Smart Switchable Biological Surfaces for On-Demand Biosensing

Abstract

Advances in biology research and clinical diagnosis require new biological inspired tools and technology platforms to measure, understand and control biological systems.1 Surface confined self-assembled monolayers (SAMs) of electro-switchable peptides have the capacity to regulate biomolecular interactions in response to an applied electrical potential.2-4 This study aims to understand the organization of charged peptides together with nanobody5 molecules (NbVCAM1) on a gold surface, in order to devise switchable surfaces with the capability to control the activity of NbVCAM1 binding to the human vascular cell adhesion hVCAM1, a molecule that attracts inflammatory cells, having an important role in the initiation of atherosclerosis.6-8 Contact Angle, Ellipsometry and X-ray Photon Spectroscopy (XPS) techniques have been used to characterize the surfaces with SAMs of charged peptides, namely, oligolysines, Cys-Lys(ε-Lys)4 (C5K) or Cys-Lys(ε-Lys)7 (C8K) on gold, individually or in the presence of the support molecule triethylene glycol mono-11-mercaptoundecyl ether (TEG11) and the NbVCAM1 nanobody. Results on mixed SAMs of C5K:TEG11 and C8K:TEG11 indicated the solution ratio of 40:1 as the optimal candidate for the switching studies. XPS results showed that the actual surface ratios are 1:(3±0.4) for C5K:TEG11 and 1:(3±0.2) for C8K:TEG11. Further characterization has been performed by Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) to demonstrate the covalent binding of the NbVCAM1 nanobody to the gold surface. Electrochemistry Surface Plasmon Resonance (E-SPR) is being used to study the switching capabilities of these SAMs that include the NbVCAM1 at the surface. SPR results confirm the binding of hVCAM1 to the surface-tethered NbVCAM1 nanobody under open circuit (OC) conditions, with an electrical potential being able to switch the binding capabilities.