- Email: [email protected]
Preparation of Nano-Copper Modified Glassy Carbon Electrode and Its Catalytic Oxidation to Glucose
CHINESE JOURNAL OF ANALYTICAL CHEMISTRY Volume 36, Issue 6, June 2008 Online English edition of the Chinese language journal
Cite this article as: Chin J Anal Chem, 2008, 36(6), 839–842.
RESEARCH PAPER
Preparation of Nano-Copper Modified Glassy Carbon Electrode and Its Catalytic Oxidation to Glucose DING Hai-Yun1, ZHOU Ye2, ZHANG Shu-Jing2, YIN Xue-Bo1, LI Yi-Jun1,*, HE Xi-Wen1 1
College of Chemistry, Nankai University, Tianjin 300071, China
2
School of Pharmaceutical Science, Tianjin Medical University, Tianjin 300070, China
Abstract:
Nano-Cu modified glassy carbon electrode (nano-Cu-GCE) fabrication by reduction of CuSO4 in the presence of
cetyltrimethylammonium bromide (CTMAB), through potentiostatic process, and catalytic oxidation of glucose on the nano-Cu-GCE were proposed. Optimum potential and time for deposition of Cu were –100 mV and 8 min, respectively. The potential used for the determination of glucose was 400 mV. The results indicated that nano-Cu-GCE showed an improved catalytic activity on oxidation of glucose compared with the electrode obtained in the absence of CTMAB. Current increment ¨i upon addition of glucose was linear with concentrations of glucose in the range of 1.0 × 10–6–3.9 × 10–4 M in 0.1 M NaOH solution with a detection limit of 2.6 × 10–7 M (S/N = 3). Ascorbic acid (AA), para-acetaminophen (AP), and L-cysteine (Cys) had almost no interference in the glucose response. Key Words: Nano-Cu; Chemical modified electrode; Cetyltrimethylammonium bromide; Glucose; Catalytic oxidation
1
Introduction
Cetyltrimethylammonium bromide (CTMAB) has been used in preparation of nanomaterials because it helps in the production of nanomaterials that are regular in shape and uniform in size[1]. Chen et al[2] prepared decanethiolate-protected Cu nanoparticles by a chemical method, where CTMAB played a critical role in controlling the size and improved the dispersibility of Cu nanoparticles. CTMAB micelles act as template for synthesis of nanomaterials[3,4]. It is, however, difficult to obtain a single product by chemical synthesis. In addition, chemical method is generally complex. Conventional electrochemical methods for synthesis of nanoparticles are prone to the formation of a single substance[5]. However, there are some shortcomings in these methods. For example, particles are easy to congregate and grow large[6]. The size of particles can, however, adjusted by controlling the condition of deposition, but the results are not satisfying. Even if a small size of particles was obtained, the amount of particles was low; if the amount of particles was enough, the size of particles was too large due to their
congregation. This work helped to prepare the nano-Cu particles in the presence of CTMAB as disperser and resolved the problem in preparation of Cu nanoparticles by electrochemistry. In addition, nanoparticles show excellent properties over bulk electrode in electrochemistry. It can promote mass transport, have high catalytic activity, large effective area, and control the microenvironment of electrode[7]. A lot of metal nanoparticles were used for electrochemical detection[8]. Copper or its oxide modified electrode can catalyze the oxidation reaction of some bio-substances such as carbohydrates, amino acids, and peptides[9–11]. Thus, some determination methods for bio-substances have been proposed in relation to the properties. Nano-Cu modified GC/Nafion electrode can catalyze neurotransmitter molecules selectively in the presence of interfering species such as ascorbic acid (AA), and uric acid[12]. Tzeng et al[13] synthesized nano copper in the presence of strong light and used it to detect bioorganic molecules. In this study, nano-Cu-glassy carbon electrode (GCE) was prepared by modifying Cu nanoparticles on GCE. Nano-Cu-
Received 30 August 2007; accepted 28 September 2007 * Corresponding author. Email: [email protected]; Tel: +86 22-23494885; Fax: +86 22-23502458 This work was supported by the State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. Copyright © 2008, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. Published by Elsevier Limited. All rights reserved.
