Nanoengineers at the University of California, San Diego are one step closer toward developing a new breed of wearable devices that can easily detect the blood sugar levels of diabetic patients without requiring them to prick their fingers every day.

Graduate student Amay Bandodkar and his colleagues at the Nanoengineering Department at the Center for Wearable Sensors of the Jacobs School of Engineering at UC San Diego have developed a proof-of-concept temporary tattoo that can be attached to the patient's skin to detect the spikes in glucose that happen after a meal rich in carbohydrates.

The tattoo consists of carefully patterned electrodes printed into a thin piece of paper that can be applied to the skin for 10 minutes. The electrodes send sodium ions into the skin to extract glucose-carrying fluids from between the skin cells. The electrical charge produced by the glucose, which is measured by sensors built into the tattoo, will be used to determine the patient's blood sugar levels.

"Presently, the tattoo sensor can easily survive for a day," says Bandodkar. "These are extremely inexpensive - a few cents - and hence can be replaced without much financial burden on the patient."

A report [pdf] published by the researchers in the Analytical Chemistry journal shows the tattoo has already been used to determine the glucose spikes in seven men and women with no history of diabetes. The volunteers, aged 20 to 40, were asked to eat a meal of sandwich and soda in the laboratory. The tattoo was then placed on their skin to detect the increase in glucose levels that normally precedes such a carbohydrate-rich meal.

None of the volunteers reported any feeling of discomfort during the test, while only "a few" people said they felt a mild but not uncomfortable feeling of tingling during the first 10 seconds the tattoo was applied.

For now, the tattoo can only detect the glucose spikes but not provide a specific numeric value of the patient's blood glucose levels. The feature is still currently in development, Bandodkar says. In the future, the final product will be able to provide a numeric readout and will have Bluetooth capabilities so it can send the information to the patient's doctor or store it in the cloud.

The tattoo can also be used to measure other important chemicals in the body, such as lactate, a metabolite used by athletes to gauge their fitness levels. It can also be used to determine levels of alcohol, illegal drugs, or other substances in the body as well as evaluate how well medicines are being absorbed.

The researchers' vision is to use these glucose tattoo sensors "to continuously monitor glucose levels of large populations as a function of their dietary habits." Bandodkar says information retrieved from a wider population could help researchers learn more about the causes and prevention of diabetes, a disease that affects millions of people worldwide.