Copyright © 2007 American Scientific Publishers All rights reserved Printed in the United States of America

Journal of Nanoscience and Nanotechnology Vol. 7, 3365–3372, 2007

Fabrication of a Gold Nanoparticles Decorated Carbon Nanotubes Based Novel Modified Electrode for the Electrochemical Detection of Glucose Kalayil Manian Manesh1
2 , Jun Heon Kim1
2 , Padmanabhan Santhosh1
2 , Anantha Iyengar Gopalan1
2
3 , Kwang-Pill Lee1
2
∗ , and Hee-Dong Kang4 Department of Chemistry Graduate School, Kyungpook National University, Daegu 702-701, South Korea 2 Nano Practical Application Center, Daegu 704-230, South Korea 3 Department of Industrial Chemistry, Alagappa University, Karaikudi 630003, India 4 Department of Physics, Kyungpook National University, Daegu 702-701, South Korea

RESEARCH ARTICLE

1

Delivered by Ingenta to: Max-Planck-Institut A modified electrode based on gold nanoparticles decorated multiwall carbon nanotubes (MWNTs), IP :are 134.105.184.136 functionalized with 4-aminothiophenol and coated over MWNT-Aunano -ME is fabricated. MWNTs Mon, Oct 2007 are 10:51:51 the glassy carbon electrode. Further, Au08 nanoparticles deposited into MWNTs coated GC elec-

trode by electrochemical reduction of HAuCl4 . Field emission transmission electron microscope (FETEM) image shows the formation of ∼5 nm sized Au nanoparticles without any agglomeration on the MWNTs surface. Further, the presence of Au nanoparticles is confirmed through X-ray photoelectron spectroscopic (XPS) studies. The electrocatalytic activity of the MWNT-Aunano -ME towards the detection of glucose is investigated. MWNT-Aunano -ME shows enhanced current response than pristine MWNT-ME over the entire (+0.05 to +0.80 V) potential range. The modified electrode shows linear response to current with the concentration of glucose between 1 and 20 mM. Larger current responses to glucose oxidation are witnessed at +0.60 V than at +0.05 V. However, a large interference signal, reflecting the accelerated oxidation of electroactive interference is observed at +0.60 V. No overlapping signal from the interferents such as ascorbic acid, acetaminophen, and dopamine are observed at the MWNT-Aunano -ME at +0.05 V. Further, the MWNT-Aunano -ME shows high resistance to the toxictiy of chloride ions.

Keywords: Multiwall Carbon Nanotubes, Gold Nanoparticles, Glucose, Sensor.

1. INTRODUCTION Blood glucose monitor is an important tool that helps people with diabetes to assess their physiological status and allow them to properly medicate themselves to have modulated food. The most investigated technology for in vivo glucose monitoring is based on implanted amperometric enzyme electrodes and devices are commercially available and used in clinical practice.1−3 Most of the recent works related to the development of amperometric glucose sensors are based on immobilization of the enzyme such as glucose oxidase,4 or glucose dehydrogenase5 which catalyzes the oxidation of glucose to gluconolactone. The enzyme immobilized electrode surfaces are fabricated to achieve rapid and direct electron transfer.6 Today most commercial amperometric biosensors ∗

Author to whom correspondence should be addressed.

J. Nanosci. Nanotechnol. 2007, Vol. 7, No. 10

rely on reactions catalyzed by oxidase enzyme and subsequent detection of H2 O2 on platinum electrodes. There is a limitation in selectivity of glucose between the biorecognition event and the amperometric detection of H2 O2 . High oxidizing potential (∼700 mV vs. Ag/AgCl) is necessary for the oxidation of H2 O2 that results in substantial interference from the oxidation of other compounds in the complex matrices. Further, the byproduct, H2 O2 , produced by enzymatic reaction denatures the enzymes. In most of the cases, the enzyme based sensors require a redox mediator7 for shuttling the electron between electrode and analyte. Such mediators can be used as replacement for O2 to increase the selectivity and sensitivity of the biosensors. Ferrocene, quinones, quinoid like dyes, organic conducting salts and viologens have been used as mediators.8 Use of mediators allows the exploitation of other oxidoreductase enzymes, including peroxidases and dehydrogenases.9 However, the stability and toxicity of

