Researchers at the University of Toronto have developed a temporary tattoo in the shape of a smiley face that can monitor metabolic stress in patients and athletes. The medical sensor is a thin and flexible solid-contact ion-selective electrode (ISE), made using standard screen printing techniques and commercially-available transfer tattoo paper.
The ‘eyes’ on the tattoo are electrodes that monitor the skin’s pH levels, which can indicate dehydration and fatigue. The ‘ears’ can be used to connect to a monitoring device to extract the data. During tests, the tattoo-based sensor stayed in place and continued to work even during exercise when the wearer was sweating.
It is applied like regular transfer tattoos, with a paper towel soaked in warm water used to remove the base paper. By using different sensing materials, the tattoos could be modified to detect other components of sweat, such as sodium, potassium or magnesium.