Amperometric Detection of Dopamine based on a Graphene Oxide/PEDOT:PSS Composite Electrode

Dopamine (DA) is a hormone and a neurotransmitter that plays many important roles within the brain and body. It is an organic compound in the catecholamines and phenethylamines groups. A considerable effort has been made since its discovery, and numerous techniques for DA detection have been developed. Graphene and its derivatives have great potential for the development of sensors and biosensors. Since it has excellent characteristics, such as good conductivity and a large surface area, a graphene-based biosensor is expected to have high sensitivity, selectivity, and long-term stability characteristics. Graphene oxide (GO) was synthesized using a chemical method through graphite oxidation. Graphene oxide/poly (3,4-ethylene-dioxythiophene):poly (4-styrenesulfonate) (GO/PEDOT:PSS) composite films were prepared using an electropolymerization method on the surface of the working electrode. The properties of this composite electrode were characterized by cyclic voltammetry (CV) and scanning electron microscopy (SEM). The performance of the composite film was evaluated using three-electrode systems that consisted of a glassy carbon electrode (GCE) modifying a composite film electrode as a working electrode, a platinum electrode as an auxiliary electrode, and Ag/AgCl as a reference electrode. The variation of the composite electrode was applied and evaluated to DA electrochemical sensing. The GO/PEDOT:PSS-modified electrode also exhibits high performance with a low detection limit of 1 ?M. The results obtained have shown that GO/PEDOT:PSS/GCE composites are promising candidates for modifying electrode material used in electrochemical sensing.

Biosensor; Dopamine; Electrochemical sensor; Electropolymerization; Graphene oxide; PEDOT:PSS

Dopamine (DA) is one of the important neurotransmitters that plays a role in memory, hormonal, and cardiovascular processes (Sun et al., 2013; Zheng et al., 2015; Rahman, et al., 2016a). Neurological conditions like dementia, schizophrenia, and Parkinson's disease are likely to cause a deficiency or insufficient DA levels (Ali et al., 2007; Caudle et al., 2008; Guo et al., 2013). Various methods have been developed for the detection of DA. Biosensor-based electrochemical sensors are highly accurate, user friendly, and have a quick response time (Rahman, et al., 2016b; Hayat et al., 2019). Recently, chemically modified electrodes were established and reported with greater sensitivity and selectivity to effectively detect DA (Zhang et al., 2013; Wu et al., 2014; Xu et al., 2014).

Graphene is widely used in electrochemical sensor production and holds great promise as an ideal candidate for sensing platforms. Materials based on graphene play an important role in every part of the environment (Arifutzzaman et al., 2019; Kusrini et al., 2019). Graphene is one of the greatest of recently studied materials, particularly in the field of electronics. It has many applications because of its characteristics, such as being the thinnest, strongest, and most conductive material (Morozov et al., 2008). Graphenes can be effectively used in electrochemical sensing systems for the selective detection of chemical species. One of the methods to synthesize graphene oxide (GO) through chemical synthesis, known as the Hummers method, is achieved by adding an oxidizing agent into the concentrated acid that contains graphite. Many researchers modify the methods to synthesize the graphene (Hummers and Offeman, 1958). One famous modification was carried out by Marcano et al. and is known as the Tour method. The Tour method demonstrates a less risky method since it does not use sodium nitrate (NaNO₃) and is a more effective graphite oxidation mechanism (Marcano et al., 2010).

The present research aimed to synthesize graphene oxide and investigate electrochemical studies of GO with poly (3,4-ethylene-dioxythiophene):poly (4-styrenesulfonate) (PEDOT:PSS) polymer on the surface of a glassy carbon electrode (GCE). GO was chosen since it is cheaper and easier to spread into a homogeneous PEDOT: PSS solution compared to reduced graphene. The properties of GO are hydrophilic and PEDOT: PSS is soluble in water. The modified electrodes used to study DA oxidation are provided by cyclic voltammetry (CV). 

The graphene oxide synthesis was achieved by mixing graphite powder into a concentrated acid medium with the existence of an oxidizing agent. Graphite oxidation using the Tour method is more efficient and less hazardous than other methods because it is cost-effective, non-toxic, and environmentally friendly. There are two major important steps to the synthesis mechanism of graphene oxide, namely oxidation and exfoliation.

The modified GCE by GO/PEDOT: PSS film exhibits high electrocatalytic behavior for DA oxidation. The electropolymerization of GO/PEDOT: PSS on the surface of the electrode exhibits a detection limit of 1 ?A and a wide linear range (1–1,000 ?M). This composite electrode was used for rapid-current response DA detection, which offered a promising method for modified electrode materials.

    We gratefully acknowledge the funding from Universitas Indonesia through Publikasi Terindeks Internasional (PUTI) Q1 2020 No. NKB-1422/UN2.RST/HKP.05.00/2020. We express our gratitude to Dr. Eng. Arief Udhiarto, S.T., M.T., Head of Laboratory Nanodevice, MRPQ building for the use of his laboratory facilities during this research.

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