Researchers at the University of Toronto Scarborough (UTSC) have developed a sensor in the form of a temporary stick-on tattoo that can monitor a range of physiological indicators.
A medical sensor that attaches to the skin in the same way as a temporary transfer tattoo could help doctors to detect metabolic problems in patients and assist those involved in training athletes. The tattoo, in the form of a ‘smiley’, can in fact detect changes in the skin’s acidity (pH) level in response to metabolic stress from exertion. Similar devices, called ion-selective electrodes (ISEs), are already being used by medical researchers and athletics trainers. They provide clues to underlying metabolic disorders such as Addison’s disease or simply signal when an athlete is fatigued or dehydrated during training and so help to refine the training programme. The devices are also useful to the cosmetics industry for monitoring skin secretions. But existing devices can be bulky, or hard to keep adhered to sweating skin. The new tattoo-based sensor stayed in place during tests and continued to work even when the people wearing them were exercising and perspiring heavily.
Tattoos are the researchers’ ‘eyes’ and ‘ears’
The new tattoo-based solid-contact ion-selective electrode (ISE) is made using standard screen printing techniques and commercially available transfer tattoo paper. To make the sensors, UTSC PhD student Vinci Hung and her Toronto colleagues used a standard screen printer to lay down consecutive layers of silver, carbon fibre-modified carbon and insulator inks, followed by electropolymerisation of aniline to complete the sensing surface. In the case of the smiley face sensor, the ‘eyes’ function as the working and reference electrodes, while the ‘ears’ are contacts to which a measurement device can connect. The tattoos were applied in a similar way as standard transfer tattoos, right down to using a paper towel soaked in warm water to remove the base paper.
A range of metabolic feedback
Vinci Hung, a PhD candidate in the Department of Physical and Environmental Sciences at UTSC who helped create the new sensor, explained that they were looking for “a design that could conceal the electrodes.” In addition, they were hoping to “showcase the variety of designs that can be accomplished with this manufacturing technique.” By using different sensing materials, the tattoos can also be modified to detect other components of sweat, such as sodium, potassium or magnesium, all of which are of potential interest to researchers in the field of medicine and also cosmetology.