Ultraflat nickel substrates for scanning probe microscopy of polyhistidine-tagged proteins

A novel approach to the preparation of ultraflat Ni substrates suitable to scanning probe microscopy imaging of immobilized polyhistidine-tagged proteins has been devised. Exploiting freshly cleaved mica, Ni thermal evaporation followed by thermal annealing in vacuum, and the template stripping method, we have obtained Ni substrates with a rms roughness as low as 0.12 nm, which bind readily polyhistidine-tagged proteins, enabling molecular resolution imaging of isolated molecules as well as of molecular submonolayers. Protein sample exposure to imidazole causes removal of the adsorbates, confirming the involvement of the polyhistidine tail in protein surface immobilization.