DING Hai-Yun et al. / Chinese Journal of Analytical Chemistry, 2008, 36(6): 839–842
GCE was able to catalyze the oxidation of glucose (Glu). The comparison between nano-Cu-GCE and bulk size of Cu particles modified GCE (Cu-GCE) was carried out. The preparation of Cu nanoparticles was simple and the detection limit for Glu was improved. The cost was lower because no glucose oxidase (GOD) was required.
2 2.1
Experimental Instruments and reagents
Electrochemical measurements were performed through the BAS Epsilon-EC (Bioanalytical Systems, Inc. USA). Three-electrode system was used, with GCE or Cu particles modified GCE as work electrode, Pt wire as count electrode, and saturated calomel electrode (SCE) as reference electrode. Scanning electron microscope (Hitachi, S-3500N) was used to characterize the morphology and size of Cu particles. Reagents, glucose (AR, Tianjin Damao Chemical Reagent Factory), para-acetaminophen (RS, National Institute for the Control of Pharmaceutical and Biological Products), ascorbic acid (GR, Northeast General Pharmaceutical Factory), and L-cysteine (BR, Beijing Aoboxing Biotechnology Ltd.) were used. All other reagents were of analytical grade, and deionized water from a Millipore milliQ system was used throughout the experiment. 2.2
Modification of GCE
GCE was polished with alumina power and washed through a supersonic operation. Cyclic voltammetry (CV) was performed in 0.1 M NaOH solution between –300 and 700 mV at a rate of 100 mV s–1 till the cyclic voltammogram became stable. Scan rate was set at 100 mV s–1 in the whole CV experiment. Cu particles was deposited through a constant potential process in the electrolyte composed of 3 ml 5.0 × 10–3 M CuSO4 + 1 ml 1.0 × 10–2 M CTMAB + 1 ml 2.5 × 10–2 M H2SO4. Then, the electrode was rinsed with water and placed in 0.1 M NaOH solution for CV scan. The potential range was from –300 to 700 mV. 2.3
Determination methods
According to a previous report[14], 0.1 M NaOH solution was used as buffer electrolyte. Glu aqueous solutions of 0.1, 0.01 and 0.001 M were prepared. A certain amount of Glu solution was added into 5 ml NaOH solution with a microinjector under electromagnetic stirring and current response was recorded by chronoamperometry.
3
Results and discussion
3.1 Catalytic oxidation of Glu on Cu modified GCE
Fig.1
Cyclic voltammograms of bare GCE (1, 2) and nano-Cu-GCE (3, 4)
1 and 3: without Glu; 2 and 4: 4.0 × 10–5 M Glu. In 0.1 M NaOH
Nano-Cu-GCE was prepared by potentiostatic deposition of Cu on GCE at 100 mV for 8 min. Nano-Cu-GCE was characterized by CV scan and compared with bare GCE (Fig.1). As observed Lines 1 and 2 is almost overlapped. The phenomena show that no oxidation reaction of Glu occurred at bare GCE in the range from –300 to 700 mV. However, oxidation current of Glu at nano-Cu-GCE was observed (Line 4) at approximately 360 mV. This indicated that nano-Cu-GCE catalyzed oxidation of Glu. CV process of Cu modified electrode in NaOH solution produced Cu(II). After addition of Glu, Cu(II) was further oxidized to higher valent Cu(III) in CV scan. Thus, Cu(III) is an effective component that catalyzes oxidation of Glu. 3.2 Deposition potential For 10 min of deposition time, effect of deposition potential was investigated through comparison of different electrodes prepared by different potentials. Cyclic voltammograms of modified electrode were recorded in NaOH solution both in the absence of Glu and in the presence of 4 × 10–5 M Glu. The Cyclic voltammograms were similar with Line 3 and Line 4 (Fig.1). The ratio D (D = ig/ib) of anodic current (at 360 mV) ig (presence) to ib (absence) was taken as criterion to denote the influence of deposition potential. The experiment showed that ib at deposition potential of –100 mV reached the largest value and D was lower than the highest D at –150 mV and the difference was only 0.015. Taking into account the sensitivity of modified electrode, –100 mV was selected as optimum deposition potential of Cu. 3.3 Deposition time Effect of deposition time (5–20 min) was examined at the optimum deposition potential (–100 mV). CV scans were carried out at different modified electrodes at different deposition time. The ratio E (E = ig/ib) of anodic current ig (4 × 10–5 M Glu) to ib (absence of Glu) was taken as criterion to denote the influence of deposition time. The ib reached steady value from 8 min and the E reached the highest value at 8 min. It was obvious that 8 min was the optimum deposition time.
