Abstract
The recent development of eumelanin pigment-based blends integrating “classical” organic conducting materials is expanding the scope of eumelanin in bioelectronics. Beyond the achievement of high conductivity level, another major goal lays in the knowledge and feasible control of structure/properties relationship. We systematically investigated different hybrid materials prepared by in situ polymerization of the eumelanin precursor 5,6-dihydroxyindole (DHI) in presence of various amounts of graphene-like layers. Spectroscopic studies performed by solid state nuclear magnetic resonance (ss-NMR), x-ray photoemission, and absorption spectroscopies gave a strong indication of the direct impact that the integration of graphene-like layers into the nascent polymerized DHI-based eumelanin has on the structural organization of the pigment itself, while infrared, and photoemission spectroscopies indicated the occurrence of negligible changes as concerns the chemical units. A tighter packing of the constituent units could represent a strong factor responsible for the observed improved electrical conductivity of the hybrid materials, and could be possible exploited as a tool for electrical conductivity tuning.
Highlights
Eumelanin belongs to the melanin pigments family and it is the pigment type mostly found in bacteria, fungi, plants, animals, and extinct organisms
As previously reported (Alfè et al, 2012; Gargiulo et al, 2015), the main spectral features of the GL layers Fourier Transform Infrared (FTIR) spectrum are: a broad band in the 3,000–3,600 cm−1 range ascribable to stretching vibrations of O–H in carboxylic and phenolic In Table 1, all samples analyzed in this work are listed with their label
The measured elemental composition is reported together with the percentages of GL and eumelanin pigment (EU) established on a ponderal basis starting from the milligrams of the GL and the EU precursor used for the preparation of each sample
Summary
Eumelanin belongs to the melanin pigments family and it is the pigment type mostly found in bacteria, fungi, plants, animals, and extinct organisms. DHI derived eumelanins have been proven to be highly biocompatible (Bettinger et al, 2009; Gargiulo et al, 2015), a feature that, together with their water dependent hybrid ionic-electronic conductor nature (Rettenwander et al, 2014; Gargiulo et al, 2015; Wunsche et al, 2015) linked to the specific functionalization of the pigment (Jastrzebska et al, 1995; Eom et al, 2016), makes such pigments of enormous potential interest for biosensing applications. The electrical (ionic as well as electronic) conductivity of these pigments suggested their application as biointerface capable to allow wealthy cell culture and at the same time to transfer electrical signaling between the cell culture and underlying electronic devices (D’Ischia et al, 2013; Barra et al, 2015)
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