Materials Science and Engineering C 34 (2014) 318–325

Contents lists available at ScienceDirect

Materials Science and Engineering C

j ourna l homepage: www.e lsev ie r .com/ locate /msec

Pd–Au nanoparticle decorated carbon nanotube as a sensing layer on thesurface of glassy carbon electrode for electrochemical determinationof ceftazidime

Saeed Shahrokhian a,b,⁎, Razieh Salimian a, Shokoufeh Rastgar a

a Department of Chemistry, Sharif University of Technology, Tehran 11155-9516, Iranb Institute for Nanoscience and Technology, Sharif University of Technology, Tehran, Iran

⁎ Corresponding author at: Department of Chemistry, STehran 11155-9516, Iran. Tel.: +98 21 66005718; fax: +

E-mail address: shahrokhian@sharif.edu (S. Shahrokhi

0928-4931/$ – see front matter © 2013 Elsevier B.V. All rihttp://dx.doi.org/10.1016/j.msec.2013.09.014

a b s t r a c t

a r t i c l e i n f o

Article history:Received 9 April 2013Received in revised form 24 August 2013Accepted 18 September 2013Available online 27 September 2013

Keywords:Palladium nanoparticleGold nanoparticleMulti-walled carbon nanotubeCeftazidimeVoltammetry

A simple electrodepositionmethod is employed to construct a thinfilmmodifier of palladium–gold nanoparticles(Pd–AuNPs) decoratedmulti-walled carbon nanotube (MWCNT) on the surface of glassy carbon electrode (GCE).Morphology and property of Pd–AuNPs–MWCNT have been examined by scanning electron microscopy (SEM)and energy dispersive spectroscopy (EDS). Electrochemical performance of Pd–AuNPs–MWCNT/GCE for detec-tion of ceftazidime (CFZ) has been investigated by cyclic voltammetry (CV). This nanostructured film modifiedelectrode effectively exhibited enhanced properties for detection of ceftazidime (CFZ). The effects of variousexperimental variables such as, the amount of casted MWCNT, time and potential of deposition of metalnanoparticles and the pH of the buffered solution on the electrode response are optimized. The proposed elec-trode showed a linear dynamic range of 0.05–50 μM and the detection limit of 1 nM for the CFZ. The modifiedelectrode successfully supports the sensitive detection of trace amounts of the CFZ in pharmaceutical and clinicalpreparations.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

Metal nanoparticles (NPs) have drawn tremendous attention alongwith their electronic, optical, magnetic, and catalytic properties. In thefield of the electrochemical sensors and biosensors, due to their poten-tial applicability, metal nanoparticles are more helpful in promoting theredox processes [1–3]. It is well established that palladium is the mostactive noble metal for heterogeneous catalysis and electrocatalysis,especially in the fuel cells. Its application in the field of analytical elec-trochemistry is considerable [4–7].

Bimetallic nanoparticle catalysts usually include a primary metalthat has a high performance in catalytic activity and a secondary metalthat can influence the catalytic activity or prevent poisoning prob-lems [8,9]. Bimetallic nanoparticles often create synergetic catalytic im-provement effects in the electrochemical reactions due to their activity,selectivity, and stability compared to the separate components [10,11].Among various bimetallic materials, palladium–gold (Pd–Au) systemis an interesting one as it shows a high activity toward useful chemicalreactions, as well as electrochemical reactions [12–15]. Recently, adrug sensing procedure using the Pd–Au modified electrode has beenreported [16].

harif University of Technology,98 21 66002983.an).

ghts reserved.

Improving the catalytic activity of metal nanoparticles can be re-markably influenced by the applied substrate [17,18]. Carbon nanotubes(CNTs), become the focus of nanotechnology and current research, dueto their special properties such as high surface area, high electricalconductivity, good mechanical strength and fascinating thermal andchemical stability [19,20]. Their ability for accelerating the electrontransfer during the electrochemical reactions makes them suitable sub-strates in reliable devices, such as electrochemical biosensor [21–23].Their unique nanostructures can play a good role as a substrate in con-trolling the size and density of distribution of NPs with the optimizedproperties [24]. Deposition of NPs on CNT has been developed byvarious deposition procedures [25–28]. The electrochemical depositionmethods with some important advantages as rapidness, simplicity,repeatability and low cost have been considered for the fabrication ofNPs. Facility to change the deposition parameters in electrochemicaltechniques provides the possibility to control the morphology of NPs[29]. Therefore, the construction of such hybrid materials, nanoparticle/nanotube is of interest with useful electrical conductive enhancementproperties [30].

