| AVS 63rd International Symposium & Exhibition | |
| Nanometer-scale Science and Technology | Thursday Sessions |
| Session NS+BI-ThA |
| Session: | Applied Nanoscale Microscopy Techniques/Biomaterial Interfaces – New Advances |
| Presenter: | Thomas Winkler, University of Maryland, College Park |
| Authors: | T.E. Winkler, University of Maryland, College Park S.L. Brady, East Carolina University E. Kim, University of Maryland, College Park H. Ben-Yoav, Ben-Gurion University of the Negev, Israel D.L. Kelly, University of Maryland, Baltimore G.F. Payne, University of Maryland, College Park R. Ghodssi, University of Maryland, College Park |
| Correspondent: | Click to Email |
Selectivity presents a crucial challenge in electrochemical sensing. One example is schizophrenia treatment monitoring of the redox-active antipsychotic clozapine (CLZ). To accurately assess efficacy, differentiation from its metabolite N-desmethylclozapine (NDMC) – similar in structure and redox potential – is critical. Here, we leverage biomaterials integration to study, and effect changes in, diffusion and electron transfer kinetics of these compounds. A key finding in our present work is differing dynamics between CLZ and NDMC once we interface the electrodes with chitosan-based biomaterial films. These additional dimensions of redox information can thus enable selective sensing of largely analogous small molecules.
Our study utilizes gold working electrodes either bare, coated with chitosan, or with our previously demonstrated redox cycling system (RCS). In the RCS, electrodeposited chitosan serves as a matrix to immobilize electroactive catechol near the electrode via electrografting. Small redox species diffuse through the film for oxidation at the electrode; the nearby catechol enables subsequent reduction of the analyte, establishing a signal-amplifying redox cycle. We execute cyclic voltammetry at 1m—10V/s sweep rates with CLZ, NDMC, or the model redox couple 1,1′-ferrocenedimethanol (FC).
With bare gold, both CLZ and NDMC exhibit similar (R²=0.99) drastic increases in peak separation even at 0.5V/s, indicating slow electron transfer kinetics, in contrast to FC (Nernstian up to 3V/s). With both chitosan and the RCS we find that similarity broken. For diffusion, the coefficients D reveal two regimes in chitosan: dominance of bulk solution below 10mV/s (values match those from bare gold and theory), and diffusion inside the film becoming limiting at higher scan rates. This is reflected in D decreasing by 1.9× for FC, 17× for CLZ, and 31× for NDMC. The sharp difference between FC and the other larger two suggests a size-restriction phenomenon. The consistently 2× lower D for NDMC over the similarly sized CLZ points to possible electrostatic effects. With the RCS, signal amplification translates into apparent D increases – 9× over bare for FC, 5× for CLZ, and 3× for NMDC. Only at high scan rates does D decrease toward the chitosan-only value as true diffusion asserts dominance.
In conclusion, our results demonstrate the intricate interplay between biomaterials, biomolecules, and electrochemistry. They reveal intriguing distinguishing characteristics of CLZ from both the largely analogous NDMC as well as the model FC. This opens up avenues of utilizing diffusion and kinetics information to enhance selectivity in electrochemical sensing.