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these mediators limit their in vivo applications. In general, 2. EXPERIMENTAL DETAILS the amperometric enzyme electrodes have several inherent 2.1. Chemicals problems such as the relatively low output current density and the gradual deterioration of the enzyme activMultiwall carbon nanotubes, MWNTs (10∼50 nm in ity. A possible solution of these problems is to search diameter) obtained from CNT Co., Ltd., Incheon, Korea for an efficient non-enzymatic electrocatalysts for glucose were rinsed with double-distilled water and dried. detection. 4-Aminothiophenol, nitric acid, thionly chloride, tetrahyCarbon nanotubes (CNTs) are one of the most promisdro furan, auric acid, ascorbic acid, acetaminophen, and ing nanomaterials for a wide range of technological dopamine of analytical grade from Aldrich were used innovations.10 Applications of CNTs as electrocatalysts as received. Double-distilled water was used throughout have been investigated widely,11–14 due to its unique comthe experiments. Aqueous solutions of glucose were prebinational properties. Owing to its high surface area and pared in phosphate buffer (pH 7) afresh at the time of good electrical conductivity, CNTs have also been regarded experiments. as perfect supporting materials for catalysts.14 Recently, Surface of glassy carbon (GC) was modified and used investigations demonstrated that metallic nanoparticles can (details are given below) as working electrode. GC elecbe decorated on the external walls or encapsulated in the trode was polished with a suspension of alumina powinterior of the CNTs.14 For example, Pt, Au, and Pt-Ru der (1 m) and then rinsed thoroughly with deionized were deposited on CNTs14–17 by different methodologies water to remove any alumina residue. Electrochemical preand the electrodes show good electrocatalyticDelivered properties by Ingenta treatmentsto:were done in a 50 mM (NH4 2 SO4 solution; for many electrochemical reactions.18
19 pH 3, being adjusted with sulfuric acid. The pretreated Max-Planck-Institut In the present investigation, a robust and non-enzymatic electrodes were allowed to stay for 10 min in deionized IP : 134.105.184.136 glucose sensor electrode based on gold nanoparticles water and used. Mon, 08 Oct 2007 10:51:51 decorated MWNTs (MWNT-Aunano ) is developed. The present investigation shows that the direct oxidation of 2.2. Functionalization of MWNTs glucose in phosphate buffer is achieved by the novel electrocatalysts without loading any enzyme or mediaMWNTs were functionalized with 4-aminothiophenol tors. The MWNT-Aunano -ME shows high sensitivity and (ATP) (Scheme 1(A)) as detailed in our previous work.14 selectivity towards the detection of glucose. Further, the In a typical method, 50 mg of MWNTs were refluxed MWNT-Aunano -ME shows high resistance to the toxicity in 4 M HNO3 for 24 h and filtered through polycarbonate membrane. The residue, MWNT-COOH, was washed of chloride ions. The results are presented herein and with deionized water and dried under vacuum at 60  C for discussed. (A) Functionalization of MWNT

HNO3

HOOC

COOH

HOOC

COOH

SOCl2

ClOC

COCl

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NHCO

CONH

SH

ClOC

COCl 4-aminothiophenol HS

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6O ˚C, 24 h

65 ˚C, 24 h ClOC HOOC

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(B) Fabrication of MWNT-Aunano-ME HS

NHCO

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NHCO

CONH

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NHCO

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NHCO

CONH

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HAuCl4 Electrochemical deposition

HS

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MWNT-Aunano Scheme 1. Functionalization of MWCNTs and fabrication of MWCNT-Aunano -ME.

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12 h. 50 mg of MWNT-COOH was refluxed in 100 ml of thionyl chloride at 65  C for 24 h to obtain MWNTCOCl. MWNT-COCl was filtered, washed with THF and dried under vacuum at room temperature. ATP functionalized MWNTs were prepared by refluxing MWNT-COCl with ATP in THF at 60  C for 24 h. The ATP functionalized MWNTs (MWNT-ATP) were separated by filtration and dried.

Fabrication of a Gold Nanoparticles Decorated Carbon Nanotubes

injections were recorded for injection of a series of concentrated solutions of glucose to the phosphate buffer solution (pH 7).

3. RESULTS AND DISCUSSION 3.1. Fabrication of MWNT-Aunano -ME

was 0.2 eV.

