Simple direct formation of self-assembled N-heterocyclic carbene monolayers on gold and their application in biosensing

Abstract

The formation of organic films on gold employing N-heterocyclic carbenes (NHCs) has been previously shown to be a useful strategy for generating stable organic films. However, NHCs or NHC precursors typically require inert atmosphere and harsh conditions for their generation and use. Herein we describe the use of benzimidazolium hydrogen carbonates as bench stable solid precursors for the preparation of NHC films in solution or by vapour-phase deposition from the solid state. The ability to prepare these films by vapour-phase deposition permitted the analysis of the films by a variety of surface science techniques, resulting in the first measurement of NHC desorption energy (158±10 kJ mol−1) and confirmation that the NHC sits upright on the surface. The use of these films in surface plasmon resonance-type biosensing is described, where they provide specific advantages versus traditional thiol-based films.

N‐Heterocyclic Carbene Self‐assembled Monolayers on Copper and Gold: Dramatic Effect of Wingtip Groups on Binding, Orientation and Assembly

“…NHC 3 must, therefore, adopt an upright geometry. This is consistent with the DFT optimized geometry (Figure c), and analogous to results obtained from NHC 3 on Au(111) …”

“…Coincident desorptions of H 2 , HCN, and C 3 H 5 + (assigned to isopropyl groups) were also detected (Figure S3), suggesting that NHC 3 desorbs intact from Cu(111). A Redhead analysis yields a desorption energy of 152±10 kJmol −1 ; indistinguishable within error from the reported value of 158±10 kJmol −1 on Au(111) . DFT analysis of a single NHC 3 species on a Cu(111) slab predicts a binding energy higher than that observed on Au (182.6 kJmol −1 (see SI)).…”

“…Seminal work by Siemeling and Johnson showed that NHCs bind to planar Au surfaces. Crudden and Horton demonstrated that NHCs form clean, well‐ordered monolayers with exceptionally high stability, surviving treatment with boiling organic solvent, acid, base, oxidant, and high temperatures . These conditions would destroy typical thiol‐based SAMs .…”

Flexible NO2‐Functionalized N‐Heterocyclic Carbene Monolayers on Au (111) Surface

“…Chemical derivatization of the NHCs′ side groups allows the formation of functional NHC‐based SAMs, which can be utilized as biosensors or as local chemical probes . Considering that the anchoring geometry of NHCs is directly controlled by the steric properties of their side groups, it is expected that chemical transformations that change the steric properties of the side groups will influence the NHCs anchoring geometry, thus providing a new route for the formation of flexible SAMs (Scheme , bottom panel).…”

Multidentate Anchors for Surface Functionalization

“…Recent works by Crudden and co‐workers demonstrate that NHCs are excellent ligands for the functionalization of metal electrodes and the resulting gold/NHCs surfaces exhibit much higher stability with respect to the conventional gold/thiolate surface . Stimulated by these results, a flexible tripodal NHC ligand 7 was recently reported by Wen and Chang, which was used to modify palladium electrode (Figure ) .…”