Molecular simulations of lysozyme adsorption on an electrically responsive mixed self-assembled monolayer

Abstract

Lysozyme adsorption on electrically responsive carboxyl/hydroxyl (SC10COOH/SC3OH) self-assembled monolayer (SAM) was investigated by molecular simulation. Results show that applied positive electric fields help to increase the surface hydrophilicity by aligning the chains parallel to the surface normal and exposing their carboxyl groups, whereas applied negative electric fields increase the surface hydrophobicity by bending the SC10COOH chains to expose their alkyl moieties. Accordingly, lysozyme behavior on the SAM was affected. Protein-surface interactions are significantly weakened by a strong negative electric field because of the decreased electrostatic interactions. However, the applied positive electric fields do not strengthen the protein-surface interactions probably because the hydrogen bonds formed within the surface chains, the binding of water molecules to form a water layer and the competitive adsorption from counterions can all decrease the interactions of the SAM with lysozyme. Adsorbed orientations of lysozyme could be regulated among “back-on”, “bottom-leaning” and “side-on” by applying a strong positive electric field or negative electric fields. Analysis of the conformational changes of lysozyme reveals that there is no direct relation between the protein deformation and the strength or direction of electric fields. This work may help to design and fabricate efficient electrically responsive surface in experiments for biotechnological applications.