Tech Briefs

Transferrable Sensor Tattoo Measures Metabolic Stress

Smiley sensor works like a temporary tattoo to detect disease.

A medical sensor, that adheres to the skin like a temporary tattoo could make it easier for doctors to detect metabolic problems in patients as well as help coaches to fine-tune athletes’ training routines, say researchers at the Department of Physical & Environ mental Sciences at the University of Toronto, Scarborough, Canada (UTSC). The entire sensor was designed as a thin, flexible package shaped like a smiley face.

alt“We wanted a design that could conceal the electrodes,” says Vinci Hung, a PhD candidate at UTSC, who helped create the new sensor. “We also wanted to showcase the variety of designs that can be accomplished with this fabrication technique.”

The new tattoo-based solid-contact ionselective electrode (ISE) is made using standard screen printing techniques and a basic commercially available transfer tattoo paper, the same kind of paper used for temporary tattoos aimed at children. The sensor’s “eyes” function as the working and reference electrodes, and the “ears” contain contacts to connect a measurement device.

The sensor she helped design can detect changes in the skin’s pH levels in response to metabolic stress from exertion. Similar devices, called ion-selective electrodes (ISEs), are currently in use by medical researchers and athletic trainers.

ISEs can help to give clues to underlying metabolic diseases such as Addison’s disease, also known as chronic primary adrenocortical insufficiency, or to simply signal whether an athlete is fatigued or dehydrated during training. The unit works by detecting various components in perspiration.

Existing devices can be bulky, or difficult to keep secured to moist skin. By eliminating a traditional adhesive, the new tattoo-based sensor stayed in place during tests, and even continued to work even when the people wearing them were exercising and sweating extensively. The tattoos were applied in a similar way to regular transfer tattoos, including using a warm, moist paper towel to remove the base paper.

To create the sensors, Hung and her colleagues used a standard screen printer to lay down consecutive layers of silver, carbon fiber-modified carbon and insulator inks, followed by electropolymerization of aniline to complete the sensing surface.

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 medicine. Hung says that the device may also prove useful in the cosmetics industry to monitor skin secretions.

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