Sensors and Actuators B 155 (2011) 145153

Contents lists available at ScienceDirect

Sensors and Actuators B: Chemical

journa l homepage: www.e lsev ier .co

A polym d pcontinu en

Wooseok a

a MicroSystems rsity ob Department o SA

a r t i c l

Article history:Received 11 AReceived in re22 NovemberAccepted 22 NAvailable onlin

Keywords:Lead (Pb(II))On-site measurementReusable polymer lab chip sensorSilver electrodeSquare-wave anodic stripping voltammetry(SWASV)

r lab cad (Pb chiat referenoringis reusecu

inside the microchannels using square-wave anodic stripping voltammetry (SWASV). With only 13.5Lof sample volume the sensor chip showed a correlation coefcient of 0.998 for the Pb(II) concentrationrange of 11000ppb with the limit of detection of 0.55ppb at 300 s deposition time. The peak potentialsduring the forty-three consecutive SWASV measurements showed a relative standard deviation of 1.0%,with a standard deviation of 0.005V. The high repeatability and linearity of the sensor over the large,

1. Introdu

With theeffects posement haveconcentratilevels in mmore attenof human awidely repoare primarithe brain anblood pressconsequencmumcontaat less thanand widesptive monitogroundwate

CorresponE-mail add

0925-4005/$ doi:10.1016/j.three orders of magnitude, dynamic range of 11000ppb showed that the developed sensor chip canbe reused for a variety of on-site measurements such as for soil pore water or groundwater, using onlymicro-volumes.

2010 Elsevier B.V. All rights reserved.

ction

increasing trend toward urbanization, the serious sided by heavy metals to human health and the environ-been a major concern [1]. In particular, as lead (Pb(II))ons in public supply wells have reached unacceptableany parts of the world, it has become obvious thattion needs to be paid to linkages between the effectsctivities on the surface and groundwater quality. It wasrted that the elevated levels of Pb(II) in drinking waterly related to human health effects such as damage ofd nervous system, behavioral and learning disabilities,ure increase, and kidney injury and anemia [2]. As ae, the current stringent potable water standard (maxi-minant level,MCL) for Pb(II) has been set by theU.S. EPA0.015mg/L of Pb(II). The combination of high toxicityread occurrence has created a pressing need for effec-ring and measurement of Pb(II) in surface waters andr. Since on-sitemeasurement is essential to achieve the

ding author. Tel.: +1 513 5561886; fax: +1 513 556 3930.ress: amjang68@gmail.com (A. Jang).

effective monitoring strategies, there is a clear need for reliable,efcient and cost-effective monitoring technologies for Pb(II) thatadversely affects human health.

Conventionally, levels of trace heavy metals in environmentalsamples have been measured by atomic absorption spectrometry(AAS) and inductively coupled plasmamass spectroscopy (ICP-MS)under highly controlled laboratory conditions. Because of theirbulky size, high cost, and long analysis time, these methods arenot suitable for on-site environmental screening analysis [3]. Alter-natively, stripping analysis has been widely studied for on-sitemeasurement of heavy metal ions [48]. In the stripping analy-sis, heavy metal ions in the sample solution can be identied andquantied by measuring the generated current at each reductionpotential that reduces specic metal ions as the potential sweepswithin the appropriate scan range after deposition of heavy metalions on sensors [911]. In particular, Mercury (Hg) working elec-trodes have shown high sensitivity in measuring heavy metal ionsusing anodic stripping voltammetry (ASV) [1214]. However, theuse of toxic Hg as a sensingmaterial for environmental monitoringis limited due to its toxicity to humans and animals. Additionally,the necessity to stir the sample solution and to renew the Hg dropfor each measurement makes Hg undesirable for sensing applica-tions [15]. As an alternative, Bismuth (Bi) has been suggested as the

see front matter 2010 Elsevier B.V. All rights reserved.snb.2010.11.039er lab chip sensor with microfabricateous and on-site heavy metal measurem

Junga, Am Jangb,, Paul L. Bishopb, Chong H. Ahnand BioMEMS Laboratory, Department of Electrical and Computer Engineering, Univef Civil and Environment Engineering, University of Cincinnati, Cincinnati, OH 45221, U

e i n f o

ugust 2010vised form2010ovember 2010e 26 November 2010

a b s t r a c t

This paperpresents a reusablepolymein nature. In particular, detection of lebeen performed using the proposed lafabricated silver working electrode thintegrated silver counter and quasi-retargets on-site environmental moniting the sensing environment when itcharacterized through forty-three conm/locate /snb

lanar silver electrode fort

f Cincinnati, Cincinnati, OH 45221, USA

hip sensor for continuous andon-siteheavymetalmonitoringb(II)), which is the most common heavy metal pollutant, hasp sensor. Theminiaturized lab chip sensor consists of amicro-places the conventional mercury and bismuth electrodes, ance electrode, and microuidic channels. The proposed sensorin a continuous fashion without disturbing or contaminat-sed. The reusability of the miniaturized lab chip sensor was

tive measurements in non-deoxygenating standard solutions

146 W. Jung et al. / Sensors and Actuators B 155 (2011) 145153

working electrode material in ASV to detect various heavy metalsin different applications because of its low toxicity while showingsimilar electrochemical performance to Hg [1621]. However, bothamalgam formation of Hg electrodes [22] and multi-componentformationoas some ofstill remain

