Operation Mechanism of n‐Type Organic Electronic Metabolite Sensors

Abstract

The integration of n‐type (electron‐transporting) polymers with oxidase enzymes has allowed building high‐performance organic electrochemical transistor (OECT) based metabolite sensors. Yet, the operation mechanism of these devices is poorly understood. Here, the process is investigated for the conversion of metabolite oxidation to electrical current in an n‐type organic electrochemical transistor (n‐OECT). By monitoring oxygen (O2), hydrogen peroxide, and pH changes in the electrolyte as well as the potential of each electrical contact of the n‐OECT during glucose detection, light is shed on the physical phenomena occurring at the polymer‐enzyme interface. It is shown that the n‐type film performs O2 reduction reaction in its doped state and that the n‐OECT characteristics are sensitive to O2. A correlation is found between the consumption of electrolyte‐dissolved O2 and the generation of n‐OECT current during the metabolite oxidation. The results demonstrate how the sensitivity of a polymer to O2, species known to deteriorate the performance of many semiconductor devices, becomes a feature to exploit in sensor applications. The importance of in operando analysis of the electrolyte composition and the terminal potentials is highlighted for understanding the operation mechanism of bioelectronic devices and for sensor design and materials development.

Origins of hydrogen peroxide selectivity during oxygen reduction on organic mixed ionic-electronic conducting polymers

“…Prior to all electrochemical experiments, p(NDI-T2 P75) was purified to remove residual Pd contamination from polymer synthesis (Figure S1, Table S1), resulting in low Pd concentrations of 2 -5 ppm. While it has been reported that a polymer much like p(NDI-T2 P75) primarily produces H2O upon reducing O2 in a 4-electron reaction, 46 we demonstrate that the removal of residual Pd is crucial for evaluating the performance of the polymer itself without Pd contributing to ORR performance. Higher concentrations of Pd shift the measured halfwave voltage, E1/2, for oxygen reduction and change whether H2O or H2O2 is the majority product (Figure S2).…”

Interactions of Catalytic Enzymes with n-Type Polymers for High-Performance Metabolite Sensors

“…Since the ntype OECT current is inherently sensitive to changes in the O 2 content of its environment, the GOx reaction with glucose led to an immediate increase in I D . 25 Although all polymers are sensitive to O 2 and all polymers except P-ZI operated sufficiently as an OECT, only P-90, P-100, and P-100B OECTs showed a current response to the oxidation of glucose (Figure 2a). Figure 2b compares the glucose sensitivity of these devices (NR OECT ).…”

“…As glucose was oxidized by GOx, the O 2 amount in the electrolyte decreased as it was used for GOx regeneration. Since the n-type OECT current is inherently sensitive to changes in the O 2 content of its environment, the GOx reaction with glucose led to an immediate increase in I D . Although all polymers are sensitive to O 2 and all polymers except P-ZI operated sufficiently as an OECT, only P-90, P-100, and P-100B OECTs showed a current response to the oxidation of glucose (Figure a).…”

“…22 The sensor operation relied mainly on the O 2 sensitivity of the n-type film, where its conductivity increased as the O 2 amount decreased in the solution when glucose bound to GOx. 25 The sensor results and spectroscopy analysis point to an intimate interface between the polymer film and the enzyme which allows the OECT to detect minute changes in O 2 concentrations and, hence, enzyme activity at its surface. Despite the promise of this platform, it has not been clear why this particular polymer led to such high-performance sensors.…”

“…The n-type polymer/GOx film also functioned as the anode of a glucose fuel cell, extracting enough power from biological media to drive small electronics . The sensor operation relied mainly on the O 2 sensitivity of the n-type film, where its conductivity increased as the O 2 amount decreased in the solution when glucose bound to GOx . The sensor results and spectroscopy analysis point to an intimate interface between the polymer film and the enzyme which allows the OECT to detect minute changes in O 2 concentrations and, hence, enzyme activity at its surface.…”