Non-enzymatic detection of glucose using poly(azure A)-nickel modified glassy carbon electrode

Talanta 156-157 (2016) 134–140

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Non-enzymatic detection of glucose using poly(azure A)-nickel modified glassy carbon electrode Tong Liu, Yiqun Luo, Jiaming Zhu, Liyan Kong, Wen Wang, Liang Tan n Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research (Ministry of Education of China), College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha 410081, PR China

art ic l e i nf o

a b s t r a c t

Article history: Received 10 February 2016 Received in revised form 17 April 2016 Accepted 24 April 2016 Available online 29 April 2016

A simple, sensitive and selective non-enzymatic glucose sensor was constructed in this paper. The poly (azure A)-nickel modified glassy carbon electrode was successfully fabricated by the electropolymerization of azure A and the adsorption of Ni2 þ . The Ni modified electrode, which was characterized by scanning electron microscope, cyclic voltammetry, electrochemical impedance spectra and X-ray photoelectron spectroscopy measurements, respectively, displayed well-defined current responses of the Ni(III)/Ni(II) couple and showed a good activity for electrocatalytic oxidation of glucose in alkaline medium. Under the optimized conditions, the developed sensor exhibited a broad linear calibration range of 5 μM–12 mM for quantification of glucose and a low detection limit of 0.64 μM (3s). The excellent analytical performance including simple structure, fast response time, good anti-interference ability, satisfying stability and reliable reproducibility were also found from the proposed amperometric sensor. The results were satisfactory for the determination of glucose in human serum samples as comparison to those from a local hospital. & 2016 Elsevier B.V. All rights reserved.

Keywords: Poly(azure A) Nickel Chemically modified electrode Glucose Electrocatalytic oxidation

1. Introduction Glucose, as one of the most widely distributed saccharides in nature, is energy source of living cells and metabolic intermediate in organisms. Diabetes mellitus, which is directly related to chronic elevations of blood glucose, has become a worldwide public health problem and it can lead to the risk for renal, retinal and neural complications [1]. The determination of glucose concentration is very important in clinical diagnoses, biochemical analyses, food industry, and so on [2,3]. Conventional glucose sensors involve the use of enzymes including glucose oxidase (GOx). In 1962, Clark and Lyons reported the first enzyme electrode [4]. Updike and Hicks measured glucose concentration in biological fluids by immobilizing GOx in a gel on an oxygen electrode for the first time [5]. Three types of enzyme-based glucose sensors have been developed at present [6]. The first generation sensors employ oxygen as an electron mediator between GOx and electrode surface. The second generation sensors exploit artificial mediators to overcome oxygen limitation under low pressure of oxygen. The glucose sensors based on the strategy of the direct electron transfer from the enzyme to the electrode belong to the third generation. Although these enzyme-based sensors display n

Corresponding author. E-mail address: [email protected] (L. Tan).

http://dx.doi.org/10.1016/j.talanta.2016.04.053 0039-9140/& 2016 Elsevier B.V. All rights reserved.

very high sensitivity and specificity to glucose, several inevitable drawbacks including chemical/thermal deformation due to the intrinsic nature of enzyme and possible interferences from some oxidable species in samples may limit their applications [7,8]. Developing non-enzymatic glucose sensors with rapid response and precise measurement is a competitive and vigorous research trend. The investigation on electrochemical oxidation of glucose began in 1960s Bagotzky and Vassilyev [9] first reported the electro-oxidation behavior of glucose in an acidic medium. Bockris et al. [10] performed the similar research at high temperature in alkaline solutions. Advantages of non-enzymatic electrochemical glucose sensor include stability, simplicity, reproducibility, free from oxygen limitation, and so on. It is unquestionable that the oxidation of glucose is thermodynamically favorable. However, its utilization for analytical purpose is limited owing to slow reaction kinetics at conventional electrodes, high overpotential, poor selectivity, electrode poisoning by the products of the oxidation reaction, and so on. Considerable attentions have been directed to the exploration and employment of special electrode substrates or modification materials on which the catalytic electro-oxidation of glucose can be achieved at constant applied potentials. It is found that some metal [11,12], metal oxides [13,14], metal alloys [15,16], and metal-complexes [17,18] can provide simple ways for this purpose. The high cost of several noble metals, such as Au, Pt, Ag and Pd may limit their commercial applications. Hence, there are increasing interests on development