Ceftazidime (CFZ) is one of the third-generation cephalosporins witha broad spectrum activity against gram-negative and gram-positive bac-teria. CFZ is an active agent against Pseudomonas aeruginosa, widely usedin the treatment of susceptible infections including respiratory-tractinfections such as pneumonia and lung infections in patients with cysticfibrosis–urinary tract infections, skin and soft tissue infections, boneand joint infections, peritonitis and other abdominal infections [31,32].

319S. Shahrokhian et al. / Materials Science and Engineering C 34 (2014) 318–325

Although CFZ has shown an excellent record of clinical successes, rigor-ous control of its dosage is required since its high dosage can causerenal tubular necrosis in humans [33].

Many techniques have been reported for analyzing theCFZ in biolog-ical samples including colorimetric, microbiological [34], HPLC [35–42]and voltammetric methods [43–50].

In the present work, a simple electrochemical method is reportedfor the decoration of Pd–AuNPs on the structure of carbon nanotubes,pre-casted on the surface of glassy carbon electrode. Characterizationof the morphology and the NP's distribution on the surface of the sur-face-casted nanotube is performed by scanning electron microscopy(SEM). The successful application of the prepared modified electrodefor the voltammetric determination of CFZ in pharmaceutical and clini-cal samples is investigated.

2. Experimental

2.1. Chemicals and reagents

Multi-walled carbon nanotube synthesized by catalytic chemicalvapor deposition (CVD, purity N 95%) with outer diameter (o.d.) of10–20 nm, inner diameter (i.d.) of 5–10 nm and tube length of0.5–200 nmwas obtained fromNanostructured &AmorphousMaterials(Houston, TX, USA). Palladium (II) chloride (PdCl2) was purchased fromAcross Chemical Company, France. Ceftazidime (CFZ, Scheme 1) waspurchased from Aldrich. Stock solutions of CFZ were freshly prepared(10−5 – 10−4 M) in distilled de-ionized water. All other chemicalswere of analytical reagent grade and obtained from Merck. The pH ofall solutions was fixed by using Britton–Robinson buffer solutions. Vialof CFZ (1000 mg) was purchased from local pharmacies. Fresh frozenhuman blood serum was obtained from the Iranian Blood TransfusionOrganization. Two percent (v/v) pure methanol was added to theserum sample. After vortexing each sample for 2 min, the precipitatedproteins were separated by centrifugation for 10 min at 10,000 rpm.Then, the samplewas diluted, spikedwith different amounts of standardCFZ without extraction or further treatment and used for the recoverytests in the voltammetric measurements.

2.2. Instruments

Cyclic voltammetric experiments and the electrodeposition of Pd–AuNPs on MWCNTs were performed using a Metrohm potentiostat/galvanostat model 797VA. A conventional three-electrode system wasused with a glassy carbon working electrode (GC, unmodified or modi-fied, diameter = 2 mm), a saturated Ag/AgCl reference electrode and aPtwire counter electrode. Themorphologies ofMWCNTs and Pd–AuNPselectrodeposited on MWCNTs were obtained using a scanning electronmicroscope (SEM). Voltammetric experiments were carried out in thebuffered solutions of CFZ, which were deoxygenated by purging withpure nitrogen (99.999% from Roham Gas Company). Nitrogen gas wasflowing over the surface of the test solutions during the experiments.

Scheme 1. CFZ's structure.

A digital pH/mV/ion meter (Metrohm, pH Lab 827) was used for prepa-ration of the buffer solutions.

2.3. Preparation of the modified electrode

The MWCNTs were purified in concentrated HNO3 (65%) at ca.300 °C for 30 h to obtain more edge sites and a better dispersion ofnanotubes by the creation of carboxylate groups, followed by rinsingwith deionized water and drying at 70 °C overnight. Before modifica-tion, each GC was polished with alumina slurry (0.1 μm) on a polishingcloth and rinsed thoroughly with water. 2.0 mg of the functionalizedMWCNTs was dispersed in 2.0 mL of DMF until a homogenous sus-pension of MWCNTs was obtained (1 mg/mL). For preparation of theMWCNT/GC electrode, 4 μL of the prepared black suspension wasapplied directly onto a well-polished GC using a micropipette and leftto dry at 50 °C in an oven.

