Electrochemistry of Redox‐Active Guest Molecules at β‐Cyclodextrin‐Functionalized Silicon Electrodes

Abstract Functionalization of silicon‐based sensing devices with self‐assembled receptor monolayers offers flexibility and specificity towards the requested analyte as well as the possibility of sensor reuse. As electrical sensor performance is determined by electron transfer, we functionalized H‐terminated silicon substrates with β‐cyclodextrin (β‐CD) molecules to investigate the electronic coupling between these host monolayers and the substrate. A trivalent (one ferrocene and two adamantyl moieties), redox‐active guest was bound to the β‐CD surface with a coverage of about 10−11 mol/cm2 and an overall binding constant of 1.5⋅109 M−1. This packing density of the host monolayers on silicon is lower than that for similar β‐CD monolayers on gold. The monolayers were comparable on low‐doped p‐type and highly doped p++ substrates regarding their packing density and the extent of oxide formation. Nonetheless, the electron transfer was more favorable on p++ substrates, as shown by the lower values of the peak splitting and peak widths in the cyclic voltammograms. These results show that the electron‐transfer rate on the host monolayers is not only determined by the composition of the monolayer, but also by the doping level of the substrate.