Sunshine on a biting fall day can feel blissful. But too much time spent basking in the sun’s ultraviolet rays can lead to sunburn and increase the risk of developing skin cancer, cataracts and wrinkles. Now, researchers have made a cheap, wearable device that keeps tabs on UV exposure. The new tech could mean soaking up the sun without overdosing on radiation.
Vipul Bansal, an applied chemist and nanobiotechnologist at the Royal Melbourne Institute of Technology in Australia, wanted to manage his sun exposure. The 38-year old social entrepreneur wasn’t getting enough vitamin D. Since the essential vitamin helps the gut absorb calcium, a deficiency can cause thin or brittle bones.
“I was after a sensor that could tell me how long to spend in the sun to get enough vitamin D, but not damage myself with a potential skin cancer,” Bansal said.
Although UV sensors already exist, current devices are expensive and need thorough calibration — not so great for the everyday consumer. So, Bansal and team set about crafting a new one.
Sun-sensitive Ink
The researchers first created a new kind of ink that monitors UV exposure. It’s made from phosphomolybdic acid, a chemical scientists who study body tissues use to stain cells with dye, and lactic acid, the compound that builds up in muscles after rigorous exercise. The ink starts out invisible but becomes blue with UV exposure. The ink can even distinguish between different types of UV radiation. UVA turns the ink a light, gray-blue, whereas UVC makes the ink a deep navy that takes on a blue-green hue after prolonged exposure, for example.
The researchers then devised a low-cost UV sensor. They loaded a typical fountain pen with the novel ink and drew smiley faces on small, circular pieces of filter paper by hand. When the scientists exposed the paper to different UV wavelengths, blue smileys appeared. The longer UV rays irradiated the ink, the bluer the ink became, the scientists report today in the journal Nature Communications.
“We can print our ink on any paper-like surface to produce cheap wearable sensors in the form of wrist-bands, head bands or stickers for example,” Bansal said in a statement.
The wearable paper-based solar UV sensor. (Credit: Ms Wenyue Zou)
Tailored Wearable
However, UV radiation affects people with dark and light skin color differently. People with darker skin can not only tolerate more UV exposure before developing sunburn than individuals with lighter skin but they also need more UV exposure to make enough vitamin D to stay healthy. So, to make a wearable UV sensor that is appropriate for different skin tones, Bansal and colleagues used transparency films. The films work as effective and economical UV filters. By layering the transparency film filters over the ink, the researchers were able to custom design six sensors for people with skin color ranging from very fair to dark brown.
The disposable sensors are simple and cheap. They feature four pieces of filter paper attached to a flexible band with happy, flat or frowny faces drawn in the new ink to indicate when the wearer has reached the maximum amount of UV exposure to prevent getting a sunburn for their skin color. Bansal estimates the sensors will only cost $1.