DING Hai-Yun et al. / Chinese Journal of Analytical Chemistry, 2008, 36(6): 839–842
3.5 Potential in measurement Current response of nano-Cu-GCE to Glu at different potentials (300, 360, 400 and 450 mV) were measured. When 10, 20 and 30 Pl Glu of 0.01 M was added into 5 ml NaOH gradually, obvious difference of current response was observed at different measured potentials. Because the largest current response appeared at 400 mV, 400 mV was selected as optimum measured potential. Fig.2 Cyclic voltammograms of different electrodes modified in the
3.6 Interference
–3
absence of CTMAB (1, 3) and in the presence of 2 × 10 M CTMAB (2, 4) –5
1, 2: without Glu; 3, 4: 4.0 × 10 M Glu. In 0.1 M NaOH
3.4 Effect of CTMAB Cu was deposited on the GCE under the optimum condition described above. A weak catalysis for oxidation of Glu was observed on the Cu modified GCE prepared in electrolyte in the absence of CTMAB (Lines 1 and 3, Fig.2); whereas obvious catalytic oxidation current appeared on the Cu modified GCE obtained in electrolyte in the presence of CTMAB (Line 4, Fig.2) and the peak potential was approximately 360 mV. The reason was that CTMAB dispersed the Cu particles on GCE in the deposition process. The Cu particles became smaller and the special surface was increased, and therefore the catalytic activity improved. The results were consistent with SEM characteristics (Fig.3). Only abundant conjugated Cu particles with diameter of 0.5 Pm were deposited when the electrolyte did not contain CTMAB. When CTMAB was added into the electrolyte, Cu particles with diameters of approximately 50 nm were obtained and they were uniform. Cu nanoclusters produced were covered by CTMAB in the solution, surface tension of nano clusters decreased, and consequently nano clusters stabilized[15,16]. It is found that CH3–N+ headgroup of CTMAB bonded to surface of Cu and its long alkyl hydrophobic chain reached outward, thereby nanoparticles were separated one by one[17].
Interference was determined by chronoamperometry under electromagnetic stirring. A certain amount of Glu solution was added into the electrolyte solution containing 5 ml 0.1 M NaOH and the stable current response was recorded (ig). Then a droplet of the respective interference solution was added and the current response was recorded (ig+i). The interference factor was denoted as Ȗ (Ȗ = ig+i/ig). Interferences of the physiological normal level in human blood to 5.5 mM Glu were examined. Their concentrations were 0.1 mM (AA), 0.1 mM (AP), and 0.05 mM (Cys). Experiments were carried out according to the concentrations after blood was diluted 50 times. The results showed that for 0.11 m M Glu, Ȗ of 2.0 × 10–6 M AA, 2.0 × 10–6 M AP, and 1.0 × 10–6 M Cys were 1.02, 1.02 and 1.00, respectively. Therefore, interference of AA or AP for the determination of Glu could be ignored, and Cys had almost no interference in the glucose response. It was found that nano-Cu-GCE has good selectivity for determination of Glu in the blood. 3.7 Analytical performance Glu was added into NaOH electrolyte gradually and i-t curve was recorded at the same time. Current increment (¨i) resulting from addition of Glu in the electrolyte was proportional to the concentration of Glu in the range of 1.0 × 10–6–3.9 × 10–4 M. The regression equation was ¨i (PA) = –1.02 – 125674.54C (M) with correlation coefficient r of 0.99 and detection limit of 2.6 × 10–7 M (S/N = 3).