T. Liu et al. / Talanta 156-157 (2016) 134–140

of electrodes with low-cost metal materials, for example, Ni, Cu, Mn, Co and Fe. Among them, Nickel-based materials, which exhibit remarkably catalytic capability for glucose in alkaline medium, attract much attention due to its virtues including low toxicity, good stability and natural abundance. It is reported that nickel ions can be immobilized on some electroconductive organic compounds such as poly(1-naphthylamine) [19], curcumin [20] and quercetin [21] and these Ni2 þ -modified electrodes exhibit catalytic effect for the electro-oxidation of glucose. So it is of significance to search new substrates or ligands and construct such Ni2 þ -modified electrodes for the non-enzymatic glucose sensing. Many organic dyes, such as neutral red, methylene blue, thionin, pyronin B, azure A, and so on, own highly conjugated ringshaped structure and have excellent electroactivity. Their polymers are generally functional π-conjugated organic materials that can exhibit unusual electrochemical properties. These dye-polymer modified electrodes have a high stability and electroconductivity, presenting excellent catalytic response. In the present work, poly(azure A) (PAA) was prepared on the electrode surface and Ni2 þ was immobilized on the dye polymer. The electrochemical response of the PAA and PAA-Ni modified electrodes to the addition of glucose were investigated, respectively. The nonenzymatic and sensitive electrochemical detection of glucose was performed. The linear range, detection limit, anti-interference performance, stability, reproducibility and actual application for human serum samples of the fabricated sensor were all evaluated.

2. Experimental 2.1. Materials and apparatus Azure A (biological stain, BS, dye content 499%) was purchased from Xiya Chemical Industry Co., Ltd. (Linshu, China) and its stock solution (5 mM) was stored in the dark due to the sensitivity of the dye. Nickel sulphate and glucose (analytical reagent, AR) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Dopamine (Aldrich), ascorbic acid (Fluka) and uric acid (Aldrich) were used as received. Other chemicals were of analytical reagent grade and all aqueous solutions were prepared in Milli-Q ultrapure water. Electrochemical measurement experiments were performed with a CHI660C electrochemical workstation (CH Instruments, China) by using a three-electrode electrolytic cell. Glassy carbon electrode (GCE, 3 mm in diameter) acted as the working electrode. A KCl saturated calomel electrode (SCE) served as the reference electrode (RE). A platinum plate served as the counter electrode (CE). Scanning electron microscopy (SEM) analysis of the modified electrode surfaces were performed on a Nova NanoSEM 450 fieldemission scan electron microscope (FEI, USA). X-ray photoelectron spectroscopy (XPS) measurements were performed on an ESCALAB 250Xi X-ray Photoelectron Spectrometer (Thermo Fisher, UK). 2.2. Preparation of the chemically modified electrode and measurement procedure Prior to modification, GCE was polished with 0.05 mm α-Al2O3 power slurries until a mirror shiny surface appeared, and it was sonicated sequentially in acetone, HNO3 (1:1, v/v), NaOH (1 M) and ultrapure water for 3 min The treated electrode was scanned between  1.0 and 1.0 V versus SCE in 0.5 M H2SO4 aqueous solution for sufficient cycles to obtain reproducible cyclic voltammograms. And then the electrode was thoroughly rinsed with ultrapure water and dried with a stream of nitrogen gas. PAA was electrochemically deposited on the GCE via two methods. One adopted direct cyclic voltammetric scan (CV scan) for 30 cycles between

135

 0.7 and 1.2 V at 100 mV s  1 in 0.1 M pH 6.5 PBS containing 0.1 mM AA and 0.1 M NaNO3. Another was carried out in two steps: (1) initiating electropolymerization via CV scan from  1.0 to 1.6 V for 3 cycles in 0.1 M pH 6.5 PBS containing 0.1 mM AA and 0.1 M NaNO3 at a scan rate of 100 mV s  1 and (2) potential cycling for 30 cycles in the same solution at 100 mV s  1 in the potential range of  0.6–0.6 V. The solution used in the electropolymerization was thoroughly deoxygenated by bubbling pure nitrogen gas, and a continuous flow of nitrogen gas was maintained over the solution during CV scan. Next, the electrodes prepared by one-step method and two-step method, which was marked as GCE/PAA′ and GCE/PAA, was immersed in 0.2 M NiSO4 solution for 30 min, respectively. Finally, the obtained electrodes were thoroughly rinsed with ultrapure water and dried with a stream of nitrogen gas. The prepared electrodes were defined as GCE/PAA-Ni′ and GCE/PAA-Ni, respectively. Amperometric measurements were performed under a stirring condition with increasing of glucose concentration at room temperature in 0.1 M NaOH as the supporting electrolyte.

