jo u r nal homep age: www.elsev ier .com/ locate /snb
lectrodeposition of palladium nanoparticles on porous graphitizedarbon monolith modified carbon paste electrode for simultaneousnhanced determination of ascorbic acid and uric acid
iriboon Mukdasaia, Una Crowleyb, Mila Pravdab, Xiaoyun Hec,katerina P. Nesterenkoc, Pavel N. Nesterenkod, Brett Paulld, Supalax Srijaranaia,eremy D. Glennonb, Eric Mooreb,e,∗
Materials Chemistry Research Center, Department of Chemistry, Faculty of Science, Khon Kaen University, Khon Kaen 40002, ThailandIrish Separation Science Cluster (ISSC), Department of Chemistry and Analytical, Biological Chemistry Research Facility, University College Cork, Cork,
relandIrish Separation Science Cluster (ISSC), Dublin City University, Glasnevin, Dublin 9, IrelandAustralian Centre for Research on Separation Science (ACROSS), University of Tasmania, Hobart, AustraliaLife Science Interface, Tyndall National Institute, Cork, Ireland
r t i c l e i n f o
rticle history:eceived 20 February 2015eceived in revised form 16 April 2015ccepted 22 April 2015vailable online 29 April 2015
eywords:alladium nanoparticles
a b s t r a c t
A novel, simple and highly sensitive electrochemical method is developed for the determination of ascor-bic acid (AA) and uric acid (UA) based on a palladium nanoparticles deposited on porous graphitizedcarbon monolith modified carbon paste electrode (PdNPs/CM/CPE). The chemical modified electrodewas characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy(EIS). The PdNPs/CM/CPE displayed excellent electrochemical catalytic activities toward AA and UA withbare CPE, PdNPs/CPE, CM/CPE and PdNPs/CM/CPE by cyclic voltammetry (CV). The oxidation potentialsof AA and UA at the PdNPs/CM/CPE shifted negatively and the peak currents were much larger than
other electrodes. The amperometric signal of PdNPs/CM/CPE showed a good linearity with correlationcoefficient greater than 0.997. The low detection limits (S/N = 3) for AA and UA were 0.53 �mol L−1 and0.66 �mol L−1, respectively. The proposed method showed easy fabrication, high sensitivity and stability,and good reproducibility. In addition, the modified electrode was applied to determine the AA and UA inhuman serum sample.
. Introduction
Electroanalytical methods have been more attractive in recentears due to their sensitivity, accuracy, lower cost and simplicity1]. Electrochemically individual and/or simultaneous determina-ions of the analytes on unmodified electrode are difficult since theyave similar oxidation potentials and the electrode fouling results
n poor reproducibility [2]. Therefore, the simultaneous determi-ation of small molecules is a major goal in this research field.
arious materials including polymer [3–6], carbon-based materi-ls [7–10] and nanocomposite [11–17] have been employed for theodification of the electrode surfaces to improve their analytical
∗ Corresponding author at: Irish Separation Science Cluster (ISSC), Department ofhemistry and Analytical, Biological Chemistry Research Facility, University Collegeork, Cork, Ireland. Tel.: +353 4902208; fax: +353 4274907.
properties. Among them, a new class of carbon materials, porousgraphitized carbon monolith (CM), has very interesting physico-chemical properties [18] and high surface area that makes it apotential material for biomolecule immobilization and biosensingapplications.
Nowadays, there is an enormous interest in the use of metalnanoparticles to modify the surface of electrode [19–22]. Becauseof their excellent conductivity and catalytic properties, they couldbe used as electronic wires to enhance the electron transferbetween target analytes and electrode surfaces, and as catalysts toincrease electrochemical reactions. Palladium nanoparticles havebeen used for the modification of electrodes to increase sensitiv-ity and selectivity of target analytes. For example, Gao et al. [23]used palladium electroplated on a carbon nanotube to catalyze
the oxidation of formaldehyde and they found that this electrodehas a high electrocatalytic activity to formaldehyde oxidation.Wang et al. [24] studied the electrocatalytic oxidation of ascor-bic acid (AA), dopamine (DA) and uric acid (UA) using a palladium
cleaned by applying a potential scan of −1.0 V to 1.0 V with a scanrate of 0.5 V/s in phosphate buffer solution (pH 4.0) until a steadyvoltammogram was obtained.
S. Mukdasai et al. / Sensors an
anoparticles/graphene/chitosan modified electrode. Raoof et al.eported the palladium nanoparticles doped mesoporous silicaBA-15 modified in carbon paste electrode for determination ofxalic acid [25]. The basic properties of the catalyst are stronglyffected by the microstructure and the surface reactivity [26,27].herefore, the morphology and nanostructure of porous graphi-ized carbon monolith are considered to be the main factors inbtaining high dispersion of palladium nanoparticle catalysis.
AA and UA play an important role in the human body, and oftenoexist in biological samples. AA is an antioxidant that plays anmportant role in proper functioning of human metabolism andentral nervous system [28]. It is commonly used as an antioxidantgent and easily found in vegetables, fruits and drinks [29,30]. UAs the primary end product of purine degradation metabolism inuman being. Its concentration level in body fluids such as humanerum and urine is maker of many clinical conditions, includingyperuricaemia, gout and Lesch-Nyan disease [31–33]. Therefore,he development of a sensitive and selective method for theirimultaneous determination is needed for analytical applicationsnd researches.
