Facile one-step electrochemical fabrication of a non-enzymatic glucose-selective glassy carbon electrode modified with copper nanoparticles and graphene
- First Online:
- Cite this article as:
- Luo, J., Zhang, H., Jiang, S. et al. Microchim Acta (2012) 177: 485. doi:10.1007/s00604-012-0795-4
- 1.4k Views
We have developed a non-enzymatic glucose sensor by using a composite prepared from copper nanoparticles (CuNPs) and graphene which can be prepared by simple 1-step electrochemical reduction using graphene oxide (GO) and copper ion as the starting materials. The GO is electrochemically reduced to graphene at a voltage of −1.5 V, and this is accompanied by the simultaneous formation of CuNPs on the surface of the graphene. This novel nanocomposite combines the advantages of graphene and of CuNPs and displays good electrocatalytic activity toward glucose in alkaline media. The performance of the respective glucose electrode was evaluated by amperometric experiments and revealed a fast response (<2 s), a low detection limit (200 nM), and high sensitivity (607 μA mM−1). The sensor also exhibits good reproducibility and very good specificity for glucose over ascorbic acid, dopamine, uric acid, fructose, lactose and sucrose.
KeywordsGrapheneCopper nanoparticlesElectrochemical reductionGlucoseSensor
In recent years, graphene has shown great potential as sensing element due to their unique advantages such as large surface area, excellent electrical conductivity, fast electron transportation, ease of functionalization and mass production . Since every atom in a graphene is a surface atom, molecular interaction and thus electron transport through graphene can be highly sensitive to absorbed molecules . The introduction of graphene into electrochemical sensors has indeed resulted in dramatic evolution of various organic compounds such as ascorbic acid , H2O2 , hydrazine , NADH  and dopamine .
Copper- and copper oxide-based materials were of great interest for the electro-oxidation of glucose for a long time [8, 9]. Recently, there is a great amount of interest on copper and copper oxide nanomaterials for the non-enzymatic detection of glucose [10–12]. For instance, Kang fabricated a Cu-carbon nanotubes composite sensor by electrochemically depositing copper nanoclusters on a multiwall carbon nanotube modified glass carbon electrode . Zhang also reported Cu nanocubes and Cu2O nanoparticles modified CNTs via electrodeposition and sputtering deposition to create nonenzymatic glucose biosensor [11, 12]. High sensitive and fast amperometric detection of glucose with low detection limit was achieved by using the above mentioned copper or copper oxide/CNTs nanomaterials due to the increased electrocatalytical area and promoted electron transfer for the reaction of the glucose oxidation. Comparing with carbon nanotubes, graphene has shown the advantages of high conductivity, ease of production and function, good biocompatibility and abundance of inexpensive source material . Considering these attractive properties of graphene, it is quite expected that graphene could provide an excellent support of the Cu nanoparticles towards the oxidation of glucose. We recently prepared a novel Cu-graphene nanocomposite based electrode by electrodepositing Cu nanoparticles on a graphene modified glass carbon electrode . The obtained Cu-graphene electrode showed outstanding electrocatalytic property for glucose detection and detection, which can be attributed to the combination of the advantages of graphene and Cu nanoparticles. However, the preparation route was tedious and inconvenient, which included chemical reduction of graphene oxide (GO) to graphene, dispersing graphene in water and then dropping the graphene dispersion on GC electrode to get the graphene electrode and finally electrodepositing Cu nanoparticles on the graphene electrode. In addition, due to the hydrophobic property of graphene, it is not so easy to get graphene dispersion. Furthermore, the chemical reduction of GO to graphene needed a large amount of toxic hydrazine. Therefore, it is quite necessary to develop a facile and environmental-friendly approach to prepare Cu nanoparticles/graphene nanocomposite.
Electrodeposition method is one of the mostly useful approaches to prepare copper nanostructures. By this means, copper NPs can be facilely synthesized on the surface of conducting surfaces, and the sizes and shapes of the prepared nanoparticles can be easily controlled by altering the conditions of electrochemical deposition [10, 11]. Meanwhile, it is reported recently that high quality graphene can be prepared by electrochemical reduction of GO at −1.5 V, which eliminate the use of excessive reducing agents which will contaminate the resultant products and can completely reduce the oxygen functionalities on GO [15, 16]. While the deposition of Cu NPs starts at much more positive potentials (normally at −0.25 V), it is expected that electrochemical reduction of GO and electrodeposition of Cu NPs can be simultaneously performed at −1.5 V vs. SCE in a solution of copper ion. This one step synthesis approach is simple, green and fast, and has been used to fabricate graphene-supported Pt NPs which displayed good electrocatalytic activity towards methanol electrooxidation .
Herein, in the current work, we describe a simple one-step electrochemical reduction approach to prepare a novel Cu NPs/graphene nanocomposite for enzyme-free glucose sensing, which has not been reported. In this one step synthesis approach, simultaneous electrochemical reductions of Cu ion and GO are performed, generating Cu NPs on graphene sheets with an average size of ca. 8 nm. Encouragingly, this new Cu NP/graphene nanocomposite material takes advantage of salient properties of both Cu NPs and graphene, exhibiting improved electrocatalytic properties for glucose oxidation and detection compared to the single graphene or Cu. The resulted Cu NP/graphene modified electrode presents fast response, high sensitivity, low detection limit, and excellent selectivity, which can open up new opportunities for fast, simple and sensitive detection of glucose.
Chemicals and apparatus
Graphite powder, copper sulfate (CuSO4), sodium sulfate (Na2SO4), glucose, dopamine, ascorbic acid, uric acid, fructose, lactose and sucrose were purchased from the Shanghai Aladdin Chemical Reagent Company (Shanghai, China, http://www.aladdin-reagent.com).
