Self-Assembled Monolayers of N-Heterocyclic Carbenes on Gold and Silver: Applications in Biosensing

Abstract

Modification of metallic surfaces using thiol-based self-assembled monolayers (SAMs) has been explored in the literature in the past three decades; silver surfaces less explored than gold. This technology has promise in many surface-based applications, specifically in micro electronics, sensors that use the surface plasmon resonance (SPR) phenomenon, and in catalysis. Unfortunately, the reactivity of silver towards sulfur means that thiol-based monolayers can form sulfide layers at the surface interface in atmospheric conditions making silver a troublesome metal for surface applications. If sulfidization could be overcome, a robust SAM on silver might prove to be an effective tool for SPR, as silver is more sensitive to surface plasmon effects than gold, the current standard. Our group has described a series of N-heterocyclic carbenes (NHC) which form SAMs on gold. As the carbene is attached to the surface via a metal-carbon bond, the problem of sulfidization may be overcome. Here, I describe the synthesis of a peptide for the application of heavy metal detection with the use of an NHC on a gold surface as well as the deposition and functionalization of silver surfaces with a series of NHCs, which might serve as appropriate candidates for use in an SPR sensor. X-ray photoelectron spectroscopy (XPS) data show the NHCs chemisorb intact on the surface, and the stability of the films to oxidation are explored under a range of conditions.