Electrochemical amplification using selective self-assembled alkanethiolate monolayers on gold: A predictive mechanistic model

Electroanalytical current measurements are often challenged by sensitivity limitations. For applications requiring enhanced sensitivity, an electrochemical signal can be amplified using a homogeneous electron-transfer reaction. This report describes the mechanistic details of a redox recycling amplification system based on monomolecular films of alkanethiolates on gold. These interfaces can be prepared to exhibit facile oxidation of functionalized ferrocenes (FcX), while markedly suppressing the electrolysis of ferrocyanide. Thus, ferrocyanide can be used as a sacrificial electron donor to electrogenerated FcX+, providing a pathway for a notable improvement of the detection limit for FcX. Electrochemical methods are used to demonstrate, evaluate, and quantify the amplification mechanism. The dependence of amplification on the rates of heterogeneous and homogeneous electron transfer is qualitatively delineated by digital simulations of cyclic voltammetric (CV) curves. This work also develops a mathematical model for prediction of the maximum amplification observed via CV that is tested by comparisons to experimental data. These results are then used as a guide in performance assessments, which yield an optimal amplification of 225 and a limit of detection of ∼500 nM.