In this work, we reported a palladium nanoparticles depositedn porous graphitized carbon monolith modified carbon paste elec-rode (PdNPs/CM/CPE) for simultaneous determination of AA andA. The scanning electron microscopy (SEM) and electrochemical
mpedance spectroscopy (EIS) were applied to study the modi-ed surfaces. The electrochemical properties of modified electrodesere investigated by voltammetry and amperometry techniques.
t was found that the PdNPs/CM/CPE electrode showed two wellesolved voltammetric peaks and high potential for simultaneousetermination of AA and UA in a mixed solution. Moreover, theodified electrode showed an excellent level of sensitivity and
erformance in stability and reproducibility. The proposed methodas applied to human serum for determination of AA and UA.
. Experimental
.1. Chemicals and reagent
All the chemicals used were of analytical grades and aque-us solutions were prepared using deionized water (Millipore,reland). Ascorbic acid (AA) and uric acid (UA) were obtained fromigma. Sodium hydroxide (NaOH), sodium phosphate monobasicehydrate (NaH2PO4·2H2O), sodium phosphate dibasic (Na2HPO4)nd phosphoric acid (H3PO4) were obtained from Sigma–AldrichGermany). Potassium hexacyanoferrate (III) (K3Fe(CN)6) wasurchased from Sigma–Aldrich (Japan). Potassium tetrachloropal-
adate (II) (K2PdCl4) and potassium chloride (KCl) were obtainedrom Sigma–Aldrich (USA). N,N-dimethylformamide (DMF) wasurchased from Sigma–Aldrich (United Kingdom).
Stock solution of AA (50 mmol L−1) was prepared daily by dis-olving a suitable amount of the reagent in water. UA (50 mmol L−1)as prepared by dissolving it in a small volume of 0.1 mol L−1 NaOH
olution and diluted with water.Phosphate-buffered solutions of different pH were prepared
y mixing solutions of 0.1 mol L−1 NaH2PO4·2H2O and 0.1 mol L−1
a2HPO4 at different ratios. The solution pH levels were adjustedy adding 1.0 mol L−1 H3PO4 solution.
.2. Apparatus
The electrochemical measurements, cyclic voltammetry (CV)
nd amperometry, were performed using a CHI 1040A elec-rochemical workstation (CH Instruments, Austin, TX) at roomemperature. A three-electrode system consisted of carbon pastelectrode (CPE) modified with CM and deposited PdNPs (PdNPs/
ators B 218 (2015) 280–288 281
CM/CPE) that was used as working electrodes, a Ag/AgCl (3 M NaCl)as reference electrode (BAS, West Layette, IN), and a platinumwire as counter electrode (Sigma–Aldrich, Dublin, Ireland). Theconvection transport during the amperometric determination wasperformed with magnetic stirring.
2.3. Preparation of the PdNPs/CM/CPE
5 mg CM was dispersed in 5 mL DMF, then ultrasonicated for 16 huntil a homogenous suspension of CM was obtained. CM dispersion(5 �L) was carefully dropped on the top of carbon paste electrode(CPE), allowing the solvent to evaporate at room temperature. TheCM/CPE was then obtained.
To prepare PdNPs/CM/CPE, the CM/CPE electrode was immersedin 0.1 mol L−1 H2SO4 solution containing 1.0 mmol L−1 K2PdCl4. Theelectrochemical deposition of the PdNPs was conducted for 50 sat −1.0 V (versus Ag/AgCl). Finally, the modified electrodes were
Fig. 1. (A) The SEM image of CM and (B) PdNPs deposited on CM.
282 S. Mukdasai et al. / Sensors and Actuators B 218 (2015) 280–288
Fig. 2. (A) Cyclic voltammogram of PdNPs/CM modified CPE in 0.1 mol L−1 PBS (pH 4.0) with scan rate of 50 mV/s. Inset: the plot of the anodic and cathodic peak currentsversus the scan rate. (B) Nyquist plots of 5 mmol L−1 Fe(CN)3−/4−
6 containing 0.1 mol L−1 KCl solution on a bare CPE (a), a CM/CPE (b) and a PdNPs/CM/CPE (c). The frequencyr
3
3
i
ange is form 1 Hz to 100 kHz. Inset: the modified Randles circuit.
. Results and discussion
.1. Morphological characterization of the PdNPs/CM/CPE
The surface morphology of the PdNPs/CM/CPE was character-zed by SEM. Fig. 1A shows the porous graphitized carbon monolith,
the SEM imaging confirmed the porous nature and irregular shapesof carbon monolith. The porous structure will significantly increase
the electroactive surface of electrode and facilitate the diffusion ofanalytes into the film. In Fig. 1B, Pd nanoparticles can be observedas dark dots; they are well distributed on the carbon monolithsurfaces, and this indicates the formation of nanocomposites.
d Actuators B 218 (2015) 280–288 283
3
scotafTf
P
crt0[pmb
I
w(t(st
PpCqoacw2FCat
t(r(FCrdTtif
3
3
(o
S. Mukdasai et al. / Sensors an
.2. Electrochemical characterization of the PdNPs/CM/CPE
Fig. 2A shows the cyclic voltammogram (CV) of PdNPs depo-ition in 0.1 mol L−1 PBS (pH 4.0). Here the CV shows theharacteristic current features of Pd reduction (−0.51 V) and Pdxide formation (0.16 V) process [34]. The deposited PdNPs are fur-her oxidized at 0.16 V (Pd0 to Pd oxide layer), undergo reductiont −0.51 V (Pd oxide to Pd0 nanoparticles) on the electrode sur-ace. Thus, PdNPs modified with CM on CPE has been fabricated.he expected reduction process of the PdCl2−
4 complex to Pd is asollows:
dCl42− + 2e− → Pd + 4Cl− (1)
Inset of Fig. 2A shows the variation of anodic and cathodic peakurrents (at 0.16 and −0.51 V, respectively) with the different scanates (10–100 mV/s) for PdNPs/CM/CPE electrode. A linear rela-ionship was found with a correlation coefficient (R2) greater than.986, which expected as a surface controlled electrode process35]. Also, the peak to peak potential separations of PdNPs is directlyroportional to the scan rate. The surface coverage (� ) was deter-ined by relationship between Ip and � which can be estimated
y the Laviron equation [36], using
p = n2F2
4RT�A� (2)
here n represents the number of electrons involved in the reactionn = 2), A is the surface area of the CPE electrode (0.16 cm2), Ip ishe peak current, � represents the surface coverage concentrationmol cm−2), F is Faraday constant (Q = 7.78 × 10−6 C) and � is thecan rate (50 mV/s). The surface coverage (� ) of PdNPs is estimatedo be about 1.80 × 10−10 mol cm−2.