2.5. Instrumentation Electrochemical measurements were carried using EG & G PAR Electrochemical Analyzer. The electrocatalytic activity of the modified electrodes was evaluated by using cyclic voltammetry in phosphate buffer solution containing 1 mM K3 Fe(CN)6 . The amperometric response of the sensor electrode was recorded under steady-state conditions in the phosphate buffer (pH 7) by applying a constant potential (+0.05 or +0.60 V) to the working electrode. The amperometric experiment was performed in an electrochemical cell that contains the modified electrode as working electrode, a SCE reference electrode, and a platinum wire auxiliary electrode. The background response of the modified electrode was allowed to decay to a steady state with stirring. When the background current became stable, a solution of glucose was injected into the electrolytic cell, and its response was measured. In the case of flow analysis, current vs. time for variable glucose concentration J. Nanosci. Nanotechnol. 7, 3365–3372, 2007

Fig. 1. FETEM image of MWNT-Aunano (scale bar: 50 nm); Inset shows the magnified image of Au nanoparticle (scale bar: 1 nm).

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Modification of the surface of working electrode (GC) was performed through sequential steps. At first instant, 2.3. Fabrication of MWNT-Aunano -ME MWNTs were functionalized with ATP (as described in A black suspension (MWNT-ATP) was prepared by disthe Experimental Details Section) and MWNT-ATP was persing 50 mg of MWNT-ATP in DMF with the aid of coated on the GC electrode surface. In the next step, ultrasonication. About 1.0 l of the black suspension was Au nanoparticles were deposited onto MWNT-ATP from dropped on the surface of the pretreated GC electrode and 0.5 M H2 SO4 solution containing HAuCl4 by employing a kept at 60  C for 12 h to evaporate the solvent. The GC repetitive potential scan from 1.1 V to 0.0 V (vs. SCE) as electrode coated with MWNT-ATP was washed with water described in the literature.14 Cyclic voltammograms (CVs) and stored under nitrogen atmosphere. show that there exits two cathodic peaks at ∼0.78 V and Au particles were electrochemically deposited onto ∼0.50 (vs. SCE). No anodic peak is observed during Delivered by IngentaVto: GC/MWNT-ATP layer from 0.5 M H2 SO4 solution of positive scan of potential. The peak at 0.50 V represents Max-Planck-Institut HAuCl4 by employing a repetitive potential scan from the reduction of solution bound AuIII to Au and the wave IP : 134.105.184.136 1.1 V to 0.0 V (vs. SCE) and thus, the modified electrode, at 0.78 V is attributed to the reduction of adsorbed AuCl− Mon, 08 Oct 2007 10:51:51 4 MWNT-Aunano -ME was fabricated. ions to Au .14 Thus, Au loaded MWNT modified electrode, MWNT-Aunano -ME was fabricated. 2.4. Characterization Figure 1 shows the FETEM image of MWNT-Aunano . Spherically shaped Au particles having average size of The morphology of MWNT-Aunano was examined by field about 5–7 nm can be seen on the surface of MWNTs emission transmission electron microscope (FETEM)— with relative uniformity. The loading of Au nanopartiJOEL JEM-2000EX with a field emission gun operated cles on the surface of MWNTs was 18%, which was estiat 200 kV. X-ray photoelectron spectroscopy (XPS) was mated by energy-dispersive X-ray spectroscopy. Generally, recorded on VG Microtech and MT 500/L with a Mo Ka most metals particles would not adhere to MWNTs due to X-rays radiation as the X-ray source for excitation. The its hydrophobicity. Further, metal particles tend to aggredata were obtained at room temperature and the operatgate to form bigger metallic particles on the surface of −9 ing pressure in the analysis chamber was below 10 Torr MWNTs. Surface modification and sensitization activation with analyzer pass energy of 50 eV. The resolution

Manesh et al. (a) 20 µA

Current

have been attempted to improve metal deposition onto the surface of MWNTs. The presence of functional groups on MWNTs increases the metal nucleation. By keeping this in view, in the present instigation, MWNTs were specifically functionalized with 4-aminothiophenol. During electrolysis of HAuCl4 , Au nanoparticles are expected to preferentially anchor into the −SH sites of MWNTs (Scheme 1(B)). The interactions between −SH moieties in MWNTs with Au nanoparticles provide uniform distribution for Au nanoparticles and further prevent aggregation. Attachment of Au nanoparticles into −SH groups is well known.20–23 The oxidation state of Au in the nanoparticles was confirmed by X-ray photoelectron spectroscopy (XPS). Figure 2 presents the XPS spectrum of MWNT-Aunano showing the characteristic Au; 4f7/2 and 4f5/2 doublets. The clear peaks centered at 83.1 eV and 87.3 eV are the signature of Au nanoparticles that exist in MWNT-Aunano .

