Facile preparation of a highly sensitive nonenzymatic glucose sensor based on multi-walled carbon nanotubes decorated with electrodeposited metals

Abstract

Novel multi-walled carbon nanotubes decorated with nickel, copper, and silver (Ni/CuAg/MWCNT) have been successfully fabricated for a nonenzymatic glucose sensor by the electrocodeposition of copper and silver and sequential electrodeposition of nickel using a MWCNT-modified electrode. The Ni, Cu, and Ag species deposited on MWCNT were indicated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Tests with various scan rates and pH conditions indicate that a diffusion-controlled in the electrochemical system and the hybrid composite is stable. In alkaline condition, the electrode shows good activity towards glucose oxidation with low overpotential with obvious oxidation peaks at +0.38 V and +0.5 V and a current response that is 1.7–5.8 times greater than those obtained using Ni/CuAg and MWCNT modified electrodes. Amperometry (E_app. = +0.6 V) indicates a response time of 10 s; one linear range of 5 × 10⁻⁶–4.05 × 10⁻⁴ M, with high sensitivity of 5007 μA mM⁻¹ cm⁻² and a low detection limit of 5 × 10⁻⁶ M (S/N = 3). It can effectively analyse glucose concentration avoiding interference. The modified electrode can be a nonenzymatic glucose sensor due to its low overpotential, high sensitivity, good selectivity, good stability, and low cost.

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1. Introduction

Regular measurements of blood glucose levels are required to determine whether the treatments are working effectively for diabetic patients.¹ Such as instability, the high cost of enzymes, complicated immobilisation procedures, and critical operating conditions are some of the disadvantages for enzyme-modified electrodes. Considerable attention had been paid to developing nonenzymatic electrodes to overcome these problems. As a result, there is an ever-growing demand to create electrochemical glucose sensors with high sensitivity, high reliability, short response times, good recyclability, and low cost, especially nonenzymatic amperometric biosensors,² which are currently the most popular.

Efforts to develop a practical nonenzymatic glucose sensor have been centred on achieving a breakthrough in electrocatalysis. Different substrates, such as platinum,³ gold,⁴ copper,⁵ alloys (containing Pt, Pb, Au, Pd, Ir, and Ru),^6–9 and metal oxidates (IrO₂, MnO₂, and CuO),^10–12 have been studied. Highly active surface area of the electrode material plays a key role in the electrooxidation of glucose. Nanomaterials, including carbon nanotubes (CNTs) and transition metallic nanoparticles (NPs) have been widely applied in sensors and biosensors. Due to the high surface/volume ratio and chemical stability, CNTs are an attractive material for electroanalysis.^13–16 Electrochemical activities can be effectively increased by transition metallic NPs, such as gold (Au), platinum (Pt), palladium (Pd), copper (Cu), nickel (Ni), and silver (Ag). NPs-based sensors and biosensors have demonstrated good performances due to their increased surface area and enhanced mass transport and catalysis as well as good biocompatibility, with control over the microenvironment, relative to macroelectrodes.^16–18 Therefore, their use has been an important strategy in the construction of nonenzymatic glucose sensors with nanomaterials, such as nanoporous Pt electrodes^19,20 and electrodes modified with CNTs,^21,22 Ni NPs,^23,24 Au NPs,^25,26 Cu NPs,^27,28 and CNTs with CuO,²⁹ Cu NPs,^30–32 Ni NPs,³³ and both Ni and Cu NPs.³⁴

Pure metal NPs (such as Ni NPs and pure Cu NPs) are difficult to prepare and have poor stability for electroanalysis due to their ready oxidisation in air and solution.¹⁸ The synthesis of colloidal Cu NPs, such as the use of reverse micelles, microemulsions, and radiation techniques, are complex and involve multiple solvent systems.^18,30 Moreover, some strategies are also carried out in high temperature method and they are complicated and expensive.^35–37 For efficient sugar analysis, nonenzymatic electrochemical detection techniques, such as pulsed amperometric detection (PAD) using Pt or Au electrodes,^38,39 have been widely used due to their good sensitivity and cost effectiveness. However, the susceptibility of Pt and Au electrodes to surface fouling during sugar analysis and the requirement for electrode surface regeneration limit the wide applications of Pt- or Au-based PAD in flow systems for continuous analysis of sugars. An alternative method for sugar detection is the constant potential amperometry, which is more applicable to flow systems and has the advantage of instrumental simplicity.³⁷

In this work, an effective nonenzymatic sensor, namely, an MWCNT-modified electrode decorated with Ni, Cu, and Ag hybrid composite was introduced for the electrocatalytic oxidation of glucose. Copper, silver, and nickel were sequentially deposited on MWCNT by a simple electrochemical method. All MWCNT were functionalised with carboxylic groups³⁵ to improve their dispersion and immobilisation on the electrode surface. The Ni/CuAg/MWCNT hybrid composite was characterised by XRD and SEM. The electrocatalytic oxidation of glucose was investigated with the related modifiers in the literature. It was also used to analyse the glucose concentration with potential interferents.