Cyclic voltammetry was used to characterize thedNPs/CM/CPE. Cyclic voltammograms were studied in theresence of 5 mmol L−1 Fe(CN)3−/4−
6 in 0.1 mol L−1 KCl on a barePE, a CM/CPE, and a PdNPs/CM/CPE (data not shown). Theuasi-reversible one-electron redox behavior of Fe(CN)3−/4−
6 wasbserved on the bare CPE with a peak separation (�Ep) of 0.579 Vt the scan rate of 50 mV/s. After being modified with CM, the peakurrent of Fe(CN)3−/4−
6 was increased; however, the �Ep decreasedhen compared with that observed at the bare CPE by the factor of
. For the deposition of PdNPs on the CM/CPE, the peak current ofe(CN)3−/4−
6 was further increased when compared with those ofM/CPE and bare CPE, indicating that the PdNPs/CM hybrid played
role in the increase of the electroactive surface area and providehe conducting bridges for the electron-transfer of Fe(CN)3−/4−
6 .EIS is an efficient tool for characterizing the interfacial proper-
ies of surface-modified electrodes. The modified Randles circuitinset of Fig. 2B) was chosen to fit the impedance data [37]. Theesistance to charge transfer (Rct) and the diffusion impedanceW) were both in parallel with the interfacial capacitance (Cdl).ig. 2B shows the results for impedance spectrum on (a) a barePE (b) a CM/CPE and (c) a PdNPs/CM/CPE. The electron-transferesistance (Rct) at the CPE was estimated to be 280 � and that hasropped to 50 � at the CM-CPE and to 8 � at the PdNPs/CM/CPE.he decrease of Rct shows that there is a much lower electron-ransfer resistance on the PdNPs/CM/CPE. This change of Rct couldndicate the successful modification of PdNPs/CM onto the CPE sur-ace.
.3. Electrochemical behavior of AA and UA
.3.1. Individual electrocatalytic oxidation of AA and UAFig. 3A shows the typical differential pulse voltammograms
DPVs) of AA and UA at bare CPE. AA and UA show broaderxidation peaks with the peak potentials at 280 mV and 390 mV,
Fig. 3. (A) The typical DPVs of AA and UA at bare CPE. (B) The DPVs of AA and UA atthe surface of PdNPs/CM/CPE.
respectively. Fig. 3B shows the DPVs of AA and UA at the surfaceof PdNPs/CM/CPE. The peak potential for the oxidation of AA was84 mV, which was 196 mV more negative than that at the bare CPE.In the case of UA, a sharp oxidation peak at 300 mV was obtainedat PdNPs/CM/CPE, the negative shift of the anodic peak potential is90 mV and the peak current is enhanced by about threefold, indi-cating the sluggish electron transfer of these compounds at bareCPE, which may be related to the electrode fouling caused by thedeposition of these compounds and their oxidation products onthe electrode surface. Electrode fouling is a common issue dur-ing electroanalysis of phenolic compounds. In the paper [38], Yangproposed a powerful scientific model and revealed the detailedmechanism of electrode fouling.
For comparison, the electrochemical behaviors of AA and UAat PdNPs/CPE were also studied under the same conditions. Theoxidation peak potentials of AA and UA are 84 mV and 300 mV,respectively. Compared with the bare CPE, the peak potentials ofthese species at PdNPs/CM are all negative, which were describedto the catalytic activity of PdNPs. These results indicated that bothPdNPs and carbon monolith were responsible for enhancing theelectrochemical sensing.
It is clear that PdNPs/CM nanocomposites have high electrocat-
alytic activities toward the oxidation of AA and UA. These specieshave different sensitivities toward the electronic properties.Moreover, the difference with the electrode surface microstructure
284 S. Mukdasai et al. / Sensors and Actuators B 218 (2015) 280–288
FiP
as
3
6(saasCattwothtar
3
3
woottcrTi
3
2P3Aa
Fig. 5. The relationship between the amount of PdNPs and the oxidation peak cur-rent. 2.62 �mol L−1 AA and 6.46 �mol L−1 UA in 0.1 mol L−1 PBS (pH 4.0).
Fig. 6. (A) Differential pulse voltammograms obtained at the PdNPs/CM/CPE in−1 −1
ig. 4. The CVs of the mixture of 2.62 �mol L−1 AA and 6.46 �mol L−1 UAn 0.1 mol L−1 PBS (pH 4.0) at bare CPE (a), CM/CPE (b), PdNPs/CPE (c) anddNPs/CM/CPE (d).
nd modified surface chemistry can be occurred the peak potentialhift.
