Ni(II)-modified solid substrates as a platform to adsorb His-tag proteins

Abstract

This work investigated a simple and versatile modification to a solid substrate to develop electrochemical bio-recognition platforms based on bio-affinity interactions between histidine (His)-tagged proteins and Ni(II) surface sites. Carboxylate (COO)-functionalized substrates were prepared in multiple steps, initiated with an amino-terminated self-assembled monolayer (SAM) on polycrystalline gold. Surface enhanced Raman spectroscopy (SERS), quartz crystal microbalance with dissipation monitoring (QCM-D) and contact angle measurements were used to follow the modification process. Upon completion of the modification process, the surface COO–Ni(II) chelate complex and the coordination mode used to bind the His-tag proteins were characterized by X-ray absorption near-edge spectroscopy (XANES). Finally, the electrochemical stability and response of the modified substrates were evaluated. The versatility of the modification process was verified using silica as the substrate. QCM-D and SERS results indicated that two types of films were formed: a COO-terminated SAM, which resulted from the reduction of previously incorporated surface aldehyde groups, and a physically adsorbed polymeric glutaraldehyde film, which was produced in the alkaline medium. XANES spectral features indicated that COO–Ni(II) formed a non-distorted octahedral complex on the substrate. The electrochemical stability and response towards a redox mediator of the COO–Ni(II)-terminated SAM indicated that this platform could be easily coupled to an electrochemical method to detect bio-recognition events.