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SensorsandActuatorsB160 (2011) 670–676

ContentslistsavailableatSciVerseScienceDirect

Sensors

and

Actuators

B:

Chemical

jou rn a l h o m e pag e :w w w . e l s e v i e r . c o m / l o c a t e / s n b

A

microfluidic

based

differential

plasmon

resonance

sensor

Melih

Okan, Osman

Balci, Coskun

Kocabas

BilkentUniversity,DepartmentofPhysics,Ankara,Turkey

a

r

t

i

c

l

e

i

n

f

o

Articlehistory: Received21March2011 Accepted17August2011 Available online 30 August 2011

Keywords:

Surfaceplasmonresonancesensor Phasesensitivedetection Lab-on-a-chipsystems Microfluidicdevices Opticalsensors

a

b

s

t

r

a

c

t

Anewtypeofdifferentialsurfaceplasmon(SPR)sensorintegratedwithamicrofluidicsystemispresented. Theworkingprincipleofthemicrofluidicdeviceisbasedonhydrodynamicmodulationoftwolaminar streamsinsideamicrochanneltoprovideperiodicchangesoftheenvironmentontheSPRsensor.The modulatedreflectanceisthendemodulatedusingalock-inamplifier.Thepresentedsensorprovides sen-sitivitiesofindexofrefractionabout4×10−8RIUtogetherwitha4ordersofmagnitudedynamicrange.

Thismethoddemonstratesasensitivedetectionschemewhichcouldbeusedforlabel-freedetection. © 2011 Elsevier B.V. All rights reserved.

1. Introduction

Phasesensitivedetectionisaremarkablysimpletechniquefor recoveringweaksignalsburiedinanoisybackground.This tech-niqueisbasedonmodulationofasignalofinterestataparticular frequencybyanexternalparameteranddetectingthemodulated signalwithaphase-sensitivedetector(i.e.,alock-inamplifier)[1]. Alock-inamplifier(LIA)amplifiesthesignalatthefrequencyof modulationandrejectstheuncorrelatedsignalfromnoiseatother frequencies.BasicallyLIAdemodulatesthesignalofinterestata particularfrequency.Signalswithasignaltonoiseratioaslowas −100dBcanberecovered.Noncontactatomicforcemicroscopyis agoodexampleofthissensitivedetectionmethod.Themethodof phasesensitivedetectionhasbeencombinedwithmanydifferent modulationtechniquessuchastemperaturemodulation[2], wave-lengthmodulation[3]andspatialmodulation[4].Forexamplelight scatteringfromasinglenanoparticle[4]oracarbonnanotube[5] canbedetectedbymodulationofthepositionoftheparticleand phasesensitivedetection.

Inthisworkweimplementthephasesensitivedetection tech-niquetomicrofluidic systems.Theideaisbasedontheperiodic modulationofliquidmediaflowingwithalowReynoldsnumber insideamicrofluidicchannel.AtlowReynoldsnumberregime,the flowinsidemicrofluidicchannelsislaminar.Takingtheadvantage oflaminarflow,wegeneratearapidperiodichydrodynamic mod-ulationoftwostreamsinsidethechannelwithoutanyturbulent mixing.Hereoneofthelaminarstreamsprovideareferencesignal

∗ Correspondingauthor.Tel.:+903122901965;fax:+903122664579. E-mailaddress:ckocabas@fen.bilkent.edu.tr(C.Kocabas).

andthedifferencebetweenthestreamsisdetectedasadifferential signal.Similarconceptsofhydrodynamicmodulationshavebeen appliedtoelectrochemicalsystemstoreducethebackground elec-trochemicalcurrents[6]andtostudythefrequencyresponseof signalingpathwaysofcells[7].