Fig.3 SEM photographs of electrode surface a, bare GCE; b, Cu-GCE (without CTMAB); c, nano-Cu-GCE (with CTMAB)
DING Hai-Yun et al. / Chinese Journal of Analytical Chemistry, 2008, 36(6): 839–842
Table 1 Electrochemical determination of glucose Electrode Poly(azure B)/Cu/GCE Au/Cu/POAP/GOD Nano-Cu-GCE
E(V)
Enzyme
DL(M)
Linear range (M)
Ref.
0.6 0.7 0.4
No GOD No
5.0 × 10–6 1.0 × 10–5 2.6 × 10–7
1.0 × 10–5–1.0 × 10–2 ~1.0 × 10–2 1.0 × 10–6–3.9 × 10–4
[18] [19] This work
*versus Ag/AgCl, the others are relative to SCE.
Table 2 Variety of current on nano-Cu-GCE Storage conditions Nano-Cu-GCE1/ambient condition Nano-Cu-GCE2/0.1M NaOH
i (PA)/2 h
2h
3h
4h
5h
16 h
2.78 2.26
100% 100%
102% 90.7%
93.9% 79.6%
85.2% 70.8%
77.7% 39.8%
The applied potential of nano-Cu-GCE for determination of Glu was 0.4 V. Compared with relevant literature[18,19] (Table 1), the applied potential was lower than that of other methods i.e. 0.6 V at poly (azure B)/Cu/GCE[18] and 0.7 V at Au/Cu/POAP/ GOD[19]. The detection limit of 2.6 × 10–7 M was also low than that reported in literature. In addition, use of GOD in traditional sensor of Glu increased the cost, and the sensor was limited by detection condition. However, the GOD in the nano-Cu-GCE did not have advantages such as high sensitivity, quick response, simple operation, and low cost. Hence, it would be of great advantage if microprobe is prepared for detection of Glu in blood and it can be used widely in the fields of biomedicine, environment, food, and medicinal industry.
[2]
3.8 Stability
[9]
Chen L, Zhang D, Chen J, Zhou H, Wan H. Mat. Sci. Eng. A, 2006, 415(1-2):156–161
[3]
Zhang H, Shen C, Chen S, Xu Z, Liu F, Li J, Gao H. Nanotechnology, 2005, 16(2): 267–272
[4]
Zhang X J, Zhang X H, Wu S K. Chem. J. Chinese Universities, 2005, 26(7): 1330–1333
[5]
Nikoliü N D, Popov K I, Pavloviü L J, Pavloviü M G. Surface & Coatings Technology, 2006, 201: 560–566
[6]
Joshi S S, Patil S F, Iyer V, Mahumuni S. Nanostruct. Mater.,
[7]
Welch C M, Compton R G. Anal. Bioanal. Chem., 2006, 384:
1998, 10(7): 1135–1144 601–619 [8]
ljukiü B, Baron R, Salter C, Crossley A, Compton R G. Anal. Chim. Acta., 2007, 590: 67–73 Qu X J, Zhang B, Ai S Y, Li J H, Zhu L S. Chinese J. Anal. Chem., 2007, 35(3): 386–389
Nano-Cu-GCE was stored in two conditions for estimation of stability. Nano-Cu-GCE1 was in ambient condition, and nano-Cu-GCE2 was stored in 0.1 M NaOH solution. Current response of the electrode at 400 mV in 1.1 × 10–4 M Glu-0.1 M NaOH solution was measured every one hour. Current response of nano-Cu-GCE1 became stable after 2 h, however, current response of nano-Cu-GCE2 decreased gradually. Current after 2 h is presumed as 100% and their variation is listed in Table 2. Consequently ambient condition was selected for preservation of nano-Cu-GCE. Relative standard deviation is 4.7% for 7 repetitive determinations of 1.0 × 10–4 M Glu solution.