3. Results and discussion 3.1. Preparation and characterization of GCE/PAA-Ni The PAA modified GCE was obtained by one-step and two-step electropolymerization, respectively. Fig. 1A displays the growth process of the PAA film on GCE surface via consecutive potential cycling between  0.7 V and 1.2 V in pH 6.5 PBS. An apparent oxidation peak at about 0.90 V, which indicates the oxidation of the azure A molecules and the generation of the cation radicals [22], appeared on the first voltammetric cycle. The currents of the redox peaks at about  0.15 V and  0.24 V, corresponding to the AA monomer, were gradually decreased and the currents of a new pair of redox peaks at about 0.04 V and  0.05 V were increased step by step with successive cycles, suggesting that the AA molecules were electropolymerized and formed conducting polymer successfully. Fig. 1B displays the growth process of the PAA film on GCE surface via consecutive potential cycling between  0.6 V and 0.6 V after initiating the electropolymerization of AA via CV scan from 1.0 V to 1.6 V for 3 cycles. The AA cation radicals, which were necessary to the formation of the dye polymer, were produced in the initiation step. One can find from Fig. 1B that the peak currents were rapidly increased with the successive cycles. It means the formation of PAA on the electrode surface. Two pairs of redox peaks were observed on the cyclic voltammetric curves (CV curves) and the currents of the redox peaks at lower potential ( 0.19 V and  0.26 V) were relatively higher. The similar experimental results can be found in our previous investigation on the electropolymerization of methylene blue, which reveals the effect of the positive potential limit in CV scan on the dye-polymer structure [23]. Nickel ions were adsorbed on the two kinds of GCE/PAA electrodes prepared by the above two methods. The CV scans using GCE/PAA-Ni′ and GCE/PAA-Ni in 0.1 M NaOH were performed, respectively, and the results are shown in Fig. 1C. The Ni modified electrodes all presented a pair of well-defined redox peaks that should be derived from the electrochemical reactions of the Ni(II)/ Ni(III) couple [24–26]. It is well known that Ni(0) can be firstly transformed into Ni(OH)2 on alkaline conditions at potential less than  0.6 V [27,28] and the oxidation product may be further oxidized into NiO(OH), as described below. Ni(0) þ 2OH  - Ni(OH)2 þ 2e 

(1)

Ni(OH)2 þ OH  - NiO(OH) þ H2O þ e 

(2)

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40

20

30

20

10

b

20

I/ A

10 a

0 0

0 -10 -10

-20 -20

-20

-0.5 0.0 0.5 1.0

-0.6 -0.3 0.0 0.3 0.6

0.2 0.3 0.4 0.5 0.6

E /V vs SCE

E /V vs SCE

E /V vs SCE

Fig. 1. (A) Cyclic voltammograms during the growth process of the PAA film on GCE in N2-saturated 0.1 M pH 6.5 PBS containing 0.1 mM AA and 0.1 M NaNO3. (B) Cyclic voltammograms during the growth process of the PAA film on GCE in N2-saturated 0.1 M pH 6.5 PBS containing 0.1 mM AA and 0.1 M NaNO3 after initiating the electropolymerization of AA via CV scan from  1.0 V to 1.6 V for 3 cycles in the same solution. (C) Cyclic voltammograms of GCE/PAA-Ni′ (a) and GCE/PAA-Ni (b) in 0.1 M NaOH. Scan rate: 100 mV s  1.

Ni(II) ⇌ Ni(III) + e−

However, it is reported that in aqueous media the oxidation of Ni(II) to Ni(III) is very difficult due to the strong hydration of nickel ions [29]. In the present work, when nickel ions was adsorbed on the PAA film, its oxidation conditions could be changed significantly and the Ni(II)/Ni(III) transformation was easily achieved on the PAA film. The relevant reaction on the electrode surface may be simply described by:

(3)

Furthermore, GCE/PAA-Ni presented higher redox-peak currents than GCE/PAA-Ni' , indicating that more amount of nickel ions were bound on GCE/PAA prepared by two-step method, which might own the PAA film with higher density. Hence, GCE/ PAA-Ni was employed in all the subsequent experiments. Fig. 2A and B shows SEM images of GCE/PAA surface and GCE/

2000 30 a b 20

1500

c

1000

0

-Z'' /

I/ A

10

c

-10

500

-20

b

-30

a 0 -0.2

0.0

0.2

E /V vs SCE

0.4

0.6

0

500

1000

1500

2000

Z' /

Fig. 2. SEM images of GCE/PAA (A) and GCE/PAA-Ni surface (B), magnification: 100,000  . Cyclic voltammograms (C) and electrochemical impedance spectra (D) of GCE (a), GCE/PAA (b) and GCE/PAA-Ni (c) in pH 7.0 PBS containing 1 mM K3Fe(CN)6, 1 mM K4Fe(CN)6, and 0.1 M Na2SO4. The scan rate: 50 mV s  1. AC frequency range 100 kHz  1 mHz, amplitude 5 mV, DC bias 0.20 V vs. SCE.

