Microscale Sensor Arrays for the Detection of Dopamine Using PEDOT:PSS Organic Electrochemical Transistors

Abstract

We present a sensor array of microscale organic electrochemical transistors (OECTs) using poly (3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) as the channel material. The devices show high sensitivity and selectivity to detect dopamine (DA) with platinum (Pt) as a pseudo-reference gate electrode. First, we describe the wafer-scale fabrication process for manufacturing the PEDOT:PSS OECTs, and then we introduce a dilution method to adjust the thickness of the PEDOT:PSS film. Next, we investigate the effect of the film thickness on the sensitivity of DA detection. Reducing the film thickness enhances the sensitivity of DA detection within the concentration range of 1 μM to 100 μM. The OECTs show impressive sensitivitywith a limit of detection (LoD) as low as 1 nM and a high selectivity against uric acid (UA) and ascorbic acid (AA). Finally, we modify the surface of the Pt gate electrode with chitosan to improve the selectivity of OECTs at high concentrations of up to 100 µM to expand the detection range.

Keywords: PEDOT:PSS; chitosan; dopamine; organic electrochemical transistor; real-time measurement.

Figure 1

Schematic of the working principle for DA detection using PEDOT:PSS OECTs [44,45]. The arrow represents the electro−oxidation reaction of DA at the surface of a gate electrode.

Figure 2

(a) Fabrication process: Step 1. Lithography for Au patterning. Step 2. Lift−off for interdigital electrodes (IDEs). Step 3. Dry etching to open IDEs and contact pads. Step 4. Lift−off and annealing process of PEDOT:PSS on IDEs. (b) Microscopy image showing 16 OECT channels and a single OECT. (c) An encapsulated chip.

Figure 3

(a) Thicknesses of PEDOT:PSS films and (b) resistances between source and drain electrodes after depositing PEDOT:PSS mixture solutions A, B, C, and D on the OECTs.

Figure 4

CV characteristics with a voltage sweep from −0.2 to +0.8 V at a scan rate of 0.05 V/s, then reversed (WE and CE: Pt electrodes, RE: Ag/AgCl electrode). (a) CV curves from five continuous scans with 1 mM DA solution applied. (b) CV curves when adding different DA concentrations.

Figure 5

(a) Transfer characteristics of PEDOT:PSS OECTs when various DA concentrations are applied (n = 3); V_GS is from −0.4 V to 0.8 V and V_DS is −0.3 V. (b) Normalization plot of the OECT responses versus the DA concentrations with three different PEDOT:PSS thicknesses; V_GS = 0.4 V and V_DS = −0.3 V.

Figure 6

Normalization plots of the OECT responses versus the analyte concentrations show the selectivity of the OECTs for DA against AA and UA before (a) and after (b) modifying the surface of Pt electrode with chitosan. V_GS = 0.4 V and V_DS = −0.3 V. The dashed lines represent linear fits line to get the sensitivity in the indicated concentration range.

Figure 7

Real-time detection of DA concentrations ranging from 1 nM to 3 mM recorded with time interval of 0.5 s. The inset displays the change in drain–source current when 1 nM of DA was added to the chips. V_DS = −0.3 V and V_GS = 0.4 V.