Silver (Arial for reuproceeds v(underpoteing the adselectrochemlead on theequation, Pbsurface remtime, resultin conjunctproviding rited excelleof sensitiviresearch shsuremicro-such as a rfabricationwith well-dworking elequasi-refereitations. Fuminiaturizecomponenton-a-chip dchemical anPolymer subeen usedsilicon andof biocompOur laboratthe COC wious heavysampling ameasuremeits use for c

For conttherefore, aWE, integradevelopedexpected thequipped odevice [33]measuremeto change sand mass peration, and

2. Experim

2.1. Chemic

All chempuricationiments. 70%(Fluka, MO,electrolytedard for th

prepared from 1000ppm stock atomic adoption standard solution(SigmaAldrich Corp., MO, USA). Necessary dilutions were com-pleted with the supporting electrolyte for daily preparation of thestandard solutions. Ready-to-use Cyless silver electroplating solu-

echn9.99enishco-Asequ

evice

18 (atedtechf 10nch bscalattered stpatteand

s toThereplatiid prsedrillinng asorn emA) toses ud intogrtes tcrocens

idic cin Fiand

hastedrati2, whted sctropc). Thanneter thip. Te thafullyion oe senpossie m

para

Senl pochemed btheys a tf Bi [23] arenotdesirableproperties for reusable sensorsthe heavy metals fused into these electrode materialsafter ASV leading to memory-effect.g) solid electrodes can be an alternative sensing mate-sable sensors because the electrodeposition of metalsia the formation of a monolayer of the target metalntial deposition, UPD) on these solid electrodes dur-orption process rather than amalgam formation. Theicalmechanism of deposition and stripping reaction ofsilver electrode surface may be simply represented by2+ +2e Pb. As a result, the structure of the electrodeains mainly unchanged during the electrodepositioning in clear removal of deposited metals based on UPDion with stripping voltammetry (UPD-SV), and thusepeatable results [22]. The Ag electrode has exhib-nt characteristics for heavy metal detections in termsty and repeatability [2429]. However, most of thisows some limitations; for example, they cannot mea-volumes of sample and they need additional equipmentotator or a stirrer. However, with improved micro-technologies, planar Ag electrodes can be producedened patterns at themicro-scale. The ready-to-use Agctrode (WE) along with the integrated Ag counter andnce electrode (CE/QRE) can overcome the above lim-rthermore, a desirable combination incorporating thed on-chip electrochemical sensors with microuidics as a micro total analysis system (microTAS) or lab-evice is achievable, which provides a good platform ford biological analyses in a miniaturized format [30,31].bstrates, such as cyclic olen copolymer (COC), havefor lab-on-a-chip materials instead of the traditionalglass substrates because of their favorable propertiesatibility, high optical transparency, and low cost [32].ory developed thebismuth-baseddisposable sensors onth microfabrication technique for on-site and continu-metal ions measurement [3]. However, the automaticnd analyzing device [33] was designed for only sevennts; the seven bismuth-based disposable sensors limitontinuous monitoring.inuous and on-site heavy metal ions measurement,reusable heavy metal sensor with on-chip planar Agted Ag CE/QRE, and microuidic channels has beenby standard microfabrication technology. It could beat when the seven developed reusable sensors aren the developed automatic sampling and analyzing, at least three hundred and forty-three consecutivents can be achieved without user intervention neededensor chips. This sensor is also suited for very low costroduction, small analyte consumption and waste gen-ease of use.

ental

als

icals were of ACS grade and used without further. De-ionized (DI)waterwas used throughout the exper-HNO3 (pharmco-AAPER, CT, USA) and 99.9995% KClUSA) were used for the preparation of the supportingcontaining 0.01M HNO3 and 0.01M KCl. Lead stan-e calibration and characterization of the sensor was

tion (Tthick 9to repl(pharming sub

2.2. D

S18spin-coraphylayer othree i(Temesired pdesignon theplatingfor 30dried.electro

Rapwere uAfter dlet usithe senusing aCA, USprocesmarize

Phoillustraandmithe dimthe utrated100mwhichintegracongu50mmfabricaAg eleFig. 2(idic chchip afidic chvolumposedreductally, thavoidwith th

2.3. Ap

Palmmerciaelectroprovidtion ofemploic Inc., RI, USA) was used for Ag electroplating. 0.1mm8% Ag foil (Alfa Aesar, MA, USA) was used as an anodethe Ag in solution during Ag electroplating. 96% H2SO4APER,CT,USA)wasused tomake10%H2SO4 for inhibit-ent tarnishing after Ag electroplating.

