A new strategy to produce low-cost sensors that allow ultrasensitive detection of ultraviolet radiation (UVR) by the naked-eye is described in Nature Communications this week. The sensors, which are paper-based and wearable, could enable users to manage the impact of UVR on their daily lives.

UVR can be classified into UVA, B and C by wavelength. To monitor the impact of different UV radiations, low-cost, spectrally-selective UV sensors are needed. However, current sensors are hindered from mass deployment owing to the cost and complexity of the processes used to create them.

Vipul Bansal and colleagues have devised a new approach for fabricating spectrally-selective and ultrasensitive UV sensors. The secret to their design is the creation of a polyoxometalate-based invisible ink. This ink shows unique properties for spectrally-selective UV sensing. When combined with low-cost and readily available components, such as filter papers, transparency sheets and a fountain pen, a wearable paper-based and low-cost UV sensor can be created.

The authors demonstrate the applicability of their new technology by developing customized paper-based, smiley, UV sensors that provide real-time dosimetry of maximum permissible exposure thresholds for each type of UVR for people with six different skin types. This suggests that the spectrally-selective UV sensors may have potential for large-scale fabrication, and can be tailored for specific skin types.