T. Liu et al. / Talanta 156-157 (2016) 134–140

PAA + Ni2 + + H2 O ⇌ PAA − NiO + 2H+ Ni 2p

(4)

C 1s

N 1s 2p

c

Counts /s

c

b

a

885

b

b

a

a

870

855 405

402

399

396

288

0

40 Ipc 20

0

100

I/ A

30

j

-30 200

v /mV s

a

-1

0 a -20 j 0.1

0.2

0.3

0.4

0.5

0.6

E /V vs SCE Fig. 4. Cyclic voltammograms of GCE/PAA-Ni in 0.1 M NaOH at different scan rates (ν), from a to j: 25, 50, 75, 100, 125, 150, 175, 200, 225 and 250 mV s  1. Inset: Plots of the anodic peak current (Ipa) and the cathodic peak current (Ipc) vs. the scan rate (ν).

PAA + Ni2 + + 2H2 O ⇌ PAA − Ni(OH)2 + 2H+

(5)

The SEM measurement result in Fig. 2B also supported this conclusion. Similar Ni 2p3/2 peaks can be found in XPS measurements on some electrode-surface films composed of Ni(II) and organic compounds such as N, N-dimethylpropargylamine [32], dimethylglyoxime and cyclohexanebutyrate [33]. The Ni 2p3/2 and 2p1/2 peaks in XPS of GCE/PAA-Ni after CV scans in 0.1 M NaOH was almost identical to that of the freshly prepared GCE/PAA-Ni, proving the stability of Ni(II) on the PAA film. The CV scan of GCE/PAA-Ni in 0.1 M NaOH at various scan rates was performed and the results are shown in Fig. 4. One can find that the current response was increased gradually with the rise of the scan rate. In the meantime, the anodic peak shifted positively but the cathodic peak moved negatively. Both the anodic and cathodic peak currents were directly proportional to the scan rate, indicating a surface controlled electrode process. The stability of GCE/PAA-Ni was examined by recording its 20 consecutive CV curves in 0.1 M NaOH at a scan rate of 200 mV s  1. There was no obvious peak current change during 20 consecutive curves, implying that the nickel ions were stably immobilized on the GCE/ PAA surface. 3.2. Electrocatalytic oxidation of glucose on GCE/PAA-Ni

2p c

Ipa

60

I/ A

PAA-Ni surface, respectively. It is observed that a lot of sub200 nm-scale poly(azure A) clusters were presented on GCE surface and they displayed irregular blocky shapes. The modified electrode surface exhibited a different appearance after adsorbing Ni2 þ . Poly(azure A) was completely covered by sheet-structure film that presented smooth surface. Fig. 2C and D exhibits the cyclic voltammograms and electrochemical impedance spectra (EIS) of GCE, GCE/PAA and GCE/PAA-Ni, respectively, in pH 7.0 PBS using ferri-/ferrocyanide probe. A couple of reversible redox peaks of ferri-/ferrocyanide probe (shown in CV curves) and a small high-frequency semicircle diameter in the Nyquist plot, which presents the charge transfer resistance (Rct), can be found on the bare GCE. By contrast, the peak currents on GCE/PAA were almost unchanged and the charge transfer resistance was increased to a small extent. It suggests that the PAA modified electrode remained a good electroconductivity. The adsorption of Ni2 þ led to the decrease of the peak currents and increase of the Rct value, respectively, indicating that the presence of nickel ions on the electrode surface resulted in the strong steric hindrance effect, blocking the charge transfer to a certain extent. XPS is a widely used method for determining the surface chemical composition. The XPS analyses for GCE/PAA and GCE/PAA-Ni were performed, respectively, and the results are shown in Fig. 3. A peak at 284.8 eV in the C 1s region due to the CH backbone and a peak at 399.5 eV in the N 1s region associated with the presence of C–N bond were presented in XPS of GCE/PAA. The binding energies of C 1s and N 1s peaks of the freshly prepared GCE/PAA-Ni remained almost unchanged. In contrast, the N 1s peak of GCE/PAANi after CV scans in 0.1 M NaOH shifted to higher binding energy (400.0 eV), which suggests the generation of the Ni-N bond between nickel ions and PAA. In the Ni 2p region in XPS of GCE/PAANi, two characteristic peaks, 2p3/2 at 856.4 eV and 2p1/2 at 873.9 eV, were observed. An intense structure at high binding energy and adjacent to both peaks was present, which was ascribed to a multi-electron excitation and was referred to as a shake-up satellite [30]. It is reported that Ni 2p3/2 peak at a higher energy ( Z855.0 eV) are associated with nickel hydroxide or nickel oxide [31]. Hence, the hydrolysis of nickel ions should be achieved in the adsorption process of Ni2 þ and nickel hydroxide/nickel oxide was bound on the dye polymer according to the following reactions.