[10] Brazill S A, Singhal P, Kuhr W G. Anal. Chem., 2000, 72(22): 5542–5548 [11] Zen J M, Hsu C T, Kumar A S, Lyuu H J, lin K Y. Analyst, 2004, 129(9): 841–845 [12] Ramaraj R. J. Chem. Sci., 2006, 118(6): 593–600 [13] Tzeng J, Shiu J, Jung S. TW Patent, TW244231-B1, 2004 [14] Luo P, Zhang F, Baldwin R P. Anal. Chem., 1991, 63(17): 1702–1707 [15] Prabhu S V, Baldwin R P. Anal. Chem., 1989, 61(8): 852–856 [16] Chen S H, Carroll D L. Nano Lett., 2002, 2(9): 1003–1007 [17] Xie S Y, Ma Z J, Wang C F, Lin S C, Jiang Z Y, Huang R B, Zheng L S. J. Solid State Chem., 2004, 177(10): 3743–3747
References
[18] Huang Y G, Wang H Y, Hu X Y. Chinese J. Anal. Chem., 2006,
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[19] Pan D, Chen J, Yao S, Nie L, Xia J, Tao W. Sensor. Actuat. B:
34(8): 1119–1121 Sun F, Guo Y, Song W, Zhao J, Tang L, Wang Z. J. Cryst. Growth, 2007, 304(2): 425–429
Chem., 2005, 104(1): 68–74
Cite this article as: Chin J Anal Chem, 2008, 36(6), 839–842.
RESEARCH PAPER
Preparation of Nano-Copper Modified Glassy Carbon Electrode and Its Catalytic Oxidation to Glucose DING Hai-Yun1, ZHOU Ye2, ZHANG Shu-Jing2, YIN Xue-Bo1, LI Yi-Jun1,*, HE Xi-Wen1 1
College of Chemistry, Nankai University, Tianjin 300071, China
2
School of Pharmaceutical Science, Tianjin Medical University, Tianjin 300070, China
Abstract:
Nano-Cu modified glassy carbon electrode (nano-Cu-GCE) fabrication by reduction of CuSO4 in the presence of
cetyltrimethylammonium bromide (CTMAB), through potentiostatic process, and catalytic oxidation of glucose on the nano-Cu-GCE were proposed. Optimum potential and time for deposition of Cu were –100 mV and 8 min, respectively. The potential used for the determination of glucose was 400 mV. The results indicated that nano-Cu-GCE showed an improved catalytic activity on oxidation of glucose compared with the electrode obtained in the absence of CTMAB. Current increment ¨i upon addition of glucose was linear with concentrations of glucose in the range of 1.0 × 10–6–3.9 × 10–4 M in 0.1 M NaOH solution with a detection limit of 2.6 × 10–7 M (S/N = 3). Ascorbic acid (AA), para-acetaminophen (AP), and L-cysteine (Cys) had almost no interference in the glucose response. Key Words: Nano-Cu; Chemical modified electrode; Cetyltrimethylammonium bromide; Glucose; Catalytic oxidation
1
Introduction
Cetyltrimethylammonium bromide (CTMAB) has been used in preparation of nanomaterials because it helps in the production of nanomaterials that are regular in shape and uniform in size[1]. Chen et al[2] prepared decanethiolate-protected Cu nanoparticles by a chemical method, where CTMAB played a critical role in controlling the size and improved the dispersibility of Cu nanoparticles. CTMAB micelles act as template for synthesis of nanomaterials[3,4]. It is, however, difficult to obtain a single product by chemical synthesis. In addition, chemical method is generally complex. Conventional electrochemical methods for synthesis of nanoparticles are prone to the formation of a single substance[5]. However, there are some shortcomings in these methods. For example, particles are easy to congregate and grow large[6]. The size of particles can, however, adjusted by controlling the condition of deposition, but the results are not satisfying. Even if a small size of particles was obtained, the amount of particles was low; if the amount of particles was enough, the size of particles was too large due to their
