijing, the Chinese Academy of Sciences, the California Institute of Technology, and the University of California-Davis – are now working on improving the device's sensitivity. A paper on their research has been published in the journal Analytical Chemistry.