fabrication

MicroChem Corp., MA, USA) positive photoresist wasand patterned on a COC substrate by the photolithog-

nique. On top of the photoresist patterns, a titaniumnm and a silver layer of 100nm were deposited on alank COC substrate using an e-beam metal evaporator

FC1800, BOC Edwards Temescal, CA, USA). The unde-ns of electrodes were lifted-off by acetone to obtain theructures. Another silver (1.7m) layer was depositedrned electrodes using the electroplating method. Afterdragging out, the device was dipped into 10% H2SO4

inhibit subsequent tarnishing. It was then rinsed andwere not any mechanical pretreatment steps after theng.ototyping methods [34] and plastic injection moldingfor high throughput polymer uidic chip fabrication.g holes for uidic interconnection at the inlet and out-micro drill bit, the microuidic chip was bonded withchip using the thermoplastic fusion bonding techniquebossingmachine (MTP-10, TetrahedronAssociates Inc.,make the nal device. The standard microfabricationsed for making the miniaturized lead sensor are sum-Fig. 1.aphs of the fabricated device are shown in Fig. 2, whichhe two-electrode conguration, electrical connections,hannels. In order tomaximize the area of the Ag CE/QRE,ions of the Ag CE/QRE are the same as the dimensions ofhannel. Details of the Ag WE and Ag CE/QRE are illus-g. 2(a). The Ag WE has a length of 22.5mm, width ofa spacing of 100m to the Ag CE/QRE. The Ag CE/QRE,

been used as a wire form in most prior literature, isinto the sensor chip. In order to enable a two-electrodeon [24], the area of the Ag CE/QRE was set to aroundich is more than 20 times to the area of the AgWE. Theensor after PR lift-off is shown in Fig. 2(b) followed bylating resulting in a 1.7-m thick sensor as shown ine injection-molded uidic chip has 220m deep u-ls as shown in Fig. 2(d). Fig. 2(e) shows the nal sensore fusion bonding between the sensor chip and the u-

he entire chip size is 3 cm2 cm, and the total samplet the chip can accommodate is 13.5L. Thus, the pro-integratedpolymermicrouidic chipenables signicantf analyte consumption andwaste generation. Addition-sor chip did not need to be stored in buffer solution toble sensor deterioration since the sensor was coveredicrouidic chip after bonding.

tus

s (Palm Instruments BV, The Netherlands), a com-rtable electrochemical analyzer, was used for theical measurements. PSTrace (version 1.4.) software

y Palm Instruments BV was used for the characteriza-microfabricated sensors. Because the fabricated sensorwo-electrode conguration, the counter electrode clip

W. Jung et al. / Sensors and Actuators B 155 (2011) 145153 147

Fig. 1. The summary of the fabrication processes for the sensor chip (I) and the uidic chip (II), respectively.

and the reference electrode clip of the PalmSens are shorted to eachother. Formeasurements, theworking electrode clip is simply con-nected to the Ag WE contact pad while the counter and referenceelectrode clip is connected to the Ag CE/QRE contact pad as shownin Fig. 2(f). The measured output was transferred to a personalcomputer via Bluetooth and displayed from the PSTrace softwareas shown in Fig. 2(g). All measurements were taken in unstirred

and non-deoxygenating solutions. Experiments were carried outat room temperature to eliminate any temperature effect.

2.4. Procedure

The analysis was performed without removal of oxygen using13.5L of solution containing 10mM HNO3 and 10mM KCl. A

Fig. 2. (a) The100nm Ag aftthe senor andcomputer withschematic illustration of the reusable on-chip heavy metal sensor using microfabricateder PR lift-off, (c) the sensor electrode after Ag electroplating gets 1.7m thick Ag, (d) tthe microuidic channel, (f) the potentiostat along with the chip for the measurement,PSTrace software.Ag electrodes, (b) the sensor electrode is composed of 10nm Ti andhe uidic chip after injection molding, (e) the entire chip includingand (g) the display of the measurement plot shown on the personal

148 W. Jung et al. / Sensors and Actuators B 155 (2011) 145153

Fig. 3. The repat anAg electroKCl) recorded

pipetter (Fito the inletthen injectedepositionno stirringwave anodiamplitude,Ebegin =0.70.2V wasPb(II) after tfor another

3. Results

3.1. Inuencurrent

Fig. 3 illuWE duringrecorded inthe AgWE sited high baPb(II) peakwas achievthe electrodthe detectio

3.2. Effect o

Optimalon iterativeducibility, awith a pulsfurtherworleft shouldestarted frompeak of thefrequency wthe peak dethe pulse fr

coarse like the teeth of a saw, resulting in poor resolution as shownin Fig. 4(a).