The electrochemical deposition of the Pd–AuNPs was conducted for5 s at a constant potential of−0.2 V (vs. Ag/AgCl) in 0.5 MH2SO4 aque-ous solution containing 0.5 mMgold (III) chloride and 1 mMpalladium(II) chloride (PdCl2). The resulting electrode, renamed as Pd–AuNPs/MWCNT/GC, was rinsed with water. The modification of the electrodesurface was refreshed daily.

3. Results and discussion

3.1. Morphological characterization of surface

The surfacemorphology of the Pd–AuNPs/MWCNT/GCwas specifiedby SEM. A homogeneous layer of MWCNTs with an average diameter of50 nm was coated on the electrode surface (Fig. 1A & B). The averagediameter of well dispersed Pd–AuNPs on MWCNT is approximately60 nm. The presence of Pd, Au and C on the electrode surface has beenshown in EDS results in Supplementary material 1 (S1).

3.2. Electrochemical behavior of the Pd–AuNPs/MWCNT/GC

Studying the electrochemical response of CFZ on the surface ofvarious electrodes including bare GC, MWCNT/GC and Pd–AuNPs/MWCNT/GC was accomplished by using linear sweep voltammetry(LSV). Voltammetric responses of 10 μmol L−1 CFZ in 0.04 mol L−1 BRbuffer solution (pH 5.0), recorded at a scan rate of 100 mV s−1 afteran accumulation time of 300 s at open circuit, are shown in Fig. 2A(current (I/μA) vs. potential). As shown, the oxidation of CFZ on the sur-face of bare electrode appeared as a weak voltammetric response withan anodic peak current of about 0.1 μA. On the other hand, at the surfaceof MWCNT/GC (4 μL casted suspension) a remarkable enhancement inthe peak current was observed (10.1 μA). The anodic peak current forCFZ is more increased on the surface of Pd–AuNPs/MWCNT/GC by a fac-tor of 2 (21.5 μA). It can be stated that, immobilization of Pd–AuNPs onthe surface ofMWCNT/GCwith their large surface area increases the ad-sorptive sites, resulting in a significant increase in the oxidation peakcurrent. In comparison to the bare electrode, only a slight shift in thepeak potential is observed in the voltammetric response of CFZ at thePd–Au/MWCNT/GC. Therefore, it can be concluded that enhancementof the CFZ response is related to the increment of the electrode surfacearea and the strong adsorption of analyte on the surface of the Pd–Au/MWCNT modified electrode.

3.3. Optimization of the amount of carbon nanotube on the electrodesurface

The drop size of the castedMWCNT suspension, prior to the electro-chemical deposition of Pd–Au alloy was optimized according to the LSVresponses. The results show an increase in the oxidation peak current of10 μMCFZ, when the amount of castingMWCNTs varies from 0 to 5 μL.As expected, by increasing the volume of MWCNT, the surface area will

Fig. 1. SEM images with different resolutions of (A) MWCNT, (B) AuNPs/MWCNT and (C) Pd–AuNPs/MWCNT.

320 S. Shahrokhian et al. / Materials Science and Engineering C 34 (2014) 318–325

be increased for depositing NPs. In our investigations, the optimal CFZsensitivitywas obtained by4 μL of theMWCNT suspension (Fig. 2B). Be-cause the large thickness of the film modifier leads to a great resistancefor the electron transfer, a remarkable decrease in the sensitivity wouldbe observed in high volume of carbon nanotube (5 μL).

3.4. Influence of pH

To evaluate the optimum pH for CFZ detection on the surface of themodified electrode, its electrochemical behavior was investigated in thebuffered solutions with various pHs in the range of 3–9 (Fig. 3A). Alinear negative shift was observed in the anodic peak potential of CFZby increasing pH (Fig. 3B) according to Eq. (1):

Ep;a mVð Þ ¼ –65:171 pHþ 1106:6 R2 ¼ 0:9873� �

: ð1Þ

E vs (Ag/AgCl)/V

I / A

I / A

0

1e-5

2e-5

3e-5

4e-5

5e-5A

Bare GC

MWCNT/GC

Pd-Au/MWCNT/GC

0.2 0.4 0.6 0.8 1.0 1.2

Fig. 2. (A) LSVs of 10 μmol L−1 of CFZ on the surface of various electrodes; bareGC (dotted line)CFZ on the surface of Pd–AumodifiedGC, coatedwith various amounts of 1 mg/mL ofMWCNTrate was 100 mV s−1.