.3.2. Electrocatalytic behavior of AA and UA in a mixtureFig. 4 shows the CVs of the mixture of 2.62 �mol L−1 AA and
.46 �mol L−1 UA in 0.1 mol L−1 PBS (pH 4.0) at bare CPE (a), CM/CPEb), PdNPs/CPE (c) and PdNPs/CM/CPE (d), respectively. It is clearlyeen that the peak potentials of AA and UA were indistinguish-ble at the bare CPE. At the PdNPs/CPE, the peak potentials of AAnd UA could be distinguished at 110 mV and 350 mV. The twopecies can be observed at approximately 197 mV and 545 mV atM/CPE. All the potentials of these two species shifted negativelyt PdNPs/CM/CPE compared with other modified electrodes andhe values were 94 mV and 360 mV, respectively. It is clearly seenhat the anodic currents of the two species at the PdNPs/CM/CPEere much higher than other electrode testes. The improvement
f electron transfer kinetics at the PdNPs/CM/CPE as modified elec-rode can be explained by the following reasons. Firstly, small size,igh loading and large surface area of PdNPs can increase oxida-ion peak current of AA and UA. Secondly, the carbon monolith has
much high surface area, therefore a much lower electron-transferesistance.
.4. Determination of AA and UA
.4.1. Effect of PdNPs deposition timeThe effect of the amount of PdNPs deposited on the peak current
as studied and the corresponding results are shown in Fig. 5. Thexidation peak current of 2.62 �mol L−1 AA and 6.46 �mol L−1 UAn the PdNPs/CM/CPE increased with increasing PdNPs depositionime from 20 to 50 s. However, when the deposition time higherhan 50 s, the peak current decreased slightly, which may be asso-iated with the decrease of the real surface area of the electrodeesulting from the aggregation of PdNPs on the electrode surface.herefore, the deposition time of 50 s was selected in the followingnvestigations.
.4.2. Effect of pHThe effect of pH on the electrochemical behavior of
.62 �mol L−1 AA and 6.46 �mol L−1 UA in a mixture at the
dNPs/CM/CPE was investigated by DPVs in the range of pH.0–7.0 in 0.1 mol L−1 PBS. From Fig. 6A, the peak current ofA and UA initially increased and reached a maximum valuet pH 4.0, and then slightly decreased with increasing pH.
the range of pH 3.0–7.0 in 0.1 mol L PBS containing 2.62 �mol L AA and6.46 �mol L−1 UA in a mixture at a scan rate of 50 mV/s. (B) The linear regressionequations between potential and pH for AA and UA. Inset: the plot of anodic currentof AA and UA versus pH values on DPVs.
S. Mukdasai et al. / Sensors and Actuators B 218 (2015) 280–288 285
Fig. 7. (A) Calibration plot obtained from the CVs recording of AA concentra-tions at PdNPs/CM/CPE in 0.1 mol L−1 PBS (pH 4.0) containing 6.46 �mol L−1 UA.(B) Calibration plot obtained from the CVs recording of UA concentrations con-taining 2.62 �mol L−1. Inset: amperometric detection (I/t) at −0.2 V versus Ag/AgCl(3 mol L−1 KCl).
Table 1Calibration curves parameters for determination of AA and UA under optimumconditions.
Analyte Regressionequation
R2 Linearrange(�mol L−1)
% RSD Limit ofdetection(�mol L−1)
ApF(pp35ea
3
poscc
Table 3Results of interference some foreign substances for AA and UA on PdNPs/CM/CPE(n = 3).
AA Y = 14.84X + 58.24 0.9976 3.266–40.51 2.39 0.53UA Y = 3.40 + 11.64 0.9988 3.263–13.89 2.75 0.66
A (pKa = 4.10) and UA (pKa = 5.7) exist in cationic form atH 4.0 [5]. The linear regression equations for AA and UA inig. 6B were: EAA (mV) = 0.3473–0.0380pH (R2 = 0.9915) and EUAmV) = 0.2715–0.0356pH (R2 = 0.9991), respectively. All the peakotentials of AA and UA shifted to more negative values with theH increasing. The calculated slopes of 38.0 mV/pH for AA and5.6 mV/pH for UA were close to the half of theoretical value of8.6 mV/pH according to the Nerst equation, suggesting that thelectrochemical oxidations of AA and UA at the prepared electrodere two-electron process [39].
.4.3. Simultaneous determination of AA and UAUnder the optimum conditions, the determination of two com-
ounds at PdNPs/CM/CPE was carried out in the potential rangef −0.5 V to 1.0 V in 0.1 mol L−1 PBS (pH 4.0) by CVs (data not
hown) and amperometry. The experiments were conducted byhanging concentration of one species while another one remainedonstant.
able 2omparison of the proposed method with the literature methods for AA and UA determin
Method Analytes Linear range(�mol L−1)
PdNPs/CM-GCE AA 3.27–40.51
UA 3.27–13.89
PdNPs/GR/Cs-GCE AA 100.0–4000.0
UA 0.5–200.0
PdNPs/CNF-GCE AA 0.05–4.0
UA 2–200
CTAB/GO/MWCNT-GCE AA 5.0–300
UA 3.0–60
a For 5% error.
Fig. 7A shows the peak current of AA increased linearly with theincrease of AA concentration from 3.27 �mol L−1 to 40.51 �mol L−1
while the concentration of UA was 6.46 �mol L−1. The regressionequation and the detection limit are shown in Table 1. There was noobvious interference for the determination of AA by the coexistedUA.
Similarly, Fig. 7B shows the peak current increased linearlywith increasing the concentration of UA from 3.26 �mol L−1
to 13.89 �mol L−1, while keeping the concentration of AA at2.62 �mol L−1. The regression equation and the detection limit arealso shown in Table 1 and the coexisted AA did not interfere thedetection of UA.