Changes of the step potential (Estep) caused increase of the peakcurrent by ca. 10% for Pb(II), from2 to3mVanddecrease of thepeak

t byore,urrenbestV. At wagrowamplt haln in

he drn thbe pren sehe dy, thalyzetionak cudep

eratuo 0e leftial thh lin

uarenaly

ASVredringtratig elecike fode wtioncon

h thetion lroducibility of the background current on the base of SWASV curvesde in non-deaerated supporting electrolyte (0.01MHNO3 and0.01Min successive electrochemical activation of the Ag electrode.

sher Scientic, PA, USA) was used for sample loadingport of the microuidic chip. Sample solutions wered into the sensing chamber via the inlet channel. Thestep was Edep =0.75V for 300 s vs. Ag QRE. There wasduring the deposition time. Conditions for the square-c stripping voltammetry (SWASV) are as follows: pulse23mV; step amplitude, 3mV; step frequency, 23Hz;5V; Eend =0.2V vs. Ag QRE. After each measurement,applied for electrochemical cleaning of any remaininghe stripping step. Then, anewtest solutionwas insertedmeasurement.

and discussion

ce of electrochemical activation on background

strates the changes of the background current in the Ag

currenTherefpeak c

Theof 20mcurrenmajorpulsepeak aas show

As tto govehas tohas bewhen ttionallthe andeposithe pe

Thethe lit0.8 tthat thpotentthe hig

3.3. SqPb(II) a

SWgreatlyrent duconcenportin

Unlelectrotaminasurfacesor witprotecelectrochemical activation. The voltammograms werenon-deaerated supporting electrolyte. The quality ofurface did not look stable for curves 13, which exhib-ckground current with rapid changes in the region ofcurrent. Low and stable background level (curves 46)ed with the consequent electrochemical activation ofe. At this point, Ag WE indicated excellent activity forn of Pb(II) with high sensitivity, stability and long-life.

f SWASV parameters

parameters of the SWASV techniquewere chosenbasedtrials. The best results with regard to precision, repro-nd the signal to background current ratiowereobtainede frequency of 23Hz, and this was the value chosen fork. The higher frequency did not give the distinguishabler of the lead peak. Rather, the left shoulder of the peak

0.75V, which is the Ebegin, and increased until thecurrent, resulting in inaccurate peak currents. As pulseas lowered, the starting point of the left shoulder ofcreased from the Ebegin to ca. 0.6V. However, whenequency was lower than 23Hz, the signal became very

cation in orsilver electbecause thelayer before

Initially,through thesensor. Anono need tobetween thequilibriumsolved oxygbecause SWand Ag elecinterferenc

The stabSWASV intion step, tthe sensingate Pb(II) stFirst, 1 ppbseven timewas applieca. 7% for Pb(II), from 3 to 10mV as shown in Fig. 4(b).the step potential of 3mV was applied for the highestt.results were obtained for the pulse amplitude (Eampl)t higher pulse amplitudes (>20mV), higher lead peaks achieved. However, higher pulse amplitudes causedth of the background current. On the other hand, loweritudes (

W. Jung et al. / Sensors and Actuators B 155 (2011) 145153 149

Fig. 4. (a) The SWASV plots when the frequency was 20, 23, 50Hz. (b) Plots when the step potential was 2, 3, 6, 10mV. (c) Plots when the pulse amplitude was 15, 20,25mV. The SWASV plots were recorded in non-deaerated supporting electrolyte with 1ppb of Pb(II) performed under conditions: Edep =0.75V, tdep = 120 s, Ebegin =0.75V,Eend =0.2V.

Fig. 5. The plots showing the peak currents and the slopes between 1ppb and 10ppb of Pb(II) when the deposition time is 180, 240, and 300 s. When the deposition timewas 300 s, the slope was 66nA/ppb while the slopes were 56nA/ppb and 39nA/ppb when the deposition timewas 180 s and 240 s, respectively. The plots are recorded underconditions dened in Section 2.4.

150 W. Jung et al. / Sensors and Actuators B 155 (2011) 145153

Fig. 6. (a) Cali 500, 1(d) Plots for PbEbegin =0.75V

face of thesolution wameasuremestandard soment. The mwere conduat 10, 20, 4sured, ve tof Pb(II) stimplementcleaning steremoval of500, and 10three measbaseline corferent Pb(IIand (d). Gotial at 0.4calibration(R2 =0.999)Fig. 6(a). Th300 s.

