Stripping Analysis of As(III) by Means of Screen-Printed Electrodes Modified with Gold Nanoparticles...

DOI: 10.1002/elan.201400041

Stripping Analysis of As(III) by Means of Screen-PrintedElectrodes Modified with Gold Nanoparticles and CarbonBlack NanocompositeStefano Cinti,[a, b] Sara Politi,[a, b] Danila Moscone,[a, b] Giuseppe Palleschi,[a, b] and Fabiana Arduini*[a, b]

1 Introduction

Arsenic is pervasive in nature: it is the 20th most abun-dant mineral in the earth�s crust and 12th most abundantmineral in the human body [1,2]. It has been used inmedicine [3] and in various fields e.g. agriculture, live-stock, electronics, industry and metallurgy [4,5]. Its inor-ganic forms are highly toxic, and arsenite is apparentlymore toxic than arsenate. The methylated organic speciesmonomethylarsonic acid (MMA) and dimethylarsinicacid (DMA) are less toxic than the inorganic forms [6].Exposure to arsenic can, in fact, cause a variety of ad-verse health effects, including dermal, respiratory, cardio-vascular and gastrointestinal damages [7–9]. The WorldHealth Organization (WHO) thus fixed the legal limit ofarsenic in drinking water to 10 mg/L [10]. For all thesereasons, the detection of arsenic in drinking water is animportant analytical issue. Arsenic determination meth-ods are generally based on atomic absorption spectrome-try (AAS) [11], inductively coupled plasma mass spec-trometry (ICP-MS) [12] and high-performance liquidchromatography with ICP-MS [13]; these techniques arecharacterized by complex instrumentation, high costs andskilled personnel, which render them entirely unsuitablefor in situ analyses. In contrast, the electrochemical strip-ping analysis, both cathodic (CSV) [14–16] and anodicstripping voltammetry (ASV) [17–19], has been widelyrecognized as a powerful technique for arsenic ion detec-tion, owing to its remarkable sensitivity. Moreover, thesetechniques can also be readily carried out with cost-effec-tive and easy-to-use instrumentation. For electrochemicalAs(III) detection, the gold electrode is the most suitableone, due to the stable Au-As intermetallic compoundsformed during the deposition step. In literature there aremany papers where the arsenic detection is carried outusing bulk or film gold electrodes [20–22]. However,these electrodes require a mechanical and/or electro-

chemical cleaning after each measurement that requirelong analysis times. Recently, nanotechnology hasbecome one of the most exciting forefront field in analyti-cal chemistry. A wide variety of nanomaterials, especiallymetal nanoparticles with different properties have founda broad application in several analytical methods. Owingto their small size (normally in the range of 1–100 nm),nanoparticles exhibit unique chemical, physical and elec-tronic properties that are different from those of respec-tive bulk materials, and can be used to construct noveland improved sensing devices [23–25]. In the case of elec-trochemical sensors, modification of electrode surfacesusing gold nanoparticles (AuNPs) has received large at-tention mainly due to their interesting electrocatalyticproperties [26,27]. Some authors showed that the strip-ping voltammetric (ASV) determination of arsenic can beimproved by nanoengineering of the electrode surface[28,29]. The AuNPs can be deposited by adsorption [30]or by electrochemical methods [31,32]. In the develop-ment of highly sensitive sensors, the use of a hybrid nano-material can be an added value, because it confers to thesensor improved electrochemical properties when com-pared with the single nanomaterial. For instance, a glassycarbon electrode modified with both multiwall carbonnanotubes and AuNPs for arsenic trace analysis was re-ported in literature: in this case the AuNPs were ad-sorbed on multiwall carbon nanotubes and the resultingcomposite was immobilized onto the surface of a glassy

Abstract : A novel sensor based on carbon black-goldnanoparticle nanocomposite modified screen-printed elec-trode (CB-AuNPs/SPE) for the detection of As(III) hasbeen developed. The sensor was prepared modifying theSPE with CB and AuNPs by a drop casting automatabledeposition. The As(III) was detected by CB-AuNPs/SPE

using anodic stripping voltammetry, with a high sensitivity(673�6 mA mM�1 cm�2) and reaching a LOD of 0.4 ppb.Finally, CB-AuNPs/SPE has been applied to As(III) traceanalysis in drinking water, obtaining satisfactory recoveryvalues (99�9 %).

