Voltammetric analysis subsequent to open‐circuit accumulation was performed with carbon paste electrodes modified with polysiloxane‐immobilized mercaptopropyl groups. By using mercury(II) as a model analyte, it was found that the electrode sensitivity was greatly influenced by the structure of the modifier by means of promoted or restricted mass transfer. Synthetic routes leading to open framework structures containing a large amount of accessible binding sites (i.e., surfactant templated organic‐inorganic mesoporous materials) gave rise to the highest mass transfer kinetics. These results open the door for further development of sensitive and selective sensors.