Visible light can be used to create electrodes from conductive plastics completely without hazardous chemicals. This is shown in a new study carried out by researchers at Linköping and Lund universities. The electrodes can be created on different types of surfaces, which opens up for a new type of electronics and medical sensors.

“I think this is something of a breakthrough. It’s another way of creating electronics that is simpler and doesn’t require any expensive equipment,” says Xenofon Strakosas, assistant professor at the Laboratory of Organic Electronics, LOE, at Linköping University.

LOE’s researchers are working with conductive plastics, also known as conjugated polymers, to develop new technologies in areas such as medicine and renewable energy. Conjugated polymers combine the electrical properties of metals and semiconductors with the flexibility of plastics.

Polymers consist of long chains of hydrocarbons. Each link in the chain is called a monomer. When the monomers are connected, polymers are formed. The process, called polymerisation, is often carried out using strong and sometimes toxic chemicals, which limits the ability to scale up the process and use the technology in e.g. medicine.

The Campus Norrköping researchers, together with colleagues in Lund and New Jersey, have now succeeded in creating a method where polymerisation can happen using visible light only. This is possible due to specially designed water-soluble monomers developed by the researchers. Thus, no toxic chemicals, harmful UV light or subsequent processes are needed to create the electrodes.

“It’s possible to create electrodes on different surfaces such as glass, textiles and even skin. This opens up a much wider range of applications,” says Xenofon Strakosas.

In practice, the solution containing the monomers could be placed on a substrate. Using, for example, a laser or other light source, it is possible to create electrodes in intricate patterns directly on the surface. The solution that is not polymerised can then be rinsed away and the electrodes remain.

“The electrical properties of the material are at the very forefront. As the material can transport both electrons and ions, it can communicate with the body in a natural way, and its gentle chemistry ensures that tissue tolerates it – a combination that is crucial for medical applications,” says Tobias Abrahamsson, researcher at LOE and lead author of the article published in the scientific journal Angewandte Chemie.

The researchers have tested the technology by photo-patterning electrodes directly onto the skin of anaesthetised mice. The results show a clear improvement in the recording of low-frequency brain activity compared to traditional metal EEG electrodes.

“As the method works on many different surfaces, you can also imagine sensors built into garments. In addition, the method could be used for large-scale manufacture of organic electronics circuits, without dangerous solvents,” says Tobias Abrahamsson.

The research was funded mainly by the European Research Council, the Swedish Research Council, the Swedish Foundation for Strategic Research, the Knut and Alice Wallenberg Foundation, the Stig Wadström Foundation, the Åke Wiberg Foundation and via the Swedish Government’s Strategic Research Area in Advanced Functional Materials (AFM) at Linköping University.