Keywords: Arsenic detection · Screen-printed electrode · Gold nanoparticles · Carbon black · Stripping analysis

[a] S. Cinti, S. Politi, D. Moscone, G. Palleschi, F. ArduiniDipartimento di Scienze e Tecnologie Chimiche, Universit�di Roma Tor Vergatavia della Ricerca Scientifica 1, 00133 Rome, Italy*e-mail: [email protected]

[b] S. Cinti, S. Politi, D. Moscone, G. Palleschi, F. ArduiniConsorzio Interuniversitario Biostrutture e Biosistemi“INBB”Viale Medaglie d�Oro, 305 Roma, Italy

www.electroanalysis.wiley-vch.de � 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electroanalysis 2014, 26, 1 – 9 &1&

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carbon electrode [33]. Another interesting nanostructuredcarbon material is the carbon black (CB). This cost-effec-tive nanomaterial is principally used as reinforcing fillerin rubber compounds, but there are few papers in litera-ture based on CB electrode for analyte detection in solu-tion [34–37]. Recently, we demonstrated the advantagesof using the CB modified screen-printed electrode (SPE)compared to the bare one, due to the electrocatalyticproperties [38–40] of the former. In addition, the SPEmodified with single-wall carbon-nanotubes were com-pared with the CB modified SPE, and a better signal/noise ratio in the case of last one was found [41]. This be-havior was also confirmed by Compton group usingglassy carbon electrode modified with multiwall carbonnanotubes; in fact they report that the results found“highlight the improvement involved in the (largely unex-plored) direct application of CB in the electrode surfacemodification” [42].

In this direction, we would like to demonstrate thatalso in the case of As(III) detection, the use of CB can bea sensitive and cost-effective alternative to carbon nano-tubes to create a nanocomposite with the AuNPs for theelectrochemical detection of As(III). The use of SPEsresult in cost-effective, mass-produced and disposable de-vices designed to work with few mL of sample, withoutrequiring precleaning of the working electrode surface asin the case of solid electrodes.

2 Materials and Methods

2.1 Apparatus

Voltammetric measurements were carried out usinga portable potentiostat PalmSens (Palm Instruments, TheNetherlands). Cyclic voltammetry (CV) was performedusing an Autolab electrochemical system equipped witha PGSTAT 10 and GPES software (Eco Chemie, Utrecht,the Netherlands). UV-vis measurements were obtainedusing a spectrophotometer UV 1800 (Shimadzu, Japan).

2.2 Electrodes

Screen-printed electrodes were produced with a 245 DEK(Weymouth, England) screen-printing machine [43,44]using graphite-based conductive ink (Elettrodag 421) forworking and counter electrode and silver-silver chlorideconductive ink (Elettrodag 477 SS) for pseudo-referenceelectrode, obtained from Acheson (Milan, Italy). The in-sulating layer was Vinilflat 38.101E from Argon (Italy).The substrate was a flexible polyester film (AutostatHT5) obtained from Autotype (Milan, Italy). The diame-ter of the working electrode was 0.3 cm resulting in anapparent geometric area of 0.07 cm2.

2.3 Reagents

All chemicals from commercial sources were of analyticalgrade. All solutions were prepared using double distilled

water from Millipore. All the As(III) solutions were pre-pared using ICP-MS standard solution 1000 mg L�1 (Inor-ganic ventures, USA); subsequent dilutions were ob-tained using HCl (Carlo Erba, Italy).

