Electrochemical determination of ascorbic acid, dopamine and uric acid based on an exfoliated graphite paper electrode: A high performance flexible sensor

Highlights

• A flexible electrochemical sensor is successfully constructed by using a consumer-grade flexible graphite paper.

• The exfoliated flexible graphite paper electrode with rough edges possesses high electrocatalytic activity toward the oxidation of ascorbic acid, dopamine and uric acid.

• The flexible sensor with merits of high selectivity and low detection limits has great potential applications in flexible electronics.

Abstract

An exfoliated flexible graphite paper (e-FGP) with rough edges is proposed as a high performance working electrode for the electrochemical determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA). Scanning electron microscopy (SEM), cyclic voltammetry (CV), different pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) were applied to investigate the unique properties of the high performance electrode. The results demonstrate its excellent electrocatalytic activity toward the oxidation of AA, DA and UA with well-separated voltammetric peaks. The calibration curves in the range of 20–400 μM, 0.5–35 μM, 0.5–35 μM, and the detection limits (S/N = 3) of 2.0 μM, 0.01 μM, 0.02 μM were obtained for AA, DA and UA in neutral phosphate buffer solutions (PBS), respectively. This mechanically flexible sensor with good selectivity and remarkable sensitivity could be used to determine DA and UA in real human urine samples.

Introduction

Sensors, acting important roles in smart sensor networks, are important components in the multifunctional integrated electrical device. With the rapid development of flexible electronics devices, flexible sensors with the merits of robust mechanical properties and space savings reveal attractive perspectives in various applications [1]. For instance, flexible electrochemical sensors have been widely explored for the determination or monitor of toxic or dangerous gases molecules such as hydrogen [2] and chlorine [3]. Carbon-based materials, from C₆₀ and carbon nanotube (CNT) to graphene, provide plenty of opportunities for constructing different types of flexible sensors. Yamada et al. developed a stretchable carbon nanotube stain sensor for human motion detection [4]. Flexible biosensors fabricated on soft substrate with carbon nanotube were also reported by Juntae et al. [5]. It has also been proved that ultrasensitive and low-cost graphene-based cancer sensor could be constructed on a flexible PET substrate [6].

Dopamine (DA), as one of the most significant neurotransmitters in the brain, has been detected by using electrochemical methods since 1970 [7] because of necessity to monitor HIV infection, neurotransmission processes and diagnose Parkinson's disease [8], [9]. However, ascorbic acid (AA), dopamine and uric acid (UA) usually coexist in real systems and their electrochemical responses are severely overlapped on traditional electrodes. To addressed the problem, considerable efforts have been made to separate their signal potentials with enhanced intensity [10], [11], [12], [13]. Recently, many advanced materials including polymers [14], [15], [16], [17], metal complexes [18], [19], [20], metal oxide [21], multi-walled carbon nanotube [22] and graphene-based nanomaterials [23], [24] are reported effectively for the detection of AA, DA and UA. Though the previous studies have made profound progress, the fabrication of the electrodes is too complex and the reported modified glassy carbon electrodes are not suitable for flexible integrated devices, thus resulting in many limitations in practical applications. We recently reported a high performance microbial fuel cell by applying a flexible graphite electrode as an anodic material due to its good mechanical strength and excellent conductivity [25].

In this work, we have demonstrated a highly sensitive and selective flexible electrochemical sensor based on an exfoliated graphite paper electrode (e-FGPE) with plenty of rough edges and wrinkles for the determination of AA, DA and UA for the first time. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to study the electrochemical behaviors of these three analytes. Satisfactory results were obtained while applying standard addition method to real human urine samples.