(b) 1.5 µA

0

0.1

0.2

0.3

0.4

0.5

Potential (V) Delivered by Ingenta to: 3.2. Electro-Catalytic Behavior of MWNT-AuMax-Planck-Institut nano -ME Fig. 3. Cyclic voltammograms of 1 mM K3 Fe(CN)6 in phosphate buffer IP : 134.105.184.136 (pH 7) at (a) MWNT-Aunano -ME and (b) MWNT-ME. The electrochemical performance of the MWNT-Au Mon, 08 nano Oct 2007 10:51:51 ME and MWNT-ME was investigated for the ferricyanide

(FeIII (CN)3− 6 ) system. Figure 3 shows the CVs of 1 mM K3 Fe(CN)6 in the phosphate buffer (pH 7) electrolyte solution at MWNT-Aunano -ME and MWNT-ME. The excellent electrochemical performance of the MWNTAunano -ME is evident by the reversibility of the FeIII /FeII electrochemistry with an ideal peak separation (Ep ) of 61 mV with a half-wave potential of (E1/2 ) of 208 mV (vs. SCE) and augmented current response. However, at MWNT-ME, the Ep was about 92 mV exhibiting pseudoreversibility; similar to the one observed at bare GC electrode. A EP value of ∼100 mV was reported for FeIII /FeII 6000 Au(4f7/2)

Au(4f5/2)

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Counts

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4000

3.3. Hydrodynamic Response of MWNT-Aunano -ME

3000

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Binding energy (eV) Fig. 2. XPS spectrum of MWNT-Aunano showing Au(4f7/2) and Au(4f5/2) double peaks.

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system at CNT paste electrodes.24 A quasi-reversible electrochemistry (Ep = 130 mV) was observed for FeIII /FeII system at Aunano /dithiol modified Au electrode.25 The enhanced electro-catalytic activity of MWNTAunano -ME is expected to arise from the smaller (∼5 nm) crystallite sizes of Au nanoparticles and fine distribution of Au nanoparticles on the surface of MWNTs via formation of Au nanoparticles through self-assembly configuration (Scheme 1). Further, Au nanoparticles provide conduction pathways to accelerate electron transfer through mediation influence of MWNTs. Smaller size (∼5 nm) and uniform distribution of Au nanoparticles in addition to the existence of MWNTs provide a high surface area for the electrocatalytic sites. The excellent electrochemical behavior of MWNTAunano -ME encourages us to develop a non-enzymatic electrode for the detection of glucose. MWNT-Aunano -ME showed augmented current response towards detection of glucose in the phosphate buffer (pH 7). The details are presented below.

Hydrodynamic voltammograms were recorded for a solution of 1 mM glucose in phosphate buffer (pH 7) at MWNT-Aunano -ME and compared with the electrochemical response at MWNT-ME (Fig. 4). Both electrodes show current response over the entire (+0.05 to +0.80 V) potential range, however, a significant increase in peak currents for the oxidation of glucose was noticed with MWNT-Aunano ME in comparison to MWNT-ME (Fig. 4). Typically, at the anodic potential of +0.60 V, MWNT-Aunano -ME shows current response of about 18 A, which is nearly three J. Nanosci. Nanotechnol. 7, 3365–3372, 2007

Fabrication of a Gold Nanoparticles Decorated Carbon Nanotubes

3 µA

Current (µA)

Manesh et al.

Current

a

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20 15 10

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times higher than the current response at MWNT-ME 30 (6.6 A). The anodic current response at MWNT-Aunano 20 ME increases rapidly between +0.05 and +0.60 V and 10 Delivered levels off at higher potential (>0.60 V). The excellent by Ingenta to: 0 0 Max-Planck-Institut sensitivity for glucose oxidation at MWNT-Aunano -ME in IP : 134.105.184.136 a wider potential range arises from the additional surMon, 08 Oct 2007 10:51:51  face area provided by Au nanoparticles for the oxidation process. This indicates that electron transfer at MWNTAunano -ME is more efficient than at MWNT-ME. Further, MWNT-Aunano -ME has a flexible operating potential window (+0.05 to +0.60 V) for monitoring the glucose oxidation process. And, this wider potential range of operation provides scope for using MWNT-Aunano -ME for glucose detection in potential avoiding signals from the electroac0 1 tive interferents.

RESEARCH ARTICLE

Current (µA)

Fig. 4. Hydrodynamic voltammograms for 1 mM glucose at (a) MWNT-Aunano -ME and (b) MWNT-ME in phosphate buffer (pH 7).

