Nanoscale Charge Carrier Transport in Melanin Extracted from Sepia Ink

Sepia melanin, a naturally occurring pigment found in the ink sac of cuttlefish, has garnered significant interest for its intriguing electrical properties and potential as an organic semiconductor material. Sepia melanin exhibits properties of disordered organic semiconductors as organic semiconductors display charge transport behavior attributable to a combination of band-like and hopping transport mechanisms [1]. The electrical conduction in Sepia melanin is influenced by its complex hierarchical structure, which consists of melanin nanoparticles self-assembled into granules. These nanoparticles result from variety of arrangements of pi-pi stacked molecules [2].<br/>Sepia melanin exhibits unique characteristics, such as its moisture-dependent electrical response and broadband optical absorption [3], making it a promising material for applications in organic electronics, energy harvesting, and bioelectronics but Sepia melanin potential is limited by its insolubility in common solvents. By comprehending nanoscale charge transport phenomena, we aim to fully harness Sepia melanin's potential for these technological applications as the size of Sepia melanin granules lie in the range ~150-200 nm.<br/>We focus our investigations on an inter-digitated planar geometry of patterns as our goal is to detect signals emitted by granules of Sepia melanin. Patterns are fabricated by Electron Beam Lithography.<br/>Preliminary findings from our ongoing study reveal the influence of structural disorder on charge carrier transport in Sepia melanin, including charge carrier localization and trapping effects. These findings provide opportunities for tailoring charge transport characteristics in devices. A nanoscale study of Sepia melanin granules reveals their remarkable high electrical conductivity. Electrochemical Impedance Spectroscopy (EIS) response in different atmospheres complemented by current-time measurement has shed light on ionic and electronic processes featuring possible interfacial processes at Sepia melanin/metal interfaces.<br/><br/>Work is in progress to study Photo-induced response of melanin granules and to calculate the extinction co-efficient of Sepia melanin.<br/>The insights gained from this research hold promise for pushing the boundaries of organic electronics and forging novel pathways in the fabrication of bioinspired electronic devices and sensors.<br/>1. Haneef, H.F., A.M. Zeidell, and O.D. Jurchescu, Charge carrier traps in organic semiconductors: a review on the underlying physics and impact on electronic devices. Journal of Materials Chemistry C, 2020. 8(3): p. 759-787.<br/>2. Clancy, C.M. and J.D. Simon, Ultrastructural organization of eumelanin from Sepia officinalis measured by atomic force microscopy. Biochemistry, 2001. 40(44): p. 13353-13360.<br/>3. Pullman, A. and B. Pullman, The band structure of melanins. Biochimica et biophysica acta, 1961. 54: p. 384-385.