3.4. Interfer

Silver elalso Cd(II)lytes with gdetecting Pbration plot from 1ppb to 1000ppb for Pb(II). (b) Plots for Pb(II) at 1, 40, 100, 200,

(II) at 1, 5, 10, 20, 40ppb. The SWASV plots were recorded in non-deaerated supportin, Eend =0.2V, Estep = 3mV, Eampl = 20mV, Freq = 23Hz.

sensor. After the electrochemical cleaning step, news injected for each measurement. After the seventhnt with 1ppb of Pb(II) standard solution, 5ppb of Pb(II)lutionwas injected for the eighth consecutivemeasure-easurements with 5ppb of Pb(II) standard solutions

cted seven times in a row. Consecutively, peak currents0, and 100ppb of Pb(II) standard solution were mea-imes at each concentration. At 200, 500, and 1000ppbandard solution, three replicate measurements wereed at each concentration. The time for electrochemicalp was increased from 20 s to 60 s to havemore time forhigher concentrations of Pb(II) on the surface at 200,00ppb of Pb(II) standard solutions. The total of forty-urements were done consecutively over 8h. Withoutrection such as background subtraction, SWASVs at dif-) concentrations (11000ppb) are shown in Fig. 6(b)od peak shapes were obtained with the peak poten-79V versus the integrated Ag QRE. The correspondingplot for Pb(II) was linear over the range of 11000ppbwith the limit of detection of 0.55ppb as shown ine sensitivity is 28.22nA/ppb at the deposition time of

ences

ectrode has been used in detecting not only Pb(II) butwhile showing the good selectivity between two ana-ood linearity [26,27,29]. This selectivity over Cd(II) inb(II) was investigated by examining the effect of co-

existing Cd40ppb of Cthe two cupeak curren

Fig. 7. TheploPb(II) + 40ppbexcept the dep000ppb. (c) Enlarged calibration plot from 1ppb to 40ppb for Pb(II).

g electrolyte performed under conditions: Edep =0.75V, tdep = 300 s,

(II) on the response for Pb(II) with 20ppb of Pb(II) andd(II). The results showed the clear separation betweenrrent peaks of Pb(II) and Cd(II) as shown in Fig. 7. Thet of the 20ppb Pb(II) decreased 8.3% when there was

ts showing thepeak currents of 20ppbPb(II), 40ppbCd(II), and20ppbCd(II). The plots are recorded under conditions dened in Section 2.4osition time of 120 s.

W. Jung et al. / Sensors and Actuators B 155 (2011) 145153 151

Fig. 8. Peak currents on the proposed sensor during forty-three consecutive measurements at each concentration from 1ppb to 1000ppb of Pb(II).

Fig. 9. Stable pmeasurement

40ppb Cd(Ipotentials o

3.5. Reusab

There arbased sensoon the elecalloys withstripping aremain insiby utilizing

consecutivemeasurements, from1ppb to1000ppbPb(II),were runto characterize the reusability of the silver sensors fabricated onpolymer lab-on-a-chip for lead detection.

As described above, seven measurements were done at eachconcentration of 1, 1, and 5ppb of Pb(II) standard solutions. Fivemeasurements were consecutively done at each concentrationof 10, 20, 40, and 100ppb of Pb(II) standard solutions followedby three measurements at each concentration of 200, 500, and

pb ofonse. 8(bher t% indt of tconp frol refyerslectrlved

Fig. 10. (a) Picsoftware.eakpotentials on the proposed sensor during forty-three consecutives.

I) on the solutionwhile therewas no change in the peakf Pb(II).

1000pthree cand Figare higthan 3a resul

A sesor chiAg/AgCAgCl laence ebe resoility of the sensor

e twomain obstacles preventing the bismuth electrode-r chip from being reused. One is the memory-effect

trode because of the formation of multi-component Binumerous heavy metals. Thus, even after the anodicnd electrochemical cleaning steps, heavy metals stillde the electrodes. This memory effect could be avoidedthe UPD-SV on silver electrodes. As a proof, forty-three

and enlargithis, the peaplotted in Fa relative sadditional Aafter Ag e-b

The bettulated to belectrode d

tures of sensors taken every 2h during 8-h longmeasurements. (b) Quantitative values oPb(II) standard solutions. Peak currents from the forty-cutive measurements are shown in Fig. 8(a) (140ppb)) (1001000ppb). At the concentrations of Pb(II) whichhan 20ppb, the relative standard deviations were lessicating there was no remaining Pb(II) on the Ag WE, ashe characteristics of UPD-SV.d reason preventing the bismuth electrode-based sen-m being reused is the short life-time of the integratederence electrode. Because of the relatively thin Ag and, which are both less than 100nm, the Ag/AgCl refer-ode quickly loses its functionality. This problem couldby increasing the thickness of the Ag QRE to ca. 1.7mng the surface area of the Ag QRE. As a result of doingk potentials in forty-three consecutive measurements,ig. 9, showed a standard deviation (STD) of 0.005V andtandard deviation (RSTD) of 1.0%. When there were nog electroplating steps, the initial 0.1m thick Ag QREeamevaporationwas dissolved away in less than 5min.er performance of the silver electrode has been spec-e due to continuous surface renewal on the workinguring the electrodeposition step, as silver ions dissolvedf AgWE and Ag CE/QRE in gray scale from 0 to 255 analyzed in ImageJ