2. Experimental

2.1 Reagents and materials

D-(+)-Glucose, galactose, sucrose, lactose, ascorbic acid, dopamine, uric acid, 4-acetamidophenol, 3,4-dihydroxyphenylacetic acid and multi-walled carbon nanotubes (MWCNT) were purchased from Sigma-Aldrich (USA) and used as received. All other chemicals (Merck) used were of analytical grade (99%). Double-distilled deionised water (>18.1 MΩ cm⁻¹) was used to prepare all solutions. All other reagents were of analytical grade and used without further purification.

2.2 Apparatus and measurements

The Ni/CuAg/MWCNTs hybrid composite was characterised. The electrochemical experiments were conducted using a CHI 1205a electrochemical workstation (CH Instruments, USA) with a conventional three-electrode setup using a glassy carbon electrode (GCE) as a working electrode, an Ag/AgCl (3 M KCl) as a reference electrode, and a platinum wire as a counter electrode. A BAS (Bioanalytical Systems, Inc., USA) GCE with a diameter of 0.3 cm was used for all electrochemical experiments. All potentials reported in this paper were referred to a Ag/AgCl electrode. The buffer solution was completely deaerated using a nitrogen gas atmosphere. The composite was analysed by XRD, and its morphology was characterised by SEM. Indium tin oxide (ITO) was used as the substrate for test convenience in characterisation (XRD and SEM tests) due to its thin flat frame. The preparation of different materials using GCE or ITO substrate is monitored and compared by voltammetry. Therefore, the materials immobilization using different electrodes (GCE or ITO) can be objectively considered in the same level based on the similar voltammograms.

2.3 Fabrication of the Ni/CuAg/MWCNT modified electrodes

Different composites, including MWCNT, CuAg, and Ni/CuAg, were coated on GCE and ITO substrates.

The CuAg electrocodeposition was easily carried out in a nitrate solution (pH 5.5) containing 5 × 10⁻³ M AgNO₃ and 5 × 10⁻² M Cu(NO₃)₂. By cyclic voltammetry, the electrocodeposition was taken in the potential range of −0.9–1.0 V with a scan rate of 0.1 V s⁻¹ and 15 scan cycles. This method was used to prepare CuAg and CuAg/MWCNT modified electrodes.

Prior to the preparation of MWCNT-modified electrodes, all MWCNT were functionalised with carboxylic groups to confer good dispersion in the prepared solution.⁴⁰ This MWCNT solution was drop-casted on the electrode surface to form a MWCNTs-modified electrode. 10 μL of the MWCNT solution was used in this work to ensure coverage of the entire electrode surface. Next, the effluent from the effective surface area was carefully removed. The electrodes were cleaned and dried in an oven at 40 °C. The MWCNT-modified electrodes (MWCNT/GCE and MWCNT/ITO) were easily prepared using this method. Metal–MWCNT films were successfully formed based on the preparation of related composites.^32,40–42 Using the concept illustrated in Scheme 1,³² Ni, Cu, and Ag NPs can be sequentially deposited on MWCNT. All modified electrodes, namely, the MWCNT, CuAg, and CuAg/MWCNT electrodes, were stored at room temperature before use.

Scheme 1 Illustration of Ni/CuAg/MWCNT hybrid composite modified electrode: (a) bare, (b) MWCNT, (c) CuAg/MWCNT, and (d) Ni/CuAg/MWCNT modified electrodes.