137

285

282

Binding Energy /eV Fig. 3. Ni 2p, N 1s and C 1s regions in XPS of GCE/PAA (a), freshly prepared GCE/PAA-Ni (b) and GCE/PAA-Ni after 10-cycle CV scans from 0 V to 0.8 V in 0.1 M NaOH (c).

Fig. 5 shows that the cyclic voltammograms of GCE/PAA and GCE/PAA-Ni in 0.1 M NaOH in the absence and presence of 5 mM glucose. GCE/PAA displayed no redox peaks in the potential range from 0 to 0.8 V (curve a) because the anodic and cathodic peak potentials of PAA were less than 0 V in alkaline media. Redox peaks were still absent on GCE/PAA after the addition of glucose (curve b), which indicates that the direct oxidation of glucose on the modified electrode was not achieved and there was no redox reaction between glucose and PAA. In addition, the currents at the higher potentials on GCE/PAA in the presence of glucose was decreased compared with those in the absence of glucose, meaning that glucose might be adsorbed on the dye polymer and it had a negative effect on the charge transfer between the electrode and the electrolyte solution. One can notice a pair of obvious redox peaks on GCE/PAA-Ni that attributed to the Ni(II)/Ni(III) transformation (curve c), as reported in Fig. 4. After the addition of 5 mM glucose, the anodic peak current increased noticeably accompanied by the positive shift of anodic peak potential (curve d),

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T. Liu et al. / Talanta 156-157 (2016) 134–140

60

60

40

40

20

20

0

0

d 200

I/ A

150

c

100 50

a b

0 -50 0.0

0.2

0.4

0.6

0.8

E /V vs SCE Fig. 5. Cyclic voltammograms of GCE/PAA (a, b) and GCE/PAA-Ni (c, d) in 0.1 M NaOH in the absence (a, c) and presence (b, d) of 5 mM glucose. Scan rate: 100 mV s  1.

which may be related to the diffusion limitation of glucose at the electrode surface. Furthermore, the cathodic peak on GCE/PAA-Ni was entirely disappeared in the presence of glucose. The experimental results demonstrate clearly that the Ni(III) species participated directly in the electrocatalytic process of glucose oxidation according to the following reaction. Ni(III) þ glucose - Ni(II) þ gluconolactone

(6)

In addition, the electrocatalytic oxidation of glucose at GCE/ PAA-Ni occurred not only in the anodic but also continued in the initial stage of the cathodic half cycle. Another anodic peak in the negative potential-scan process should attribute to the oxidation of Ni(II), which was generated by chemical reaction shown in Eq. (6), at the high positive potentials. The above CV response to glucose can be also found in some similar researches using the modified electrodes with nickel-based materials [21,34–36].

Ipa / A

3.3. Electrochemical detection of glucose

0

200 400 600 800 1000

c Ni 2+ /mM

0

20

40

60

Ipa / A

It is found from Fig. 5 that GCE/PAA-Ni could effectively catalyze the oxidation of glucose. Some factors affecting the catalytic

performance of the modified electrode were investigated, respectively, for developing a sensitive non-enzymatic glucose sensor and the results are shown in Fig. 6. The panels A and B show the effects of the concentration of Ni2 þ solution and the adsorption time of Ni2 þ on the anodic peak current change of GCE/PAANi before and after the addition of 5 mM glucose (ΔIpa). It is obvious that the ΔIpa value was rapidly increased with the enhancement of the Ni2 þ concentration from 10 μM to 200 mM and then displayed a declined trend when the latter was further enhanced. Moreover, the ΔIpa value gradually rose with the increasing Ni2 þ -adsorption time from 5 to 30 min and then remained almost unchanged when the adsorption time was further prolonged. The experimental results indicate that the electrocatalytic oxidation of glucose had a close relationship with the amount of the bound Ni2 þ on the electrode surface. The more nickel ions immobilized on PAA was, the higher the peak currents of GCE/PAA-Ni in CV scan were. The more Ni(II) was generated according to Eq. (6) in the presence of a given amount of glucose (5 mM). As a result, the change-degree of anodic peak current would be enhanced. However, the binding of nickel ions had a negative effect on the electroconductivity of the PAA-modified electrode to a certain extent, which can be confirmed by EIS measurement in Fig. 2D. The XPS analyses prove that the hydrolysis of nickel ions was achieved and nickel hydroxide/nickel oxide was generated on the PAA film in the adsorption process of Ni2 þ . Too thick nickel hydroxide/nickel oxide film on the electrode surface could result in the decrease of the ΔIpa value. Thus, the optimal concentration and adsorption time of Ni2 þ were selected at 200 mM and 30 min, respectively. The detection of glucose using chronoamperometry was performed based on the oxidation-current change of Ni(II) on GCE/ PAA-Ni. Fig. 7 exhibits the amperometric responses of the modified electrode upon successive addition of glucose into the stirring 0.1 M NaOH under the applied potential of 0.55 V. The continuous oxidation current jumps were observed and the current response was enhanced rapidly to arrive at a steady-state value within 5 s as the glucose was added in succession. Inset B of Fig. 7 shows the plots of the oxidation-current change before and after the glucose addition (ΔI) versus the concentration of glucose. The ΔI value was obviously increased with the enhancement of the glucose content but the curve became deflexed gradually. The current change was proportional to the glucose concentration in the range