152 W. Jung et al. / Sensors and Actuators B 155 (2011) 145153

at the counter silver electrode are uniformly redeposited. Thisphenomenon is attributed to the large current during the elec-trodeposition step, the close proximity between the counter andtheworking electrodes, and the nite rate of the precipitation reac-tion of Ag+ +ions towardphenomenothe distanc100m expto Ag WE. Pthe sensorelectrode wthe surfacethe photogby ImageJ schange of ttime. As shAg WE maitive experimto the form

4. Conclus

This papheavy metstate sensostable peakmetal ionswaste. Micrnew fully incounter/qustable peakorders of mfor forty-threusability,for sensor csensors theThus, the sifor detectin

Acknowled

This womental HeaInstitute ofthe Instituteof Cincinnaandalso thaing the Palm

References

[1] A. Jang, Ysorption

[2] M.F.M. Nelectrode2095210

[3] Z. Zou, A.tally frienelectrode(2008) 18

[4] E.P. Achtetrace metin marine

[5] D.DesmoronmentaSens. Act

[6] Kh.Z. Braronmenta

[7] K.C. Honeychurch, J.P. Hart, D.C. Cowell, D.W.M. Arrigan, Voltammetric studiesof lead at calixarene modied screen-printed carbon electrodes and its tracedetermination in water by stripping voltammetry, Sens. Actuat. B Chem. 77(2001) 642652.

[8] E. Shams, R. Torabi, Determination of nanomolar concentrations of cadmiumanodionium92.. Sabautionsanagimed onhnol.aschi,of tr

Reay,ed elehem.Choi,ppingm. AcZhu, Croeleillon,lysis mang, Jdic stefalaelec

tammter anDememuth-g voltconomelectrvancanomoppinganalysaldriaew tym. Acerzoositio05) 20ang, S05) 13Branddic st, Analirowations om. Aconl,cadm

m. Aconl,g volt(200as, Th160as, Manodiovalanz,N

ovel corabowroui. 84 (2. Ahn,posab(2004ou, A.on-sitpling. Browpolymp 9 (2

phie

k Junty, KoCl AgCl resulting in movement of part of the silverthe working electrode before precipitation [25]. Thisn was clearly observed in the experiment; shorteninge between the counter and the working electrodes toedited the transport of the silver ions from Ag CE/QREhotographs taken every 2h from the initial status ofto 8h showed that the surface quality of the workingas maintained during the 8h of the experiment due torenewal phenomenon. For quantitativemeasurements,raphs of the Ag WE and the Ag CE/QRE were analyzedoftware (National Institute of Health) to evaluate thehe brightness in the Ag WE and the Ag CE/QRE overown in Fig. 10, it was experimentally veried that thentained its brightness during the forty-three consecu-ents while the Ag CE/QRE decreased its brightness due

ation of silver chloride.

ions

er characterized newAg electrodes used for continuousal detections on polymer lab-on-a-chips. This solid-r provides reusability with effective detection of thepotentials for on-site SWASV measurement of heavyin non-deaerated solutions without generating toxicofabrication technology has been utilized to realize ategrated sensor with planar Ag working electrode, Agasi-reference electrode and microuidic channel. Thepotentials and the dynamic response over the threeagnitude concentration range, from 1ppb to 1000ppb,ree consecutive measurements establish the sensorsthereby greatly minimizing the analysts labor neededhange, and for reduction in waste generation from themselves, making them more environmental friendly.mple sensor structure and the detection scheme t bestg trace metal from on-site environmental samples.

gements

rk was supported by the National Institute of Environ-lth Sciences (NIEHS, R01 ES015446) in the NationalHealth (NIH). The authors thank Mr. Ron Flenniken inforNanoscaleScienceandTechnologyat theUniversityti for his technical support regarding Ag evaporation,nkMr. Kees vanVelzen for his technical support regard-Sens and PSTrace operation.

.W. Seo, P.L. Bishop, The removal of heavy metals in urban runoff byon mulch, Environ. Pollut. 133 (2005) 117128.oh, I.E. Tothill, Development and characterisation of disposable golds, and their use for lead (II) analysis, Anal. Bioanal. Chem. 386 (2006)6.Jang, E. MacKnight, P-M.Wu, J. Do, P.L. Bishop, C.H. Ahn, Environmen-dly disposable sensors with microfabricated on-chip planar bismuthfor in situ heavy metal ions measurement, Sens. Actuat. B Chem. 13424.rberg, C. Braungardt, Stripping voltammetry for the determination ofal speciation and in-situ measurements of trace metal distributionswaters, Anal. Chim. Acta 400 (1999) 381397.nd, B. Lane, J. Alderman,M.Hill, D.W.M.Arrigan, J.D. Glennon, Anenvi-l monitoring system for trace metals using stripping voltammetry,uat. B Chem. 48 (1998) 409414.inina, N.A. Malakhova, N.Yu. Stojko, Stripping voltammetry in envi-l and food analysis, Fresenius J. Anal. Chem. 368 (2000) 307325.