2.4 Synthesis of AuNPs

In this work the AuNPs were synthesized accordingly toZanardi et al. [45] with slight modifications: 314 mL of43 mM NaBH4 aqueous solution were added by twoequal aliquots to 3 mL of 1 mM HAuCl4 aqueous solutionunder vigorous stirring every 15 min. The synthesis pro-ceeded at room temperature for 20 min. We found thatall the glassware and magnetic stir bar used in this syn-thesis should thoroughly be cleaned in aqua regia (HCl/HNO3 3 : 1, v/v), rinsed in bidistilled water and thencleaned with piranha solution (H2SO4/H2O2 7 :3, v/v) andrinsed again with bidistilled water before the use. UV-Visspectroscopy is the first analytical method to verify if theAuNP synthesis gave a good result in terms of concentra-tion and medium size [46]. To obtain a good spectropho-tometric characterization of the obtained AuNPs, we di-luted the samples in bidistilled water by a factor of 10, inorder to stay in the linear range of the Lambert�Beerlaw. Light scattering phenomenon assumes an importantrole and for this purpose we tried to minimize this effectusing diluted samples. The characteristic plasmonic sur-face resonance (SPR) band of the AuNPs is narrow andlocated at 514 nm. The resultant AuNPs dispersion isstable and, when stored at 4 8C remained unchanged afterseveral weeks.

2.5 Preparation of CB/AuNPs SPE

Prior to AuNPs modification, SPEs were modified withCB dispersion. Commercial CB N220 with surface area of120 m2/g and carbon nanoparticles having diameters com-prised between 17.95 and 32.50 nm was obtained fromCabot Corporation (Ravenna, Italy) [40]. The dispersionof CB was prepared adding 20 mg of CB powder to20 mL of solvent (a mixture dimethylformamide(DMF):water in ratio 1 : 1) and sonicated for 60 min at59 kHz. The CB/SPEs were prepared by drop casting ac-cordingly to our previous papers [38,41], depositing dif-ferent drops (2 mL each, from 2 up to 10 mL) onto work-ing electrode of 1 mg/mL CB dispersion in a 1 :1DMF:H2O mixture. The deposition of CB was performedby solvent evaporation contained in the drop (2 mL) caston the working electrode surface. The AuNPs-CB/SPEswere prepared by depositing different drops (2 mL each,from 2 up to 20 mL) of the AuNPs solution on the CB/SPE. In the case of the first study (see Figure 1) AuNPs/SPEs were prepared by depositing (3 mL) of AuNP solu-tion on a bare SPE and the CB/SPEs were prepared bydepositing (3 mL) of CB dispersion.



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2.6 As(III) Measurements

Measurements of As(III) were performed using anodicstripping voltammetric analysis consisting of three con-ventional steps: time-controlled electrochemical deposi-tion with solution stirring, rest period, and a positive-going voltammetric stripping scan under selected condi-tions. The system is accessorized by a switch box that au-tomatically controls the magnetic stirrer during the vol-tammetric experiment. In details, an aqueous solutioncontaining 0.1 M HCl and 0.01% w/v ascorbic acid wasused as working solution, a deposition potential of�0.4 V was applied for 5 minutes, and then a strippingrange potential from �0.3 to 0.5 V with a potential scanrate of 0.8 Vs�1 was applied for the voltammetric strip-ping scan.

In the case of As(III) measurement in tap water, thetap water was collected from the city of Veroli (Fr, Italy).To 10 mL of tap water, ascorbic acid (final concentration0.01% w/v) and concentrated HCl (final concentration0.1 M) were added and the sample was analyzed.

3 Results and Discussion

3.1 Characterization of SPE Modified with AuNPs

A bare SPE was modified with 3 mL of the AuNPs andleft at room temperature to let solvent to evaporate. Thisprocedure resulted in the immobilization of the AuNPson the working electrode surface. In order to characterizethe AuNPs modified SPEs (AuNPs/SPEs), cyclic voltam-metry studies were performed.

In order to demonstrate the presence of AuNPs on thesurface of the working electrode, cyclic voltammetry in0.1 M H2SO4 in the potential range from 0 to 1.6 V (vs.Ag/AgCl) with a scan rate of 100 mVs�1 was performed.The corresponding voltammogram is shown in Figure 1a,displaying a reduction peak close to 0.9 V, these processes(formation and removal of a monolayer of oxygen spe-cies) are electrochemically limited in the extent by thequantity of a given material that can be deposited whenreduced at the surface of the gold surface, thereby givingrise to the current peaks. When working in acidic media,the proton concentration is very high, the formation ofa monolayer of oxide and its reduction does not alter thepH at the level of the electrode surface and thereforedoes not modify the profile of the current in this region[46]. For each event, the reactions in aqueous acid solu-tion can be represented by

Auþ nH2O! AuðOHÞn þ nHþ þ ne�

and

AuðOHÞn þ ne� ! Auþ nOH�

where parentheses indicate the absorbed species.