Hereweimplementthishydrodynamicmodulationtechnique withsurfaceplasmonresonance(SPR)sensors.Overthelastdecade, surfaceplasmon sensorshaveattractedmuch interestowingto theirhighlevelofsensitivityandabilityofsurfacespecific detec-tion.Withasuitablesurfacechemistry,SPRsensorsprovideunique meansof studyinginteractionof biomoleculesonsurfaces.The Kretschmannconfigurationismostcommonlyusedtechniqueto excitesurfaceplasmononaflatmetalsurface.Thephase match-ing conditioncan beachievedat the resonanceangle which is writtenas

ksp=k0nglasssin(r) (1)

wherekspandk0arethewavevectorofsurfaceplasmonsand

exci-tationphotonandristheresonanceangle.Theresonanceangle

depends onthewavevector ofthesurfaceplasmon.The dielec-tric constantof themediumonthemetallayerdetermines the wavevectoroftheSP.ThegeneralsensingmechanismofSPR sen-sorsisbasedondetectingchangesintheintensityofthereflected lightasthedielectricconstantofthemediumchanges.The sensi-tivityofSPRsensorsispredictedashighas10−7RIU[8],however, randomfluctuationsbecauseoflasernoise,thermaldriftand vibra-tionssignificantlyreducetheminimumdetectablesignalof the sensor.Furthermore,duringthemeasurements,thegradualchange ofthebackgroundlevel,likelybecauseofthermaleffects,reduces therepeatabilityofthemeasurements.Theseproblemsfosterthe development of new techniques to eliminate the random and

0925-4005/$–seefrontmatter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2011.08.046

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Fig.1. Schematicrepresentationofthemicrofluidicdeviceandexperimentalsetupusedforhydrodynamicmodulation.Athinlayerofgoldfilmwithathicknessof50nm isfabricatedinsidethemicrofluidicchannels,formingaY-junction.Theflowinsidethechannelisdrivenbyagravityinducedpressuredifferencethatgeneratesrateofflow about∼10␮L/s.ThepressureoftheonearmoftheY-junctionismodulatedbyasolenoidvalveatafrequencyof2.5Hz.Surfaceplasmon-polaritonongold-liquidinterface isexcitedusingahighrefractiveindexprism,theKretschmannconfiguration.Thereflectedlightfromgoldfilmisdetectedbyaphotodiodeandalock-inamplifier.The referencesignalisusedtodrivethesolenoidvalve.Theinsetgraphshowsthepressureasafunctionoftime.

systematicerrorsassociatedwiththeexperimentalsetuporthe environment.Wesummariescoupleofdevelopedmethodsto over-cometheseproblems.Wuetal.[9]andLietal.[10]formedan interferometerwhichdetects thephase changeof thereflected lightfromthemetalsurface.Thismethodispartiallyimmuneof theenvironmentaleffects,thereforeprovidesahighlevelof sensi-tivity.Zhangetal.[11]introducedasecondarySPRsensoradjacent tothemainsensorasareference.Simultaneouslydetectingthe sig-nalfromthereferencesensorandthemainsensorprovidesmore reliablemeasurements.Morerecently,Williamsetal.[12] intro-ducedsignal-lockingSPRsensorwhichusesaperiodicexcitation ofanalyteandareferenceSPRsensorwithfrequencydomain sig-nalprocessingtoreducetheuncorrelatedsignal.Thesemethods andothersimilarones[9,13–21]requireverytediousalignment for interferometers or a complicated data processing. SPR sen-sorsbasedonspectroscopyofsurface-plasmonsintegratedwith multichannel detectors provide higher sensitivities [22]. Slavík andHomolademonstratedasensitiveSPRsensorbasedon long-rangesurfaceplasmon-polaritonswhichprovidessensitivitiesof 2.5×10−8RIU[23].Here,weintroduceasimple,yetvery sensi-tiveSPRsensorbasedonaphasesensitivedetectionschemeusing ahydrodynamicmodulationinsideamicrochannelwithratesof flowatlowReynoldsnumbers.Thepresentedmethodeliminates mostoftherandomfluctuationsandbackgroundshiftduringthe measurementsduetorandomvibrations,thermaldriftandlaser noise.The highsensitivity of SPRsensor togetherwiththe sig-nalrecoverybythephasesensitivedetectionprovideextremely

high sensitivities even at very large uncorrelated background noise.