congregation. This work helped to prepare the nano-Cu particles in the presence of CTMAB as disperser and resolved the problem in preparation of Cu nanoparticles by electrochemistry. In addition, nanoparticles show excellent properties over bulk electrode in electrochemistry. It can promote mass transport, have high catalytic activity, large effective area, and control the microenvironment of electrode[7]. A lot of metal nanoparticles were used for electrochemical detection[8]. Copper or its oxide modified electrode can catalyze the oxidation reaction of some bio-substances such as carbohydrates, amino acids, and peptides[9–11]. Thus, some determination methods for bio-substances have been proposed in relation to the properties. Nano-Cu modified GC/Nafion electrode can catalyze neurotransmitter molecules selectively in the presence of interfering species such as ascorbic acid (AA), and uric acid[12]. Tzeng et al[13] synthesized nano copper in the presence of strong light and used it to detect bioorganic molecules. In this study, nano-Cu-glassy carbon electrode (GCE) was prepared by modifying Cu nanoparticles on GCE. Nano-Cu-
Received 30 August 2007; accepted 28 September 2007 * Corresponding author. Email: [email protected]; Tel: +86 22-23494885; Fax: +86 22-23502458 This work was supported by the State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. Copyright © 2008, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. Published by Elsevier Limited. All rights reserved.
DING Hai-Yun et al. / Chinese Journal of Analytical Chemistry, 2008, 36(6): 839–842
GCE was able to catalyze the oxidation of glucose (Glu). The comparison between nano-Cu-GCE and bulk size of Cu particles modified GCE (Cu-GCE) was carried out. The preparation of Cu nanoparticles was simple and the detection limit for Glu was improved. The cost was lower because no glucose oxidase (GOD) was required.
2 2.1
Experimental Instruments and reagents
Electrochemical measurements were performed through the BAS Epsilon-EC (Bioanalytical Systems, Inc. USA). Three-electrode system was used, with GCE or Cu particles modified GCE as work electrode, Pt wire as count electrode, and saturated calomel electrode (SCE) as reference electrode. Scanning electron microscope (Hitachi, S-3500N) was used to characterize the morphology and size of Cu particles. Reagents, glucose (AR, Tianjin Damao Chemical Reagent Factory), para-acetaminophen (RS, National Institute for the Control of Pharmaceutical and Biological Products), ascorbic acid (GR, Northeast General Pharmaceutical Factory), and L-cysteine (BR, Beijing Aoboxing Biotechnology Ltd.) were used. All other reagents were of analytical grade, and deionized water from a Millipore milliQ system was used throughout the experiment. 2.2
Modification of GCE
GCE was polished with alumina power and washed through a supersonic operation. Cyclic voltammetry (CV) was performed in 0.1 M NaOH solution between –300 and 700 mV at a rate of 100 mV s–1 till the cyclic voltammogram became stable. Scan rate was set at 100 mV s–1 in the whole CV experiment. Cu particles was deposited through a constant potential process in the electrolyte composed of 3 ml 5.0 × 10–3 M CuSO4 + 1 ml 1.0 × 10–2 M CTMAB + 1 ml 2.5 × 10–2 M H2SO4. Then, the electrode was rinsed with water and placed in 0.1 M NaOH solution for CV scan. The potential range was from –300 to 700 mV. 2.3
Determination methods
According to a previous report[14], 0.1 M NaOH solution was used as buffer electrolyte. Glu aqueous solutions of 0.1, 0.01 and 0.001 M were prepared. A certain amount of Glu solution was added into 5 ml NaOH solution with a microinjector under electromagnetic stirring and current response was recorded by chronoamperometry.
