One of the challenges that scientists face in developing bioelectronic
devices is identifying and finding ways to use materials that conduct not only
electrons but also ions, as most communication and other processes in the human
organism use ionic biosignals (e.g., neurotransmitters). In addition, the
materials must be biocompatible.
Resolving this challenge is one of the motivations for researchers at São
Paulo State University's School of Sciences (FC-UNESP) at Bauru in Brazil. They
have succeeded in developing a novel route to more rapidly synthesize and to
enable the use of melanin, a polymeric compound that pigments the skin, eyes and
hair of mammals and is considered one of the most promising materials for use in
miniaturized implantable devices such as biosensors.
"All the materials that have been tested to date for applications in
bioelectronics are entirely synthetic," said Carlos Frederico de Oliveira
Graeff, a professor at UNESP Bauru and principal investigator for the
"One of the great advantages of melanin is that it's a totally natural
compound and biocompatible with the human body: hence its
potential use in electronic devices that interface with brain neurons, for
According to Graeff, the challenges of using melanin as a material for the
development of bioelectronic devices include the fact that like other
carbon-based materials, such as graphene, melanin is not easily dispersible in
an aqueous medium, a characteristic that hinders its application in thin-film
Furthermore, the conventional process for synthesizing melanin is complex:
several steps are hard to control, it can last up to 56 days, and it can result
in disorderly structures.
In a series of studies performed in recent years at the Center for Research
and Development of Functional Materials (CDFM), where Graeff is a leading
researcher and which is one of the Research, Innovation and Dissemination
Centers (RIDCs) funded by FAPESP, he and his collaborators managed to obtain
biosynthetic melanin with good dispersion in water and a strong resemblance to
natural melanin using a novel synthesis route.
The process developed by the group at CDMF takes only a few hours and is
based on changes in parameters such as temperature and the application of oxygen
pressure to promote oxidation of the material.
By applying oxygen pressure, the researchers were able to increase the
density of carboxyl groups, which are organic functional groups consisting of a
carbon atom double bonded to an oxygen atom and single bonded to a hydroxyl
group (oxygen + hydrogen). This enhances solubility and facilitates the
suspension of biosynthetic melanin in water.
"The production of thin films of melanin with high homogeneity and quality is
made far easier by these characteristics," Graeff said.
By increasing the density of carboxyl groups, the
researchers were also able to make biosynthetic melanin more similar to the
In living organisms, an enzyme that participates in the synthesis of melanin
facilitates the production of carboxylic acids. The new melanin synthesis route
enabled the researchers to mimic the role of this enzyme chemically while
increasing carboxyl group density.
"We've succeeded in obtaining a material that's very close to biological melanin by
chemical synthesis and in producing high-quality film for use in bioelectronic
devices," Graeff said.
Through collaboration with colleagues at research institutions in Canada, the
Brazilian researchers have begun using the material in a series of applications,
including electrical contacts, pH sensors and photovoltaic cells.
More recently, they have embarked on an attempt to develop a transistor, a
semiconductor device used to amplify or switch electronic signals and electrical
"Above all, we aim to produce transistors precisely in order to enhance this
coupling of electronics with biological systems," Graeff said.