Observation of a slope of −65 mV per pH unit confirms the contri-bution of an equal number of protons and electrons in the electrochem-ical reaction of CFZ. Based on such investigations, a buffered solution ofpH 5.0 was chosen as an optimum condition in order to obtain the bestsensitivity in all voltammetricmeasurements. Based on the previous ob-servation, the anodic oxidation of CFZ on the electrode surface can be at-tributed to the conjugate base of the 2-aminothiazole group in itsstructure, which provides a suitable response for analytical determina-tions [51].

3.5. Effect of potential scan rate

The cyclic voltammetric behavior of 10 μM CFZ at the surface of themodified electrode in buffered solution of pH 5.0 was investigated atdifferent potential scan rates from 20 to 400 mV s−1 (Fig. 4A). The lin-ear relationship between the peak current and the square root of thesweep rate (Fig. 4B) describes the diffusion-controlled process for the

E vs (Ag/AgCl)/V0.2 0.4 0.6 0.8 1.0 1.2

0.00000

0.00002

0.00004

0.00006

0.00008

0.00010

0.00012

L

5

1

L

B

μ

μ

, MWCNT/GC (dashed line) and Pd–Au/MWCNT/GC (solid line). (B) LSVs of 10 μmol L−1 ofsuspension. Supporting electrolyte was 0.04 mol L−1 BR buffer solution of pH 5 and sweep

I / A

E vs (Ag/AgCl)/V

5.0e-6

1.0e-5

1.5e-5

2.0e-5

2.5e-5

3.0e-5

3.5e-5A

39

3

4

5

67

8

9

pH

0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 2 4 6 8

E/m

V

500

600

700

800

900

1000B

Ep,a (mV) = - 65.171 pH + 1106.6 (R =0.9873)2

Fig. 3. (A) LSVs for 10 μmol L−1 CFZ at Pd–Au/MWCNT/GC in various pHs (from 3.0 to 9.0) of buffer solution, (B) dependence the oxidation peak potential (Ep,a) with pH solution.Supporting electrolyte was 0.04 mol L−1 BR buffer solution and sweep rate was 100 mV s−1.

321S. Shahrokhian et al. / Materials Science and Engineering C 34 (2014) 318–325

reaction of CFZ on the surface of Pd–AuNPs/MWCNT filmmodified elec-trode (Eq. (2)):

ip;a μAð Þ ¼ 0:9328v1=2 þ 1:8316; R2 ¼ 0:9991: ð2Þ

The positive shift in potential of the oxidation peak with increasingscan rate (Fig. 4C) demonstrates the irreversible nature of the electro-chemical process for CFZ that defined by Eq. (3):

Ep;a mVð Þ ¼ 96:459 log vð Þ þ 611:42; R2 ¼ 0:9911: ð3Þ

According to Laviron Eq. (4) [52]:

Ep ¼ E0 þ 2:303RTαnF

� �log k∘þ 2:303RT

αnF

� �log υð Þ; υ : Vs–1

� �: ð4Þ

E vs (Ag/AgCl)/V

I/μ

A

-60

-40

-20

0

20

40

60

80

100A

20 mV/s

400 mV/s

I / A

0

5e-6

1e-5

2e-5

2e-5

ip,a(A) = 0.9328 1/2 +

B

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 5 10

ν

Fig. 4. CVs of 10 μMCFZ at Pd–AuNPs/MWCNT/GC (A) at various potential scan rates from 20 towas 0.04 mol L−1 BR buffer solution of pH 5.0.

For an irreversible charge-transfer electrode process, the plot of Epversus log(υ) is a straight line with a slope = 2.303RT/αnF (where αstands for the electron transfer coefficient). From Fig. 4C, we can obtainthe slope of Ep vs. log(υ) as 96.459 mV, which a value of αn = 0.61 canbe resulted. By assumption of α = 0.5 for this totally irreversible elec-trode process, participation of one electron and one proton is suggestedin the electro-oxidation of CFZ, under the experimental conditions(buffered solution of pH 5.0).

