Researchers from Osaka University have created a soft, flexible and wireless optical sensor using carbon nanotubes and organic transistors on an ultrathin polymer film. This innovation is poised to create new possibilities in imaging technologies and non-destructive analysis techniques.

Recent years have seen significant advances in imaging technology, from high-speed optical sensors that can capture more than two million frames per second to compact lensless cameras that can capture images with just a single pixel.

In a recently published study Advanced MaterialsResearchers at Osaka University SANKEN (Institute for Scientific and Industrial Research) have developed an optical sensor on an ultra-thin flexible sheet that can be bent without breaking. In fact, this sensor is so flexible that it can work even after being rolled into a ball.

The optical sensor in a camera is a device that detects light passing through a lens, similar to the retina inside the human eye.

Innovations in sensor design

“Conventional optical sensors are manufactured using inorganic semiconductors and ferroelectric materials,” says Rei Kawabata, lead author of the study. “This makes the sensors rigid and unbendable. To avoid this problem, we looked for another way to detect light.”

Instead of traditional light sensors, the researchers use an array of tiny photodetectors made of carbon nanotubes printed on an ultrathin polymer substrate (less than 5 microns). Under the influence of light, carbon nanotubes heat up, creating a thermal gradient, which then produces a voltage signal. Doping the nanotubes with chemical carriers during printing further increases their sensitivity. Using these nanotubes, visible light as well as heat or infrared light associated with molecules can be measured.

Integration of wireless technologies

Besides carbon nanotube sensors, organic transistors are also printed on a polymer substrate to convert voltage signals into an image signal. The computer does not need to physically connect wires to the sensor to read this signal. A wireless Bluetooth module is used instead.

“With this wireless system, our thermal imaging device can connect and analyze soft and curved objects without damaging their surfaces or internal parts,” says Teppei Araki, senior author of the study.

The researchers created a prototype sheet-like optical sensor and tested its ability to detect heat from objects such as human fingers or wires, as well as glucose flowing through tubes. They found that the optical sensor had high sensitivity over a wide wavelength range. Additionally, tests at room temperature and under atmospheric conditions showed that it has high bending strength and works even after being crushed.

The unique advantages of this wireless measurement system and sheet optical sensor will lead to new and easier ways to perform many tasks, such as evaluating the quality of a liquid without the need for sampling. Researchers believe it holds promise in many applications, such as non-destructive imaging, wearable devices, and soft robotics.