Flexible fiber-shaped non-enzymatic sensors with a graphene-metal heterostructure based on graphene fibres decorated with gold nanosheets
Graphical abstract
Flexible fiber-shaped non-enzymatic sensors with a graphene-metal heterostructure based on graphene fibers decorated with gold nanoparticles were developed for sensitive and selective detection of H2O2 and glucose.
Introduction
Flexible and lightweight fibre-shaped devices have attracted a great deal of interest for portable and wearable electronics [1,2]. Of particular interest, wearable sensors, including electronic and electrochemical biosensors, have shown commercial and social potential for real-time monitoring personal health [[3], [4], [5]]. Compared to conventional electrodes for electrochemical sensing, fibre-shaped microelectrode sensors offer many advantages, such as a small amount of sample(s) required, improved signal-to-noise ratio, rapid flux to the electroactive region, and high current density [6,7]. The most essential component needed to fabricate the fibre-shaped microelectrode sensors is the electrical conductive fibre. However, most conventional conductive fibres, such as carbon fibres [8] and metal fibres [9], have a low specific surface area. To overcome this limitation, we developed a novel graphene fibre decorated with gold nanosheets by electrochemical deposition (GF/AuNSs).
Graphene, an atomically thick two-dimensional carbon sheet, has a large surface area and high conductivity [10,11], which can support a high uptake of sensing molecules to lower the detection limit. Its high electrical conductivity and high electrochemical activity also make graphene an idea material for electrochemical sensing applications. Indeed, graphene fibres (GF) [12] with a high flexibility have recently attracted considerable interest for potential applications in wearable electronics [13,14].
Complementary to the performance of graphene fibres, gold nanomaterials exhibit high catalytic activity and low biological toxicity and as such are promising as active materials for wearable and implantable sensors for real-time monitoring human health [15,16]. In order to incorporate gold nanomaterials into wearable sensors, it is highly desirable to decorate gold nanomaterials along a conductive fibre-shaped electrode. Thus, the use of graphene fibre with a large surface area and high electrical conductivity/electrochemical activity as a fibre-shaped electrode to support gold nanomaterials in the GF/Au hybrid creates synergistic effects. This far, no fibre-shaped sensor based on graphene and gold nanomaterials has been reported.
Hydrogen peroxide (H2O2) plays an essential role in environmental, biological, pharmaceutical, food and many other industrial sectors [[17], [18], [19]]. H2O2 is also a by-product generated by various oxidase enzymes, including glucose oxidase (GOx), lactate oxidase (LOx), glutamate oxidase (GLOx), and lysine oxidase (LyOx) [20]. Therefore, it is very important to develop efficient sensors for sensitive and selective detection of H2O2. Various sensors, including chemluminescence [21], photospectrometry [22,23], fluorescence [23], and electrochemical sensors [24,25] have been developed for H2O2 sensing. Among them, electrochemical sensors have multiple advantages, including low cost, easy operation, high sensitivity, and low detection limit.
Along with the H2O2 sensing, the detection of glucose, another well-known biomolecule, is also essential for food industry, clinical diagnostics, and human health. Although enzymes have been widely used to detect both H2O2 and glucose with a high sensitivity and selectivity, the lifetime of enzyme based electrochemical sensors is limited by the lifetime of the enzymes. Therefore, non-enzymatic electrochemical sensors have been developed as alternatives for the detection of H2O2 and glucose [26].
In this study, we developed a novel flexible wire-shaped sensor for detecting hydrogen peroxide and glucose using electrodes based on a graphene fibre decorated with gold nanosheets (GF/AuNSs). It was demonstrated that the newly-developed GF/AuNS sensors have excellent performance for the electrochemical detection of H2O2 and glucose with detection limits of 1.62 and 1.15 μM as well as sensitivities of 378.1 and 1045.9 μA mM−1•cm−2, respectively.
Section snippets
Chemicals and methods
Graphite powder, hydrogen peroxide (30%) and gold (III) chloride solution were purchased from Aladdin Reagent Co. Ltd., Shanghai, China, and were used as received. Raman spectra were recorded on a Nicolet Almega Raman spectrometer with the excitation line of 514 nm. Atomic Force Microscopy (AFM) measurements were performed using a MultiMode 8 (Bruker). Scanning electron microscopic (SEM) imaging was recorded on a Phenom Pro SEM.
Preparation of graphene fibre
First, graphene oxide (GO, cf. Fig. S1) was prepared from graphite
Results and discussion
Fig. 1a schematically shows the as-prepared flexible graphene fibre microelectrode with a 10-mm long graphene fibre connected to a copper wire and inserted into the PVDF tube, as described in Section 2.3. Fig. 1b shows a photograph for a flexible fiber-shaped microelectrode based on graphene fibre (see, the top tip). The graphene fibre can be bent into any shapes (Fig. 1c) and even can be made into a knot (Fig. 1d). Similar to the graphene fibre, the as-prepared whole microelectrode is also
Conclusions
A novel flexible graphene/gold nanosheet (GF/AuNS) composite fibre has been developed by electrochemical depositing gold species onto a graphene fibre microelectrode. SEM imaging revealed that the gold species were almost fully covered on the graphene fibre surface. The resultant fibre-shaped GF/AuNS microelectrode sensor exhibited a high sensitivity and selectivity for H2O2 and glucose sensing with a low detection limit of 1.62 and 1.15 μM as well as a high sensitivity of 378.1 and 1045.9 μA mM
Acknowledgements
The authors are very grateful for the financial support from the National Natural Science Foundation of China (51202167, 51433005), the National “Thousand Talents Program” of China, Case Western Reserve University–Wenzhou Medical University (CON115346) and UNSW Vice-Chancellor's Research Fellowship (RG142412).
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