3.6. Choice of deposition time and potential for the Pd–AuNPs

The potential and time of the electrodeposition of Pd–AuNPs, as twoimportant parameters that affect themorphology of nanoparticles, wereexamined. As expected, increasing the deposition timewill give a chancefor the particle to grow on the electrode surface. In addition, potentialwould control the size and density of particles on the surface. Decreasing

1.8316, R2=0.9991

log ν

15 20 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8

Ep

(mV

)

720

740

760

780

800

820

840

860

880

900

Ep,a(mV) = 96.459 log + 611.42, R2=0.9911

C

ν1/2

ν

400 mV s−1 and (B) plot of Ipa vs. v1/2 and (C) plot of Ep vs. log(v). Supporting electrolyte

E vs (Ag/AgCl)/V0.2 0.4 0.6 0.8 1.0 1.2

1.5e-5

2.0e-5

2.5e-5

3.0e-5

3.5e-5

4.0e-50.1 mM HAuCl 4 + 1mM H 2PdCl 40.5 mM HAuCl 4+ 1 mM H 2PdCl 41 mM HAuCl 4+ 1mM H 2PdCl 41mM H2PdCl 4

I / A

Fig. 6. LSVs for 10 μM CFZ on the surface of MWCNT/GCE coated with various ratios ofPd–AuNPs. Supporting electrolyte was 0.04 mol L−1 BR buffer solution of pH 5 and sweeprate was 100 mV s−1.

322 S. Shahrokhian et al. / Materials Science and Engineering C 34 (2014) 318–325

size and increasing number of nucleus were observed with increasingthe applied potential [29]. The results show that as the deposition timeincreases, the total amount of themetal NPS loaded on the electrode sur-face increases. Consequently, the average particle size of NPs,which theirnucleus formed initially, increases. The same behavior can be observedfor the effect of increasing the deposition potential on the average sizeand compactness of NP layer on the electrode surface. When there isenough increase in the NP size(s), the overlapping diffusion fields ofneighboring particles can result in a linear rather than convergent diffu-sion, leading to a decrease in the response sensitivity toward CFZ. Basedon these investigations, values of −0.2 V for the potential (Fig. 5A) and5 s for time (Fig. 5B) were selected for the electrodeposition of NPs onthe surface of the electrode.

3.7. Effect of the ratio of Pd/Au nanoparticles

For a constant concentration of Pd, as a nanoparticle with a criticalrole on the electrochemical behavior of CFZ, we have tried to improvethe results by adding Au nanoparticles to achieve the unique propertyof the bimetallic layer. Therefore, we have investigated the molar con-centration of Au that may showmuch better results than the monome-tallic Pd nanoparticle layer. It can be seen that, as the concentration ofAu solution increased more than “0.5” mM, the sensitivity toward CFZwill decrease, which may arise from the relation between the concen-trations of used salts and the size and morphology of nanoparticlesformed (Fig. 6).

3.8. Effect of the potential and time of accumulation

From the improvement of the peak currentwith increasing the accu-mulation time it can be deduced that the determination of CFZ has twosteps, including the adsorption on the electrode surface and then diffu-sion through Pd–AuNPs/MWCNT/GC. The stabilization of the peak cur-rent after appropriate accumulation time was observed due to thesurface saturation (Supplementary material 2). In these investigations,the optimization of the accumulation time is performed on a solutionwith a low concentration of CFZ, 1 μM. Changing the accumulation po-tential from 0.3 to −0.3 V has no effect on the peak current of CFZ,which reveals that the accumulation potential has no influence on theoxidation peak current of CFZ. Therefore, the accumulation of CFZ wascarried out under open circuit conditions.

E vs (Ag/AgCl)/V0.2 0.4 0.6 0.8 1.0 1.2

1e-5

2e-5

3e-5

4e-5

5e-50.2 V0.3 V0.4 V

A

I / A

Fig. 5. Effect of (A) deposition potential and (B) deposition time of Pd–Au NPS on the LSV resp0.04 mol L−1 BR buffer solution of pH 5 and sweep rate was 100 mV s−1.