250

80

Adsorption time /min

Fig. 6. Effects of the concentration of Ni2 þ solution (A) and the adsorption time of Ni2 þ (B) on the anodic peak current change of GCE/PAA-Ni before and after addition of 5 mM glucose (ΔIpa). Results are presented as mean 7 SD (error bar) of triplicate experiments.

T. Liu et al. / Talanta 156-157 (2016) 134–140

36 M

80

7.0 6.5

5 M

6.0

A

glucose 12

5.5

cglucose /mM

500 600 700 800

t /s

40

80

I/ A

I/ A

60

13

20

0

5

10 15 20

500

1000

1500

10

8

B

2000

2500

7

3000

650

700

750

t /s

Table 1 Comparison of electrode composition, linear ranges and detection limits of some non-enzymatic electrochemical glucose sensors. Linear range (μM)

Ni(II)-Qu-MWCNT-IL-PE 5–2800 Hierarchical NiO SS/foam Ni 18–1200 GCE/MWCNT/NiO 200–12000 Ni/ITO 1–350 RGO-Ni(OH)2/GCE 2–3100 Ni(OH)2/ERGO-MWCNT/ 10–1500 GCE CuO nanoparticles/GCE 5–2300 MWCNTs-COOH-P2AT100–30000 AuNPs/GCE AuNPs-FLG/ITO 6–28500 GCE/PAA-Ni 5–12000

800

850

900

950

t /s

Fig. 7. Amperometric responses of GCE/PAA-Ni upon the successive addition of glucose into 0.1 M NaOH with an applied potential 0.55 V under a stirring condition. Inset A: the magnification of the circled part. Inset B: plots of the oxidation current change (ΔI) vs. the concentration of glucose. Results are presented as mean 7 SD (error bar) of triplicate experiments.

Modified electrode

uric acid

40

0

0

glucose

dopamine

9

60

20

0

ascorbic acid

11

I/ A

106 M

I/ A

100

139

Detection limit (μM)

References

1.0 6.15 160 0.5 0.6 2.7

[21] [26] [35] [36] [37] [38]

0.5 3.7

[39] [40]

1 0.64

[41] This work

Qu: quercetin, MWCNT: multi-wall carbon nanotube, IL: ionic liquid, PE: paste electrode, SS: superstructures, GCE: glassy carbon electrode, ITO: indium tin oxide, GRO: reduced graphene oxide, ERGO: electroreduced graphene oxide, P2AT: Poly(2aminothiophenol), AuNPs: gold nanoparticles, FLG: few layered graphene.

from 5 μM to 12 mM with a correlation coefficient of 0.999. The detection limit was estimated to be 0.64 μM at the signal-to-noise ratio of 3. Some non-enzymatic electrochemical glucose sensors [21,26,35–41] were summarized in Table 1 with respect to the electrode composition, the applied potential, the linear range and the detection limit. The proposed sensor in this work presents a low detection limit and a wide linear range in comparison with others, revealing the excellent performance of GCE/PAA-Ni as a promising electrochemical sensor in glucose detection. The possible interferences from some co-existing electroactive compounds, such as dopamine, ascorbic acid and uric acid, in real samples were assessed in order to investigate the selectivity of the developed sensor. The physiological glucose is in millimole-level while DA, AA and UA are present at micromole levels in human blood. So glucose and interferents with a mole ratio of 30:1 were detected in the present work. Fig. 8 displays the amperometric responses of GCE/PAA-Ni upon successive addition 0.15 mM glucose, 5 μM dopamine, 5 μM ascorbic acid, 5 μM uric acid and 150 μM glucose into 0.1 M NaOH. The two electrochemical signals derived from glucose were basically identical. The current-changes caused by dopamine and ascorbic acid were relatively weaker and

