Selectivity presents a crucial challenge in direct electrochemical sensing. One example is schizophrenia treatment monitoring of the redox-active antipsychotic clozapine. To accurately assess efficacy, differentiation from its metabolite norclozapine-similar in structure and redox potential-is critical. Here, the authors leverage biomaterials integration to study, and effect changes in, diffusion and electron transfer kinetics of these compounds. Specifically, the authors employ a catechol-modified chitosan film, which the authors have previously presented as the first electrochemical detection mechanism capable of quantifying clozapine directly in clinical serum. A key finding in our present work is differing dynamics between clozapine and norclozapine once the authors interface the electrodes with chitosan-based biomaterial films. These additional dimensions of redox information can thus enable selective sensing of largely analogous small molecules.