All above results are summarized in Fig. 7 and Table 1 stronglysuggesting that AA and UA at PdNPs/CM/CPE could be simultane-ously and sensitivity detected without any obvious interferences.
The analytical performance of the PdNPs/CM/CPE was comparedwith the literature methods in Table 2. This electrode is superior tothe other modified electrodes reported previously for the electro-catalytic detection of AA and UA, especially for the LOD.
3.5. Interference, reproducibility and stability of the modifiedelectrode
To evaluate the influences of some potential interference on thedetermination of 2.62 �mol L−1 AA and 6.46 �mol L−1 UA at thePdNPs/CM/CPE, various foreign species were added into 0.1 mol L−1
PBS (pH 4.0) containing AA and UA. The tolerance limit was takenas the maximum concentration of foreign substances which causedan approximately ±5% relative error in the determination of AA andUA. The results are shown in Table 3, which indicated that no inter-ference was observed for the following compounds: NaCl, MgCl2,citric acid, lysine, glucose and cysteine. The reproducibility of mod-ified electrode was compared with the same electrode five timesof the mixture of AA and UA. Good reproducibility was obtainedwith relative standard deviation (RSD) of 2.4% for AA and 2.8% forUA. The stability of the modified electrode decreased 2% of its ini-
tial response after 2 days. The PdNPs/CM/CPE could be used for 1month with 10% of electrochemically signal loss.
Table 4The recovery of the proposed method (n = 3).
Analyte Human serum sample
Spiked (�mol L−1) Found (�mol L−1) Recovery (%)
AA – nd –5.2 4.8 92.3 ± 4.37.7 7.0 90.9 ± 2.9
10.2 9.5 93.1 ± 3.2
UA – nd –6.5 5.8 89.2 ± 5.29.6 8.9 92.7 ± 4.2
n
3
ri1sPwwaptd
4
PdmrTtippfptFtc
A
IbTe
R
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
333–344.
12.7 11.2 88.2 ± 2.5
d, not detected.
.6. Sample analysis
The accuracy of the method was evaluated by recovery. Theecovery of AA and UA was determined in human serum by spik-ng the AA and UA standards at three concentration levels (5.2, 7.7,0.2 �mol L−1 for AA, and 6.5, 9.6, 12.7 �mol L−1 for UA) into theamples before the electrochemical determination by the modifieddNPs/CM/CPE. The standard addition method was used. AA and UAere not detected in the studied samples. The recovery (Table 4)as obtained between 89.2 and 93.1%. The high recovery indicated
negligible matrix effect on the modified PdNPs/CM/CPE in sam-le matrices. According to high recovery, it can be concluded thathe modified electrode has potential for the applicability for theetection of AA and UA in real samples.
. Conclusions
The modification of carbon paste electrode (CPE) withdNPs/CM nanocomposites (PdNPs/CM/CPE) was described for theetermination of AA and UA using voltammetry techniques. Theodified electrode showed a good linear concentration range and
eproducibility, high stability and low detection limit as detailed inable 1. The PdNPs/CM/CPE has electro-catalytic activities towardhe oxidation of AA and UA by decreasing over-potentials andncreasing the peak currents, which could be attributed to the supererformance of PdNPs/CM nanocomposites film. The results of theresent work indicated that the modified electrode was suitableor the sensitive detection of AA and UA concentrations. The pro-osed method is rapid, simple and sensitive, and can be used forhe electrochemical sensing of AA and UA in human serum sample.urthermore, this approach can alternatively be applied for simul-aneous determination of AA and UA in biological samples, whichan be great interest in clinical research.
cknowledgements
The authors gratefully acknowledged the Science Foundationreland (SFI) for Irish Separation Science Cluster (ISSC) grant num-er 08/SRC/B1412. The Development and Promotion of Science andechnology Talents Projects (DPST), Thailand is gratefully acknowl-dged for granting to S. Mukdasai.
eferences
[1] C.L. Bian, Q.X. Zeng, L.J. Yang, H.Y. Xiong, X.H. Zhang, S.F. Wang, Voltammetricstudies of the interaction of rutin with DNA and its analytical applications onthe MWNTs–COOH/Fe3O4 modified electrode, Sens. Actuators B 156 (2011)
615–620.
[2] J.W. Mo, B. Ogorevc, Simultaneous measurement of dopamine and ascor-bate at their physiological levels using voltammetric microprobe based onoveroxidized poly(1,2-phenylenediamine)-coated carbon fiber, Anal. Chem. 73(2001) 1196–1202.
[
ators B 218 (2015) 280–288
[3] P.R. Roy, T. Okajima, T. Ohsaka, Simultaneous electrochemical detection of uricacid and ascorbic acid at a poly(N,N-dimethylaniline) film-coated GC electrode,J. Electroanal. Chem. 561 (2004) 75–82.
[4] X. Yang, J. Kirch, E.V. Olsen, J.W. Fergus, A.L. Simonian, Anti-fouling PEDOT:PSSmodification on glassy carbon electrodes for continuous monitoring of tricresylphosphate, Sens. Actuators B 177 (2013) 659–667.
[5] P. Kalimuthu, S.A. John, Simultaneous determination of ascorbic acid,dopamine, uric acid and xanthine using a nanostructured polymer film modi-fied electrode, Talanta 80 (2010) 1686–1691.
[6] Y. Li, X. Lin, Simultaneous electroanalysis of dopamine, ascorbic and uric acidby poly (vinyl alcohol) covalently modified glassy carbon electrode, Sens. Actu-ators B 115 (2006) 134–139.