Current

Potential / V

3.4. Amperometric Response for Glucose at Low and High Potentials We have assessed the electrocatalytic behavior of MWNTAunano -ME for glucose (Fig. 5) at a low (+0.05 V) and a relatively higher potential (+0.60 V). Figure 5 compares the amperometric current response to successive additions of 1 mM glucose at MWNT-Aunano -ME (a) and MWNTME (b) at the operating potentials of +0.05 V (i) and +0.60 V (ii), respectively. It can be seen from Figure 5 that both electrodes respond to glucose oxidation at +0.05 and +0.60 V. MWNT-Aunano -ME offers larger current signals (Fig. 5(i) and (ii); line (a) than MWNT-ME (Fig. 5(i) and (ii); line (b) reflecting the augmented electrocatalytic activity of MWNT-Aunano -ME. Further, the current noticed at +0.60 V is comparatively higher than noticed at +0.05 V. It is reported that the amperometric response of glucose is insensitive at Pd-nafion-CNT electrode when the potential was held at +0.70 V,26 however in an another report, Au nanoparticles-flavin adenine dinucleotide/ glucose oxidase (Au-FAD/GOx) shows high sensitive for glucose at 0.60 V.27 In the present investigation, MWNTAunano -ME shows higher response to glucose detection J. Nanosci. Nanotechnol. 7, 3365–3372, 2007

b

2

3

4

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Time (min)

Fig. 5. Amperometric response for successive addition of 1 mM glucose at (a) MWNT-Aunano -ME and (b) MWNT-ME measured at different potentials (i) +0.05 V and (ii) +0.60 V, respectively in phosphate buffer (pH 7).

at 0.60 V. Further, higher sensitivity (increased current response) is observed at MWNT-Aunano -ME when the applied potential is held at +0.60 V than at +0.05 V (vs. SCE). The steady-state calibration exhibits linearity upto 20 mM with the detection limit being 0.01 mM. MWNT-Aunano -ME reaches 95% of the steady-state current within 6 s. Also, with a low-potential of operation (+0.05 V), MWNT-Aunano -ME shows linearity for the current response in the concentration range of 1–20 mM. MWNT-Aunano -ME exhibits a rapid and sensitive response to the changes of glucose concentration, indicating excellent electrocatalytic behavior. 3.5. Flow Injection Analysis Flow injection analysis (FIA) is widely used as an analytical tool due to its versatility such as low sample consumption, repeatability of results and high throughput. Further, it is anticipated that FIA can eliminate the diffusion 3369

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restriction of glucose at high concentrations. By considering the ease of FIA in the analytical application, FIA measurements were made using MWNT-Aunano -ME as working electrode. The operating parameters such as flow rate and applied potential were optimized to have better sensitivity at MWNT-Aunano -ME for detection. Figure 6(A) shows the FIA response for with increasing concentration of glucose in phosphate buffer (pH 7) at an applied potential of +0.05 V at a flow rate of 2 ml/min. The calibration plot was linear up to 15 mM glucose with a high sensitivity and regression coefficient of 0.999 and shows curvature at higher concentration (Fig. 6(B)). Reproducibility of MWNT-Aunano -ME was evaluated by successive injection of glucose and an RSD value of 0.5% was observed. Thus, MWNT-Aunano ME shows good reproducibility for repeated detection of glucose and offers to work with low working volumes of about 20 l using FIA.

