PEDOT-Polyamine-Based Organic Electrochemical Transistors for Monitoring Protein Binding

Abstract

The fabrication of efficient organic electrochemical transistors (OECTs)-based biosensors requires the design of biocompatible interfaces for the immobilization of biorecognition elements, as well as the development of robust channel materials to enable the transduction of the biochemical event into a reliable electrical signal. In this work, PEDOT-polyamine blends are shown as versatile organic films that can act as both highly conducting channels of the transistors and non-denaturing platforms for the construction of the biomolecular architectures that operate as sensing surfaces. To achieve this goal, we synthesized and characterized films of PEDOT and polyallylamine hydrochloride (PAH) and employed them as conducting channels in the construction of OECTs. Next, we studied the response of the obtained devices to protein adsorption, using glucose oxidase (GOx) as a model system, through two different strategies: The direct electrostatic adsorption of GOx on the PEDOT-PAH film and the specific recognition of the protein by a lectin attached to the surface. Firstly, we used surface plasmon resonance to monitor the adsorption of the proteins and the stability of the assemblies on PEDOT-PAH films. Then, we monitored the same processes with the OECT showing the capability of the device to perform the detection of the protein binding process in real time. In addition, the sensing mechanisms enabling the monitoring of the adsorption process with the OECTs for the two strategies are discussed.

Keywords: PEDOT; conducting polymers; organic electrochemical transistors; protein binding.

Figure 1

(A) Scheme of the synthesis of PEDOT-PAH films by spin coating. (B) Raman spectra of PEDOT (black), PEDOT-PAH 1 (red), PEDOT-PAH 2 (blue), and PEDOT-PAH 3 (green) films deposited on glass substrates. (C) Relative intensity of the Raman peak at 1541 cm⁻¹ to the maximum intensity (Intensity _max), corresponding to the peak at 1431 cm⁻¹, for PEDOT-PAH blends of different compositions. Error bars correspond to SD (n = 4).

Figure 2

(A) Characteristic transfer curve and transconductance as a function of the gate potential for a PEDOT-PAH-based OECT. (B) I_{DS max} and V_{G gm, max} for 30 different OECTs synthesized in the same conditions. Bars represent the mean values, and the error bars are the SD. (C) g_m vs. V_G for seven representative OECTs (arrow indicates decreasing transconductance values corresponding to thinner films). (D) V_{G gm, max} as a function of I_{DS max} for different PEDOT-PAH-based OECTs. (KCl 10 mM + HEPES 1 mM, V_DS = −50 mV).

Figure 3

(A) Reflectivity curves of the PEDOT-PAH substrate before (blue) and after (red) PSS deposition. (B) Real-time change in the SPR signal Δ(θ_min–θ_tir) during the deposition of PSS on a gold substrate modified with PEDOT-PAH under flow conditions. (C) Transfer curves and (D) transconductance values of a PEDOT-PAH OECT in 0.1 M KCl before (blue) and after (red) PSS deposition (E) Real time change in the OECT ΔI_DS% current during PSS adsorption. (F) Scheme of the flow cell employed for the electrochemical measurements.

Figure 4

(A) Real time change in the SPR signal Δ(θ_min–θ_tir) during GOx deposition on a gold substrate modified with PEDOT-PAH under flow conditions. (B) Transfer curves and g_m vs. V_G of a PEDOT-PAH OECT in 10 mM KCl and 1 mM HEPES pH = 7.2 before (blue) and after (red) GOx deposition. (C) Relative change in the OECT I_DS current during GOx adsorption. (D) V_{G gm, max} changes (average of four devices. Error bars correspond to SD). V_DS = −50 mV and V_G = 54 mV.

Figure 5

(A) Scheme of the PEDOT-PAH films covalently modified with DVS and mannose employed for the study of specific recognition of ConA. (B) Change in the SPR signal Δ(θ_min–θ_tir) during the subsequent deposition of ConA and GOx on the gold substrate modified with PEDOT-PAH, DVS, and mannose under flow conditions. (C) Transfer curves of a PEDOT-PAH OECT before (blue) and after DVS-mannose (yellow), ConA (green), and GOx (red) modification steps. (D) Real time changes in the I_DS% upon ConA and GOx binding (10 mM KCl + 1 mM HEPES, pH = 7.2).