byzirc86

[9] S.Bsol

[10] I. YbasTec

[11] S. Ltion

[12] R.J.catB C

[13] J.Y.striChi

[14] X.mic

[15] G. Bana

[16] J. Wano

[17] G. Klmvolwa

[18] D.bispin

[19] A. Efor

[20] I. SEcostritro

[21] L. Ba nChi

[22] G. Hdep(20

[23] J. W(20

[24] M.anogen

[25] E. KtraChi

[26] Y. BandChi

[27] Y. Bpin464

[28] B. B156

[29] B. Bforrem

[30] A.Ma n

[31] I. GMicEng

[32] C.HDis92

[33] Z. ZAnsam

[34] A.WforChi

Biogra

WooseoUniversic-stripping voltammetry at a carbon paste electrode modied withphosphated amorphous silica, Sens. Actuat. B Chem. 117 (2006)

n, R.B. Darling, Multi-element heavy metal ion sensors for aqueous, Sens. Actuat. B Chem. 61 (1999) 128137.achi, N. Nashida, K. Iwasa, H. Suzuki, Detection of heavy-metal ionsevaporative concentration using a super-hydrophobic surface, Sci.Adv. Mater. 6 (2005) 671677.I. Palchetti, M. Mascini, Gold-based screen-printed sensor for detec-ace lead, Sens. Actuat. B Chem. 114 (2006) 460465.A.F. Flannery, C.W. Storment, S.P. Kounaves, G.T.A. Kovacs,Microfabri-ctrochemical analysis system for heavy metal detection, Sens. Actuat.34 (1996) 450455.K. Seo, S.R. Cho, J.R. Oh, S.H. Kahng, J. Park, Screen-printed anodicvoltammetric sensor containing HgO for heavy metal analysis, Anal.ta 443 (2001) 241247.. Gao, J.W. Choi, P.L. Bishop, C.H. Ahn, On-chip generated mercuryctrode for heavy metal ion detection, Lab. Chip 5 (2005) 212217.C.M.G. van den Berg, Gold and silver micro-wire electrodes for traceetals, Electroanalysis 16 (2004) 15831591.

. Lu, S.B. Hocevar, P.A.M. Farias, Bismuth-coated carbon electrodes forripping voltammetry, Anal. Chem. 72 (2000) 32183222., A. Economou, A. Voulgaropoulos, M. Sofoniou, A study of bismuth-trodes for the detection of trace metals by anodic strippingetry and their application to the determination of Pb and Zn in tap-d human hair, Talanta 61 (2003) 603610.triades, A. Economou, A. Voulgaropoulos, A study of pencil-leadlm electrodes for the determination of trace metals by anodic strip-ammetry, Anal. Chim. Acta 519 (2004) 167172.ou, Bismuth-lmelectrodes: recent developments andpotentialities

oanalysis, Trends Anal. Chem. 24 (2005) 334340.ra, L. Baldrianova, E. Tesarova, S.B. Hocevar, S.A.A. Elsuccary, A.u, S. Sotiropoulos, B. Ogorevc, K. Vytras, Recent advances in anodicvoltammetry with bismuth-modied carbon paste electrodes, Elec-is 18 (2006) 177185.nova, I. Svancara, S. Sotiropoulos, Anodic stripping voltammetry atpe of disposable bismuth-plated carbon paste mini-electrodes, Anal.ta 599 (2007) 249255.g, D.W.M. Arrigan, Determination of trace metals by underpotentialnstripping voltammetry at solid electrodes, Trends Anal. Chem. 248217.tripping, Analysis at bismuth electrodes: a review, Electroanalysis 17411346., I. Eshkenazi, E. Kirowa-Eisner, The silver electrode in square-waveripping voltammetry. Determination of Pb2+ without removal of oxy-. Chem. 69 (1997) 46604664.-Eisner, M. Brand, D. Tzur, Determination of sub-nanomolar concen-f lead by anodic-stripping voltammetry at the silver electrode, Anal.ta 385 (1999) 325335.E. Kirowa-Eisner, Determination of nanomolar concentrations of leadium by anodic-stripping voltammetry at the silver electrode, Anal.