The area of the peak due to the Au surface oxide re-duction is proportional to the total surface area of goldon the SPE surface, in a ratio of 390 mC cm�2 [47]. Alarge peak area due to the oxide reduction on modifiedSPE indicate a high gold exposed surface and thereforeaccessible by the analyte in solution.

In order to investigate the electrochemical properties,cyclic voltammetry using AuNPs/SPEs was performed in0.1 M phosphate buffer (pH 7) containing 1 mM of potas-sium ferro/ferricyanide in the potential range from �0.5to 0.5 V with scan rate of 50 mV s�1 and the data com-pared with the ones performed using bare SPE and SPEmodified with CB (CB/SPE). Using AuNPs/SPEs, a re-duced peak-to-peak separation and an enhanced voltam-metric current in comparison with the bare SPE was ob-tained as expected, demonstrating the good electrochemi-cal properties of the synthesized AuNPs. Moreover, we

Fig. 1. (a) Cyclic voltammetry in 0.1 M H2SO4 in the potentialrange from 0–1.6 V (vs. Ag/AgCl) with scan rate of 100 mVs�1

using bare SPE (dotted line), SPE modified with 3 mL of AuNPs(solid line) and SPE modified with 3 mL of CB (dashed line); (b)Cyclic voltammetry of 1 mM of potassium ferro/ferricyanide in0.1 M phosphate buffer (pH 7) in the potential range from �0.5to 0.5 V with scan rate of 50 mV s�1 using bare SPE (dotted line),SPE modified with 3 mL of AuNPs (solid line) and SPE modifiedwith 3 mL of CB (dashed line).



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confirm the good electrochemical behavior of CB/SPE inagreement with our previous results [38–41].

3.2 Characterization of SPE Modified with CB-AuNPs

CB has been used to improve the analytical performancesof the electrode exploiting its large surface area and elec-trochemical properties. An advantage of utilizing CB is toincrease the surface area, thus CB could help the deposi-tion of AuNPs to be more homogenous distribution com-pared to the bare SPE. In order to choice the optimalamount of CB and AuNPs for modifying the SPE reach-ing high sensitivity and repeatability, an initial study wasperformed through ASV in 200 ppb As(III) solution in0.1 M HCl with a fixed quantity of AuNPs and varyingthe CB. As shown in Figure 2a, the presence of the 2 mLof CB (a single layer of CB) confers a sufficient highersensitivity and repeatability to the sensor, in fact in thecase of bare SPE modified with 10 mL of AuNPs (5layers) we have obtained a higher RSD% (20%) whencompared with SPE modified with a layer of CB and10 mL of AuNPs (13 %). In order to confirm the results,we have performed the study of the repeatability of thedeposition of different amounts AuNPs varying from 2 to20 mL using bare SPE and SPE modified with 2 mL of CB.The study was performed by means of cyclic voltamme-tries in sulfuric acid and evaluating the area of the reduc-tion peak close to 0.9 V vs. Ag/AgCl (data not shown).We have observed a comparative area of the reductionpeak between the bare SPE and the SPE modified withCB that increases at the increasing of amount of AuNPsdeposited on the working electrode surface. Howevera significant improvement in terms of repeatability wasobtained using SPE modified with a layer of CB. In factthe mean of the RSD% was 3.8 % in the case of SPEmodified with CB-AuNPs, which is rather lower than theone obtained for bare SPE modified with AuNPs (13 %),confirming a better deposition of AuNPs on SPE modi-fied with a layer of CB, thus CB/SPE was selected for thefurther study. Figure 2b shows the response of the As(III)varying the amount of AuNPs with the achievement ofa plateau in the range between 4 and 10 mL, while the re-sponse relative to 20 mL does not appear to be directlyproportional to the amount deposited. Furthermore,a better repeatability of the measurements carried outemerges using sensors modified with 6 and 8 mL ofAuNPs: the amount that reflects the best ratio sensitivity/production time results to be 6 mL and it was chosen forthe rest of work.

