On the Origin of Reduced Cytotoxicity of Germanium-Doped Diamond-Like Carbon: Role of Top Surface Composition and Bonding

Abstract

This work attempts to understand the behaviour of Ge-induced cytotoxicity of germanium-doped hydrogen-free diamond-like carbon (DLC) films recently thoroughly studied and published by Jelinek et al. At a low doping level, the films showed no cytotoxicity, while at a higher doping level, the films were found to exhibit medium to high cytotoxicity. We demonstrate, using surface-sensitive methods—two-angle X-ray-induced core-level photoelectron spectroscopy (ARXPS) and Low Energy Ion Scattering (LEIS) spectroscopy, that at a low doping level, the layers are capped by a carbon film which impedes the contact of Ge species with tissue. For higher Ge content in the DLC films, oxidized Ge species are located at the top surface of the layers, provoking cytotoxicity. The present results indicate no threshold for Ge concentration in cell culture substrate to avoid a severe toxic reaction.

Electron Spin Resonance Study of Hydrogen‐Free Germanium‐Doped Diamond‐Like Carbon Films

“…The θ, χ CW /χ P , g NE , g LE , and a values obtained for DLC:Ge films with various Ge content. The sp 3 /sp 2 ratio is taken from Zemek et al [20] Ge content [at%] contribution of LE becomes higher with the increase of Ge content, we may suppose that the increase of the a values effect can be due to the higher density of states of LE on Fermi energy level caused by Ge doping.…”

“…The detailed procedure is described by Jelinek et al [19] The thickness of obtained films was about 160 nm. The investigated films were previously characterized by two-angle X-Ray-induced core-level photoelectron spectroscopy (ARXPS), low-energy ion scattering (LEIS) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), wavelength-dependent X-Ray spectroscopy (WDS), and VIS-near-infrared (IR) transmittance methods as reported by Jelinek et al [19] and Zemek et al [20] The continuous-wave ESR spectra were measured on the Bruker ELEXSYS E580 spectrometer at the X-band frequency range (ν % 9.4 GHz). We used the ER 4122 SHQE SuperX High-Q cavity with ER 4112HV variable-temperature He-flow cryostat.…”

“…The detailed procedure is described by Jelinek et al [ 19 ] The thickness of obtained films was about 160 nm. The investigated films were previously characterized by two‐angle X‐Ray‐induced core‐level photoelectron spectroscopy (ARXPS), low‐energy ion scattering (LEIS) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), wavelength‐dependent X‐Ray spectroscopy (WDS), and VIS–near‐infrared (IR) transmittance methods as reported by Jelinek et al [ 19 ] and Zemek et al [ 20 ]…”

“…The recent study of Ge‐doped DLC films by X‐Ray‐induced core‐level photoelectron spectroscopy, low‐energy ion scattering, and Raman spectroscopy methods has shown that Ge doping induces bonding transformation from C in sp 3 to C in the sp 2 hybridized state. [ 20 ] Moreover, the GeC bonds dominate the GeGe and GeO ones in the DLC:Ge films. It was concluded that low cytotoxicity in DLC films with low Ge content could be shielded by the capping C film formed on the top surface of the sample as the Ge doping level is low and due to the mixture of Ge oxide and C species at the surface when the Ge content is higher.…”