Fig. 8. Amperometric responses of GCE/PAA-Ni upon the successive addition of 150 μM glucose, 5 μM dopamine, 5 μM ascorbic acid, 5 μM uric acid and 150 μM glucose into 0.1 M NaOH with an applied potential 0.55 V under a stirring condition.

the response derived from uric acid could be negligible. The experimental results suggest that the proposed non-enzymatic sensor can be employed in the selective detection of glucose in the presence of these common physiological materials. The stability and reproducibility of the developed sensor, which are also critically important in the practical application, were investigated by measuring the anodic peak current change before and after addition of glucose in the CV scan. Three GCE/PAA-Ni electrodes, on which the redox peaks of Ni(III)/Ni(II) were basically identical, were prepared and they were stored under nitrogen atmosphere when they were not in use. The ΔIpa value induced by 5 mM glucose on the modified electrodes after 7-day and 40-day storage keep 98% and 95% of the initial current-change on the freshly prepared GCE/PAA-Ni, respectively. The reproducibility of the proposed sensor was investigated by measuring the ΔIpa value induced by 5 mM glucose on the three independently prepared GCE/PAA-Ni electrodes. The relative standard deviation was calculated to 3.4%. The above results indicate that the developed sensor had a satisfying long-term stability and a reliable reproducibility. The applicability of the present sensor was evaluated for the determination of glucose in human serum samples. The concentrations of glucose in two samples were measured to be 5.66 and 7.25 mM, respectively, by standard addition method. They were comparable with those measured by a local hospital, 5.60 and 7.20 mM. The results after addition of glucose were obtained and they are listed in Table 2. The calculated recovery values were varied from 96.8% to 102.8%, suggesting that the developed sensor has potential applications in determination of glucose in real samples. Table 2 Determination of glucose in human serum samples. Sample No. Value found in human serum (mM)

Added (mM)

Found (mM)

Recovery (%)

1 2 3 4 5 6

– 8.40 11.2 – 10.8 18.0

– 8.13 11.0 – 11.1 17.9

– 96.8 98.2 – 102.8 99.4

5.66 5.66 5.66 7.25 7.25 7.25

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4. Conclusions Poly(azure A) was generated on the GCE surface by using the CV scan but it exhibited no catalytic ability to the oxidation of glucose. GCE/PAA-Ni was fabricated owing to the binding of nickel hydroxide/nickel oxide with the dye polymer, which was confirmed by SEM, CV, EIS and XPS measurements. This nickel modified electrode presented a pair of well-defined redox peaks derived from the Ni(II)/Ni(III) transformation. Glucose could be oxidized by Ni(III) and result in a great increase of anodic peak of the latter's reduction-product, Ni(II), in the electrode process. The optimal concentration of Ni2 þ solution and the adsorption time of Ni2 þ were selected at 200 mM and 30 min, respectively. A linear relationship between the current change and the glucose concentration was obtained in the range of 5 μM–12 mM with a low detection limit of 0.64 μM under the optimized conditions. The developed non-enzymatic electrochemical sensor exhibited some characteristics including simple structure, fast response time, good immunity from interference of electroactive materials, satisfying stability and reliable reproducibility and it was successfully applied to the determination of glucose in human serum samples.

[7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26]

Acknowledgments

[27] [28]

This work was supported by the Scientific Research Fund of Hunan Provincial Education Department (14A095), the Open Sustentation Fund of State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University (2014007) and Aid Program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province.

[29] [30] [31] [32] [33]

[34]

References [1] A.P. Turner, B. Chen, S. Piletsky, Clin. Chem. 45 (1999) 1596–1601. [2] J. Jia, B. Wang, A. Wu, G. Cheng, Z. Li, S. Dong, Anal. Chem. 74 (2002) 2217–2223. [3] E. Crouch, D.C. Cowell, S. Hoskins, R.W. Pittson, J.P. Hart, Anal. Biochem. 347 (2005) 17–23. [4] L.C. Clark Jr., C. Lyons, N.Y. Ann, Acad. Sci. 102 (1962) 29–45. [5] S.J. Updike, G.P. Hicks, Nature 214 (1967) 986–988. [6] S. Park, H. Boo, T.D. Chung, Anal. Chim. Acta 556 (2006) 46–57.