3
Results and discussion
3.1 Catalytic oxidation of Glu on Cu modified GCE
Fig.1
Cyclic voltammograms of bare GCE (1, 2) and nano-Cu-GCE (3, 4)
1 and 3: without Glu; 2 and 4: 4.0 × 10–5 M Glu. In 0.1 M NaOH
Nano-Cu-GCE was prepared by potentiostatic deposition of Cu on GCE at 100 mV for 8 min. Nano-Cu-GCE was characterized by CV scan and compared with bare GCE (Fig.1). As observed Lines 1 and 2 is almost overlapped. The phenomena show that no oxidation reaction of Glu occurred at bare GCE in the range from –300 to 700 mV. However, oxidation current of Glu at nano-Cu-GCE was observed (Line 4) at approximately 360 mV. This indicated that nano-Cu-GCE catalyzed oxidation of Glu. CV process of Cu modified electrode in NaOH solution produced Cu(II). After addition of Glu, Cu(II) was further oxidized to higher valent Cu(III) in CV scan. Thus, Cu(III) is an effective component that catalyzes oxidation of Glu. 3.2 Deposition potential For 10 min of deposition time, effect of deposition potential was investigated through comparison of different electrodes prepared by different potentials. Cyclic voltammograms of modified electrode were recorded in NaOH solution both in the absence of Glu and in the presence of 4 × 10–5 M Glu. The Cyclic voltammograms were similar with Line 3 and Line 4 (Fig.1). The ratio D (D = ig/ib) of anodic current (at 360 mV) ig (presence) to ib (absence) was taken as criterion to denote the influence of deposition potential. The experiment showed that ib at deposition potential of –100 mV reached the largest value and D was lower than the highest D at –150 mV and the difference was only 0.015. Taking into account the sensitivity of modified electrode, –100 mV was selected as optimum deposition potential of Cu. 3.3 Deposition time Effect of deposition time (5–20 min) was examined at the optimum deposition potential (–100 mV). CV scans were carried out at different modified electrodes at different deposition time. The ratio E (E = ig/ib) of anodic current ig (4 × 10–5 M Glu) to ib (absence of Glu) was taken as criterion to denote the influence of deposition time. The ib reached steady value from 8 min and the E reached the highest value at 8 min. It was obvious that 8 min was the optimum deposition time.
DING Hai-Yun et al. / Chinese Journal of Analytical Chemistry, 2008, 36(6): 839–842
3.5 Potential in measurement Current response of nano-Cu-GCE to Glu at different potentials (300, 360, 400 and 450 mV) were measured. When 10, 20 and 30 Pl Glu of 0.01 M was added into 5 ml NaOH gradually, obvious difference of current response was observed at different measured potentials. Because the largest current response appeared at 400 mV, 400 mV was selected as optimum measured potential. Fig.2 Cyclic voltammograms of different electrodes modified in the
3.6 Interference
–3
absence of CTMAB (1, 3) and in the presence of 2 × 10 M CTMAB (2, 4) –5
1, 2: without Glu; 3, 4: 4.0 × 10 M Glu. In 0.1 M NaOH
3.4 Effect of CTMAB Cu was deposited on the GCE under the optimum condition described above. A weak catalysis for oxidation of Glu was observed on the Cu modified GCE prepared in electrolyte in the absence of CTMAB (Lines 1 and 3, Fig.2); whereas obvious catalytic oxidation current appeared on the Cu modified GCE obtained in electrolyte in the presence of CTMAB (Line 4, Fig.2) and the peak potential was approximately 360 mV. The reason was that CTMAB dispersed the Cu particles on GCE in the deposition process. The Cu particles became smaller and the special surface was increased, and therefore the catalytic activity improved. The results were consistent with SEM characteristics (Fig.3). Only abundant conjugated Cu particles with diameter of 0.5 Pm were deposited when the electrolyte did not contain CTMAB. When CTMAB was added into the electrolyte, Cu particles with diameters of approximately 50 nm were obtained and they were uniform. Cu nanoclusters produced were covered by CTMAB in the solution, surface tension of nano clusters decreased, and consequently nano clusters stabilized[15,16]. It is found that CH3–N+ headgroup of CTMAB bonded to surface of Cu and its long alkyl hydrophobic chain reached outward, thereby nanoparticles were separated one by one[17].