3.3 Choice of the Electrolyte

After the optimization of the amount of CB and AuNPs,the concentration of the supporting electrolyte was select-ed. The stripping analyses were performed with the addi-tion of 0.01% w/v ascorbic acid to stabilize the As(III) asreported in Metrohm bulletin [48]. Hydrochloric acidconcentrations were 0.001, 0.01, 0.1 and 1 M as reported

in Figure 3. The 0.1 M and 1 M gave a similar highest cur-rent intensity (12 mA for As(III) 200 ppb); nevertheless,0.1 M provided a better repeatability, thus, 0.1 M HCl+0.01% w/v ascorbic acid were chosen as supporting elec-trolyte for the rest of the work.

Fig. 2. (a) Optimization of the amount of CB. LS-ASV meas-urements were performed using a 200 ppb As(III) standard solu-tion in 0.1 M HCl+0.01% w/v ascorbic acid, Edeposition =�0.3 V,scan rate=0.2 V/s, tdeposition =120 s. (b) Optimization of theamount of AuNPs. LS-ASV measurements were performed usinga 200 ppb As(III) standard solution in 0.1 M HCl+0.01% w/vascorbic acid, Edeposition =�0.3 V, scan rate=0.2 V/s, tdeposition =120 s.



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3.4 Electrochemical Parameters

3.4.1 Choice of Dissolution Technique

In order to obtain the best response in terms of sensitivi-ty, both linear sweep and square wave voltammetry wereused. For this purpose, 200 ppb As(III) solution in the op-timized supporting electrolyte were analyzed using a po-tential and time for deposition of �0.3 V and 120 s re-spectively. This study reported in Figure 4 shows that thelinear sweep technique (solid line) provides much highersensitivity than the square wave (dashed line); thus thelinear sweep has been chosen as dissolution technique.

3.4.2 Optimization of Deposition Potential

The deposition potential for an easily reduction of Asions should generally be 0.3–0.5 V more negative than E8of As. In the case of the CB-AuNPs/SPE, the dependenceof the peak current on the deposition potential is shownin Figure 5a. A 200 ppb As(III) standard solution wasused and the deposition potential of �0.4 V was chosendue to no apparent difference in the average peak currentin the range from �0.2 to �0.4 V coupled with lowerRSD% (8 %).

3.4.3 Optimization of Scan Rate

The effect of the scan rate on the peak intensity was eval-uated, founding that the stripping peak current was pro-portional to the scan rate as shown in Figure 5b up to0.8 Vs�1. A broad peak was obtained at a scan rate of1 Vs�1, thus a scan rate of 0.8 Vs�1 was chosen as a com-promise between a satisfactory sensitivity and a well-de-fined peak.

3.4.4 Optimization of Deposition Time

Preconcentration or deposition time is the time duringwhich As ions are reduced at the CB-AuNPs/SPE. Differ-ent deposition times of 30, 60, 120, 240, 300 and 600 swere investigated. As shown in Figure 5c, the peak cur-rent increased proportionally with time between 30 and300 s. The stripping current of the peak is not anymoreproportional over 300 seconds, probably due to the satu-ration of the available Au surface sites for As(III) deposi-tion. Based on these results, a deposition time of 300 swas selected for further studies.

3.4.5 Optimization of Potential and Time of Cleaning

In order to avoid the memory effect and the overestima-tion of As in the sample, the potential and time of clean-ing were optimized. As shown in Figure 5d, a pretreat-ment potential at �0.2 V minimizes the memory effect ofthe working electrode surface. The best time of cleaningpotential is found to be 10 s (not shown): the choice ofthis short time leads to a very satisfactory response interms of repeatability (RSD%=8 %).

3.5 Calibration Curve

The CB-AuNPs sensor was challenged using standard sol-utions of As(III). Figure 6 shows the voltammograms rel-ative to anodic peak current of several As(III) levelstested. Under the optimized conditions, the relationshipbetween the peak current of As(III) and its concentrationis described by the following equation: y= (0.629�0.006)x�(0.25�0.09) with a sensitivity of 673�6 mAmM�1 cm�2

and R2 =0.999 in the linear dynamic range from 2 ppb to30 ppb. LOD calculated as 3 times the standard deviationof the blank solution divided by the slope of the calibra-

Fig. 3. Choice of the HCl concentration. LS-ASV measure-ments were performed using a 200 ppb As(III) standard solutionin HCl+0.01% w/v ascorbic acid, Edeposition =�0.3 V, scan rate=0.2 V/s, tdeposition =120 s.

