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Simulation and analysis of phase-sensitive surface plasmon resonance sensor based on enhanced optical transmission through arrays of nanoholes in silver films

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Simulation and analysis of phase-sensitive surface plasmon resonance sensor based on enhanced optical transmission through arrays of nanoholes in silver films

    Simulation and analysis of phase-sensitive surface plasmon resonance sensor based on enhanced optical transmission through

    arrays of nanoholes in silver films 3卷第1

    20102

    中国光学与应用光学

    ChineseJournalofOpticsandAppliedOptics

    Vo1.3No.1

    Feb.201O

    文章编号16742915(2010)014)057-07

    Simulationandanalysisofphase?sensitivesurfaceplasmonresonance sensorbasedonenhancedopticaltransmission

    througharraysofnanoholesinsilverfilms

    YANGT.HOHP

    (1.JiangsuKeyLaboratoryforOrgalzicElectronics&InformationDisplays.NanjingUniversity

    ofPostsandTelecommunications,Nanjing(210000),China;

    2.DepartmentoJ'ElectronicEngineering,CentreforAdvancedReSearchinPhotonics, TheChineseUniversityoJ'HongKong,Shatin,,HongKongSAR,China)

    Abstract:Ahighspatialresolution,phase

    sensitiveSurfacePlasmonResonance(SPR)sensorbasedOilEx.

    traordinal7OpticalFransmission(EOT)isproposedtomonitorthebindingoforganicandbiologicalmolecules

    tothesilversurface.The2Dnanohole

    arrayconfigurationiswellsuitedfordenseintegrationinasensorchip.

Theopticalgeometryiscollinear,whichsimplifiesthealignmentwithrespecttothetraditiona

    lKretschmann

    arrangementforSPRsensing.Variousdesignparametersofthedevicehavebeenstudiedbysi

    mulation.

    The

    heterodynetechniqueisusedtoimprovethesensitivity.Theoptimizationresultsindicatethat

    thesensorhas

    theadvantagesofachievinghighresolutionandawidedynamicrangesimuhaneously. Keywords:SUrfaceplasmonresonancesensor;extraordinaryopticaltransmission;phasein

    terrogation;nano

    hole:silverfilm

    1Intr0ducti0n

    Inrecentyears,SPRtechnologyhasbeencomnler

    cialize(jandSPRsensorshavebecomecentI-a1tnols

    forcharacterizingandquantifyingbiomolecularinter

    actionsbothinthelifesciencesandpharmaceutical

    researchesduetotheircapabilit),forrealtimenleas-

    urenlen[withhighdetectionsensitivity.Current

    researchattentioninSPRsensinghasshiftedto

    measuretheSPRphaseshift:,astheresonant

    phasebehaviouroffersthepotentialinachievingtill

    extremelyhighdetectionsensitivity,Thetraditional phasesensorscouplelightintothesurfaceplasmon

    usingaprismintheKretschmannconfiguration,

    also

    knownastheAttenuatedTotalReflection(ATR)

    configuration.However,thismethodsuffersfromthe

    disadvantagesot'Iargesizeandnarrowdynamic.

    range?

    Inthispaper,wereportacompactandwide

    dynamicrangebiosensorbasedondetectingthe phasechangeofEOTlightfromaholearray.Ape

    riodicsquarearrayofsub?-wavelengthholesonasil?- vetfilmisutilizedastheSPRphasesensor.Com

    paredwiththetypicalKretschmannconfiguration, theholean'ayconfigurationoperatesinthetransmis- siongeometry.Thisallowsforasimplercollinear opticalarrangement,thusprovidingasmallerpro

    Received(1ate:200910-11;Revised(1ate:200912-17.

    Foundationitem:Supt)ort(,dbythefhndingfromtheHongKongResearchGrantsCouncilun

    derCERGproject#411907and

    #41228;NationalBasisResearchProgramofChina(973)(No.2009CB930600).

    58中国光学与应用光学第3

    bingareaandhighthroughputsensing[.Inaddi

    tion,theheterodynetechniqueisusedforphasede

    tectionsoastorealizeanevenhighsensitivity.The uniqueadvantageofthesensorsmayenhancethe preferenceofusingsuchdevicesinanumberofap

    plicationsespeciallyfortheintegrationwithlab?-on'- chipplatforms.