Interference was determined by chronoamperometry under electromagnetic stirring. A certain amount of Glu solution was added into the electrolyte solution containing 5 ml 0.1 M NaOH and the stable current response was recorded (ig). Then a droplet of the respective interference solution was added and the current response was recorded (ig+i). The interference factor was denoted as Ȗ (Ȗ = ig+i/ig). Interferences of the physiological normal level in human blood to 5.5 mM Glu were examined. Their concentrations were 0.1 mM (AA), 0.1 mM (AP), and 0.05 mM (Cys). Experiments were carried out according to the concentrations after blood was diluted 50 times. The results showed that for 0.11 m M Glu, Ȗ of 2.0 × 10–6 M AA, 2.0 × 10–6 M AP, and 1.0 × 10–6 M Cys were 1.02, 1.02 and 1.00, respectively. Therefore, interference of AA or AP for the determination of Glu could be ignored, and Cys had almost no interference in the glucose response. It was found that nano-Cu-GCE has good selectivity for determination of Glu in the blood. 3.7 Analytical performance Glu was added into NaOH electrolyte gradually and i-t curve was recorded at the same time. Current increment (¨i) resulting from addition of Glu in the electrolyte was proportional to the concentration of Glu in the range of 1.0 × 10–6–3.9 × 10–4 M. The regression equation was ¨i (PA) = –1.02 – 125674.54C (M) with correlation coefficient r of 0.99 and detection limit of 2.6 × 10–7 M (S/N = 3).
Fig.3 SEM photographs of electrode surface a, bare GCE; b, Cu-GCE (without CTMAB); c, nano-Cu-GCE (with CTMAB)
DING Hai-Yun et al. / Chinese Journal of Analytical Chemistry, 2008, 36(6): 839–842
Table 1 Electrochemical determination of glucose Electrode Poly(azure B)/Cu/GCE Au/Cu/POAP/GOD Nano-Cu-GCE
E(V)
Enzyme
DL(M)
Linear range (M)
Ref.
0.6 0.7 0.4
No GOD No
5.0 × 10–6 1.0 × 10–5 2.6 × 10–7
1.0 × 10–5–1.0 × 10–2 ~1.0 × 10–2 1.0 × 10–6–3.9 × 10–4
[18] [19] This work
*versus Ag/AgCl, the others are relative to SCE.
Table 2 Variety of current on nano-Cu-GCE Storage conditions Nano-Cu-GCE1/ambient condition Nano-Cu-GCE2/0.1M NaOH
i (PA)/2 h
2h
3h
4h
5h
16 h
2.78 2.26
100% 100%
102% 90.7%
93.9% 79.6%
85.2% 70.8%
77.7% 39.8%
The applied potential of nano-Cu-GCE for determination of Glu was 0.4 V. Compared with relevant literature[18,19] (Table 1), the applied potential was lower than that of other methods i.e. 0.6 V at poly (azure B)/Cu/GCE[18] and 0.7 V at Au/Cu/POAP/ GOD[19]. The detection limit of 2.6 × 10–7 M was also low than that reported in literature. In addition, use of GOD in traditional sensor of Glu increased the cost, and the sensor was limited by detection condition. However, the GOD in the nano-Cu-GCE did not have advantages such as high sensitivity, quick response, simple operation, and low cost. Hence, it would be of great advantage if microprobe is prepared for detection of Glu in blood and it can be used widely in the fields of biomedicine, environment, food, and medicinal industry.
[2]
3.8 Stability
[9]
Chen L, Zhang D, Chen J, Zhou H, Wan H. Mat. Sci. Eng. A, 2006, 415(1-2):156–161
[3]
Zhang H, Shen C, Chen S, Xu Z, Liu F, Li J, Gao H. Nanotechnology, 2005, 16(2): 267–272
[4]
Zhang X J, Zhang X H, Wu S K. Chem. J. Chinese Universities, 2005, 26(7): 1330–1333
[5]
Nikoliü N D, Popov K I, Pavloviü L J, Pavloviü M G. Surface & Coatings Technology, 2006, 201: 560–566
[6]
Joshi S S, Patil S F, Iyer V, Mahumuni S. Nanostruct. Mater.,
[7]
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