3. Results and discussion

3.1 Preparation and characterisation of the Ni/CuAg/MWCNT hybrid composite

A simple electrochemical synthesis of Ni/CuAg/MWCNT hybrid composite was presented in this work. Fig. 1A shows the voltammograms of the CuAg electrodeposition using a MWCNT-modified electrode. It depicts the typical voltammogram of copper and silver electrodeposition with current increase at characteristic peaks. The redox peaks are close so that they are not easily to define. However, the redox peaks can be recognized for Ag⁺ (E_pa ≒ 0 V, E_pc ≒ −0.4 V) and Cu²⁺ (E_pa ≒ 0.1 V, E_pc ≒ −0.85 V) based on the related ref. 43 and 44 The voltammogram indicates that the electrocodeposition of Cu and Ag is successful because both cathodic and anodic peak currents are increasing with the increase of scan cycles. The modified electrode was further transferred to have electrodeposition of nickel in the tetraborate solution (pH 9) containing nickel chloride. Fig. 1B presents the consecutive voltammograms of the Ni electrodeposition using a CuAg/MWCNT modified electrode. It shows two characteristic peaks (E_pa = +1.05 V and E_pc = +0.7 V) involving Ni(II)/Ni(III) redox processes. Both anodic and cathodic peak currents increase with the increase in scan cycles, indicating the Ni electrodeposition can be well deposited on a CuAg/MWCNT-modified GCE in the tetraborate solution. Hereafter, the modified electrode was mentioned as Ni/CuAg/MWCNT modified electrode for convenience.

Fig. 1 Consecutive cyclic voltammograms of (A) MWCNT/GCE examined in pH 5.5 nitrate solution containing 5 × 10⁻³ M AgNO₃ and 5 × 10⁻² M Cu(NO₃)₂; and (B) CuAg/MWCNT/GCE examined in pH 9 tetraborate solution containing 5 × 10⁻⁵ M NiCl₂, respectively. Scan rate = 0.1 V s⁻¹. 15 scan cycles.

Fig. 2 shows the XRD patterns for (a) Ni/CuAg/MWCNT/ITO, (b) Ni/CuAg/ITO, (c) CuAg/ITO, and (d) MWCNT/ITO. These composites can be clearly identified using the standard patterns (Fig. S1, ESI†) for Ag, Cu, Ni, Cu₂O, AgCl, and ITO, respectively. When the MWCNT was immobilised on ITO, it exhibited patterns (Fig. 2d) almost identical to those of ITO. This phenomenon might indicate the MWCNT is well dispersion and very thin on ITO surface. When the Ni/CuAg/MWCNT, Ni/CuAg, and CuAg was coated on the ITO (Fig. 2a–c), four characteristic peaks were observed for Ag at 2θ = 38.1°, 44.3°, 64.5°, 77.4°, and 81.6° corresponding to Miller indices (1 1 1), (2 0 0), (2 2 0), (3 1 1), and (2 2 2), respectively. Three characteristic peaks were observed for Cu at 2θ = 43.3°, 50.4°, and 74.1°, corresponding to Miller indices (1 1 1), (2 0 0), and (2 2 0), respectively. Another three characteristic peaks were observed for Ni at 2θ = 44.5°, 51.8°, and 76.4°, corresponding to Miller indices (1 1 1), (2 0 0), and (2 2 0), respectively. These three composites (Fig. 1A(a)–(c)) were also found for Cu₂O characteristic peaks at 2θ = 29.6°, 36.4°, 42.3°, 61.4°, 73.5°, and 77.4°, corresponding to Miller indices (1 1 0), (1 1 1), (2 0 0), (2 2 0), (3 1 1), and (2 2 2), respectively. Particularly, the Ni/CuAg/MWCNT and Ni/CuAg hybrid composites exhibit AgCl characteristic peaks at 2θ = 27.8°, 32.3°, 46.3°, 54.9°, 57.5°, 67.5°, and 76.8°, corresponding to Miller indices (1 1 1), (2 0 0), (2 2 0), (3 1 1), (2 2 2), (4 0 0), and (4 2 0), respectively. One can know that the Ni/CuAg/MWCNT has specific hybrid composites including Ag, Cu, Ni, Cu₂O, and AgCl. This result proves that the resultant particles can be easily prepared by electrocodeposition of copper and silver and sequential electrodeposition of nickel on MWCNT to form a specific Ni/CuAg/MWCNT hybrid composite modified electrode.

Fig. 2 XRD spectra of different modified ITO electrodes.

The morphology of the different composites was studied by SEM. Fig. 3A–D show the AFM images for (A) CuAg/ITO, (B) Ni/CuAg/ITO, (C) MWCNT/ITO, and (D) Ni/CuAg/MWCNT/ITO, respectively. Both CuAg and Ni/CuAg hybrid composites exhibit globular clusters different from fiber-like MWCNT. The Ni/CuAg/MWCNT exhibits specific globular and fiber-like structure with smaller particle size among these materials. It indicates that the Ni, Cu, and Ag hybrid composite can be successfully formed on MWCNT. This phenomenon might be caused by high conductivity and specific surface area of MWCNT. It provides more active space allowing the electrodeposition for more and smaller composites. As the results, one can conclude that the Ni/CuAg/MWCNT hybrid composite can be easily prepared by this simple electrochemical method.

