Organic Electrochemical Transistors as Versatile Analytical Potentiometric Sensors.

Isacco Gualandi,Erika Scavetta,Federica Mariani,Beatrice Fraboni,Domenica Tonelli,Marta Tessarolo

doi:10.3389/fbioe.2019.00354

Abstract

Potentiometric transduction is an important tool of analytical chemistry to record chemical signals, but some constraints in the miniaturization and low-cost fabrication of the reference electrode are a bottleneck in the realization of more-advanced devices such as wearable and lab-on-a-chip sensors. Here, an organic electrochemical transistor (OECT) has been designed with an alternative architecture that allows to record the potentiometric signals of gate electrodes, which have been chemically modified to obtain Ag/AgnX interfaces (X = Cl−, Br−, I−, and S2−), without the use of a reference electrode. When the OECT is immersed in a sample solution, it reaches an equilibrium state, because PEDOT:PSS exchanges charges with the electrolyte until its Fermi level is aligned to the one of Ag/AgnX. The latter is controlled by Xn− concentration in the solution. As a consequence, in this spontaneous process, the conductivity of PEDOT:PSS changes with the electrochemical potential of the modified gate electrode without any external bias. The sensor works by applying only a fixed drain current or drain voltage and thus the OECT sensor operates with just two terminals. It is also demonstrated that, in this configuration, gate potential values extracted from the drain current are in good agreement with the ones measured with respect to a reference electrode being perfectly correlated (linear slope equal to 1.00 ± 0.03). In the case of the sulfide anion, the OECT performance overcomes the limit represented by the Nernst equation, with a sensitivity of 0.52 V decade−1. The presented results suggest that OECTs could be a viable option to fabricate advanced sensors based on potentiometric transduction.

Highlights

Potentiometric sensors are important tools in analytical chemistry to quantify the concentration of chemical species in solution, some constraints hinder their low cost-fabrication, miniaturization, and their reliable use in some emerging fields such as wearable and lab-on-chip technologies (Sophocleous and Atkinson, 2017; Parrilla et al, 2019)
The transistors were fabricated with a geometry that is ideally similar to the one proposed by Wrighton’s group (Kittlesen et al, 1984; Paul et al, 1985) in the first articles describing organic electrochemical transistor (OECT), because the gate electrode is in electrical contact with the conductive polymer present in the channel (Figure 2A)
The results reported in this paper show that an OECT can measure an electrochemical potential and it can be used to acquire potentiometric signals

Summary

Introduction

Potentiometric sensors are important tools in analytical chemistry to quantify the concentration of chemical species in solution, some constraints hinder their low cost-fabrication, miniaturization, and their reliable use in some emerging fields such as wearable and lab-on-chip technologies (Sophocleous and Atkinson, 2017; Parrilla et al, 2019). OECTs as Potentiometric Sensors of the species that is quantified during the analysis, as ruled by Nernst equation. Among these sensors, the glass electrode for pH measurement has remained the gold standard for more than a century (Haber and Klemensiewicz, 1909; Skoog et al, 1992; Harris, 2016). Potentiometric measurements can be applied to very diverse fields in analytical chemistry due to their simplicity and fast response time, even if their use is limited by the difficulty in the fabrication of membranes able to selectively detect the target analyte

Methods

Results

Conclusion