ta 457 (2002) 285296.M. Brand, E. Kirowa-Eisner, Characteristics of subtractive anodic strip-ammetry of Pb and Cd at silver and gold electrodes, Anal. Chim. Acta2) 99114.e renovated silver ring electrode, Electrochem. Commun. 10 (2008).. Jakubowska, M. Jez, F. Ciepiela, Novel renovated silver ring electrodec stripping analysis of Pb(II) andCd(II) traces inwater sampleswithoutof oxygen and surfactants, J. Electroanal. Chem. 638 (2010) 38..Graber,H.M.Widmer,Miniaturized total chemical analysis systems:ncept for chemical sensing, Sens. Actuat. B: Chem. 1 (1990) 244248.ska, M. Sajnoga, M. Juchniewicz, M. Chudy, A. Dybko, Z. Brzozka,dic systemwith electrochemical and optical detection,Microelectron.007) 17411743.J.W. Choi, G. Beaucage, J.H. Nevin, J.B. Lee, A. Puntambekar, J.Y. Lee,le smart lab on a chip for point-of-care clinical diagnostics, Proc. IEEE) 154173.Jang, E.T. MacKnight, P-M. Wu, J. Do, J.S. Shim, P.L. Bishop, C.H. Ahn,e heavy metal analyzer with polymer lab-on-a-chips for continuousand monitoring, IEEE Sens. J. 9 (2009) 586594.ne,M.J. Rust,W. Jung, S.H. Lee, C.H. Ahn, A rapid prototypingmethodermicrouidics with xed aspect ratio and 3D tapered channels, Lab.009) 29412946.

s

g received his BS degree in biomedical engineering from Yonseirea, in 2006. He is currently working toward the Ph.D. degree in elec-

W. Jung et al. / Sensors and Actuators B 155 (2011) 145153 153

trical engineering at the University of Cincinnati, Cincinnati, OH, USA. Mr. Jungsresearch interests focus on BioMEMS, micro total analysis system (microTAS) andlab-on-a-chip, microuidics, miniaturized electrochemical sensors, and a closedmicro-volume blood sampling device.

Am Jang is currently research assistant professor at the University of Cincinnati,Cincinnati, OH, USA. He joined the Department of Civil and Environmental Engi-neering, University of Cincinnati in 2003 as a post-doctoral fellow. He receivedhis PhD from the Gwangju Institute Science and Technology (GIST), South Koreain 2002. His current research interests are to monitor soil biolms contaminatedwith heavymetals and to develop portable heavymetal sensors using lab-on-a-chiptechnologies.

Paul L. Bishop is currently the Environmental Engineering Program Director at theNational Science Foundation.He is also theAssociateVice President for Research andProfessor of Environmental Engineering at the University of Cincinnati, Cincinnati,OH, USA. He received his PhD in 1972 from Purdue University, USA. His currentresearch interests aremeasuring the impacts of in situ environmental conditions onbiodegradation of toxic chemicals in biolm treatment processes and polyaromatichydrocarbons (PAHs) in soils at Superfund sites.

Chong H. Ahn received the PhD degree in electrical and computer engineeringfrom Georgia Institute of Technology, Atlanta, in 1993. From 1993 to 1994, hewas a Postdoctoral Associate with the Georgia Institute of Technology and thenwith the IBM T.J. Watson Research Center. In 1994, he joined the Department of

Electrical and Computer Engineering and Computer Science, University of Cincin-nati, Cincinnati, OH, as an Assistant Professor and is currently a Professor with theMicrosystems and BioMEMS Laboratory, Department of Electrical and ComputerEngineering, and the Department of Biomedical Engineering. He is also the Directorof theCenter for BioMEMSandNanobiosystems.He is currently amember of theEdi-torial Board of the Journal of Micromechanics and Microengineering, Microuidicsand Nanouidics, and Small. He has published approximately 300 journal and peerreviewed conference proceedings papers related to microelectromechanical sys-tems, bioMEMS, microuidics, and lab-on-a-chip areas. He is the holder of four U.S.patents. His research interests include the design, fabrication, and characterizationof nanostructures and nanobiosensors, magnetic sensors, magnetic MEMS/NEMSdevices, magnetic nano bead-based immunoassays, microuidic devices and sys-tems, BioMEMS/NEMS devices, plastic based disposable biochips, point-of-careblood analyzers, portable biochemical detection systems, protein chips, lab on achip, and biophotonic devices. Dr. Ahn is a Co-chair and Organizer of several inter-national conferences on MEMS/NEMS and BioMEMS/NEMS. In addition, he servedon the program committee of numerous international conferences onmicrosensors,BioMEMS, and MEMS, including the IEEE International Conference on Microelec-tromechanical Systems (MEMS) and the International Conference on Solid-StateSensors and Actuators (TRANSDUCERS). He has presented numerous invited talks inseveral international conferences. From2003 to 2004, hewas an Associate Editor forthe IEEE Sensors Journal. He is currently a Subject Editor of the IEEE/ASME Journalof Microelectromechanical Systems (JMEMS).

A polymer lab chip sensor with microfabricated planar silver electrode for continuous and on-site heavy metal measurementIntroductionExperimentalChemicalsDevice fabricationApparatusProcedure

Results and discussionInfluence of electrochemical activation on background currentEffect of SWASV parametersSquare wave anodic stripping voltammetry (SWASV) for Pb(II) analysisInterferencesReusability of the sensor

ConclusionsAcknowledgementsReferencesBiographies