Fig. 3 SEM images of (A) CuAg, (B) Ni/CuAg, (C) MWCNT, and (D) Ni/CuAg/MWCNT coated ITO electrodes. (E) Cyclic voltammograms of (a) Ni/CuAg/MWCNT, (b) Ag/MWCNT, (c) Ni/MWCNT, (d) Ni/Cu/MWCNT, and (e) MWCNT modified GCEs examined in pH 13 alkaline solutions. Scan rate = 0.1 V s⁻¹.

The materials have been used to have electrocatalytic oxidation of glucose in different pH conditions. They show good current response in alkaline solution. Therefore, we present the voltammograms of these materials modified electrodes only in alkaline solution. Fig. 3E shows the voltammograms of different modifiers including (a) Ni/CuAg/MWCNT, (b) Ag/MWCNT, (c) Ni/MWCNT, (d) Ni/Cu/MWCNT, and (e) MWCNT. Except of MWCNT, the other four modifiers exhibit two characteristic redox peaks at E_pa = +0.5 V, E_pc = −0.06 V; E_pa = +0.42 V, E_pc = +0.05 V; E_pa = +0.58 V, E_pc = +0.35 V; E_pa = +0.68 V, E_pc = +0.5 V, respectively. They are easily recognized as the redox processes involving Ag(0)/Ag(I) and Ni(II)/Ni(III) for Ag/MWCNT and Ni/MWCNT, respectively. The Ni/Cu/MWCNT hybrid composite exhibits one redox couple involving Ni(II)/Ni(III) redox process in this pH condition. Particularly, the Ni/CuAg/MWCNT hybrid composite shows specific current response greater than those of other modifiers. This result indicates that the Ni/CuAg/MWCNT can be an electrocatalyst for electrocatalytic oxidation of glucose.

3.2 Electrocatalysis of glucose at the Ni/CuAg/MWCNT electrode

Fig. 4A displays the cyclic voltammograms of glucose oxidation using Ni/CuAg/MWCNT/GCE. It shows obvious anodic peak current increase at E_pa = +0.38 V and E_pa = +0.5 V with the addition of glucose. It is also noticed that the cathodic peak current increases at E_pc = −0.08 V in the backward scan segment. This phenomenon indicates that glucose can be electrocatalytic oxidized by the hybrid composite and the catalyzed product also can be electrocatalytic reduced by the composite. The result indicates that the reaction might be involving the generation of H₂O₂ similar to the enzymatic glucose sensors.^44–46 Electrocatalytic oxidation of glucose is compared with the relative modified electrodes including MWCNT/GCE, CuAg/MWCNT, Ni/CuAg/GCE, Ag/MWCNT, Cu/MWCNT, Ni/MWCNT, and Ni/Cu/MWCNT. As shown in Table 1, the activity of the relative modifiers is compared with the electrocatalytic oxidation peak and net current response in the presence of 3 mM glucose. One can know that the hybrid composite has two oxidation peaks for glucose oxidation with low overpotential (E_pa = +0.38 V and E_pa = +0.5 V) although the net current response is not the best among these modifiers.

Fig. 4 (A) Cyclic voltammograms of Ni/CuAg/MWCNT/GCE examined in pH 13 alkaline solutions in the (a) absence and (b) presence of 3 mM glucose. Scan rate = 0.1 V s⁻¹. Amperograms of Ni/CuAg/MWCNT/GCE examined in pH 13 containing (B) [Glucose] = 5 × 10⁻⁶ − 4.5 × 10⁻⁴ M and (C) potential interferents: galactose, sucrose, lactose, ascorbic acid, dopamine, uric acid, 4-acetamidophenol and 3,4-dihydroxyphenylacetic acid (10⁻⁵ M for each addition). Insets are the scale-up amperomogram and the calibration curve.

