THz spectroscopy on graphene-like materials for bio-compatible devices

Abstract

Graphene-like (GL) layers and eumelanin-based graphene-like (EUGL) hybrids have been investigated through THz time domain spectroscopy. The interest in these materials lies on their peculiar chemical-physical properties: the former are conductive water stable materials, whereas the latter are biocompatible materials with good conductive and adhesive properties. Both exhibit promising optoelectronic and bioelectronic applications. We measured mixtures of GL layers or EUGL hybrids with KBr, shaped in pellets with uniform thickness, in order to circumvent problems related to sample inhomogeneity and roughness. A mean field theory was applied to extract direct information on permittivity and conductivity. Data have been carefully fitted through the Drude-Smith theory, confirming the conductive nature of the hybrid materials. The results show that EUGL hybrid-based devices can be promising for the next generation of printable bio-circuits.

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“…This formula is frequently used to describe the transport properties in a large number of nanomaterials in the THz band. [81][82][83] The corresponding complex conductivity can be obtained using the expression:s(u) ¼ Ài [3(u)À3 N ]3 0 u, where 3 0 is the free space permittivity.…”

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“…Tuning the concentration of the guest material (GL, EU or EUGL) in the KBr pellet, we inferred relevant intrinsic electrodynamic parameters of the materials (EP), such as the complex permittivity and hence the conductivity. The measured values of conductivity are encouraging and open the possibility to employ GL and EUGL hybrids for the development of bio-compatible circuitry and devices working up to the THz range [36].…”

“…The peculiar characteristic of GL layers to establish stable colloidal suspensions after dispersion in water without the use of any surfactant make them particularly suitable for the preparation of a wide array of electrically conductive hybrid materials including intercalated metal organic frameworks MOFs [26,34], biocompatible interfaces [35][36] and photoactive materials [37][38].…”

“…Following this approach, a conductive interface was designed and fabricated by an efficient integration of EU and graphene like (GL) layers [35]. The hybrid EUGL was produced allowing EU precursors (5,6-dihydroxyindole (DHI) and/or 5,6-dihydroxyindole-2-carboxylic acid, DHICA [46]) to polymerize in water in presence of suspended GL layers [35][36]. The hybrid material (EU:GL ratio 1:1 wt/wt) was characterized by chemical-physical, electrical and morphological analyses and its biocompatibility was proven toward mammalian cell cultures (Murine Embryonic Stem Cell and Rat Microglial Cell) in vitro in view of its potential exploitation as bio-interface [35].…”

“…A detailed investigation on the high frequency electrodynamics (THz region) in GL layers and its biocompatible hybrid EUGL via THz spectroscopy was also performed [36]. A mean field theory is applied to extract direct information on the permittivity and conductivity.…”