2. Materialsandmethods

Fig.1 shows the schematicrepresentation of the fabricated microfluidicdevice.Athree-waysolenoidvalve(LFAA1201418H, TheLeeCorporation),derivedwithafunctiongenerator,controls thepressureontheonearmoftheY-junctionmicrofluidic chan-nel.Theotherarmiskeptataconstantpressure.Agravitydriven pressurecontrollerisusedtocontroltheinputpressures.ATM polarizedHe–Nelaserisusedtoexcitesurfaceplasmonsonthegold layeratbottomofthemicrofluidicchannel.Thereflectedbeamis detectedwithanunbiasedphotodiode(Newport818)connectedto thelock-inamplifier.Thelock-inamplifier(LIA,StanfordResearch, SR830)isoperatedatcurrentamplificationmodewithagainof 106.Thecontrolsignalofthevalveisusedasthereferencesignalof

theLIA.Theamplitudeandthephaseofthedifferentialsignalare recordedusingacomputerandadata-acquisitionsoftware.

Fig.2showsthefabricationstepsofthesensor.The fabrica-tionstartswithastandardUVphotolithographytopatternthethin layerofgoldfilm(thicknessof50nm)andfollowedby metalliza-tionandlift-offprocess.Themicrofluidicchannelsarefabricated by standard rapid prototyping using the soft lithography tech-nique. A photoresist master (SU-8-50 Micro Chem.) fabricated by UV photolithography is used to mold Polydimethylsiloxane (PDMS)elastomer.PDMSmicrofluidicchannelwithaY-junction

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672 M.Okanetal./SensorsandActuatorsB160 (2011) 670–676

Fig.2.Preparationofthedifferentialplasmonicsensor.Athinlayerofgoldwithathicknessof50nmispatternedonaglassslidebystandardUVphotolithography.The Y-junctionmicrofluidicchannel,moldedfromaphotoresistmaster,issealedontheglassslidebymicrowaveplasmatreatment.Arefractiveindexmatchingfluidisusedto attachtheglassslidetothehighrefractiveindexprismwithrefractiveindexof1.78.

geometry is sealed on a glass slide using a 900W homemade microwaveplasmasystem.Duringthesealingprocess,thegold stripisregisteredunderneaththemicrofluidicchannel.The fab-ricatedmicrofluidicsystemisattachedonahighrefractiveindex prism(Thorlabs,N-SF11,refractiveindexof1.78)usinganindex matchingfluid.Thesurfaceplasmon-polaritonsonthegoldstrip isexitedbya5mWHe–NelaserwiththeKretschmann configura-tion.Asiliconphotodiode(Newport818)connectedtothelock-in amplifierisusedtodetecttheintensityofthereflectedbeam.

3. Resultsanddiscussion

Athree-waysolenoidvalveisusedtocontrolrateofflowof oneofthearms.Maximumoperationfrequencyofthesolenoid valveisaround200Hz.Fig.3ashowsthefabricatedmicrofluidic chipwhichhasfourSPRsensors.Totestthedeviceseveralissues, suchasexcitation angleand frequencyof modulation, mustbe considered.First,wegeneratealaminar flowusingtwoliquids, whicharenamedasliquidAandliquidB,withrefractiveindex dif-ferencearound0.01RIU.HereliquidAisDIwater(nA=1.33)and

liquidBis 10%ethylglycol(EtG,nB=1.34)inwater. Fig.3band

cshowstheopticalmicrographsofthechannelfilledwithliquid AandliquidBfortwodifferentpressurelevels.Thelaminarflow boundarybetweenthetwostreamsisseenduetolargerefractive indexdifference(0.01RIU).ByswitchingthepressureofliquidA betweentwodifferentpressurelevels(∼15kPaand13kPa)while keepingthepressureofliquidBconstant(∼13kPa),we periodi-callymoduletheindexof refractionofthemediumontheSPR sensor.Astheindexofrefractionchanges,thesurfaceplasmon res-onanceangleandreflectedpowerchangesaccordingly.Tofindthe

optimumoperationpointwemeasurethereflectionofthelaser beamfromthegoldsurfaceasafunctionofincidenceangle.Fig.3d showstheintensityofthelaserbeamreflectedfromthegoldstrip underneaththemicrofluidicchannelfilledwithliquidA(RA())and

