The fundamental unit of synthetic melanin: a verification by tunneling microscopy of X-ray scattering results

Zając, G.; Gallas, James M.; Cheng, Jin Q.; Eisner, M.; Moss, S. C.; Alvarado-Swaisgood, Aileen E.

doi:10.1016/0304-4165(94)90006-x

Cited by 188 publications

(234 citation statements)

References 20 publications

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“…16,30 High-resolution AFM images indicate that islands are made-up of diskshaped nanoaggregates, with a lateral extension of 10-30 nm ( Fig. 3b; occasionally larger as for the drop cast lm, Fig.…”

Section: Film Growthmentioning

confidence: 99%

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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Section: Film Growthmentioning

confidence: 99%

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

et al. 2013

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“…Most multinm-sized particles were liberated from the μm-sized polymers and no aggregates similar to natural melanin were observed. There have been a variety of spectroscopic and imaging studies on synthetic eumelanins arguing that the pigment is an aggregated system of small oligomeric molecules (Zajac et al 1994). Our results suggested that the μm-sized insoluble natural melanin polymers might be dissociated into nm-sized particles using UAD process.…”

Section: Afm Imagementioning

confidence: 99%

Preparation of water-soluble melanin from squid ink using ultrasound-assisted degradation and its anti-oxidant activity

Guo

Chen

et al. 2013

J Food Sci Technol

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Water-soluble squid melanin fractions were firstly prepared using ultrasound-assistant degradation method under alkaline condition, which is optimized by response surface methodology. The processing melanin fractions were divided into different molecular weight (Mw) fractions by membrane separation (below 10 kDa, among 10-50 kDa and over 50 kDa). The AFM image and particle-size analysis showed monomer units of the melanin were destroyed, and huge polymers were degraded into smaller soluble particles after ultrasound. While, UV, IR and solid 13 C NMR spectra indicated that the basic structure of melanin fraction was still retained after ultrasound process. Further analysis showed soluble melanin fractions obtained in 0.5 and 1 M NaOH, with Mw above 10 kDa exhibited much higher in vitro antioxidant potency. The IC 50 of these fractions (IC 50 among 19-80 μg) on scavenging O 2¯i s more efficient than carnosine (IC 50 = 355 μg/ml.), a commercialized antioxidant. They (IC 50 mong 115-180 μg/ml) are as efficient as carnosine (IC 50 = 110 μg/ml) on scavenging OH. Our research has reported a novel method for preparation of water-soluble melanin fractions from squid ink, which could be a promising free radical scavenger from nature resource.Keywords Squid ink melanin . Water-soluble . Ultrasound . Structure, anti-oxidation Practical applicationWe developed a novel method using ultrasound processing to obtain water-soluble squid ink melanin under alkaline condition. Our results showed that soluble squid ink melanin fraction as a natural pigment, is a new free radical scavenger with a promising prospect. The excellent solubility can increase absorption and enhance utilization rate in vivo, providing a potential prospect for squid ink melanin products as a nature antioxidant.

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“…18,19 Melanins do not have broad molecular regularity, and it is believed that its structure is mainly composed of macromolecules of disordered arrangements of 5,6 dihydroxyindol-quinone (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) monomers (Figure 1). 18,[20][21][22] The structural features of melanins make them interesting candidates for application in EGFETs, due to the large number of potential binding sites for H + ions; the two hydroxyl groups of the aromatic ring, the quinone imine and the hydroxyl group of carboxylic acid in the case of DHICA. 23 Melanin films shows semiconductor behavior dependent on water content.…”

Section: Introductionmentioning

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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The fundamental unit of synthetic melanin: a verification by tunneling microscopy of X-ray scattering results

Cited by 188 publications

References 20 publications

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

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

Preparation of water-soluble melanin from squid ink using ultrasound-assisted degradation and its anti-oxidant activity

Melanin as an active layer in biosensors

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