Novel insights into L-cysteine adsorption on transition metal doped graphene: Influences of the dopant and the vacancy

Exploring potential applications of transition metal (TM) doped graphene in biomolecular adsorption is of fundamental relevance to the area of nanobiotechnology. Herein, we investigated L-cysteine adsorption on first-row transition metal (Sc–Zn) doped single-vacancy and double-vacancy graphenes (MSVs and MDVs) using density functional theory calculations. Three types of upright adsorption configurations, via unprotonated S-end, O-end and N-end functional groups, were considered. All the MSVs chemically adsorb L-cysteine with no regular variation tendency. MDVs show decreasing chemisorption from V to Co, followed by emergence of physisorption from Ni to Zn. L-Cysteine adsorption on MDVs is weaker than that on MSVs, starting from Mn to Zn. Both the TM dopant and the vacancy type contribute to adsorption tendency. In addition, site-specific chemisorption is revealed. The magnetic behaviour of the adsystems is also interesting. In particular, FeSV, ZnSV and NiSV become magnetic after all three end-type adductions. L-Cysteine adsorption induced distribution of the increasing number of 3d electrons and TM–C interactions could account for the magnetism mechanism. Interesting magnetization patterns of MSVs and MDVs occur in most magnetic chemisorbed systems, exhibiting different mirror symmetries. This study could facilitate applications of TM doped graphenes in biosensing, biomolecule immobilization, magnetic bioseparation and other fields in bionanotechnology.