Chemical Sensing with Chemically Modified Electrodes that Mimic Gating at Biomembranes Incorporating Ion-Channel Receptors

Selective binding of electroinactive analytes to electrodes that are chemically modified with receptors can be used to control heterogeneous redox reactions of electroactive species. The latter are in this context often called markers because their use allows the indirect determination of the electroinactive analytes with the inherent possibility for chemical signal amplification. Two different approaches can be distinguished. To structurally mimic natural ion-channel proteins, electrodes are modified with artificial receptors having intramolecular channels that can be blocked by formation of inclusion complexes with the analyte. In more abstract analogy to the working principle of ion-channel proteins, binding of usually charged analytes to receptors without intramolecular channels is used to control redox reactions of the marker species on the basis of electrostatic interactions, and, occasionally, of steric repulsion. The versatility and general characteristics of this type of chemically gated sensors are discussed, and specific examples from recent studies are presented.