simultaneously oxidized with glucose at these electrode surfaces and gives interfering electrochemical signal. It is to remember that MWNT-Aunano -ME has a flexible operating potential window (+0.05 to +0.60 V) for monitoring the glucose oxidation process (Fig. 5). MWNT-Aunano -ME shows significant current at +0.05 V (Fig. 5). And, at such a low applied potential (+0.05 V), the current responses of common interferences are minimum and current from the reduction of oxygen is negligible. Figure 7(i) and (ii) represent the amperometric response of MWNT-Aunano -ME with 1 mM glucose and with the addition of relevant physiological levels (0.5 mM) of ascorbic acid (AA), acetaminophen (AP), and dopamine (DA) measured at +0.05 V and +0.60 V, respectively. As it can been seen from the figure that MWNT-Aunano -ME shows current response to glucose at both applied potentials. The subsequent injection of relevant physiological levels of AA, AP, and DA did not show any additional signal or to: modify the current response at MWNT-Aunano Delivered by Ingenta ME when 3.6. Influence of Interferences Max-Planck-Institut the potential was held at +0.05 V (Fig. 7(i)). However, at +0.60 V, the glucose response is modified IP : 134.105.184.136 Electrocatalysts based on metals such as Pt, lose their or increased Mon, 08 Oct 2007 10:51:51by anodic contribution of the electroactive activity rapidly by the accumulation of chemisorbed interspecies (AA, AP, and DA) (Fig. 7(ii)). No interfering elecmediates, which block the electrocatalyst surface. Another trochemical signals was observed at +0.05 V. It is reported disadvantage of these metal catalysts is that they lack the that a large response signal from AA and DA is observed selectivity for glucose. Various organic substances can be at MWNT electrode28 and Au nanoparticles.29 The accelerated electron transfer due to the combined presence of (A) MWNT and Au nanoparticles allows glucose detection at a very low potential (+0.05 V). The low-potential detection leads to high selectivity with effective discrimination against coexisting electroactive species. Note that, a high selective response for glucose detection is obtained at MWNT-Aunano -ME (+0.05 V) in the absence of any external (permselective) coating. Most of the electrochemical glucose sensors based on metals30 or alloys31 can easily lose their activity due to the poisoning of chloride ions. The amperometric glucose signal at Pt and Pt2 Pb diminishes rapidly in the presence of 0.01 M NaCl and eventually almost disappears.31 In order to understand the effect of chloride ions on the 40 (B) glucose detection at MWNT-Aunano -ME, the amperometric Fitted response for glucose was examined by addition of 0.01 N NaCl to the electrolyte solution. A stable, linear response 30 for glucose detection without change in the response cur30 rent is observed at MWNT-Aunano -ME before and after 20 20 addition of 0.01 N NaCl. This infers that the MWNT10 Aunano -ME is not subjected to surface fouling by the action r = 0.999 Expt. points 10 of chloride ions. 0 0 3 6 9 12 15 18 Generally, glucose oxidation at metal electrocatalysts suffers from poisoning resulting from the adsorption of 0 0 10 20 30 40 gluconolactone. Gluconolactone is the intermediate formed Conc./mM during the oxidation of glucose in phosphate buffer at potential negative to Au oxide formation.32 Amperometric Fig. 6. (A) FIA response for MWNT-Aunano -ME with increasing conmeasurements were made at MWNT-Aunano -ME for glucentration of glucose in phosphate buffer (pH 7); E = +005 V; Flow cose detection in order to study the poisoning effect by rate: 2 ml/min. (B) Calibration curves. Current /µA

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Fabrication of a Gold Nanoparticles Decorated Carbon Nanotubes (c)

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Fig. 7. Amperometric response of MWNT-Aunano -ME with Max-Planck-Institut 1 mM glucose and with the addition 0.5 mM of ascorbic acid (AA), acetaminophen (AP), and dopamine (DA) measured at (i) +0.05 V and (ii) +0.60IP V, :respectively. 134.105.184.136

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gluconolactone. No significant difference in response was observed for glucose detection at MWNT-Aunano -ME in the presence and absence of gluconolactone. 3.7. Stability of MWNT-Aunano -ME The most common and serious problem in glucose biosensors based on enzyme immobilization is its insufficient stability. A gradual deterioration of the enzyme activity was observed. Further, these biosensors are susceptible to denaturing. Generally, such problems are not encountered in enzyme-less sensor electrodes. We have monitored the stability of MWNT-Aunano -ME by measuring the response from day to day during storage in phosphate buffer (pH 7) at room temperature for a period of 10 days. During the test period, the MWNT-Aunano -ME showed no apparent decrease in current response for the detection of glucose, which demonstrates the good stability of the electrode.

The authors acknowledge the Korea Basic Science Institute (Daegu) and Kyungpook National University Center for Scientific Instrument.

References and Notes 1. 2. 3. 4. 5. 6. 7. 8.

9. 10.

4. CONCLUSIONS

11.

A new modified electrode based on gold nanoparticles decorated multiwall carbon nanotubes was fabricated. The MWNT-Aunano -ME shows high selective and sensitive response for glucose detection in the absence of any enzyme. Further, MWNT-Aunano -ME has a flexible operating potential window (+0.05 to +0.60 V) for monitoring the glucose oxidation process. High selectivity and high sensitivity for glucose detection was observed at this electrode when the potential was held at +0.05 V and +0.60 V, respectively.

12.

Acknowledgments: The work was supported by Korean Research Foundation Grant (KRF-2006-J02402). J. Nanosci. Nanotechnol. 7, 3365–3372, 2007

13. 14. 15.

16. 17. 18. 19.

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