    2Principleofphasesensor

    Thestructureofthesilvernanoholestructureisde. positedonasilicondioxidesubstrateasshownin Fig.1.Theperiodofthearraysisd,thewidthof thesquareholesisa,andthethicknessofthesilver filmish.Thearraysofsubwavelengthholescanbe

    fabricatedbytbcusedionbeam(FIB),electron beamlithography(EBL)orUVinterferencetech

    niques.Fortherealtimebiomoleculesensingap

    plications,thenanoholedeviceshouldbeimmersed

inanethanoicsolutionof11mercaptoundecanoic

    acid(MUA)priortothedetectionprocedures. Whenthepopulationofbiomoleculesimmobilized

    onthesensorsurfaceincreases,theeffectiverefrac- tiveindexofthethinsurfacelayer(alsocontaining MUAandprotein)increasesaccordingly.The changeofrefractiveindexwil1thenresultsinaphase shiftinthetransmittedbeaminthefarfield.thus leadingtothepossibilityofquantitativedetectionof thedensityoftheimmobilizedbiomolecularmaterial

    withoutusinganyfluorescencetag.

    hI

    Fig.1Schematicofpmposed

    sensor(a=holesize,

    depth).

    nanoholearraySPRphase

    d=holeperiod.h=hole

    Fig.2showsanexperimentalphaseinterroga- tionschemebasedonahetcrodyneinterferometrie system,whichoffersthebenefitsofdetectingonly timevaryingsignalsandahighnoiserejectioncapa

    bilitybyusingthelongintegrationtimef..A

    typicalheterodyneinterferometerusesanaeoustoop

    ticmodulatortoimposeafrequencyshiftOllthein- putlaserbeam.Whenthefrequency-shiftedrefer- encebeaHiinterfereswiththesignalbeam,the phaseofthebeatfrequency,whichmaybereadily measuredwiththelockintechnique,willprovide

    thephasereadingintroducedbythesensordevice. Fig.2Optica|setupforStRphaseshiftmeasurement

    Inordertoappreciatetheunderlyingphysicsof thephasesensor,weuseasimplemode1.Asshown schematicallyintheenlargedareaofFig.3,the extraordinary.

    opticaltransmissioneffectmaybe

    Silicon

    dioxide

    B;o.molecule

    Fig.3Crosssectionof'proposedphasesensitiveSPR

    sensor.

    separatedintotwocontributions.ThefirstoneCOITe? spondstothedirectivetransmissionoftheincoming

1YANGT,eta1.:Simulationandanalysisofphasesensitivesurfaceplasmon59

    fieldtl-u'oughtheholes.i.e.theBethetypediffrae

    ti()nregimewiththetransmissioncoeffieientrepre

    sentedbyTI{_h..,

    whichiswavelengthdependentand

    pr()portionaltotheidentitymatrix.Thesecondcon

    tribution.withatransmissiontoemcientdescribe({ byTIl_l'

    correspondstotileresonantpartofthe

    transmissionmatrixandisrelatedtotheplasmonic effect.Inthepresentcase,TllisthemainCOIl

    tributionwhichprovidesthephasechangeinthede

    vice.

    Theresonanttransmissionprocessmaybede

    scribedbyatourstepprocess:(i)theinci

    (tentplanewaveiseonverte(1intoasurfacewaveata

givenpointscatterer;(ii)thesurfacewavepIopa

    gatesonthesurtaceoftheholean'ayandtmildsup severalconstructiveinterferencenlodesaccordingto thepropagationdistance;(iii)thesuflhcewaveis coupledinto011eottheholesandisreflectedback

    wardsandf()rwardsseveraltimesinthehole.thus resuhinginaeonsti'uctiveinterferenceeft)ct;and (iv)thesurfacewaveswithintheholearrayalsopro

    (]uceconstl'uetiveinterfel'encebetweenthem,and solneenergywillbereemittedfroHIthesystemasa

    planewave.Thefourstepprocessindicatesthat

    whentheeffeetiverefractiveindexofthedielectricin thevicinityoftheholesexpel'iencesaehange,the resonancepal'ameterswillalsoshiftaccordingly, thusleadingtoasharpchangeinthephaseofthera

    diationwhichdrivestheFesonance.Theretore,the nlaxitnunlchangeofthephaseshouldOCCUI'it,the regionwhiehisclosetotheresonantpollIt,whilethe resonaueeparametersaredependenlonthechoices otholepet'i()(1ieity,shapeandsizeoftheholesand thir.knessl1fthnlta1.

    (LumeriealSolutions,Inc)withaminimum1nm meshsizeisusedtostudythedevicestructure.In ordertoshortenthesimulationtime.anareawith justonesquareholeismeshedandtheperiodic boundaryconditionsareusedaroundtheho1e.We useaplanewavewithawavelengthof632.8nmand thepropagationdirectionisnormaltothestructure. Perfectlymatchedlayer(PMI)boundaryconditions with200layersareusedinthesourcedirections.