liquidB(RB()).Thereflectivitydependsontheincidenceangleand

thewavelengthofthelaser.TheSPRangleforDIwateris56.76◦and for10%EtGis57.49◦.Theresonanceangleshiftstolargeranglesas weincreasetheindexofrefractionoftheliquidbyaddingethyl glycol.Fig.3eshowsthechangeoftheintensityofthereflected beamasfunctionoftimeforthreedifferentconcentrationsofethyl glycol(10%(redcurve),2%(greencurve),and0.4%(bluecurve)). (Forinterpretationofthereferencestocolorintext,thereaderis referredtothewebversionofthisarticle.)Forconcentrationsless than0.4%,thechangeinthereflectivityduetothemodulationis buriedundernoise.Themodulationofthereflectanceprovidesthe differentialsignal.Astheliquidsoscillateontopofthegoldlayer, theSPRanglemodulatesatthesamefrequencyaswell.The dif-ferenceofthereflectivityforthetwocasesgeneratesaperiodic signalonthedetector.Theoutputofthelock-inamplifierprovides theamplitudeandthephaseoftheperiodicsignalbetweenthe liquids.

Tounderstandmoreinsideabouttheworkingprincipleofthe device,wedriveanexpressionforthedifferentialsignal.The reflec-tivityfromthegoldsurfaceisa linearcombinationofRA()and

RB().Thetotalreflectivitycanbewrittenas

R()= x wRA()+

w−x

w RB() (2)

wherexisthepositionofthelaminarflowboundarywhichisa peri-odicfunctionandwisthewidthofthechannel.Astheboundary oscillates,thedifferentialsignal (S)can befoundbytaking the

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Fig.3.(a)Theimageofthefabricatedchipwhichhas4SPRsensor.ThedevicehasaY-junctiongeometrywithtwoinputandavent.Thegoldstripisregisteredunderneath themicrochannel.(bandc)Zoomedopticalmicrographsofthemicrofluidicchannelshowingtheboundaryofthelaminarflowforthetwopressurelevels.Thelabels‘A’and ‘B’showtheliquids(waterand10%ethyleneglycolinwater,respectively)withdifferentindexofrefraction.(d)Experimentalreflectancecurvesforthegoldstripcovered by‘A’and‘B’,respectively.TheSPRanglesforwaterand10%ethyleneglycolinwater56.7and57.49degrees,respectively.(e)Timetraceofthereflectedbeamwhilethe mediuminthechannelismodulatedbetween‘A’and‘B’.Theresponsetimeoftheboundaryisaround100ms.(f)Differentialsignalobtainedbythelock-inamplifierasa functionoftheexcitationangle.ThereferencesignalofLIAisat2.5Hzandthetimeconstantis3s.

differenceofthereflection.Thedifferentialsignalcanbewritten as

S=R= |x|

w(RA()−RB()) (3)

where|x|istheoscillationamplitudeoftheboundary.Forsmall changesintheindexofrefractionwherethedifferencebetween RA()andRB()isverysmall,wecanfurthersimplifytheequation

as S=C|x|

wn dR()

d (4)

wherenisthedifferenceintheindexofrefractionbetweenthe liquids,andC istheproportionality constantwhich definesthe changeoftheresonanceanglewithrespecttothechangeinindex ofrefractionofthemedium.Thedifferentialsignalisdirectly pro-portionalwiththeoscillationamplitude,thedifferenceofindexof refractionandtheslopeofthereflectivitycurve.Thedifferential

signalobtainedforwaterand10%ethylglycolasafunctionofthe incidenceangleisgiveninFig.3f.Thesignalgoestominimawhere thereflectivitycurvescrossanditgoestomaximaatananglewhich providesthesteepestslopeinthereflectivitycurve.

To understand the mechanism of the hydrodynamic modu-lation, the frequency dependent measurements are performed. Fig. 4a shows the power spectrum of the signal obtained by changingtheinternalfrequencyofthelock-inamplifier.Forthis measurementthemodulationfrequencyiskeptconstantat3Hz. Thetimedependentsignalshowsanonsinusoidalformwhichhas higherorderharmoniccomponents.Theintensityofthethird har-monicislargerthanthesecondharmoniccomponentbecauseof thesquarelikewaveformoftheboundaryofthetwoliquids.The frequencydependenceofthedifferentialsignalisgiveninFig.4a. Weobtaintheoptimumfrequencyofoperationaround2–3Hz.The optimumfrequencyofoperationdependsonthegeometryofthe channelandtherateofflows.