3.9. Voltammetric determinations of CFZ

LSV studies for various concentrations of CFZ (in the range of0.05–50 μM) were performed on the surface of Pd–AuNPs/MWCNT/GCE (Fig. 7A). Based on the plot of peak currents versus the concentra-tion of CFZ, two linear ranges with the following regression equationswere obtained (Fig. 7B):

ip;a μAð Þ ¼ 1:3968C μMð Þ þ 1:4421 R2 ¼ 0:9921� �

ð5Þ

ip;a μAð Þ ¼ 0:2331C μMð Þ þ 11:963 R2 ¼ 0:9918� �

: ð6Þ

Using the calibration curve, a detection limit of 1 nM (S/N = 3)is resulted for the determination of CFZ. The repeatability for the

0.2 0.4 0.6 0.8 1.0 1.2

E vs (Ag/AgCl)/V

0

1e-5

2e-5

3e-5

4e-5

5e-55 s10 s15 s

B

I / A

onses of 10 μM CFZ on the surface of Pd–AuNPs/MWCNT/GC. Supporting electrolyte was

E vs (Ag/AgCl)/V

1e-5

2e-5

3e-5

4e-5

A

CCFZ /

0.0

5.0e-6

1.0e-5

1.5e-5

2.0e-5

2.5e-5

ip,a(A) = 1.3968 C ( M)+1.4421, (R2=0.9921)

ip,a(A)= 0.2331 C ( M) + 11.963, (R2=0.9918)

B

I / A

I / A

0.2 0.4 0.6 0.8 1.0 1.2 0 20 40 60

μ

μ

μmol L-1

Fig. 7. (A) LSVs for various concentrations of CFZ in the range of 0.05–50 μM. (B) Linear calibration curve of peak current vs. CFZ concentration (0.05–50 μM) at Pd–AuNPs/MWCNT/GC.Supporting electrolyte was 0.04 mol L−1 BR buffer solution of pH 5 and sweep rate was 100 mV s−1.

323S. Shahrokhian et al. / Materials Science and Engineering C 34 (2014) 318–325

determination with this modified electrodewas evaluated by recordingthe peak currents of 3 determinations. The relative standard deviation isabout 4.8%.

3.10. Analytical applications

3.10.1. Determination of CFZ in pharmaceutical preparationsA standard addition method was used to assess the applicability of

the proposed method for determination of the content of CFZ in the“ceftazidime” vial as a real pharmaceutical sample by applying the LSVmethod. For this purpose, a known amount of the powdered tablet

E vs (Ag/AgCl)/V

1.5e-5

2.0e-5

2.5e-5

3.0e-5

3.5e-5

4.0e-5A

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

I / A

Fig. 8. (A) LSVs for the tablet samples spiked with CFZ (from down to up: 0.0, 1.0, 2.0, 4.0, 5concentration of CFZ. Supporting electrolyte was 0.04 mol L−1 BR buffer solution of pH 5 and

was spiked with different concentrations of CFZ standard solutionswithin the range of 1–10 μM and diluted with the BR buffer solutionof pH 5. The voltammetric responses and the corresponding standardaddition plot are shown in Fig. 8. Eq. (7) indicates the relation betweenthe peak current and the concentration of CFZ in these studies:

ip;a μAð Þ ¼ 1:5299C μMð Þ þ 1:0452 R2 ¼ 0:9961 : ð7Þ

The resulted recovery data in Table 1 confirms that the tablet matrixdoes not show any considerable interference with the electrochemicaldetermination of CFZ.

C/μM

0 2 4 6 8 100.0

2.0e-6

4.0e-6

6.0e-6

8.0e-6

1.0e-5

1.2e-5

1.4e-5

1.6e-5ip,a(A)= 1.5299 C ( M) + 1.0452, (R2=0.9961)

B

I / A

μ

.0, 6.0, 8.0 μmol L−1) at Pd–AuNPs/MWCNT/GC. (B) The plot of peak current vs. addedsweep rate was 100 mV s−1.

Table 1Results of the recovery analysis of CFZ spiked tablet samples.

No. Spiked (μM) Expected (μM) Found (μM) Recovery (μM)

1 0.1 0.1 0.09818 –

2 1 1.1 0.9966 90.60%3 2 2.1 2.2712 108.15%4 4 4.1 4.3432 105.93%5 5 5.1 5.193 101.82%6 6 6.1 6.1146 100.24%7 8 8.1 7.8794 97.27%

Table 2Results of the recovery analysis of CFZ spiked plasma samples.

No. Spiked (μM) Found (μM) Recovery (μM)

1 1 1.0245 102.45%2 2 2.0871 104.35%3 4 3.6884 92.21%4 6 6.2774 104.62%5 8 7.9236 99.05%

Table 3Effects of interferences on the voltammetric response of CFZ.