Fig. 4. Choice of dissolution technique using a 200 ppb As(III)standard solution in 0.1 M HCl+0.01% w/v ascorbic acid withLinear Sweep (solid line) conditions: Edeposition =0.3 V, scan rate=0.2 V/s, tdeposition =120 s and Square Wave (dashed line) condi-tions: Edeposition =�0.3 V, tdeposition =120 s, frequency=50 Hz,Eampl =20 mV, Estep =2 mV.



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tion curve was found equal to 0.4 ppb. The inter-electroderepeatability of the AuNPs-CB/SPE sensor was estimatedfrom the response to 10 ppb As(III) using ten modifiedSPEs of the same batch, and the RSD% never exceed11%. The sensors were tested daily after the preparationand were stable for a week at RT in dry conditions.

3.6 Interferences Study

In order to evaluate the interference of some heavymetals usually measured by stripping analysis, Hg2+, Pb2+,Cd2+ were analyzed at the legal limit value (Hg2+

(1 ppb), Pb2+ (10 ppb), Cd2+ (5 ppb)) [55], observing theabsence of interference in all cases. In order to confirmthe selectivity of the sensor proposed towards As(III),calibration curves (n=3) were constructed in presence of100 ppb of As(V) observing no significant variation of thesensitivity when compared with the calibration curves ob-

Fig. 5. a) Effect of deposition potential: LS-ASV using 200 ppb As(III) in 0.1 M HCl +0.01% w/v ascorbic acid, scan rate=0.2 V/s,tdeposition =120 s. b) Effect of scan rate: LS-ASV using 200 ppb As(III) in 0.1 M HCl+0.01% w/v ascorbic acid, Edeposition =�0.4 V,tdeposition =120 s. c) Effect of deposition time: LS-ASV using 200 ppb As(III) in 0.1 M HCl +0.01% w/v ascorbic acid, Edeposition =�0.4 V, scan rate=0.8 V/s. d) Effect of cleaning potential: LS-ASV using 10 ppb As(III) in 0.1 M HCl+0.01% w/v ascorbic acid,Edeposition =�0.4 V, scan rate=0.8 V/s, tdeposition =300 s, tcleaning =10 s.

Fig. 6. Calibration curve using LS-ASV in 0.1 M HCl +0.01%w/v ascorbic acid, scan rate=0.8 V/s, tdeposition =300 s, Ecleaning =0.2 V, tcleaning =10 s.



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tained in absence of As(V). As reported in literature,Cu2+ can interfere with As(III) e.g. developing binarycompounds [46]. We have performed calibration curves(n=3) at four levels of Cu2+ (10, 20, 50 and 100 ppb). InTable 1 is reported the effect of Cu2+ on LOD and sensi-tivity of As(III) confirming its interference at high con-centration as shown also in the Figure 7. Any suspectedCu2+ interference can be evaluated simply observing thevalue of peak at around 0.3 V, thus in the case of a signifi-cant Cu2+ interference, it is possible to perform a pretreat-ment of the water sample by means of solid phase extrac-tion (e.g. using AnaLig TE-3 cartridge, GL Sciences,Japan) [54].

In order to evaluate the effect of Cu2+ . in the case oftap water, a series of experiments adding increasing con-centrations of Cu2 + to a constant As(III) concentration(namely 20 ppb) were performed. As highlighted inFigure 8, the stripping peak current of As(III) is fullyhidden by the addition of 5-fold copper excess; howeverthe voltammogram obtained in real samples, showed also

the peak at around 0.3 V due to the presence of Cu2 +

without interfere with the As(III) detection.