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674 M.Okanetal./SensorsandActuatorsB160 (2011) 670–676

Fig.4. (a)Powerspectrumofthedifferentialsignalobtainedforthehydrodynamicmodulationfrequencyof3Hz.(b)Thefrequencydependenceofamplitudeofthesignal.

We test thesensitivity ofthe fabricatedsensorby changing theconcentrationoftheethyleneglycolfrom5.0×10−2Mdownto 4.0× 10−5M.Foreachconcentrationwetakethepowerspectrum

ofthephotocurrentandrecordthedifferentialsignalfromthe spec-trum.Fig.5ashowsthepowerspectrumforvariousconcentrations ofEtG.Fig.5bshowstheamplitudeofthedifferentialsignalasa functionofrefractiveindexdifference.Thesignalshowsalinear dependenceforaverybroadrangeofrefractiveindexchange.The fabricatedsensorprovidesverywidedynamicrangecoveringmore than4ordersofmagnituderefractiveindexchange.Usually sen-sitivityanddynamicrangeofasensorprovideatradeoffdueto thelimitedbandwidth.ThedifferentialSPRsensorsimultaneously provideshighsensitivityandwidedynamicrange.Fig.5cshows

therealtimeresponseofthesensorforverylowrefractiveindex changes.WeaddsmallamountofEtGinwaterandrecordthe differ-entialsignal.Asteplikeresponseisobserved.Thecalculatedchange ofrefractiveindexforeachstepisgivenonthecurve.Thestabilityof thebackgroundlevelisalsoimportantforreliablemeasurements. Anotheradvantageofthepresentedsensoristhatbackgroundlevel isconstantoveralongperiodoftime.TheinsetatFig.5cshowsthe timetraceofthesignallevelfor1.5-htimescale.Thestandard devi-ationofthesignalisaround10pAwhichprovidesarefractiveindex changeof7×10−8RIU.Theoriginofthisextremestabilityisthat, thetwolaminarstreamsprovideaselfreferencedetectionscheme forthermaldrifts.Thereforethebackgroundlevelshowsextreme stabilityoverlongtimescales.Theresponseofthedeviceforlow

Fig.5. (a)Powerspectrumofthephotocurrentforvariousethyleneglycolconcentrations.(b)Thevariationoftheintensityofthedifferentialsignalversusrefractiveindex differenceofthetwolaminarstreams.(c)Realtimeresponsecurveofthedifferentialsignal.Theinsetshowsthetimetraceofthesignalforalongtimescale.Thenumbers onthecurveshowsthecalculatedrefractiveindexchanges.(d)Thechangeofthedifferentialsignalforlowrefractiveindexchanges.Thestandardvariationofeachpointis lessthanthesizeofthescatteredplot.Theminimumdetectablerefractiveindexdifferenceisaround7×10−8RIU.

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Fig.6.(a)Variationofthedifferentialsignalasafunctionoftime.(b)Histogramofthedifferentialsignal.

refractiveindexchangesisgiveninFig.5d.Theerrorinthedata pointsislessthanthesizeofthescatteredplot.

Tounderstandtheultimatesensitivitylimitofthedevicewe analyzesourcesofnoise.Fig.6ashowsthenoiseofthe differen-tialsignal.ThehistograminFig.6bhasastandardvariationaround 0.3pAwhichcorresponds4×10−8RIU.Theinternalnoiseofthe LIA,shot noise of thedetector, and mechanical deformation of thePDMSchannelarethemainsourceofnoiseinthesetup.The noiselevelofthesensorisaround20pA.Theinternalelectronic noiseoftheLIAisaround0.12pAfor3stimeconstantat2.5Hz. Totalnoiseofthedetectorandlaserisaround2.5pA.Thelimiting noisesourceseemsduetomechanicaldeformationorcorrelated scatteringduetoimpuritiesintheliquid.Sincethelaserbeamis reflectedfromtheglasssideofthedevice,themechanical defor-mationofPDMSduringthehydrodynamicmodulationdoesnot affecttherecordedsignaltoomuch.Wespeculatethatthe mini-mumdetectablesignalislimitedbyimpuritiesorinhomogeneities intheliquidswhichgenerateacorrelatednoiseatthemodulation frequency.