Table 1 Electrocatalytic oxidation peak potential and net current contribution for glucose oxidation using different modifiers

Modifiers	Epa^a/V	ΔIpa^b/μA
a The electrocatalytic oxidation peak potential of different modifiers for glucose oxidation.b The net current estimated at the electrocatalytic oxidation peak in the absence/presence of 3 × 10^−3 M glucose.
MWCNT	0.60	8
CuAg	0.35	66
	0.43	38
Ni/CuAg	0.33	35
Ag/MWCNT	0.30	21
Cu/MWCNT	0.52	91
Ni/MWCNT	0.60	222
Ni/Cu/MWCNT	0.58	155
Ni/CuAg/MWCNT	0.38	61
	0.50	46

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The oxidation potentials may correspond to a redox couple for Ni(II)/Ni(III),^24,47–49 Cu(II)/Cu(III),^28,32,50,51 and Ag(0)/Ag(I). These results are in good agreement with previous works. As indicated in the literature, the oxidation of glucose to gluconolactone was catalysed by the Ni(III)/Ni(II), Cu(III)/Cu(II), and Ag(I)/Ag(0) redox couples according to the following reactions:

NiO(OH) + glucose → Ni(OH)₂ + e⁻ + gluconolactone (1)

CuO(OH) + glucose → Cu(OH)₂ + e⁻ + gluconolactone (2)

Ag(OH) + glucose → Ag + H₂O + e⁻ + gluconolactone (3)

Due to AgCl and Cu₂O are found significant amount with the hybrid system apart from Ni, Cu and Ag metals. The influence of AgCl and Cu₂O on the glucose oxidation part is also considered. In alkaline solution, AgCl might change to AgOH and it has electrocatalytic oxidation of glucose following the eqn (3). Cu₂O might change to CuOH and it has electrocatalytic oxidation of glucose as following:⁵²

Cu(OH) + glucose → Cu + H₂O + e⁻ + gluconolactone (4)

One can know that all species in the hybrid composites are active for nonenzymatic glucose oxidation. As the result, the hybrid composite can be expected for high current response for glucose.

Further considering the activity of the relative modifiers for glucose as shown in Table 1, it indicates that the Ni/CuAg/MWCNT hybrid composite maintains the catalytic activity of Ni, Cu, and Ag species for electrocatalytic oxidation of glucose. The hybrid composite shows competitive performance with low overpotential and high current response. This finding suggests that the Ni/CuAg/MWCNT composite can be an active electrocatalyst for the electrocatalytic oxidation of glucose.

Because two oxidation peaks are observed at +0.38 V and +0.5 V in the voltammogram, both of them can be selected as the working potential for the amperometric determination of glucose oxidation using the Ni/Cu/MWCNT electrode. In this work, the amperograms were obtained at E_app. = +0.6 V due to the much higher current response at this voltage, which provides the well-defined and stable amperometric response with response time of 10 s (shown in Fig. 4B).

Fig. 4B shows the amperometric response of the Ni/CuAg/MWCNT electrode examined with several additions of 5 μM glucose spiked into 0.1 M NaOH solution. The response curve turns downward with increasing concentration because an increasing amount of intermediate species is adsorbed onto the electrode surface, prolonging the reaction time. The calibration curve for the glucose sensor is shown in the inset (b) of Fig. 4B, which provides the regression equation, I_pa(μA) = 0.354c_glucose(μM) + 7.7, with correlation coefficient of R² = 0.995. The electrode has a linear concentration range of 5 × 10⁻⁶–4.05 × 10⁻⁴ M, a sensitivity of 5007 μA mM⁻¹ cm⁻², and a detection limit of 5 μM (5 × 10⁻⁶ M) (signal/noise = 3). Five samples (n = 5) have been measured to confirm the detection limit.

Various nonenzymatic glucose sensors are summarised in Table 2. Although the sensor shows relative narrow linear concentration range, its high sensitivity is still attractive to develop a nonenzymatic glucose sensor in the literature. The high sensitivity of the Ni/CuAg/MWCNT hybrid composite might be caused by the high active metal species and further enhanced by the high conductive and high steric MWCNT.