XRD profiles were obtained (XD-3A, Shimadzu, Japan, http://www.shimadzu.com) with high-intensity Cu Kα radiation (λ = 1.5406 nm). Morphologies and nanostructures of Cu NPs/graphene nanocomposites were determined using scanning electron microscopy (SEM) (Hitachi S-3700N, Tokyo, Japan, http://www.hitachi.com). Electrochemical measurements were performed on a CHI 660C electrochemical analyzer (CH Instruments, Chenhua Corp., Shanghai, China, http://www.chinstruments.com/schi.html). A conventional three-electrode system was employed, involving a modified GC electrode as the working electrode, a platinum wire as the counter electrode and a saturated calomel electrode (SCE) as the reference electrode.
Preparation of Cu NPs/graphene electrode
Graphene oxide (GO) was synthesized from graphite by the Hummers method . All other reagents used in this study were of analytical grade. Deionized water (>18.4 MΩ·cm) was used for all solutions’ preparation. The prepared GO powder was exfoliated by ultrasonication to form a 1.0 mg mL−1 GO colloidal dispersion. GC electrode was polished with 1 and 0.5 μm Al2O3 powder and then rinsed by ethanol and deionized water, dried in N2. A 5 μL portion of the resulting GO dispersion was spread on the pretreated bare GCE and dried at room temperature to afford the GO-modified GC electrode. To fabricate the Cu nanoparticles modified graphene electrode, a one step electrochemical reduction was carried out: using the potentiostatic technique, the GO modified electrode was reduced at a potential of −1.5 V (vs. SCE) in 10 mM CuSO4 and 100 mM Na2SO4 for 500 s with N2 bubbling. The bare graphene electrode was prepared by electrochemical reduction of GO-modified GC electrode at −1.5 V in aqueous solution without CuSO4. The controlled Cu modified GC electrode was prepared under the same experimental condition with that of Cu NPs/graphene electrode except that bare GC electrode was used instead of the GO modified GC electrode.
Results and discussion
The Cu NPs/Graphene nanocomposite prepared by using the one-step method was characterized by Raman spectroscopy as shown in Fig. 1c. For comparison, the Raman spectrum of GO is also displayed (curve b). Both the GO and the electrochemically reduced GO display a strong D peak (defect peak due to intervalley scattering) at about 1,340 cm−1 and a strong G peak (the graphene peak) at about 1,600 cm−1 . However, the D/G ratio of the electrochemically reduced GO (1.38) is higher than that of GO (1.17), indicating an increase in the number of smaller graphene domains upon reduction of GO . In addition, 2D band (at 2,637 cm−1) and 2G band (2,915 cm−1) appeared after electrochemical reduction. These results demonstrate that graphene oxide has been successfully electrochemically reduced to graphene.
The XRD patterns of the GO and Cu NPs/graphene nanocomposite are illustrated in Fig. 1d. The disappearance of the peak at about 10.4° in the pattern of GO (Fig. 1d, curve b) revealed that it was successfully reduced to graphene [17, 21]. As shown in the XRD pattern of Cu NPs/Graphene nanocomposite (Fig. 1d, curve a), the strong diffraction peaks at 43.5, 50.5 and 74.5° correspond to the (111), (200) and (220) facets of the face-centered cubic structures of Cu crystal, respectively . The broad peak centered at 24° is related to the diffraction of loosely stacked graphene .
Furthermore, the CVs of oxidation of glucose on Cu NPs/graphene electrode at different scan rates were recorded (Fig S1, Electronic Supplementary Material, ESM), showing the anodic peak current of oxidation glucose is proportional to the scan rate. The results indicate that the electrochemical kinetics is controlled by the absorption of glucose. The CVs of the Cu NPs/graphene electrode in different concentrations of glucose were also measured, as indicated in Fig S2 (ESM), and a gradual increase in the current was observed with increasing the glucose concentration, pointing to its potential for developing Cu NPs/graphene electrode as a non-enzymatic glucose sensor.
The reproducibility and stability of the Cu NPs/graphene electrode were performed by measuring the current response of the electrode upon 0.5 mM glucose in 0.1 M NaOH. The average relative standard deviation (RSD) was no more than 4.5 %. In a series of 8 sensors prepared in the same way, a RSD of 3.8 % was obtained, indicating the reliability of this method. The prepared electrode was stored in air at ambient conditions. In order to investigate the stability of the sensor, the current response to 0.5 mM of glucose was recorded each 3 days. It was found that the current could retain 90 % of its original signal after 2 weeks storage, showing long-term stability.
We have demonstrated a fast, green, effective and one-step electrochemical method to synthesize a novel Cu NPs/graphene nanocomposite as a new non-enzymatic glucose sensor. Graphene oxide (GO) was electrochemically reduced to graphene, accompanied by the simultaneous formation of Cu nanoparticles (NPs) via cathodic electrochemical deposition. The resulted Cu NPs/graphene nanocomposite exhibited a synergistic combination of the advantages of Cu NPs and graphene toward the electrochemical oxidation of glucose. We have demonstrated that this Cu NPs/graphene nanocomposite based sensor shows fast response, low detection limit and high sensitivity to glucose detection. These excellent performance characteristics are combined with ease of fabrication, good reproducibility and perfect specificity to glucose in the presence of various common interferents, which makes our Cu NPs/graphene electrode as a potential candidate for glucose analysis.
We acknowledge financial support from the National Natural Science Foundation of China (under Grant Nos. 21174056 and 51103064) and the Fundamental Research Funds for the Central Universities (JUSRP31003 and JUSRP11108).