Measuring solution Peak current (μA)

Ceftazidime (10 μM) 24 (±0.05) μACeftazidime (10 μM) 22 (±0.03) μAAA (1 mM)DP (0.01 mM)UA (0.1 mM)

324 S. Shahrokhian et al. / Materials Science and Engineering C 34 (2014) 318–325

3.10.2. Determination of CFZ in human blood serumFor preparation of human serum samples, methanol was added to

them (2% (v/v)) and thoroughly mixed. Then, the serum samples werediluted with BR buffer solution (pH 5) in the range of 2–8 μM. The pro-portion of the peak currents with the CFZ concentration (Supplementarymaterial 3) is in conformity with Eq. (8):

ip;a μAð Þ ¼ 0:6682C μMð Þ þ 2:2554; R2 ¼ 0:9943 : ð8Þ

The results showed an acceptable recovery of CFZ in human bloodserum within the range 99.05%–104.35% (Table 2).

Electrochemical investigations were performed in the presences ofsome potentially interfering studies. As can be seen in Fig. 9, the LSV sig-nal of CFZ is completely resolved fromAA, DA and UA. Results of Table 3revealed that the prepared modified electrode can be successfully ap-plied for simultaneous determination of CFZ in the presence of high con-centrations of these biologically important compounds.

Fig. 9. LSVs for solution containing CFZ (10 μM), AA (1 mM), DP (0.01 mM) and UA(0.1 mM) at Pd–AuNPs/MWCNT/GC. Observed peaks (left to right) are corresponding toAA, DA, UA and CFZ. Supporting electrolyte was 0.04 mol L−1 BR buffer solution of pH 5and sweep rate was 100 mV s−1.

4. Conclusion

We reported a new electrochemical sensor for the determinationof CFZ. The applications of nanostructures including bimetallic nanopar-ticle and carbon nanotube as amodifier film on the surface of a GC elec-trode showed a promising result for the oxidation of CFZ. Low detectionlimits, good repeatability and accuracy of data, all together make it anappropriate device for determination of CFZ in the clinical and pharma-ceutical preparations.

Acknowledgments

The authors gratefully acknowledge the support of this work by theResearch Council and the Center of Excellence for Nanostructures ofSharif University of Technology, Tehran, Iran.

Appendix A. Supplementary data

Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.msec.2013.09.014.

References

[1] A.N. Shipway, E. Katz, I. Willner, ChemPhysChem 1 (2000) 18.[2] L. Rassaei, M. Amiri, C.M. Cirtiu, M. Sillanpa¨a¨, F. Marken, M. Sillanpa¨a¨, Trends Anal.

Chem. 30 (2011) 1704.[3] X. Luo, A. Morrin, A.J. Killard, M.R. Smyth, Electroanalysis 18 (2006) 319.[4] L. Meng, J. Jin, G. Yang, T. Lu, H. Zhang, C. Cai, Anal. Chem. 81 (2009) 7271.[5] C. Bianchini, P.K. Shen, Chem. Rev. 109 (2009) 4183.[6] X. Ji, C.E. Banks, A.F. Holloway, K. Jurkschat, C.A. Thorogood, G.G. Wildgoose, R.G.

Compton, Electroanalysis 18 (2006) 2481.[7] Y. Shen, L. Bi, B. Liu, S. Dong, New J. Chem. 27 (2003) 938.[8] C.H. Yen, K. Shimizu, Y. Lin, F. Bailey, I.F. Cheng, C.M.Wai, Energy Fuel 21 (2007) 2268.[9] J.R. Croy, S. Mostafa, L. Hickman, H. Heinrich, B.R. Cuenya, Appl. Catal. A Gen. 350

(2008) 207.[10] N. Toshima, T. Yonezawa, New J. Chem. 22 (1998) 1179.[11] R. Ferrando, J. Jellinek, R.L. Johnston, Chem. Rev. 108 (2008) 845.[12] M. Łukaszewski, A. Czerwiński, Electrochim. Acta 48 (2003) 2435.[13] D. Wang, A. Villa, F. Porta, L. Prati, D. Su, J. Phys. Chem. C 112 (2008) 8617.[14] W.J. Zhou, J.Y. Lee, Electrochem. Commun. 9 (2007) 1725.[15] F. Ksar, L. Ramos, B. Keita, L. Nadjo, P. Beaunier, H. Remita, Chem.Mater. 21 (2009)3677.[16] L.G. Shaidarova, I.A. Chelnokova, A.V. Gedmina, G.K. Budnikov, J. Anal. Chem. 64

