Membrane‐Free Detection of Metal Cations with an Organic Electrochemical Transistor

Abstract

Alkali-metal ions are the messengers of all living cells, governing a cascade of physiological processes through the action of ion channels. Sodium (Na +) and potassium (K +) are the two alkali metals found in human blood serum. Devices that can monitor, in real time, the concentrations of these cations in aqueous media are in demand not only for the study of cellular machinery and dysfunctions, but also to detect conditions in the human body that lead to electrolyte imbalance, such as hypernatremia, hyperkalemia or dehydration. In this work, we developed conducting polymers that respond rapidly and selectively to varying concentrations of Na + and K + in aqueous media. These polymer films, bearing crown-ether-functionalized thiophene units specific to either Na + or K + ions, generated an electrical output proportional to the cation type and concentration. Using electropolymerization, we deposited the ion-selective polymers onto microscale gold patterns and integrated them as the gate electrode of an organic electrochemical transistor (OECT). The OECT current changed with respect to the concentration of the ion to which the polymer electrode was selective. Designed as a single, miniaturized chip, the OECT enabled the selective detection of Na + and K + within a physiologically relevant range. These electrochemical ion sensors required neither a complex functionalization route to fabricate, nor ion-selective membranes or a reference electrode to operate. Such customized conducting polymers have the potential to surpass existing technologies for the detection of alkali-metal ions in aqueous media and for further development into implantable medical devices.

In Situ Electrochemical Synthesis of a Conducting Polymer Composite for Multimetabolite Sensing

“…The OECT is an electrolyte gated transistor consisting of a (semi)conducting polymer film deposited between two metal electrodes (the source and the drain), and a gate electrode that is physically separated from the channel through an electrolyte . Because of the high gain of these devices resulting from the volumetric charging of the CP channel upon application of a gate voltage, the OECT configuration has been explored to sense a variety of biologically relevant species such as metabolites, ions, neurotransmitters and proteins such as Immunoglobulin G and amyloid beta . Ever since this first report of the electrodeposited OECT channel, only a recent work has demonstrated that a CP can be electropolymerized within the source and drain electrodes separated by a few tens of micrometers .…”

“…The PEDOT film exhibits a relatively smooth surface, while EDOTOH‐based film surfaces are rougher with a larger area, which is expected to contribute to the high capacitance (compare Figure c with d and e). The dense population of OH groups in the homopolymer pEDOTOH, however, may lead to steric hindrance during bioconjugation, providing a low degree of conformational freedom for biorecognition units . Second, EDOTOH monomer has low solubility in water with aggregates visible to bare eye in the reaction mixture.…”

“…The dense population of OH groups in the homopolymer pEDOTOH, however, may lead to steric hindrance during bioconjugation, providing a low degree of conformational freedom for biorecognition units. [9,28,33,46] Second, EDOTOH monomer has low solubility in water with aggregates visible to bare eye in the reaction mixture. Despite the superior electrochemical performance of pEDOTOH, we thus chose to further work with the copolymer p(EDOT-ran-EDOTOH).…”

Organic Bioelectronics: From Functional Materials to Next‐Generation Devices and Power Sources

“…Two types of crown-ether functionalized EDOT monomers were synthesized and electropolymerized on the microscale gate electrodes of OECTs ( Figure 8B, i). [144] The ring-size of the crownether unit determines which cation, sodium (Na + ) or potassium (K + ), will be captured in the measurement solution. Each metal cation that complexes with a corresponding crown ether unit in the bulk of the porous conducting polymer film electrochemically reduces the film at the gate electrode ( Figure 8B, ii).…”

“…Reproduced with permission. [144] Copyright 2019, Wiley-VCH. C-i) An NDI-T2-based copolymer, P-90, has electrical contact with glucose oxidase drop cast on top of its film.…”