    Weassumethetotalthicknessofthereceptorlayer andtheimmobilizedmoleculesis5llnl,andthere

    fraetiveindexot.thesurroundingaqueousmediumis takenas1.33(water).Iftheeffectiverefractivein

    dexofthiscompositelayeris(:hangedfrom1.33to 1.50,thephasevariationofthetransmissionbeam inthefarfield,whichpassespassingthroughahole array(typicallyr1O0×100)Callbecalculatedac

    cordingly.Becausetheholeperiodandthemetal thicknessai.ethetwomainparametersaffectingthe resonanceonthefihnsurfaceandtheresonancein theholes,respectively,wecanfixoneparameter andchangetheothertoobtaintheoptimalvaluesof thesetwoparametersforthelargestphasechange whentheeffeetiverefractiveindexiSvariedfrom 1.33to1.50.Inthepresentcase,wefirstfixthe silverfilmthicknessat10811111andfindtherelation

    shipbetweentheholeperiodandthephasechange asshowninFig.4.Herewecanseefromthesharp g0

    O

    3Simulati0nresuitsanddiscussi0n4o

    Weha,eperformedaseriesofsinmlationexperi

    mentsbyvaryingtheholeperiod,holeshapeand silverfilmthickness,respectively,inordertofind theoptimizeddeviceparameters.FDTDSolutions 350400450500550600

    Squareholeperiode|iiii1

    Fig.4Squareholeperiodversusphasewithparatemers

asn:1.331.50.h=108ilm.andd=

    446n111

    .

    J/0L1LIuLI

    中国光学与应用光学第3

    resoDancepeaksthattheoptimalvalueofthehole periodis446nm.

    FromthetheoryoftheEOT,wecanexplain whythephasechangeisthelargestwhenthehole periodis446nm.Aswehavedemonstrated,the maximumphasechangeshouldoccurnearthereso

    nantregion.TheSPRresonanceconditionforthe normallyincidentlightisgivenbyRef.[14] (iA,=dRe[(SPffcv

    e+

    )],(1)

    whereiandareintegers,Al

    isthewavelengthof

    theincidentlight,distheperiodofthearray,. is

    theeffectivedielectricconstantofthesilverfilm, ande

    istheeffectivedielectricconstantatthemet

    aldielectricinterface.Theeffectivedielectriccon. stantcanbeestimatedbyperformingaweightedav

    eragewithintheextensionZoftheevanescentSP modeintothedielectric(zdirection),accordingto Ref.15]

    :

)exp(-

    AccordingtoEq.(1),whenA=632.8rim,

    aresonantpeakoccurswhentheholeperiodis 429.7nmassuming=1.33and=17.65+

    0.50i.Consideringtheeffectiverefractiveindex, s?mustbegreaterthan1.33duetotheexistenceof theMUAandproteinaccordingtoEq.(2).Howev

    er,theeffectivepermittivityofthemetal8mustbe alittlesmallerthanthepermittivityofthepuresilver

    l7.65+0.50iduetotheexistencesoftheholes. Therefore,theresonantpedodshouldbecloseto 451.3nm.Oursimulationresultsshowthatthe maximuminthephasechangeOCCURSwhentheperi

    0doftheholeis446nlnwhichisreasonablec0nsid eringtheuncertaintiesinthemode1.

    Thesilverlayerthicknessalsoplaysanimpor

    tantroleinthecalculationofphasechange.Wefirst fixtheperiodattheoptimizedvalue,i.e.446nm, andthenwevarythesilverlayerthicknessandmo nitorthephasechange.Theresultsareshownin Fig.5wherewecanseethatthelargestphasechart

    Fig.5Silverlayerthicknessversusphasechange withparametersas/z=1.331.50.h

    44613111.andd:153nm.

    gesoccurat110nmthickness.Thephysicalmecha- nismforsucharesonantpeaktooccurat110nmis duetothesurfaceplasmontrappedandoscillating insidethehole,therebybuildingupconstructivein- terencelI7

.IfweassumethatthesulaceDiasm0n

    intheholepropagatesalonganinterfacebetweenan infiniteinsulatorandametaldespitethefactthatit isametal/insulator/metal(MIM)heterostrueture, thenthepropagationlengthofasurfaceplasmonwith 2~rphasechangeiscalculatedas451.3nm.Since fourtimes110nlnequals440nmwhichiscloseto 451.3nm,wecanconcludethattheplasmoninthe holeshouldexperienceconstructiveinterferenceif thesilverthicknessis】】0nm.Thisalsomeansthat

    whentheconstructiveinterferenceisnolongerpossi

    bleduetothechangeofterraetiveindexinthesur- roundingmedium,thephasechangesrapidly.Inad

    dition,wealsoexploredtheeflbctofvaryingthe widthoftheholes,whichhastheobviouseffectof changingtheeffectivepermittivityoftheMIMhet

    erostrueture.Thephasechangeintherangeofre

    fractiveindexbetween1.33airl1.50isshownin Fig.6.

    Abovesimulationresultsindicatethatifweuse 153nmastheholewidth.446nmastheholeperiod and110nmasthesilverfilmthickness,thesepa- rameterValuescorrespondtothelargestvalueofthe phasechangewhichcanbeachieved.Foramaxi. 广.\cLIuLI

    1YANGT,eta1.:Simulationandanalysisofphasesensitivesurfaceplasmon6l

    Squareholewidth/nm

    Fig.6Squareholewidthversusphasewithparame

    tcrsasn=1.331.55.h=110nn1.and

    d=446nn1.

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