Physical and Chemical Control of Interface Stability in Porous Si–Eumelanin Hybrids

Abstract

The organic/inorganic interface in thin nanosized porous structures has a key role in determining the final properties of the composite materials. By use of the porous silicon/eumelanin hybrids as a case study, the role of this interface was investigated by experimental and computational methods. Our results show that an increased polymer density close to the hybrid interface strongly modifies the diffusion of the chemical species within the polymer molecule, affecting then the oxidation level of the pores’ inner Si surface. We observed a greater stability induced by increased pore diameter, a behavior that with computational and chemical arguments we attributed to a modified diffusion of the hydrogen peroxide toward the Si/eumelanin interface. Our results show that the overall behavior of a polymer when inserted in a tiny nanoscale structure must be taken into account for a correct understanding and control of the hybrids properties and that the formation of the interface alone may not be sufficient.

Eumelanin Adsorption on Silicon: Optical Properties of Si(001)-Adsorbed Eumelanin Tetrameric Protomolecules

“…Computational investigations have been reported on the energetics, adhesion properties, electronic properties and interface stability of simplified models of the PSi-eumelanin interface, consisting of tetramers of DHI-like molecules interacting with the Silicon(001) surface. 12,13 Clearly, a theoretical understanding of the effects of eumelanin on the optical properties of the substrate, in addition to the above-mentioned issues, is of paramount importance to control and optimize the behaviour of these composite materials both in terms of stability and photovoltaic properties. First principles calculations on organically functionalized surfaces are able to yield valuable highlights in this respect (e.g.…”

Progress and challenges of implantable neural interfaces based on nature-derived materials

“…Nevertheless, in recent years, novel examples of electroconductive polymers inspired by nature-derived materials have been explored for use in organic electronics. In this regard, natural compounds such as eumelanin, a protein derived from the oxidative polymerization of 5,6-dihydroxyindoles and used as UV-protection molecules, have already been used to enhance photocurrent production in porous silicon-based optoelectronic devices (Antidormi et al 2018 ). In the framework of neural engineering, spin-coated melanin films have been reported to support and enhance PC12 growth and neurite sprouting (Bettinger et al 2009 ).…”

“…Moreover, NMs coating of neural interfaces has also been envisioned for fabricating multifunctional NIs with increased electrical performance and drug release functionality, as demonstrated by Abidian and Martin (2009); in their work, an alginate hydrogel was fabricated on an electrode surface previously coated with dexamethasone (DEX)-loaded PLGA nanofibers. Alginate was exploited for subsequent electrodeposition of PEDOT to enhance electrical performance.…”

Melanins as Sustainable Resources for Advanced Biotechnological Applications

“…[ 399,400 ] Studies of reduction/oxidation processes and electron transfer using cyclic voltammetry are particularly useful for melanins, with fundamental studies on melanins formed chemically from single monomers (e.g., l ‐DOPA, [ 401 ] DHI, [ 402 ] 3,4‐dihydroxyphenylacetic acid, [ 403 ] HGA, [ 404,405 ] DHN [ 231 ] ), combinations of DHI and DHICA, [ 406–408 ] and natural melanins from bacteria (e.g., Shewanella oneidensis MR‐1, [ 157 ] Pseudomonas aeruginosa [ 409 ] ), plants (including fungi: basidial fungi, [ 410 ] Cryptococcus neoformans [ 411 ] and Nigella sativa [ 412 ] ), cuttlefish ( Sepia officinalis [ 407 ] ), and human hair‐derived pheomelanins. [ 413 ] Electrochemical impedance spectroscopy and dielectric spectroscopy enabled the rational investigation of the protonic and electronic contributions, suggesting melanins are protonic conductors, [ 414–416 ] which is important because the electrical properties of melanins [ 417–422 ] underpin their potential technical and medical applications, [ 423–425 ] and it is noteworthy that the potential for melanins in electronics has seen an explosion of interest (see Figure [ 426 ] ).…”