Fig. 1

a Crystal structure of LLO monomer (pdb:4CDB) highlighting the acidic triad and H311 amino acid residue; b scheme of the surface functionalization of Au-NP; c In-vitro calcein release experiments in the presence of increasing amounts of His-LLO H311A at pH 5, 6, 7, and 8 at 37 °C; d In-vitro binding and release of His-LLO H311A to/from Au-NPs. The supernatant was separated from the Au-NPs by centrifugation, showing the unbound excess of LLO H311A at pH 8 (lane 1), loosely bound His-LLO H311A fraction washed with sodium phosphate buffer at pH 8 (lane 2), and the specifically bound Ni-NTA-bound His-LLO H311A fraction eluted with sodium phosphate buffer at pH 5 (lane 3). His-LLO H311A was visualized by western blotting with monoclonal anti-histidine antibody