Membrane-Free, Selective Ion Sensing by Combining Organic Electrochemical Transistors and Impedance Analysis of Ionic Diffusion

Abstract

Precise monitoring of changes in ion concentration in electrolytic environments is of growing interest in multiple fields, such as bioelectronics, food packaging, agricultural sensing, and control of industrial chemical processes. However, combining sensitivity, ion-selectivity, and cost reduction has been proven to be a difficult task. In this work, we use an organic mixed ionic–electronic conductor [poly­(3,4-ethlyenedioxythiophene) doped with poly­(styrene sulfonate), PEDOT:PSS] to realize a sensor showing good selectivity and sensitivity to alkali ions without employing ion-selective membranes. We achieve this by combining a straightforward impedance analysis and static current–voltage measurement of an organic electrochemical transistor. We show that, after a calibration stage, the composition of unknown solutions can be determined. The ease of fabrication of this system, combined with the proposed measurement method and the potential biocompatibility of the organic semiconductor, makes such a sensor suitable for applications in biological environments, such as within the body or soil.

Ion-Selective Organic Electrochemical Transistor Sensors Using Molecularly Imprinted Polymers

“…First, to assess the potential contributions of introducing a MIP atop the OECT channel, the performances of both MIP-OECTs and their uncovered counterparts were evaluated. Here, sodium ions (Na + ) were used to gate devices, and they were evaluated at room temperature using 100 mM NaNO 3 , a typical electrolyte concentration for OECTs. − In these measurements, the drain current ( I D ) is tracked when the gate voltage ( V G ) is swept at a constant drain voltage ( V D ). The uncovered OECT exhibited a peak transconductance (evaluated as ∂ I D /∂ V G ) of 3.6 mS (Figure S4a) when the V G was scanned at 6.67 mV s –1 , a reasonable result for PEDOT:PSS OECTs .…”

“…To this end, we demonstrate how a MIP can be incorporated into an OECT to produce species-selective intercalation and gating. Rather than focusing on high electrolyte concentrations (i.e., from 1 mM to 1 M), ,, we turn our attention to lower concentration regimes as many of the aforementioned applications rely on detecting materials at sub-1 mM concentrations. For instance, the United States Environmental Protection Agency recommends levels of nitrate in water not exceed ∼100 μM and levels of many metals (e.g., nickel and iron) remain less than 10 mg L –1 .…”

Thermodynamics of organic electrochemical transistors

“…A few studies put forth the idea, or the necessity, to investigate the metal/electrolyte/polyelectrolyte system on a thermodynamic basis, therefore rendering the purely electrostatic picture insufficient 23 . For example, thermodynamic notions (Nernst law and Boltzmann statistics) need to be integrated into the model in order to describe the concentration-dependent threshold voltage exploited in OECTs for ion sensing 7 , 24 . Romele et al 25 investigated the transport properties of OMIECs and observed that the channel resistance and capacitance are independent of the electrolyte concentration, in contrast to the double-layer theory.…”

Bio-Compatible Sensor for Middle Ear Pressure Monitoring on a Bio-Degradable Substrate

“…Bio-compatible electronic devices are a rapidly developing field of technology that may not only provide a way to achieve green, environmental-friendly electronics (Irimia-Vladu, 2014) but also have the potential to revolutionize the world of medical therapies. In particular, small, flexible, and versatile sensors [e.g., for ion (Tseng et al, 2021), chemical, electrical sensing (Bai et al, 2019;Keene et al, 2020), etc. ], which can be integrated in the human body, enable completely new treatment and monitoring methods (Lee et al, 2015;Minev et al, 2015;Someya et al, 2016;Torricelli et al, 2021).…”