Dr. Alexander Oleinick #2 @ FLOGEN SIPS 2022 Yoshikawa Intl. Symposium on Oxidative Stress

FLOGEN SIPS 2022: Yoshikawa International Symposium on Oxidative Stress for Sustainable Development of Human Beings (2nd international Symposium)

Presenter:
Dr. Alexander Oleinick, CNRS, Paris, France

Title:
Modelling detection of key biomolecules with enzymatic electrodes: Diffusion towards randomly distributed active sites

Abstract
Monitoring of key biomolecules and/or oxidative stress at cellular or sub-cellular levels by means of electrochemistry requires electrodes with good selectivity and sensitivity. These both characteristics often achieved by employing enzymatic electrodes. At these electrodes the enzymes are generally dispersed within a polymer layer covering electrode surface, where product(s) of the enzymatic conversion are detected. Rationalization of the experimental data imply understanding mass transport towards an enzymatic electrode which is a complicated process due to random distribution of the enzymes along the electrode surface. This process can be considered through the framework of random arrays, that is a set of active sites distributed randomly, which is also useful for description of many practical micro- and nanoscale systems [1]. As shown previously these systems can be efficiently addressed theoretically by using Voronoi diagrams [1, 2] which allows facile tessellation of the system into the unit cells around each active sites. The overall current flowing in the system can then be evaluated by modelling diffusion-reaction processes inside every unit cell and summing the contributions from individual active sites. Although this approach is tempting by its simplicity and efficiency [1] one should bear in mind that Voronoi diagram representing the unit cells by polygonal prisms remains approximation and as each approximation remains valid only under certain conditions. We have shown [3] that even for the case of diffusion limited electron transfer (ET) the actual shapes of the unit cells are more complicated and depend on the local configuration of the neighbouring active sites. This was exemplified on the small patches of the random arrays with band-like and disk-like active sites via simulations and analytical derivations. Importantly, by comparing the total and individual electrode currents obtained by employing Voronoi tessellation and simulation of the system without any approximations we found that the former are reproduced with a good accuracy while the latter are evaluated with a much larger relative error [3], thus demonstrating the limits of Voronoi tessellation for representation of such systems. Moreover, diffusion interaction between the neighbouring sites compensate the differences in unit cell sizes leading to a more uniform unit cell sizes then predicted by Voronoi tessellation [4]. This, in particular explains why the early theory of random arrays using uniform representation of the system were quantitatively successful [5].

References:

[1] O. Sliusarenko, A. Oleinick, I. Svir, C. Amatore. J. Electrochem. Soc. 167, 2020, 013530.

[2] T. J. Davies and R. G. Compton. J. Electroanal. Chem. 585, 2005, 63.

[3] G. Pireddu, I. Svir, C. Amatore, A. Oleinick, ChemElectroChem 8, 2021, 2413.

[4] G. Pireddu, I. Svir, C. Amatore, A. Oleinick, Electrochim. Acta 365, 2021, 137338.

[5] C. Amatore, J.-M. Savéant, D. Tessier, J. Electroanal. Chem. 147, 1983, 39.