[7] W. Zhang, R. Yuan, Y.-Q. Chai, Y. Zhang, S.-H. Chen, A simple strategy based onlanthanum-multiwalled carbon nanotube nanocomposites for simultaneousdetermination of ascorbic acid, dopamine, uric acid and nitrite, Sens. ActuatorsB 166–167 (2012) 601–607.
[8] B. Zhang, D. Huang, X. Xu, G. Alemu, Y. Zhang, F. Zhan, Y. Shen,M. Wang, Simultaneous electrochemical determination of ascorbic acid,dopamine and uric acid with helical carbon nanotubes, Electrochim. Acta 91(2013) 261–266.
[9] Y. Li, J. Du, J. Yang, D. Liu, X. Lu, Electrocatalytic detection of dopamine in thepresence of ascorbic acid and uric acid using single-walled carbon nanotubesmodified electrode, Colloids Surf. B 97 (2012) 32–36.
10] M. Noroozifar, M.K. Motlagh, R. Akbari, M.B. Parizi, Simultaneous and sensitivedetermination of a quaternary mixture of AA, DA, UA and Trp using a modifiedGCE by iron ion-doped natrolite zeolite-multiwall carbon nanotube, Biosens.Bioelectron. 28 (2011) 56–63.
11] T.T. Baby, S. Ramaprabhu, SiO2 coated Fe3O4 magnetic nanoparticle dispersedmultiwalled carbon nanotubes based amperometric glucose biosensor, Talanta80 (2010) 2016–2022.
12] W. Liang, W. Yi, Y. Li, Z. Zhang, M. Yang, C. Hu, A. Chen, A novelmagnetic Fe3O4@gold composite nanomaterial: synthesis and appli-cation in regeneration-free immunosensor, Mater. Lett. 64 (2010)2616–2619.
13] E. Omidinia, N. Shadjou, M. Hasanzadeh, (Fe3O4)-graphene oxide as a novelmagnetic nanomaterial for non-enzymatic determination of phenylalanine,Mater. Sci. Eng. C 33 (2013) 4624–4632.
14] M. Roushani, M. Shamsipur, H.R. Rajabi, Highly selective detection of dopaminein the presence of ascorbic acid and uric acid using thioglycolic acid cappedCdTe quantum dots modified electrode, J. Electroanal. Chem. 712 (2014)19–24.
15] M. Arvand, M. Hassannezhad, Magnetic core-shell Fe3O4@SiO2/MWCNTnanocomposite modified carbon paste electrode for amplified electrochemicalsensing of uric acid, Mater. Sci. Eng. C 36 (2014) 160–167.
16] N. Butwong, L. Zhou, W. Ng-eontae, R. Burakham, E. Moore, S. Srijaranai, J.H.T.Luong, J.D. Glennon, A sensitive nonenzymatic hydrogen peroxide sensor usingcadmium oxide nanoparticles/multiwall carbon nanotube modified glassy car-bon electrode, J. Electroanal. Chem. 717–718 (2014) 19–24.
17] Y. Wang, K. Qu, L. Tang, Z. Li, E. Moore, X. Zeng, Y. Liu, J. Li, Nanomaterials incarbohydrate biosensors, Trends Anal. Chem. 58 (2014) 54–70.
18] X. He, L. Zhou, E.P. Nesterenko, P.N. Nesterenko, B. Paull, J.O. Omamogho,J.D. Glennon, J.H.T. Luong, Porous graphitized carbon monolith asan electrode material for probing direct bioelectrochemistry andselective detection of hydrogen peroxide, Anal. Chem. 84 (2012)2351–2357.
19] T. Selvaraju, R. Ramaraj, Simultaneous detection of ascorbic acid, uric acid andhomovanillic acid at copper modified electrode, Electrochim. Acta 52 (2007)2998–3005.
20] T.-Q. Xu, Q.-L. Zhang, J.-N. Zheng, Z.-Y. Lv, J. Wei, A.-J. Wang, J.-J. Feng, Simul-taneous determination of dopamine and uric acid in the presence of ascorbicacid using Pt nanoparticles supported on reduced graphene oxide, Electrochim.Acta 115 (2014) 109–115.
21] A. Vulcu, C. Grosan, L.M. Muresan, S. Pruneanu, L. Olenic, Modified gold elec-trodes based on thiocytosine/guanine-gold nanoparticles for uric and ascorbicacid determination, Electrochim. Acta 88 (2013) 839–846.
22] G. Hu, Y. Ma, Y. Guo, S. Shao, Electrocatalytic oxidation and simul-taneous determination of uric acid and ascorbic acid on the goldnanoparticles-modified glassy carbon electrode, Electrochim. Acta 53 (2008)6610–6615.
23] G.Y. Gao, D.J. Guo, H.L. Li, Electrocatalytic oxidation of formaldehyde on pal-ladium nanoparticles supported on multi-walled carbon nanotubes, J. PowerSources 162 (2006) 1094–1098.
24] X. Wang, M. Wu, W. Tang, Y. Zhu, L. Wang, Q. Wang, P. He, Y. Fang, Simultaneouselectrochemical determination of ascorbic acid, dopamine and uric acid usinga palladium nanoparticle/graphene/chitosan modified electrode, J. Electroanal.Chem. 695 (2013) 10–16.
25] J.B. Raoof, F. Chekin, V. Ehsani, Palladium-doped mesoporous silica SBA-15modified in carbon-paste electrode as a sensitive voltammetric sensor fordetection of oxalic acid, Sens. Actuators B 207 (2015) 291–296.
26] X. Wu, L.R. Radovic, Catalytic oxidation of carbon/carbon composite mate-rials in the presence of potassium and calcium acetates, Carbon 43 (2005)
27] M.C. Roman-Martinez, D. Cazorla-AmorÓs, A. Linares-Solano, C. Salinas-Martinez De Lecea, H. Yamashita, M. Anpo, Metal-support interaction in Pt/Ccatalysts: influence of the support surface chemistry and the metal precursor,Carbon 33 (1995) 3–13.