(2009) 36.[17] D. Vairavapandian, P. Vichchulada, M.D. Lay, Anal. Chim. Acta. 626 (2008) 119.[18] G.G. Wildgoose, C.E. Banks, R.G. Compton, Small 2 (2006) 182.[19] S. Iijima, Nature 354 (1991) 56.[20] Y. Sun, K. Fu, Y. Lin, W. Huang, Acc. Chem. Res. 35 (2002) 1096.[21] I. Streeter, G.G. Wildgoose, L. Shao, R.G. Compton, Sens. Actuators B 133 (2008) 462.[22] P. Yanez-Sedeno, J. Riu, J.M. Pingarron, F.X. Rius, Trends Anal. Chem. 29 (2010) 939.[23] J. Wang, Electroanalysis 17 (2005) 7.[24] M. Carmo, V.A. Paganin, J.M. Rosolen, E.R. Gonzalez, J. Power Sources 142 (2005) 169.[25] V. Georgakilas, D. Gournis, V. Tzitzios, L. Pasquato, D.M. Guldi,M. Prato, J. Mater. Chem.

17 (2007) 2679.[26] B. Wu, Y. Kuang, X. Zhang, J. Chen, Nano Today 6 (2011) 75.[27] L. Qian, X. Yang, Talanta 74 (2008) 1649.[28] V. Lordi, N. Yao, J. Wei, Chem. Mater. 13 (2001) 733.[29] T.M. Day, P.R. Unwin, J.V. Macpherson, Nano Lett. 7 (2007) 51.[30] S. Shahrokhian, S. Rastgar, Electrochim. Acta 78 (2012) 422.[31] The Merck Index, 10th ed. Merck and Co., Inc., N.J. Rahway, U.S.A., 1983. 1913.[32] K. Florey, Ceftazidime, Analytical Profiles of Drug Substances, 19, Academic Press,

1990, p. 95.[33] M.J. Barza, J. Infect. Dis. 137 (1978) 560.[34] J.E. Thornton, J. Antimicrob. Chemother. 8 (1981) 225.[35] P.T.R. Hwang, P.G. Drexler, M.C. Meyer, J. Liq. Chromatogr. 7 (1984) 979.[36] J.S. Leeder, S.M. Tesoro, A.M. MacLeod, M. Stuart, Antimicrob. Agents Chemother. 24

(1983) 720.

325S. Shahrokhian et al. / Materials Science and Engineering C 34 (2014) 318–325

[37] J. Ayrton, J. Antimicrob. Chemother. 8 (1981) 227.[38] C.M. Myers, J.L. Blumer, Antimicrob. Agents Chemother. 24 (1983) 343.[39] K.L. Tyczkowska, S.S. Seay, M.K. Stoskopf, D.P. Aucoin, J. Chromatogr. B Biomed. Appl.

114 (1992) 305.[40] M.C. Nahata, R.S. Morosco, J. Liq. Chromatogr. 15 (1992) 1507.[41] A.R. Barnes, J. Liq. Chromatogr. 18 (1995) 3117.[42] M.A. Campanero, A.M. Zamarreno, M. Simon, M.C. Dios, J.R. Azanza,

Chromatographia 46 (1997) 374.[43] N.A. El-Maali, M.A. Ghandour, J.-M. Kauffmann, Bioelectrochem. Bioenerg. 38 (1995)

91.[44] N.A. El-Maali, Talanta 51 (2000) 957.

[45] V.S. Ferreira, M.V.B. Zanoni, M. Furlan, A.G. Fogg, Anal. Chim. Acta. 351 (1997)105.

[46] V.S. Ferreira, M.V.B. Zanoni, A.G. Fogg, Microchem. J. 57 (1997) 115.[47] N.A. El-Maali, M.M. Ali, M.K. Maala, M.A. Ghandour, J. Electroanal. Chem. 321 (1991)

485.[48] B. Ogorevc, A. Krasna, V. Hudnik, S. Gomiscek, Mikrochim. Acta 1 (1991) 131.[49] J. Kim, X. Wu, M.R. Herman, J.S. Dordick, Anal. Chim. Acta 367 (1998) 251–258.[50] N.A. El-Maali, A.H. Osman, A.A.M. Aly, G.A.A. Al-Hazmi, Bioelectrochemistry 65

(2005) 95.[51] S.A. Özkan, B. Uslu, P. Zuman, Anal. Chim. Acta. 457 (2002) 265.[52] E. Laviron, J. Electroanal. Chem. 101 (1979) 19.