4. Conclusion

Asaconclusion,wepresentanewtypeofmicrofluidicdevice thatuseshydrodynamicmodulationschemeforaphasesensitive detection.Weimplementthismethodtoasurfaceplasmon sen-sorintegratedinamicrofluidicdevice.Thefabricatedsensorcan detecttherefractiveindexdifferenceassmallas4×10−8RIUwith anextremelystablesignallevelandmorethan4ordersof magni-tudedynamicrange.Theprimaryconclusionofthisstudyisthatby usingahydrodynamicmodulationandphasesensitivedetection technique,a simpleplasmonsensorwithintensityinterrogation canproviderefractiveindexsensitivitiesashighasplasmonsensors withspectralinterrogation.

Acknowledgements

ThisworkwassupportedbytheScientific andTechnological Research Council of Turkey (TUBITAK)Grant No. 110T304 and Marie Curie International Reintegration Grant (IRG) Grant No. 256458.

References

[1]M.Cardona,ModulationSpectroscopy,AcademicPress,1969.

[2] D.Baurecht,I.Porth,U.P.Fringeli,Anewmethodofphasesensitive detec-tioninmodulationspectroscopyappliedtotemperatureinducedfoldingand unfoldingofRNaseA,VibrationalSpectroscopy30(1)(2002)85–92.

[3]D.S.Bomse,A.C.Stanton,J.A.Silver,Frequencymodulationandwavelength modulationspectroscopies:comparisonofexperimentalmethodsusinga lead-saltdiodelaser,AppliedOptics31(6)(1992)718–731.

[4]P.Billaud,S.Marhaba,N.Grillet,E.Cottancin,C.Bonnet,J.Lerme,etal.,Absolute opticalextinctionmeasurementsofsinglenano-objectsbyspatial modula-tionspectroscopyusingawhitelamp,ReviewofScientificInstruments81(4) (2010).

[5]F.Wang,D.J.Cho,B.Kessler,J.Deslippe,P.J.Schuck,S.G.Louie,etal., Observa-tionofexcitonsinone-dimensionalmetallicsingle-walledcarbonnanotubes, PhysicalReviewLetters99(November(22))(2007).

[6]J. Wang, Hydrodynamic modulation voltammetry, Talanta 28 (6) (1981) 369–376.

[7] P.Hersen,M.N.McClean,L.Mahadevan,S.Ramanathan,Signalprocessing by theHOGMAP kinase pathway,Proceedings ofthe NationalAcademy of Sciences of the United States of America 105 (May (20)) (2008) 7165–7170.

[8] J.Homola,S.S.Yee,G.Gauglitz,Surfaceplasmonresonancesensors:review, SensorsandActuatorsB:Chemical54(1–2)(1999)3–15.

[9]S.Y. Wu, H.P. Ho, W.C. Law, C.L. Lin, S.K. Kong, Highly sensitive dif-ferential phase-sensitive surface plasmon resonancebiosensor based on the Mach–Zehnderconfiguration,OpticsLetters 29(October(20))(2004) 2378–2380.

[10]Y.-C.Li,Y.-F.Chang,L.-C.Su,C.Chou,Differential-phasesurfaceplasmon reso-nancebiosensor,AnalyticalChemistry80(14)(2008)5590–5595.

[11] H.Q.Zhang,S.Boussaad,N.J.Tao,High-performancedifferentialsurface plas-monresonancesensorusingquadrantcellphotodetector,ReviewofScientific Instruments74(1)(2003)150–153.

[12]L.D.Williams,T.Ghosh,C.H.Mastrangelo,Lownoisedetectionof biomolec-ularinteractionswithsignal-lockingsurfaceplasmonresonance,Analytical Chemistry82(July(14))(2010)6025–6031.

[13]H.P.Ho,W.W.Lam,Applicationofdifferentialphasemeasurementtechnique tosurfaceplasmonresonancesensors,SensorsandActuatorsB:Chemical96 (December(3))(2003)554–559.