3.7 As(III) in Drinking Water Sample

In the case of tap water analyzed, no As(III) was detect-ed in the sample at our detection limit. In order to evalu-ate the accuracy of the sensor, the same tap water sam-ples were spiked with 10 ppb (legal limit) and 20 ppb ofAs(III). Three replicate determinations using the stan-dard addition method gave average recovery results of99�9 % and 108�4 % for 10 ppb and 20 ppb As(III), re-spectively, confirming the good accuracy of the sensor de-veloped.

4 Conclusions

Arsenic detection is an important goal in analyticalchemistry due to the high toxicity of this element and toreal problems of its pollution. This work demonstratesa fast and easy way to detect As(III) using for the firsttime CB-AuNPs multilayer nanocomposite deposited onSPE. The possibility to use a cost-effective sensor for thedetection of As(III) allows its single use, avoiding thememory effect. The sensor allows to obtain a high sensi-tivity of 673�6 mAmM�1 cm�2 when compared with theAuNPs/SPE reported in literature (see Table 2). In orderto confirm, also in this case, that CB can be a successfullyalternative to carbon nanotubes, we have compared ourresults with the ones obtained using glassy carbon elec-trode modified with both multiwall carbon nanotubes andAuNPs [33], using the same dissolution technique (ASV)and the same deposition time (240 s). A sensitivity of528 mAmM�1 cm�2 and a detection limit of 1 ppb were ob-tained, which are comparable with those reported in liter-ature (sensitivity of 464 mAmM�1 cm�2 and detection limitof 0.6 ppb) [33]. The stripping analysis requires only few

Table 1. LOD variation for different Cu2+ levels.

Cu2+ level(ppb)

Curve equation Sensitivity(mA/mMcm2)

LOD(ppb)

0 x�(0.25�0.09)y= (0.629�0.006)

673 0.4

10 x�(0.45�0.26)y= (0.566�0.024)

607 1.4

20 x�(0.58�0.37)y= (0.409�0.030)

438 2.7

50 x�(0.21�0.20)y= (0.235�0.015)

252 2.6

100 x�(0.18�0.37)y= (0.133�0.018)

143 8.3

Fig. 7. Evaluation of LOD variation caused by different Cu2+

levels in standard solution using LS-ASV under optimized condi-tions see Figure Caption 6. Solid line represents 20 ppb As(III)without Cu2+ , dashed lines represent the signal of 20 ppb As(III)in the presence of 10, 20, 50 and 100 ppb of Cu2+ .

Fig. 8. Copper presence evaluation in tap water using LS-ASVunder optimized conditions see caption of Figure 6.



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minutes and this sensor provides the detection of As(III)with high values of percentage recovery (99�9 %) ina tap water sample spiked with the legal limit amount(10 ppb). The electrodes are easily fabricated at low cost,are disposable, and suitable for in situ analysis in realtime. Further studies are planned to develop a sensor forthe total arsenic in real samples allowing the speciation ofAs(III) and As(V) by means the electrochemical reduc-tion of As(V) and As(III) at a more negative potential[54] or by means chemical reduction of As(V) to As(III)followed by anodic stripping voltammetry of As(III) [56].

Acknowledgements

The authors would like to thank Dr Chiara Zanardi forthe helpful discussion about AuNPs synthesis and BASFItalia S.p.A. , Divisione Catalizzatori, Rome, Italy.

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Material SPE�s modification Method Deposition time(s)

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Sensitivity(mA/mM

Sensitivity(mA/mM cm2)

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PLA-AuNPs Adsorption DP-ASV 130 up to 4000 0.09 6.6 33 [50]Citrate-AuNPs Adsorption LS-ASV 160 3–18 0.4 0.91 13 [51]Gold SPE – SW-ASV 60 0–200 2.5 2.2 32 [52]Ibu-AuNPs Adsorption CV 180 (N2 purging) 0.1–1800 0.018 0.36 [a] [53]Au Electrochemical SI-ASV 120 1–100 0.03 25 [a] [54]Cl AuNPs Adsorption ASV 300 2–30 0.4 47 673 This work

[a] WE area was not reported in [53,54].



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Received: January 26, 2014Accepted: February 7, 2014

Published online: && &&, 2014



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Stripping Analysis of As(III) by Means of Screen-Printed Electrodes Modified with Gold Nanoparticles...

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