28] U. Yogeswaran, S. Thiagarajan, S. Chen, Nanocomposite of functionalized mul-tiwall carbon nanotubes with nafion, nanoplatinum, and nanogold biosensingfilm for simultaneous determination of ascorbic acid, epinephrine, and uricacid, Anal. Biochem. 365 (2007) 122–131.
29] L. Zhang, Z.N. Wang, Y. Xia, G.Y. Kai, W.S. Chen, K.X. Tang, Metabolic engineeringof plant l-ascorbic acid biosynthesis: recent trends and applications, Crit. Rev.Biotechnol. 27 (2007) 173–182.
30] Z. Chen, T.E. Young, J. Ling, S.C. Chang, D.R. Gallie, Increasing vitamin C contentof plants through enhanced ascorbate recycling, Proc. Natl. Acad. Sci. U. S. A.100 (2003) 3525–3530.
31] P. Elena, Y. Kubota, D.A. Tryk, A. Fujishima, Selective voltammetric and amper-ometric detection of uric acid with oxidized diamond film electrodes, Anal.Chem. 72 (2000) 1724–1727.
32] J.M. Zen, P.J. Chen, A selective voltammetric method for uric acid anddopamine detection using clay-modified electrodes, Anal. Chem. 69 (1997)5087–5093.
33] S. Zhang, M. Xu, Y. Zhang, Simultaneous voltammetric detection of salsolinoland uric acid in the presence of high concentration of ascorbic acid with goldnanoparticles/functionalized multiwalled carbon nanotubes composite filmmodified electrode, Electroanalysis 21 (2009) 2607–2610.
34] S. Thiagarajan, R.-F. Yang, S.-M. Chen, Palladium nanoparticles modi-fied electrode for the selective detection of catecholamine neurotrans-mitters in presence of ascorbic acid, Bioelectrochemistry 75 (2009)163–169.
35] S. Palanisamy, C. Karuppiah, S.-M. Chen, Direct electrochemistry and electro-catalysis of glucose oxidase immobilized on reduced graphene oxide and silvernanoparticles nanocomposite modified electrode, Colloids Surf. B 114 (2014)164–169.
36] Y.H. Kim, T. Kim, J.H. Ryu, Y.J. Yoo, Iron oxide/carbon black (Fe2O3/CB) compositeelectrode for the detection of reduced nicotinamide cofactors using an amper-ometric method under a low overpotential, Biosens. Bioelectron. 25 (2010)1160–1165.
37] S. Mukdasai, E. Moore, J.D. Glennon, X. He, E.P. Nesterenko, P.N. Nesterenko, B.Paull, M. Pravda, S. Srijaranai, Comparison of electrochemical property betweenmultiwall carbon nanotubes and porous graphitized carbon monolith modifiedglassy carbon electrode for the simultaneous determination of ascorbic acid anduric acid, J. Electroanal. Chem. 731 (2014) 53–59.
38] X. Yang, J. Kirsch, J. Fergus, A. Simonian, Modeling analysis of electrode foul-ing during electrolysis of phenolic compounds, Electrochim. Acta 94 (2013)259–268.
39] B. Rezaei, S.Z.M. Zare, Modified glassy carbon electrode with multiwall car-bon nanotubes as a voltammetric sensor for determination of noscapinein biological and pharmaceutical samples, Sens. Actuators B 134 (2008)292–299.
40] J. Huang, Y. Liu, H. Hou, T. You, Simultaneous electrochemical determinationof dopamine, uric acid and ascorbic acid using palladium nanoparticle-loaded carbon nanofibers modified electrode, Biosens. Bioelectron. 24 (2008)632–637.
41] Y.J. Yang, W. Li, CTAB functionalized graphene oxide/multiwalled carbon nan-otube composite modified electrode for the simultaneous determination ofascorbic acid, dopamine, uric acid and nitrite, Biosens. Bioelectron. 56 (2014)300–306.
iographies
Siriboon Mukdasai is currently a PhD student in Chem-istry Program, Department of Chemistry, Faculty ofScience, Khon Kaen University (Thailand). She receivedher B.Sc. (Hons.) in Chemistry, Khon Kaen University(Thailand) in 2010. She was awarded a scholarship fromthe Development and Promotion of Science and Tech-nology Talents Projects (DPST), Thailand. Her currentresearch is focused on the applications of magneticnanoparticles (MNPs) and nanomaterials as a novel sor-bent in micro solid phase extraction and their potential tobe used as sensor.
Una Crowley received her B.Sc. in Chemistry with ForensicScience from the National University of Ireland Cork in
2010. She then went on to receive her PhD in AnalyticalChemistry in 2014 under the supervision of Prof. Jeremy D.Glennon and Dr Eric Moore. Her research interests focuson the development of low-cost sensing and separationdevices based on macro, micro and nano technology.
ators B 218 (2015) 280–288 287
Mila Pravda is a lecturer in analytical chemistry at the Uni-versity College Cork, where he started as a senior researchfellow in the development of clinical and environmentalsensors with Prof. G. Guilbault in 2000. He received hisPhD in Pharmaceutical Sciences from Free University ofBrussels in 1998 for his work on the development andcharacterisation of electrochemical and neurochemicalsensors and biosensors for biological systems in collab-oration with the Dublin City University. He has MSc inanalytical chemistry and a degree in chemistry and pro-cess engineering from the University of Pardubice since1993. His research interests include development homo-geneous and heterogeneous electrochemical sensors and
biosensors using nanomaterials.
