Device‐Quality Electrically Conducting Melanin Thin Films

Bothma, Jacques P.; Boor, Johannes de; Divakar, Ujjual; Schwenn, Paul; Meredith, Paul

doi:10.1002/adma.200703141

Cited by 195 publications

(227 citation statements)

References 22 publications

(21 reference statements)

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“…The synthesis procedure was described elsewhere. 19 The melanin powder was used to prepare three different solutions, respectively adding 700 mg (solution I), 26 500 mg (solution II) and 300 mg (solution III) of melanin to a mixture of 5 ml of deionized water and 10 ml of concentrated ammonium hydroxide (28%). The solutions were stirred at room temperature for 1 h and then ultrasonicated for a further hour.…”

Section: Methodsmentioning

confidence: 99%

Melanin as an active layer in biosensors

et al. 2014

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The development of pH sensors is of great interest due to its extensive application in several areas such as industrial processes, biochemistry and particularly medical diagnostics. In this study, the pH sensing properties of an extended gate field effect transistor (EGFET) based on melanin thin films as active layer are investigated and the physical mechanisms related to the device operation are discussed. Thin films were produced from different melanin precursors on indium tin oxide (ITO) and gold substrates and were investigated by Atomic Force Microscopy and Electrochemical Impedance Spectroscopy. Experiments were performed in the pH range from 2 to 12. EGFETs with melanin deposited on ITO and on gold substrates showed sensitivities ranging from 31.3 mV/pH to 48.9 mV/pH, depending on the melanin precursor and the substrate used. The pH detection is associated with specific binding sites in its structure, hydroxyl groups and quinone imine.

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Section: Methodsmentioning

confidence: 99%

Melanin as an active layer in biosensors

et al. 2014

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“…Furthermore, Au or Ag were typically used as electrode materials in melanin thin lm devices. 13,15,21,22,25 However the use of these metals should be avoided, since they can electrochemically react with eumelanin, as we recently demonstrated.…”

Section: 17mentioning

confidence: 99%

“…19 Only recently, protocols for the solution processing of synthetic eumelanin thin lms have been reported and the selection of potentially suitable solvents seems to be restricted to dimethyl sulfoxide (DMSO), 20 dimethyl formamide, 20 and ammonia solutions. 21 Therefore, there is an urgent need to investigate the effect of the synthesis route and processing conditions on the growth mechanism of eumelanin thin lms and their nal properties.…”

Section: 17mentioning

confidence: 99%

“…low lm hydration) 13,15,20,[22][23][24] or are limited to the determination of the lm conductivity at 100% relative humidity (RH). 21,25 Studies on (partly) hydrated eumelanin lms were commonly performed at high voltages ($10 V), 22,24,25 which might result in undesired currents due to water electrolysis, for example. Furthermore, Au or Ag were typically used as electrode materials in melanin thin lm devices.…”

Section: 17mentioning

confidence: 99%

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Eumelanin thin films: solution-processing, growth, and charge transport properties

et al. 2013

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Eumelanin pigments show hydration-dependent conductivity, broad-band UV-vis absorption, and chelation of metal ions. Solution-processing of synthetic eumelanins opens new possibilities for the characterization of eumelanin in thin film form and its integration into bioelectronic devices. We investigate the effect of different synthesis routes and processing solvents on the growth, the morphology, and the chemical composition of eumelanin thin films using atomic force microscopy and X-ray photoelectron spectroscopy. We further characterize the films by transient electrical current measurements obtained at 50% to 90% relative humidity, relevant for bioelectronic applications. We show that the use of dimethyl sulfoxide is preferable over ammonia solution as processing solvent, yielding homogeneous films with surface roughnesses below 0.5 nm and a chemical composition in agreement with the eumelanin molecular structure. These eumelanin films grow in a quasi layer-bylayer mode, each layer being composed of nanoaggregates, 1-2 nm high, 10-30 nm large. The transient electrical measurements using a planar two-electrode device suggest that there are two contributions to the current, electronic and ionic, the latter being increasingly dominant at higher hydration, and point to the importance of time-dependent electrical characterization of eumelanin films.

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“…[1][2][3][4][5] This interest stems from a desire to understand fundamental processes in biology and from the intriguing possibilities of using bio-molecules in electronics, 6 i.e., bioelectronics. The skin pigment eumelanin (hereafter referred to as melanin 7 ) is one system that has recently emerged as a strong candidate for bioelectronics because of the advances in producing device-quality thin films [8][9][10] and the prevailing model that it is perhaps the only biological amorphous semiconductor. 7,[11][12][13][14][15][16] A full model of charge transport in melanin has remained elusive for a number of reasons including (1) its electrical properties are very sensitive to hydration 9,[16][17][18][19][20] and (2) there are difficulties associated with forming good ohmic contacts for accurate and reproducible measurements (due to surface roughness).…”

mentioning

confidence: 99%