Using PET as a substrate, it is now possible to design systemon-foil sensing solutions that combine optical sensors, discrete components such LED and flexible interconnections. In this way, contactless user interfaces can be built using organic
photodetectors, offering functionalities such as hand proximity detection and gesture recognition for power on/off or linear control (slider and vertical distance detection). These conformable system-on-foil user interfaces can even be integrated in smart
textiles products. The optical solution relies on the detection by organic photodetectors of the reflected infra-red light emitted by IR-LEDs directly mounted on a flex circuit, as shown in figure. For this purpose, the organic semiconductor materials can
be tuned to operate both in visible and near infra-red bands. Being very thin and easy to glue to other substrates such as paper, these new sensors can easily turn plastic and paper into interactive surfaces for merchandising and smart packaging solutions or to detect nearby motion.