|M.Sc Student||Brod Elad|
|Subject||Electrical Control over Antibody Antigen Interaction|
|Department||Department of Physics||Supervisor||Professor Uri Sivan|
|Full Thesis text|
In the present work we show that the binding of an antibody to its antigen can be controlled electrically in a reversible manner. The antibody-antigen interaction is monitored by an electrochemical Surface Plasmon Resonance (SPR) instrument. The SPR gold chip is divided to three parts serving as working, counter and reference electrodes. The antigen is immobilized on the working electrode using a thiol group while the antibody is injected in solution. After binding, application of a bias more negative than -0.5 Volt vs. reference electrode causes rapid detachment of the antibody molecules from the antigens. Removal of the applied voltage restores the antigen ability to bind antibody molecules. The reported effect is pronounced in solutions having low buffer capacity. The mechanism underlying the reported phenomenon is traced to deprotonation of positively charged amino acids, particularly Lysine, by hydroxyl ions generated at the electrode-solution interface, by the hydrogen evolution reaction. Hydroxyl ions recombine with solvated protons thereby raising the local pH in the vicinity of the interacting molecules. The pH increase ,in turn, causes deprotonation of the Lysine residues which are believed to be responsible for much of the electrostatic interaction between the antibody-antigen pair. Upon deprotonation, the interaction between the molecules sharply diminishes. When the bias is removed, hydrogen production halts, leading to reprotonation of Lysine residues and restoration of the electrostatic interaction. This finding is supported by corroboration of electrochemical and dissociation data, studies of the effect as a function of pH and bias, and mapping the effect of buffering capacity on the observed phenomenon. The finding of this work facilitates exquisite control over one of the main interactions responsible for biomolecular recognition, namely, the attraction between positively and negatively charged residues. Potential applications to diagnostics and sensing are briefly discussed.