Melanin (from the Greek melanos, meaning “dark”), the pigment which is responsible for the coloring of the skin, is normally associated with solar protection: in the process of absorbing light, it protects the organism from the sun rays. It also acts as a semiconductor – and it is this characteristic that increases its importance. For this reason, Carlos Graeff, associate professor of the Department of Physics and Mathematics of the University of São Paulo (USP) in Ribeirão Preto, immersed himself in the study of melanin to research beyond its natural function and evaluate the possibility of new applications.
Melanin is a different biological material, due to its semi-conductive quality. Semiconductors are basic components in electronic devices such as integrated circuits. The mastery of semiconductor preparation and analysis with the goal of producing such devices is presently crucial to scientific and technological development. The project which Graeff used as a vehicle to study the production and the characteristics of melanin is entitled “Opto-electronic Properties of Conductor Polymers and Bio-polymers”, completed between 1997 and 1999 with funding from FAPESP.
Skin, feathers and squid
In fact, there are various types of melanin, classified in groups according to origin. They exist for example as pheomelanins, responsible for red colored hair and the allomelanins, found in plants.
However, the group which is most studied is that of the eumelanins, which eliminate free radicals and act as antioxidants. This type of melanin is found in may natural systems from plants such as bananas to fungi. Its presence in the skin and hair protects against lesions caused by sunlight and by pollutants. It is the pigment which is responsible for the color of the skin, of the hair, of the feathers and fur – and even the ink of the squid and the octopus, according to work done by the American research scientists Miles Chedekel and Lisa Zeise in the publication “Cosmetics & Toiletries”. The eumelanina is also edible: the ink of the squid is used to color, aromatize and give texture to sauces.
Among those studying melanin in Brazil is Professor Amando Ito, of the Physics Institute of USP in São Paulo. He drew Graeff’s attention to the properties of melanin as an amorphous semiconductor (non-crystalline). Among the advantages of amorphous semiconductors over crystalline ones, is the possibility of lower production costs and larger coverage areas (such as a cell of a solar panel, for example). Other research scientists such Douglas Galvão, of the State University of Campinas (Unicamp), and Marília Caldas, of USP, have made important contributions to the study especially on the electronic structure of melanin.
Electronic properties
It is unusual for a material of biological origin to have the property of a semi conductor, hence Graeff’s interest. One of the priorities of the study on amorphous semiconductors made by master’s degree student, Pablo José Gonçalves, under Graeff’s supervision, was to investigate the interaction between water molecules and melanin.
This study was made with synthetic melanin called DOPA-melanin. Graeff explains that DOPA-melanin in its solid phase is composed of 20% water, but little was known about the role of the water in its overall structure. To study this, the group used the electronic paramagnetic resonance technique (EPR): “We were able to obtain indirect information on the link with water and its role in the physical and electronic structure of the melanin”, informs the physicist.
Water has an importance, which up to then had not been evaluated in the electric conductivity of melanin: when the proportion of water is altered, for example, the conductivity can be reduced by up to a thousand times according to measurements and experiments done in the laboratory.
In the final stages of the project, Graeff found out that Professor Melvin Eisner of the University of Houston had been doing research along the same line. Both ended up doing a joint study on the subject. The project also aroused the interest of the chemist, Sérgio Galembeck, who is making the calculations to describe the interaction water-melanin at the molecular level.
Better batteries
Another theme for study still within the project financed by FAPESP, is made in collaboration with Professor Herenilton Oliveira, of the Chemistry Department of USP in Ribeirão Preto: the objective is to evaluate the intercalation of DOPA-melanin with vanadium pentoxide.
Research already carried out indicates that in the process of combining melanin and vanadium pentoxide, a new compound is formed: it is hybrid with conductivity significantly greater than pure vanadium pentoxide and can be used in lithium batteries. The results from the study of the synthesis, characterization and properties of this new material were published in the US periodical, “Journal of Material Chemistry” and received with interest at a seminar held in San Francisco in 1999, where Oliveira was a speaker.
“The melanin improves the stability of the material after the charging and discharging of lithium ions”, explains Graeff, based on the first experiments. The important consequence: increase the useful life of the batteries based on this hybrid material and reduce the time necessary for charging and recharging.
Bio-electronics
Besides melanin, Graeff has taken an interest in other materials and devices potentially useful in the so-called bio-electronic field. The objective of bio-electronics is to couple units of bio-molecular functions, such as molecules and proteins, with electronic devices. One example is the sensors capable of measuring and stimulating neuronal impulses. This can be used to understand the functions or correct dysfunction in the brain.
“Let us consider the human brain as comparable with computers”, says Graeff. “ It is clear that a major challenge will be to amalgamate in future devices, the advantages of biological systems with the modern world of electronics based on inorganic semiconductors.” As it is a material of biological origin, melanin is naturally bio-compatible and therefore it can be useful in the development of new technology which couples electronics to living beings.
As such, Graeff believes that organic and inorganic hybrid materials such as vanadium pentoxide intercalated with melanin, have a big potential for use in several areas such as in the battery industry for cellular telephones. One classic example of the use of organic and inorganic materials is the so-called bio-sensors (see “Notícias FAPESP”, Number 46). For the time being, all lies in the realms of possibility. Graeff and his team are proceeding with their studies in materials of interest to the area of bio-electronics, in search of new low-cost technologies.
Profile:
Carlos Frederico de Oliveira Graeff, 32, born in Ribeirão Preto, State of São Paulo, graduated in Physics (1989) from the State University of Campinas (Unicamp), where he obtained a master’s degree (1991) and Ph.D. (1994) in Applied Physics. Took a post-doctorate degree in Electronic Magnetic Resonance, Semiconductors and Electronic Devices at Walter Schottky Institut, Munich. Has been Associate Professor of the Physics and Mathematics Department of USP in Ribeirão Preto since 1999, is vice-coordinator of post-graduation in Applied Physics to Medicine and Biology.
Project: Opto-electronic Properties of Conductor Polymers and Bio-polymers
Investment: R$ 16,489.99 and US$ 33,293.50