[14]H.PHo,W.C.Law,S.Y.Wu,X.H.Liu,S.P.Wong,C.L.Lin,etal.,Phase-sensitive surface plasmon resonance biosensor using the photoelastic modulation technique, Sensors and Actuators B: Chemical 114 (March (1)) (2006) 80–84.

[15]A.V.Kabashin,S.Patskovsky,A.N.Grigorenko,Phaseandamplitude sensitivi-tiesinsurfaceplasmonresonancebioandchemicalsensing,OpticsExpress17 (November(23))(2009)21191–21204.

[16]W.C.Law,P.Markowicz,K.T.Yong,I.Roy,A.Baev,S.Patskovsky,etal.,Wide dynamicrangephase-sensitivesurfaceplasmonresonancebiosensorbasedon measuringthemodulationharmonics,Biosensors&Bioelectronics23 (Decem-ber(5))(2007)627–632.

[17]Y.C. Li, Y.F. Chang, L.C. Su, C. Chou, Differential-phase surface plas-mon resonance biosensor, Analytical Chemistry 80 (July (14)) (2008) 5590–5595.

[18]P.P.Markowicz,W.C.Law,A.Baev,P.N.Prasad,S.Patskovsky,A.V.Kabashin, Phase-sensitivetime-modulatedsurfaceplasmonresonancepolarimetryfor widedynamicrange biosensing,OpticsExpress 15(February (4))(2007) 1745–1754.

[19]S.Patskovsky,R.Jacquemart,M.Meunier,G.DeCrescenzo,A.V.Kabashin, Phase-sensitivespatially-modulatedsurfaceplasmonresonancepolarimetry fordetectionofbiomolecularinteractions,SensorsandActuatorsB:Chemical 133(August(2))(2008)628–631.

[20]S.Patskovsky, M.Meunier,P.N.Prasad,A.V. Kabashin,Self-noise-filtering phase-sensitivesurfaceplasmonresonancebiosensing,OpticsExpress18(July (14))(2010)14353–14358.

[21]W. Yuan, H.P. Ho, C.L. Wong, S.K. Kong, C.L. Lin, Surface plasmon resonance biosensor incorporated in a Michelson interferometer with enhancedsensitivity,IEEESensorsJournal7(January–February(1–2))(2007) 70–73.

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676 M.Okanetal./SensorsandActuatorsB160 (2011) 670–676

[22]J.Homola,Surfaceplasmonresonancesensorsfordetectionofchemicaland biologicalspecies,ChemicalReviews108(2)(2008)462–493.

[23]R.Slavík,J.Homola,Ultrahighresolutionlongrangesurfaceplasmon-based sensor,SensorsandActuatorsB:Chemical123(1)(2007)10–12.

Biographies

MelihOkaniscurrentlyaseniorundergraduatestudentatBilkentUniversity, DepartmentofPhysics.

OsmanBalcireceivedhisBSdegreefromBilkentUniversity,DepartmentofPhysics in2009. Heis currentlya Ph.D.studentatBilkent University,Departmentof Physics.

CoskunKocabasreceivedhisBSdegreein2001fromMiddleEastTechnical Univer-sity,DepartmentofPhysics.HereceivedhisPhDdegreefromUniversityofIllinois atUrbanaChampaign,DepartmentofPhysicsin2007.Between2007and2009he workedasapostdoctoralresearcheratHarvardUniversitydepartmentofChemistry andChemicalBiology,Prof.GeorgeWhitesides’group.Heiscurrentlyanassistant professoratBilkentUniversity,DepartmentofPhysics.Hiscoreresearchinterests includedynamicmicrofluidicsystemsandsensors.

Şekil

Fig. 1. Schematic representation of the microfluidic device and experimental setup used for hydrodynamic modulation
Fig. 2. Preparation of the differential plasmonic sensor. A thin layer of gold with a thickness of 50 nm is patterned on a glass slide by standard UV photolithography
Fig. 3. (a) The image of the fabricated chip which has 4 SPR sensor. The device has a Y-junction geometry with two input and a vent
Fig. 5. (a) Power spectrum of the photocurrent for various ethylene glycol concentrations
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