Table 2 Performance comparison of the Ni/CuAg/MWCNT electrode and other nonenzymatic glucose sensors

Electrode	Detection potential (V vs. Ag/AgCl)	Sensitivity (μA mM^−1 cm^−2)	Linear range (M)	Detection limit (μM)	Ref.
Porous Au	0.35	11.8	2 × 10^−3–1 × 10^−2	5	4
MnO2/MWCNT	0.3	33.2 μA mM^−1	1 × 10^−5–2.8 × 10^−2	—	11
CuO nanowires	0.33	0.5	4 × 10^−7–2 × 10^−3	0.049	12
Mesoporous Pt	0.4	9.6	0–1 × 10^−2	—	19
MWCNT	0.2	4.4	2 × 10^−6–1.1 × 10^−2	1	21
Ni nanowires	0.55	1043	5 × 10^−7–7 × 10^−3	0.1	24
Cu nanoparticles	0.65	—	1 × 10^−6–5 × 10^−3	0.5	28
CuO/MWCNT	0.4	2596	4 × 10^−7–1.2 × 10^−3	0.2	29
Cu/MWCNT	0.65	251.4	7 × 10^−4–3.5 × 10^−3	0.21	32
Ni–MWCNT	0.6	67.19	3.2 × 10^−6–1.75 × 10^−2	0.89	33
Ni/Cu/MWCNT	0.575	2633	2.5 × 10^−8–8 × 10^−4	0.025	34
	0.575	2437	2 × 10^−3–8 × 10^−3	0.025
Pd–Ni/Carbon nanofiber	0.4	—	1 × 10^−7–5.4 × 10^−3	0.06	37
Ni/CuAg/MWCNT	0.6	5007	5 × 10^−6–4.05 × 10^−4	5	This work

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The cost is roughly discussed with the use of method and materials including enzyme. The consideration of high cost is due to not only enzyme itself but also its complicated immobilization. Most of enzymatic sensors still need to add active materials to enhance the response signal. Moreover, the use of some noble metals such as gold and palladium are expensive not only in their original metal types but also their precursors. In contrast, the materials and method we proposed are competitive low-cost and easy to fabricate a nonenzymatic glucose sensor especially for the effective immobilization of different metals using less amount of MWCNT. Particularly, the proposed sensor can show highly sensitivity. As the result, the proposed sensor can be considered as a low-cost and effective glucose sensor.

3.3 Reproducibility, stability, and anti-interference property of the Ni/CuAg/MWCNT electrode

The reproducibility and stability of the sensor were evaluated. Five Ni/Cu/MWCNT electrodes were investigated by amperometry (E_app. = +0.6 V). The amperometric responses of the Ni/CuAg/MWCNT/GCE were obtained in 0.1 M NaOH (pH 13) with sequential additions of 1 mM glucose. The relative standard deviation (R.S.D.) was 1.98%, confirming the high reproducibility of the preparation method. Ten successive measurements of glucose on one Ni/CuAg/MWCNT electrode yielded an R.S.D. of 4.3%, indicating that the sensor was stable. The long-term stability of the sensor was also evaluated by measuring its current response to glucose within a 7 days period. The sensor was exposed to air, and its sensitivity was tested every day. The current response of the Ni/Cu/MWCNT electrode was approximately 90% of its original counterpart, which can be mainly attributed to the chemical stability of Ni, Cu, and Ag in basic solution. The current response of the Ni/CuAg/MWCNT electrode was also examined by adding 1 M KCl to the solution as a supporting electrolyte. Based on this result, the Ni/Cu/MWCNT electrode shows a nearly constant peak current towards glucose oxidation, indicating that the electrode is not poisoned by chloride ions.

Anti-interference studies are also important and necessary for sensors. Some easily oxidative species, such as galactose, sucrose, lactose, ascorbic acid, dopamine, and uric acid, usually co-exist with glucose in human blood. Thus, the electrochemical response of the interfering species was also examined at the Ni/CuAg/MWCNT electrode. Fig. 4C shows the amperometric response of Ni/CuAg/MWCNT/GCE examined in 0.1 M NaOH (pH 13) with sequential additions of glucose and potential interferents. A well-defined glucose response was obtained, and insignificant responses were observed for interfering species. It can be concluded that the Ni/CuAg/MWCNT electrode shows good selectivity for glucose detection.

4. Conclusions

Novel Cu, Ag, and Ni hybrid composites have successfully deposited on the MWCNT modified electrode by consecutive cyclic voltammetry. Based on the high conductive and high specific area of MWCNT, the hybrid composites can be can be easily prepared on electrode surface by a simple electrochemical synthesis involving the sequential electrodeposition of copper, silver, and nickel species. The novel nonenzymatic glucose sensor presents attractive features, such as low overpotential, high sensitivity, high selectivity, simple synthesis, and low cost.

Acknowledgements

We acknowledge the Ministry of Science and Technology (Project No. 101-2113-M-027-001-MY3), Taiwan.

Notes and references

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Footnote

† Electronic supplementary information (ESI) available. CCDC 010893722 010713761 and 010714654. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4ra11465e

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