Modulating the Faradic Operation of All-Printed Organic Electrochemical Transistors by Facile in Situ Modification of the Gate Electrode

Abstract

Organic electrochemical transistors (OECTs) operated in the faradic regime were shown as outperforming transducers of bioelectric signals in vitro and in vivo. Fabrication by additive manufacturing techniques fosters OECTs as ideal candidates for point-of-care applications, as well as imposes limitations on the choice of materials and their processing conditions. Here, we address the question of how the response of fully printed OECTs depends on gate electrode material. Toward this end, we investigate the redox processes underlying the operation of OECTs under faradic regime, to show OECTs with carbon gate (C-gate) that exhibit no current modulation gate voltages <1.2 V. This is a hallmark that no interference with the faradic operation of the device enabled by redox processes occurs when operating C-gate OECTs in the low-voltage range as label-free biosensors for the detection of electroactive (bio)­molecules. To tune the faradic response of the device, we electrodeposited Au on the carbon gate (Au–C-gate), obtaining a device that operates at lower gate voltage values than C-gate OECT. The presence of gold on the gate allowed further modification of the electrical performances by functionalization of the Au–C-gate with different self-assembled monolayers by fast potential-pulse-assisted method. Moreover, we show that the presence in the electrolyte solution of an external redox probe can be used to drive the faradic response of both C- and Au–C-gate OECTs, impacting on the gate potential window that yields effective drain current modulation. The results presented here suggest possible new strategies for controlling the faradic operation regime of OECTs sensors by chemical modification of the gate surface.

Interfacing aptamers, nanoparticles and graphene in a hierarchical structure for highly selective detection of biomolecules in OECT devices

“…2 A)) with a profile quite different from the nearly-linear trend of the bare PMLG gate electrode (red line). This enhancement, already reported by Sensi et al for carbon based gate electrodes decorated by AuNPs 36 , reveals an electron transfer process between AuNPs and the graphene electrode 37 and is demonstrated by the appearance of a well-defined peak at 0.1 V in the gate current profile (Fig. 2 B, black curve), as well as by a step-like trend of Ids between 0.2 and 0.6 V (Fig.…”

Multifunctional Operation of an Organic Device with Three-Dimensional Architecture

“…The higher applied V gs values fall in the range at which water hydrolysis takes place (the reaction has a standard potential of −1.23 V), undesirable for bio-applications due to the arising of faradaic currents. However, in our case the device shows a transconductance peak value and related ion-to-electron transduction effectiveness by the PEDOT:PSS transducer below the electrochemical window of water (i.e., at V gs = 0.6 V), hence the device operation is compatible with biological ambient applications even without recurring to a specific gate electrode functionalization, as reported in the case of different gate materials [27]. Low V gs values in correspondence with the transconductance peak have also been reported in the case of all-PEDOT:PSS 2D devices.…”

Flexible Printed Organic Electrochemical Transistors for the Detection of Uric Acid in Artificial Wound Exudate

“…In order to enhance gate modulation capability and catalyze the oxidation of hydrogen peroxide within the 0-1 V potential range, a Pt layer was electrodeposited on the gate [50] ( Figure S1A, Supporting Information). In 50 × 10 -3 m phosphate buffer saline (PBS), the carbon gate exhibits no oxidation processes below 1 V, [44] also in the presence of the Pt layer ( Figure S1B, Supporting Information). Both the transfer www.advmatinterfaces.de characteristics (I DS versus V GS at constant V DS ) and the output curves (I DS versus V DS at constant V GS ) show that, at variance with what can be achieved with the C gate, the C/Pt gate can lead to drain current modulation as expected from a depletionmode OECT.…”

“…Conversely, here, in the presence of UA and Uricase, the OECT works in the Faradic regime: H 2 O 2 oxidation takes place at the gate and might lead to concomitant reduction of PEDOT, with accompanying penetration of cations in the semiconductor channel, resulting in a decrease of the drain current. [38,44] Alternatively, the working principle underlying the operation of OECTs as enzyme-based www.advmatinterfaces.de biosensors has been previously described [64] in terms of increased electrolyte potential caused by an increase in H 2 O 2 concentration through the Nernst equation, resulting in a more positive effective gate potential, which impacts on the cation drift in the porous PEDOT:PSS channel and thus decreases the drain current. [65][66][67] To mimic the complex environment of an infected wound, we performed measurements in an aqueous solution serving as artificial wound exudate, [14] the composition of which can be found in the Experimental Section.…”

“…Amorphous carbon is a suitable material for the gate electrode since it is cost effective, its printing process is well established, and it can be employed as a substrate for further modification via electrochemical deposition of metals, such as platinum, [43] or gold. [44] Previous works have demonstrated the possibility of coupling transistors operating in liquid (in particular graphene-FET) to enzymes, to obtain biosensors selective for neurotransmitters, [45][46][47] drugs, [46] or biomarkers. [48,49] Our approach for UA detection is based on the catalytic activity of the enzyme Urate oxidase (UOx, also known as Uricase) that ultimately produces hydrogen peroxide.…”