Xiaoyun He graduated from Dublin Institute of Technol-ogy with B.Sc degree in Chemical and PharmaceuticalScience in 2008. Later she was awarded Ph.D. degree fromIrish Separation Science Cluster, Dublin City University in2014. The same year she joined the CRANN (the Centre forResearch on Adaptive Nanostructures and Nanodevices),School of Physics, Trinity College Dublin as a postdoctoralresearcher. Her research interests mainly focuses in thefields of material science, from fabrication of porous car-bon materials for multifunctional adsorbents and slowlyexpands to preparation of 2d hydroxides for various elec-trochemical applications.
Ekaterina Nesterenko received her M.Sc. in Chemistryfrom M.V. Lomonosov Moscow State University (Russia) in2004, and in 2008 was awarded Ph.D. degree from DublinCity University (Ireland). The same year she joined theCentre for Bioanalytical Sciences/Bristol-Myers Squibb,and in 2009 moved to the Irish Separation Science Cluster.Dr Nesterenko is an author of 36 scientific publications,over 90 conference presentations and three patents. Herresearch interests lie in the fields of analytical chemistry,stationary phase design for various applications and thedevelopment of analytical instrumentation.
Pavel Nesterenko obtained M.Sc. in Petrochemistry andOrganic Catalysis, Ph.D. and D.Sc. degrees in AnalyticalChemistry in M.V. Lomonosov Moscow State Univer-sity, Russia. In 1987–2006 worked as Senior and LeadingResearcher at the Department of Analytical Chemistry ofthis university. In 2007 he moved to University of Tas-mania to carry out research as Quantum Leap Professorand since 2012 as New Stars Professor. Author of morethan 280 scientific publications including 3 monographs,8 chapters in books, 266 regular papers and 12 patents.Member of advisory and editorial boards of 6 internationaljournals on analytical chemistry and separation sciences.
Brett Paull is a University of Plymouth (UK) B.Sc. (Hons),Ph.D. and D.Sc. graduate, and a Fellow of the Royal Soci-ety of Chemistry. He took up his first lectureship at theUniversity of Tasmania from 1995 to 1997, before mov-ing to Dublin City University (1998–2011). In 2011 Brettrejoined the University of Tasmania as Professor in theSchool of Chemistry, and is currently Director of the Aus-tralian Centre for Research on Separation Science.
Supalax Srijaranai received BSc (Chemistry) from KhonKaen University, Thailand in 1981, MSc (Analytical Chem-istry) from Chulalongkorn University, Thailand in 1984and PhD in Analytical Chemistry from University CollegeCork, Ireland in 1990. Currently she is Associate Professorin the Department of Chemistry at Khon Kaen University,Thailand. Her research interests include the development
of analytical procedures employing chromatography andrelated techniques emphasis on green and miniaturizedsample preparation techniques and their applications inthe determination of trace analytes in environmental andfood samples.
Jeremy D. Glennon (PhD, 1979, University College Dublin,Ireland, and PDF at the Research Institute, Hospital for SickChildren, Toronto, Canada) is Professor Chair of AnalyticalChemistry at the Department of Chemistry at UniversityCollege Cork (UCC), Ireland. He is co-Director of the SFIfunded Irish Separation Science Cluster (ISSC), co-founderof the Analytical and Biological Research Facility (ABCRF)at UCC, Ireland delegate on the Division of AnalyticalChemistry (EuCheMS), and to the EuSSS, and RegionalRepresentative of the Institute of Chemistry in Ireland.He is the author and co-author of over 200 research andconference papers. Within the ISSC, his Innovative Chro-matography research group focuses on the incorporation
f selectivity into analytical separation devices and bonded phase materials for bio-
nalysis, metabolite and trace metal analysis. Researchers in the team have won theorvath Award at the international HPLC conference series (Norma Scully, inaugu-
al Horvath Award at HPLC 2006 in San Francisco, and Jesse Omamogho at HPLC010 in Boston), and more recently, the group has developed and patented noveluperficially porous (Eiroshell) particles for chromatography.
ators B 218 (2015) 280–288
Eric Moore is an Academic Member within the LifeScience Group at Tyndall National Institute, UniversityCollege Cork, Ireland. He has a PhD in Chemistry andhas over sixteen years’ experience in the developmentand application of chemical and biosensor technology. Hereceived his B.Sc. in Chemistry from the National Uni-versity of Ireland Cork in 1998, graduated with a M.Sc.in 2001 and he went on to receive his PhD in Analyti-cal Chemistry in 2003 under the supervision of Prof. G.G.Guilbault. Following a short postdoctoral research posi-tion with Prof. Guilbault, he joined the Nanobiotechnologyteam in February 2004 at the National MicroelectronicsResearch Centre (NMRC) as a postdoctoral researcher. In
2006 he became a staff researcher at Tyndall National Institute (formally NMRC) inthe Life Sciences group and in 2010 was promoted to a team leader. In December2012 Dr Moore joined the Chemistry Department as a College Lecturer and Directorof the taught postgraduate courses in Analytical Chemistry. He remains a principleinvestigator at Tyndall National Institute and in 2013 he became an Academic mem-ber. He is also currently on the board for the Royal Society of Chemistry AnalyticalCommittee in Ireland. His current principle research activities are focused on devel-
oping integrated bio/sensor platforms for monitoring cell health, surface attachmentchemistry, process analytical technologies, electrochemical sensing/analysis andmicro-fluidics. He has a broad range of both chemistry and biochemistry skills withover 30 publications. He is specialising in the development of nanobiotechnologyand novel sensor platforms.
