Comparison between FTIR and XPS characterization of amino acid glycine adsorption onto diamond-like carbon (DLC) and silicon doped DLC

Abstract

Diamond-like carbon (DLC) coatings are extremely useful for creating biocompatible surfaces on medical implants. DLC and silicon doped DLC synthesized on silicon wafer substrate by using plasma enhanced chemical vapour deposition (PECVD). The adsorption of glycine onto prepared samples has been investigated with a range of surface analysis techniques. The effects of surface morphology on the interaction of glycine with doped and undoped DLC films have been investigated. The chemical composition of the surface before and after adsorption was analyzed using X-ray photoelectron spectroscopy (XPS). For undoped DLC the spectra show peaks at 285eV (C 1s), 532eV (O 1s) and in the case of Si-doped DLC films a band at ∼100eV (Si 2p) is observed. Following exposure to solutions containing (0.001M) glycine, for undoped DLC the peaks at ∼285.0, ∼399 and ∼532eV reduced in intensity and for Si-DLC samples, the peak at 100eV was reduced. This gives an indication of the quantitative change in the amounts of C, N and O on the surfaces. From Fourier transform infrared (FTIR) spectrum, the peaks occur the following functional groups were assigned as COOR, COŌ, NH3+, NH2, CH and CCN. Both XPS and FTIR spectroscopy confirm that glycine was bound onto the surfaces of the DLC and Si-DLC films via interaction of ionized carboxyl groups and the amino group did not play a significant role in the adsorption of glycine. These results from SE show that an adsorbed layer of glycine is higher at low silicon doping whilst increased doping levels led to a reduced adsorption compared to undoped DLC. Therefore doping of DLC may provide an approach to controlling the protein adsorption.