Melanin links biology and electronic sensors

Melanin - the pigment that colours skin, eyes and hair - could soon be the face of a new generation of biologically friendly electronic devices used in applications such as medical sensors and tissue stimulation treatments.

Led by Prof Paul Meredith and Assoc Prof Ben Powell at the University of Queensland, an international team of scientists has published a study that for the first time gives insight into the electrical properties of this pigment and its biologically compatible ‘bioelectronic’ features.

“Semiconductors are arguably the most important, modern-day, high-tech material - they drive all modern electronics,” said Prof Meredith.

“The majority of semiconductors are made from inorganic elements or compounds such as silicon or gallium arsenide.”

Organic semiconductors, on the other hand, are a relatively new member of the semiconductor family and are composed of molecules containing carbon, hydrogen and other elements.

“There are very few examples of natural organic semiconductors, and melanin was thought to be the very first example, demonstrated to be such in the early ’70s,” he said.

Co-author Assoc Prof Powell said that in semiconductors, such as those found in computers and mobile phones, electronics can carry the electrical current. However, in biological systems, such as brains and muscles, ions carry the current.

“We’ve now found that in melanin, both electrons and ions play important roles,” he said.

The study - published recently in Proceedings of the National Academy of Sciences - points to a new way of interfacing conventional electronics to biological systems using a combination of ion- and electron-conducting biomaterials such as melanin.

“Melanin can ‘talk’ to both electronic and ionic control circuitry and hence can provide that connection role,” said Prof Meredith about the study’s finding, which are the culmination of 10 years of research and experiments.

“There are very few materials that meet these compatible bioelectronic requirements and an insight into melanin’s important biological functions and properties has been really crucial in this study.”

In recent years, the electronics industry has been driven to develop materials and components that are cheaper and more environmentally friendly.

“There is a realisation that in many such applications we should move on from the relatively more expensive inorganic semiconductors. We need cheaper, safer electronic materials with greener credentials,” said Prof Meredith.

“Organic conductors and semiconductors are widely viewed as having enormous potential in this regard; and in the area of medical sensors and devices, biocompatibility will be a key requirement.”

The team is currently working on creating ion-based electrical devices using melanin, with a view to ultimately connecting them to actual biological systems.

“A critical area that one could foresee for bioelectronics is stimulating or repairing signal-carrying pathways in tissues such as muscle or brain,” said Prof Meredith.

Other researchers in the study are Prof Ian Gentle, Prof Graeme Hanson, Dr Bernie Mostert (currently at Lancaster University and a central figure in the research) - all from the University of Queensland, as well as researchers from Britain and Poland.