Oral communication, CS2 / C7

Official XXIst International Pigment Cell Conference website - 21-24 Sept 2011, Bordeaux - France | updated: September 04 2011

Is melanin a semiconductor: the mysteries of electrical conduction and melanin bioelectronics?

Melanins have been known to conduct and photo-conduct electricity for more than four decades¹. Renewed interest in melanins as advanced functional materials has emerged more recently, particularly in the context of a biological electrical interface material². Since the early 70’s the standard model for melanin in the solid-state has been as an amorphous semiconductor as per the Mott-Davis formalism³. This assertion was derived primarily from observations of electrical switching between high and low resistive states. Indeed, it has been argued that melanin constituted the first demonstrated electrically active organic device and organic semiconductor⁴. However, it is by no means clear that this is the appropriate or correct description and multiple observations of more exotic phenomena such as apparent ambipolar behavior and humidity dependent electrical conductivity have very much cast doubt on amorphous semiconductivity being the necessary and sufficient model⁵. In our paper we will describe recent work focused on unraveling this difficult and seemingly intractable problem. We have used a combination of techniques including muon-spin relaxation (µSR), electron paramagnetic resonance and conductivity measurements and find that melanin has characteristics of a hybrid ion (proton)-electron conductor. Its electronic biophysics is dominated by ionic behavior and we show that this originates from the so-called comproportionation equilibrium whereby protons are released in a hydroquinone-to-quinone reaction. We also demonstrate how this exotic behavior can be used in an all-solid-state organic electrochemical transistor to affect ion-to-electron transduction – a key element in bioelectronic interfacing. A full understanding of melanin’s electrical properties will not only allow its potential as a bioelectronic material to be realized but could have major implications for advancing our knowledge of its biological role and function. References: 1. Meredith et al, Soft Matter, 2006, 2, 37-44 2. Bothma et al, Adv. Mater., 2008, 20, 3539-3542 3. McGinnes et al, Science, 1974, 183, 853-855 4. The device is now housed in the Smithsonian Institute Chip Collection (http://smithsonianchips.si.edu/proctor/index.htm) 5. Meredith and Sarna, PCR, 2006, 19(6), 572-594

Advertisement from our sponsor: