Handbook of Photonics for Biomedical Engineering

841 Pages·2015·40.009 MB·English

by  Aaron H.-P. Ho, Donghyun Kim, Michael G. Somekh (eds.)

Development of Extraordinary Optical
Transmission-Based Techniques
for Biomedical Applications
Seunghun Lee, Hyerin Song, Seonhee Hwang, Jong-ryul Choi,
and Kyujung Kim
Contents
Introduction....................................................................................... 2
TheoreticalBackground.......................................................................... 3
Fabrication........................................................................................ 3
FocusedIon-BeamLithography.............................................................. 4
Electron-BeamLithography.................................................................. 5
Nanoimprinting............................................................................... 6
Photolithography.............................................................................. 7
Applications...................................................................................... 9
EOTGasSensing............................................................................. 9
BiologicalSensing............................................................................ 13
EOT-BasedImagingTechniques............................................................. 17
Summary.......................................................................................... 20
References........................................................................................ 20
Abstract
Highly sensitive detection techniques have drawn tremendous interest because
thismethodallowstheprecisetrackingofmolecularinteractionsandtheobser-
vation of dynamics on a nanometric scale. Intracellular and extracellular
S.Lee(cid:129)H.Song(cid:129)K.Kim(*)
DepartmentofCogno-MechatronicsEngineering,PusanNationalUniversity,Busan,SouthKorea
e-mail:[email protected];[email protected];[email protected];
[email protected]
S.Hwang
DepartmentofAdvancedCircuitInterconnection,PusanNationalUniversity,Busan,SouthKorea
e-mail:[email protected]
J.-r.Choi
MedicalDeviceDevelopmentCenter,Daegu-GyeongbukMedicalInnovationFoundation
(DGMIF),Daegu,SouthKorea
e-mail:[email protected]
#SpringerScience+BusinessMediaDordrecht2015 1
A.H.-P.Hoetal.(eds.),HandbookofPhotonicsforBiomedicalEngineering,
DOI10.1007/978-94-007-6174-2_1-1
2 S.Leeetal.
processes can be measured at the molecular level; thus, highly sensitive tech-
niques advance our understanding of biomolecular events in cellular and sub-
cellular conditions and have been applied to many areas such as cellular and
molecularanalysisandexvivoandinvivoobservations.
Inthischapter,wereviewnear-fieldbasedbiosensorsthatrelyonextraordi-
nary optical transmission (EOT) and some application techniques that have
emerged recently based on the localization of a surface plasmon. Also, we
refertothefabricationmethodsformakingvariousnanostructures:first,focused
ion beam that employs the high-energy ions to create high-precision
nanopatterns. Second, electron-beam lithography that capitalizes on highly
focusedelectronbeamtodrawsubmicronsizepatternsonthemetallicsurfaces.
Third,nanoimprintlithographysuitable formassive nanostructurefabrications.
Finally, photolithography feasible for the cost-effective fabrication. At the end
ofthischapter,weintroducesomeapplicationsbasedonEOTforenhancement
ofsensitivityandtechniqueswhichassisthigh-resolutionimaging.
Keywords
ExtraordinaryOpticalTransmission(EOT)(cid:129)SurfacePlasmonPolaritons(SPPs)(cid:129)
Nanoaperature(cid:129)Nanoplasmonics(cid:129)Sensors,ImagingTechnique
Introduction
Usingnewlydevelopedmeasurementandimagingtechniques,biomolecularactiva-
tionandcellulardynamicscanbeanalyzed,anddetectionofsmallmolecularevents
in subcellular environments is now possible. A significant restriction in previous
optical imaging measurements is the lateral or axial spatial resolution caused by
Abbe’sdiffractionlimits.Todetectorobservemoleculardynamicsonsubnanometric
scales, diffraction limitsshouldberesolved. Therefore,new opticaltechniquesthat
canbreakthediffractionlimitandenhancespatialresolutionaredesired.
Recently, multiple microscopic methods that can replace current techniques
have been proposed. Stimulated emission and depletion microscopy (STED) [1],
which is based on the establishment of narrow excitation light spots, is one such
strategy.Photo-activatedlightmicroscopy(PALM)[2](obtainedbythecomputa-
tion of the stochastic photo-activation of fluorescent molecules) and structured
illuminationmicroscopy(SIM)acquiredbyreconstructinghigh-resolutionimages
frompartialimageswithsinusoidalilluminationthatarespatiallyencoded[3]can
also provide a good solution. Additionally, other perspectives focusing on tomo-
graphicsystemsthatreinforcesectionmeasurementandimagingcapabilitieshave
beenintroduced:totalinternalreflectionfluorescencemicroscopy(TIRFM)[4]and
selectiveplaneimagingmicroscopy(SPIM)[5].
These techniques have become the focus of attention, but they retain barriers to
commercialization such as limited detection, limited imaging speed, experimental
complexity, and high cost. Meanwhile, surface plasmon (SP) phenomena can be a
DevelopmentofExtraordinaryOpticalTransmission-BasedTechniquesfor... 3
goodalternativeforimagingenhancementsbyvirtueofnanotechnology[6].Applying
nanotechnology on the surface has many merits, notably resolution improvement
because of field relocalization using nanostructures. Additionally, localized field
sizescanbedesignedtobesmallerthanthediffractionlimit.Whenanareaoflocalized
fieldsisnearlyidenticaltothatofasinglefluorescencemolecule,wecanassumethat
light emitted is given by a single molecule [5]. An extraordinary transmission phe-
nomenonisoneoftherepresentativetechniquesfortheSPbasedapproach[6].
In the chapter, we summarize varied lithographic techniques to fabricate opti-
mized nanoapertures for extraordinary optical transmission (EOT) and introduce
interesting applications using EOT samples. E-beam lithography is one kind of
methodthatcanperforatenanosizehole.Whenthehigh-precisionnanoholearrayis
needed,focusedion-beam(FIB)lithographyisabetterwaytosatisfythatquality.
Anotherstrategyformakinglargeareapatterningisnanoimprintlithographywhich
issuitableformassproduction.SomeEOTbasedapplicationsfortheenhancement
ofsensitivityisintroduced.
Theoretical Background
Whenthelightpassesthroughthematterthebeamspreadsinalldirections.Sofar,
thematterhowthelightinteractswithotherobjectsisanoldprobleminoptics.In
1944,afundamentaltheorywasknownbyBethe[7].Hefoundthattheformulaof
opticaltransmissionthroughanarrayofcircularholeperforatinganinfinitelythin
perfectelectricconductor.
(cid:1) (cid:3)
64 r 4
T(cid:1)
27π2 λ
where λ is the wavelength of the incident light and r is the radius of the hole.
AccordingtoBethe’stheory,alightpassingthroughthesubwavelengthholerarely
exists.However,Ebbesenetal.foundthatarrayofholesshowhighlyunusualzero-
order transmission spectra at wavelength larger than the array period without
diffractionthatiscalledextraordinaryopticaltransmission[8].Theweirdthingis
the intensity of transmission light. According to the Bethe’s previous theory, the
transmission of light is expected to be lower than ever. One of the reasons this
unusualphenomenonoccursisthecouplingoflightwithSP,notablyonaperiod-
ically patterned metallic nanostructure. SP is a collective oscillation of electrons
betweentheedgeofthemetalandinsulator[8].
Fabrication
Although theoretical fundamentals of EOT through various nanoapertures are
wellestablished,theaccuratefabricationofnanoaperturesforEOTandplasmonic
applicationsarerequiredforexperimentalandindustrialimplementations.During
4 S.Leeetal.
the last few decades, several fabricating techniques have been developed and
appliedtoinvestigateplasmonicnanostructuresincludingnanoaperturesforEOT.
Several techniques for producing nanohole structures have been developed.
Notably, two main concepts suited for the fabrication of nanohole arrays have
been introduced: dead-ended nanohole arrays and through-nanohole arrays [9].
Dead-ended nanoholes are used when fluid-containing analyte is moved over
the nanohole array; through-nanohole arrays are used for nanoconfinement of
analyte. Here, we describe several techniques related to nanohole array-based
sensing. In this section, we explore relevant fabrication methods, ranging from
techniques used in industrial areas to newly investigated and experimentally
appliedmethods.
Focused Ion-Beam Lithography
FIB lithography was the first developed method that can create high-precision
nanohole arrays on a metal surface. The main principle of this method is that
ion-material collisions which remove the target from the sample. FIB comprises
twoprocesses:sputtering(removalofthematerialfromthesubstrate)usinghigh-
energy ions and redeposition (relocation onto the other surface). The FIB tech-
nique has many advantages: FIB can fabricate various nanostructures on the
substrate directly without the mask, the resist, and the chemical developer.
Additionally, FIB provides improved resolution compared to photolithography
and e-beam lithography because ion beams have smaller wavelengths than opti-
cal/UVlightandelectronbeams.Also,byregulatingtheionenergy,thepenetra-
tiondepthoftheioniseasilycontrolled.Therefore,FIBhasbeenusedtofabricate
accuratenanostructuresincludingnanoaperturesforplasmonicapplications.Fig-
ure1showsthe300-nmnanoholepatternwhichwasfabricatedbyFIBonsilicon
nitride substrate. The single nanohole, which has a 100-nm height, is clear and
solid, while deep and clear nanohole patterns cannot be easily fabricated by
e-beamlithography.
Lesuffleuretal.investigatedreal-timebiosensorsusingperiodicnanoholearrays
constructed using ion-beam lithographic fabrication as shown in Fig. 2 [10]. Xue
et al. introduced surface plasmon enhanced EOT of gold quasicrystals using
focused ion-beam fabrication [11]. Furthermore, ion-beam lithography can be
employed to construct complicated nanostructures that cannot be established by
photolithographic and e-beam lithographic methods such as three-dimensional
nanostructures and metamaterials [12, 13]. A drawback of ion-beam lithography
isthattheconsumedtimeperfabricatedunitareaislongerthaninphotolithography
ande-beamlithography.Thislongertimeiscausedbythesmallsizeofthebeams
used in the lithography processes. Because of the shortage, the integration of
ion-beam lithographic techniques in massive fabrications of nanostructures is not
appropriate.
DevelopmentofExtraordinaryOpticalTransmission-BasedTechniquesfor... 5
Fig.1 ASEMimageofa
300-nmdiameternanohole
fabricatedbyfocused
ion-beamlithography
Fig.2 ASEMimageofafabricateddouble-holearrayusingfocusedion-beamlithography.The
periodofeachdouble-holeis800nm.Aninletgraphillustratestheopticaltransmissionthrough
thedouble-holearray(ThisfigureisusedwithpermissionfromRef.[10]bytheAmericanInstitute
ofPhysics)
Electron-Beam Lithography
Electron-beamlithography(EBL)isacommonlyusedtechniqueinthefabrication
of metallic nanostructures. The main principle of EBL is identical to scanning
electron microscopy (SEM). Therefore, this process utilizes an electron lens to
focustheelectronbeam.EBLusesfocusedelectronbeamstodrawwantedmicro-
6 S.Leeetal.
Fig.3 ASEMimageofa
250-nmdiameternanohole
arrayonSiglassfabricated
usinge-beamlithography
and nanopatterns on an electron-beam-sensitive resist above the substrate. The
electron beams alter the properties of the resist; therefore, micro- and
nanostructures can be established using selective eliminations of areas that are
exposed or notexposed to a chemical developer. EBL combines otherfabrication
procedures, often containing in excess of three steps. First, positive or negative
photoresistisspin-coatedonasurface;Siglasscanbeusedasthesurface.Second,
thesoft-bakedsampleisexposedtoane-beamtocreateintendedpatterns.Third,a
chemical development exposes the negative resist patterns on the substrate. The
final step provides a metallic coating on the surface with intermediate adhesive
layers.Forexample,toobtaintheAunanoholearray,athinlayerofCr(~5nm)is
coatedtoprovideaproperadhesionbeforealayerofAuisdeposited(Fig.3).
AremarkableadvantageofEBLcomparedtophotolithographyistheenhanced
fabricating resolution. The size of the focused electron beam is smaller than the
diffraction limit in photolithographic fabrications using an optical or UV beam.
Although applications to large areas or multiple sample fabrications remain diffi-
cult, e-beam lithography has been employed to fabricate various types of
nanoaperturesforplasmonicenhancementincludingforEOT.Forexample,Sharpe
et al. introduced gold nanoaperture arrays fabricated by e-beam lithography to
produce immunobiosensors [14]. Additionally, various nanogratings and
nanoapertures (as illustrated in Fig. 4) for plasmonic enhancements of biosensing
oroftheresolutioninimagingwereconstructedbyEBLbecauseoftheappropriate
lithographicresolutionandabsenceofphotomasks[15,16].
Nanoimprinting
Nanoimprintlithographyisarecentlyinvestigatedfabricationmethodtoconstruct
nanoscale patterns in a cost-effective and high-throughput manner. During
nanoimprinting,designedpatternscanbecreatedbymechanicallystampingresists
onamasterstructure.Generally,amonomerorpolymerresistthatcanbecuredby
heatorlightexposuresisemployedinnanoimprintlithography.
DevelopmentofExtraordinaryOpticalTransmission-BasedTechniquesfor... 7
Fig.4 ASEMimageofthe
nanoaperturesantennaarray
fabricatedbytheprocessof
e-beamlithographyand
postdevelopment.
Nanoapertureswitha300-nm
holediameterand1-μm
periodarefabricatedintoa
goldfilm(t =30nm)(The
film
useofthisfigurefromRef.
[16]ispermittedbyWiley-
VCHVerlagGmbH&
Co.KGaA)
Theremarkableadvantagesofnanoimprintlithographyincludethesimplicityof
lithographic processes, accessibility of the massive nanostructure fabrication, and
costefficiency.Forthesereasonsandwiththeimprovementoffabricatingresolu-
tions,nanoimprintlithographyhasbeendevelopedtoinvestigatenanoaperturesfor
EOT.Forexample,Martinez-Perdigueroetal.introducedthenanoimprintfabrica-
tion to demonstrate gold nanoaperture array-based sensors [17]. Barbillon
describedhigh-densityplasmonicgoldnanodisksonaglasssubstrateforbiomed-
ical sensing applications produced with soft UV nanoimprint lithographic
fabrication[18].
Photolithography
Photolithography is a fabrication method applied for establishing micro- and
nanopatternsonathinfilmsubstrate.Thismethodusestransferredlightthrougha
microscalephotomasktoestimatedesignedpatternsonalight-sensitivelayer;this
layer is called a photoresist. After the development of the photoresist with
patterned-light illuminated structures, several chemical processes and the deposi-
tion of a specific material results in micro- or nanopatterns on the substrate
(Fig. 5a). A main advantage of photolithography is the accessibility of cost-
effective, large-area microfabrication. Larger collimated light sources and photo-
masksexpandthephotolithographicfabricatingareainbothresearchandindustrial
applications. High-precision motorized nanoscale stages also offer parallel fabri-
cationprocessesforcost-effectivemultiple-sampleestimations.
8 S.Leeetal.
Optical/UV light
a
Mask
Photoresist
Nanostructured material
Substrate
Positive Negative
photoresist photoresist
Photoresist
development
Etching
b
t = 0.2
t = 0.5
t = 0.9
1 µm
Fig.5 (a)Simplifiedillustrationofphotolithographicfabricationproceduresusingpositiveand
negativephotoresists.(b)SEMimages(viewingangle=45(cid:3))ofnanoaperturesestablishedbythe
combination of photo- and nanosphere lithography using 600 nm nanosphere particles. The
differencesintheembeddedthickness(t)causethepropertiesofnanoaperturestoberelevantly
changed(TheuseofthisfigurefromRef.[19]ispermittedbytheAmericanPhysicalSociety)
DevelopmentofExtraordinaryOpticalTransmission-BasedTechniquesfor... 9
OnecriticalissueinthephotolithographicfabricationofnanoaperturesforEOT
islimitedfabricatingresolution.Theresolutionofphotolithographyisboundedby
the Abbe’s lateral diffraction limit and the effective resolution is a little broader
because of reflection and scattering. General photolithography using optical or
ultraviolet (UV) light can be applied in microfabrication; these processes have
resolutionsofapproximatelyafewhundredsofnanometers.Toexceedtheresolu-
tion limit and build nanostructures for plasmonic applications including EOT,
several alternative fabrication approaches based on photolithography have been
suggested. Kelf et al. fabricated metallic circular nanoapertures to generate a
localized plasmon using the combination of photo- and nanosphere lithography
(Fig.5b)[19].Usinganidenticalmethod,Goncalvesetal.describedthefabrication
of triangular nanoapertures [20]. Henzie et al. introduced phase-shifting photoli-
thography, a high-resolution photolithographic fabrication method using phase-
changinglightilluminationstoinvestigateplasmonicnanostructures[21].
Applications
Nanoholearray structureshavebeen widelyusedinmultiple fields suchaschem-
ical, medical, and biological sensors for sensitively detecting dielectric changes
[22]. It also can be applied to the EOT-based super resolution imaging technique
[23].ThedetailedinformationoftheEOT-basedhigh-sensitivitysensorsandhigh-
resolutionimagingtechniquesareintroducedbelow.
EOT Gas Sensing
Recently, a chemoselective gas sensor was designed using plasmonic nanohole
arraystructures.Gasmoleculesaresmall,complicatingdetection,butitispossible
todetectgasmoleculesusingthenanoholearrays[24].Thus,thisplasmonicsensor
isdesignedtodetectgaseouscompoundssensitivelyusingEOT.
Figure 6 shows a schematic design of the gas detecting sensor composed of
periodic nanohole arrays and a voltage-directed assembly. A variety of methods
such ase-beam lithography,photolithography,andFIB were used tofabricate the
nanohole structures. A nanohole array structure that is fabricated using e-beam
lithographyisineachsensorregionA,B,andN(seeFig.6a)[25,26].Allsensorsin
Fig.6aattachedtoanelectricalcontacthaveananoholearray,andanelectricalbias
isprovidedforvoltage-directedassemblyprocess.Adifferenttypeofmoleculewas
composed to the surface chemistry. These nanohole arrays are connected to an
electrical contact to supply an electrical bias. All sensor regions are comprised of
different molecular conditions and can display chemoselectivity, a developing
multiplexed sensor. The characteristic of voltage-directed assembly process
makeslocalizedsensingbyelectricalisolationpossible.Avoltage-directedassem-
blywasimplementedusingopticallithographytoobtaindifferentchemistries.
10 S.Leeetal.
Fig. 6 (a) Schematic representation of the different steps for achieving a multiplexed
chemoselectivesensorarray.(b)Assemblyprocessofaseriesofchemoselectivecompoundsto
constructamultiplexedsensorarray.Chemoselectivityisgiventoanindividualsensingareausing
a voltage-directed assembly technique. Since the assembly occurs only in the presence of an
applied voltage, separate sensors can be given different chemistries in subsequent steps (The
permissionofreprintingFig.6fromRef.[25]wasgrantedbytheOpticalSociety)
b
a
60 Experiment
Simulation
%)
n (
o 40
si
s
mi
s
n
a
Tr 20
500 600 700 800 900 1000
Wavelength (nm)
Fig. 7 (a) Schematic representation ofthe difficulty ofgas sensing using plasmonics. (b) The
results of simulated (blue-solid) and measured (dotted-red) transmission through a nanoscale
perforated gold film (The permission of reprinting Fig. 7 from Ref. [25] was granted by the
OpticalSociety)