[35] [36] [37] [38] [39] [40] [41]

T. Kohma, D. Oyamatsu, S. Kuwabata, Electrochem. Commun. 9 (2007) 1012–1016. K.E. Toghill, R.G. Compton, Int. J. Electrochem. Sc. 5 (2010) 1246–1301. V.S. Bagotzky, Yu.B. Vasilyev, Electrochim. Acta 9 (1964) 869–882. J.O.’M. Bockris, B.J. Piersma, E. Gileadi, Electrochim. Acta 9 (1964) 1329–1332. M. Tominaga, T. Shimazoe, M. Nagashima, I. Taniguchi, Electrochem. Commun. 7 (2005) 189–193. H. Shua, L. Cao, G. Chang, H. He, Y. Zhang, Y. He, Electrochim. Acta 132 (2014) 524–532. C. Batchelor-McAuley, Y. Du, G.G. Wildgoose, R.G. Compton, Sens. Actuators B 135 (2009) 230–235. L. Kang, D. He, L. Bie, P. Jiang, Sens. Actuators B 220 (2015) 888–894. M. Tominaga, T. Shimazoe, M. Nagashima, I. Taniguchi, J. Electroanal. Chem. 615 (2008) 51–61. H. Li, C. Guo, C. Xu, Biosens. Bioelectron. 3 (2015) 339–346. K. Bamba, J.M. Léger, E. Garnier, C. Bachmann, K. Servat, K.B. Kokoh, Electrochim. Acta 50 (2005) 3341–3346. L. Özcan, Y. Şahin, H. Türk, Biosens. Bioelectron. 24 (2008) 512–517. R. Ojani, J.B. Raoof, P. Salmany-Afagh, J. Electroanal. Chem. 571 (2004) 1–8. M.Y. Elahi, H. Heli, S.Z. Bathaie, M.F. Mousavi, J. Solid State Electrochem. 11 (2007) 273–282. L. Zheng, J. Zhang, J. Song, Electrochim. Acta 54 (2009) 4559–456. Q. Gao, W. Wang, Y. Ma, X. Yang, Talanta 62 (2004) 477–482. X. Xiao, B. Zhou, L. Tan, H. Tang, Y. Zhang, Q. Xie, S. Yao, Electrochim. Acta 56 (2011) 10055–10063. H. Nie, Z. Yao, X. Zhou, Z. Yang, S. Huang, Biosens. Bioelectron. 30 (2011) 28–34. L. Luo, F. Li, L. Zhu, Y. Ding, Z. Zhang, D. Deng, B. Lu, Colloid Surf. B 102 (2013) 307–311. L. Wang, Y. Xie, C. Wei, X. Lu, X. Li, Y. Song, Electrochim. Acta 174 (2015) 846–852. L. Lu, L. Zhang, F. Qu, H. Lu, X. Zhang, Z. Wu, S. Huan, Q. Wang, G. Shen, R. Yu, Biosens. Bioelectron. 25 (2009) 218–223. J. Yang, J. Yu, J.R. Strickler, W. Chang, S. Gunasekaran, Biosens. Bioelectron. 47 (2013) 530–538. A. Ciszewski, Electroanalysis 7 (1995) 1132–1135. T.R.I. Cataldi, R. Guascito, A.M. Salvi, J. Electroanal. Chem. 417 (1996) 83–88. T. You, O. Niwa, Z. Chen, K. Hayashi, M. Tomita, S. Hirono, Anal. Chem. 75 (2003) 5191–5196. M.V. Russo, G. Lucci, A. Furlani, G. Polzonetti, Polymer 36 (1995) 4867–4875. C.D. Wanger, W.M. Riggs, L.E. Davis, J.F. Moulder, G.E. Muilenberg (Eds.), Handbook of X-Ray Photoelectron Spectroscopy, Perkin-Elmer Corporation, Physical Electronics Division, Eden Prairie, Minnesota, USA, 1979. I. Danaee, M. Jafarian, F. Forouzandeh, F. Gobal, M.G. Mahjani, Electrochim. Acta 53 (2008) 6602–6609. M. Shamsipur, M. Najafi, M.M. Hosseini, Bioelectrochemistry 77 (2010) 120–124. H. Tian, M. Jia, M. Zhang, J. Hu, Electrochim. Acta 96 (2013) 285–290. Y. Zhang, F. Xu, Y. Sun, Y. Shi, Z. Wen, Z. Li, J. Mater. Chem. 21 (2011) 16949–16954. W. Gao, W.W. Tjiu, J. Wei, T. Liu, Talanta 120 (2014) 484–490. S. Liu, J. Tian, L. Wang, X. Qin, Y. Zhang, Y. Luo, A.M. Asiri, A.O. Al-Youbi, X. Sun, Catal. Sci. Technol. 2 (2012) 813–817. R. Sedghi, Z. Pezeshkian, Sens. Actuators B 219 (2015) 119–124. T.D. Thanh, J. Balamurugan, J.Y. Hwang, N.H. Kim, J.H. Lee, Carbon 98 (2016) 90–98.