Surface plasmon resonance sensor

Different Surface Plasmon Resonance based sensors for various applications

1. Surface plasmon resonance sensors –A future sensing technology
Presented by
R.Gandhimathi

2. Sensors-convertoneformenergyintoelectricalenergy
Opticalsensors-convertlightenergyintoelectricalenergy
Surfaceplasmonresonance(SPR)sensor-anopticalsensorfabricatedbasedonphotonicexcitation
Introductiontosurfaceplasmonresonancesensor
Classification
▪Surface Plasmon Polariton (SPP) based sensor
▪Localized surface plasmon resonance (LSPR) based
sensors
Plasmonic sensors are fabricated using
▪nanoparticles
▪nanopatternedgratings
▪Prismcouplers
▪Metal/Dielectricwaveguide
Characteristics of sensors
▪Sensitivity
▪Detectionlimit
▪Dynamicrangeperformance
SPR sensor applications
▪Biomedical
▪Food science
▪Environmental monitoring
▪Toxic or chemical compound
detection
▪Pharmacy and industry
▪Medical diagnostics
SPRsensorisveysensitivetovariationintherefractiveindexofthemediumlocatednexttothemetallicfilm

3. ▪The incident light is directly coupled with SPs (tightly
confined optical field)
▪Change in the refractive index of the analyte produces a
variation in the propagation constant of the surface plasmon
▪It means a modification in one of the characteristics of the
optical wave interacting with the surface plasmon
▪Binding between the analyte and the recognition molecule
caused changes in the refractive index of the dielectric and is
monitored as a shift in the resonance wavelength of the light
AstrongEMfieldoscillationattheinterfaceofmetal/dielectricmediawith
p-polarizedincidentlightresultinginadarkbandprofileinthelight
reflectivityataspecificwavelength(
res)andincidentangle(
I).
SPR Sensor Configuration
Surface plasmon Polariton
SPRconditionissensitivetotheenvironmentvariationsandthatcanbeutilizedassensors
Principle
Prism coupler-based SPR sensor
Prismcoupleremployingtheattenuatedtotalreflectionmethodin
KretschmanngeometryisthewidelyusedmethodinSPRbiosensors
applications

4. At Resonance z SPP
kk= 2
00 2
sin
mra
p
mr a
n
knk
n



=
+
The expression for the sensitivity is obtained by
differentiating resonant condition equation with respect to
, , I, and n
a
SPRsensorwith
▪AngularModulation
▪WavelengthModulation
▪IntensityModulation
▪Phaseorpolarizationmodulation0
sin
zp
k k n=
Incident light m mr
= 2
da
n=
where2
00 2
sin
mra
zp
mr a
n
kknk
n



==
+
�
0−??????������������������
�
??????�−�����������??????������??????�����������������
�
??????−�������??????��index of prism
�
??????−�������??????��??????�������������
Propagation
constant
TheexcitationofsurfaceplasmonsintheSPRsensorresultsinachangeinone
ofthecharacteristicsofthelightwave.Basedonwhichcharacteristicsofthe
lightwaveisinteractingwithsurfaceplasmonismeasuredandusedasasensor
output.P
a
S
n



= I
a
I
S
n


=
�
??????=
�??????
��
??????
�
??????=
�??????
�??????�
��
??????2
md
SPP
md
k

  
=
+
SPP2
2
sin
mr a
p
mr a
n
n
n



=
+
Resonance condition
Classification
Angular, Wavelength, Intensity and phase sensitivity

5. ▪Amonochromaticlightwaveisemployed
toexcitethesurfaceplasmon
▪Theexcitedsurfaceplasmonisobservedat
multipleanglesofincidentlight
▪Thestrengthofcouplingbetweenthe
incidentwaveandthesurfaceplasmon
dependsupontheanglesofincidentlight
▪Angleofincidenceyieldingthestrongest
couplingismeasuredandusedasasensor
output
▪Thesensoroutputiscalibratedtorefractive
indexdeg
a
S
nRIU



==
Angular sensitivity
2deg
10S
RIU

=
-represents the change of resonance angle
-change in the refractive index
�??????
��
??????
At constant wavelength
The angle yielding the minimum light intensity on the SPR curve is
denoted as the resonance angle
Additionofdiffractivegratingand
temperatureandnoisestabilizationare
thewaystoincreaseangular
sensitivity2 2 2 22
()()
mr mr
a
mr a mra p ap
S
n nnnnn



−
==
+ −−
Angular modulation

6. ▪Surfaceplasmonisexcitedbyacollimatedlightwavecontainingmultiplewavelengths.
▪Angleatwhichthelightwaveisincidentontothemetalfilmiskeptconstant.
▪CouplingstrengthbetweentheincidentwaveandSPisobservedatmultiplewavelengthsandthewavelengthyieldingthestrongest
couplingismeasuredandusedasasensoroutput
▪Resonancewavelengthisknowntoshifttothelongerwavelength(redshift)astherefractiveindexatthesensor/dielectricmediumis
increased
▪wavelengthModulationbasedSPRsensorsusingprismcouplersprovidemuchbettersensitivitythantheirgrating-basedcounterparts
▪UsageofFuriespectrometers,andmulti-channelsensinghelptoimprovesensitivity
34
10 10
nm
S
RIU

=−
ThewavelengthsensitivityoftheSPRsensorisdefinedastheratiobetweenthe
resonancewavelengthshifttothevariationoftherefractiveindexofthesurrounding
medium
Wavelengthmodulation
whereS
λistheSPRsensorsensitivity
istheshiftintheSPRresonancewavelength
isthechangeintherefractiveindex
�??????
�??????�
��
??????
Wavelength sensitivity 2
3
2
()
2
res mr
pa mr aa
mr amr
p
S
nnd nn
n
n

 


 
==
++

7. ��
??????=�
2−�
1
▪Excitationbysingleincidenceangleandwavelengthbychangingtheintensityoflight
▪P-polarizedwaveincidentlightisusedandtheyareverysensitivetoanyintensityfluctuationsofthelightsource
▪Lightsourcemustbeofhighqualityandstability
▪Intensityisspatiallymodulatedduetotheexcitationofsurfaceplasmonsandthechangesaresimultaneouslymeasuredinsensing
channelbymeansofaspatiallysensitivedetectorsuchastwo-dimensionalchargecoupleddevice
▪Sensoroutputisdefinedasthedifferenceofthesetworeflectedintensitieswhichisproportionaltothereflectance
34
1
%
10 10S
RIU
=− I
a
I
S
n


=
Intensity modulation
Thedetectionofsmallrefractiveindexchangesovera
relativelylargevolumeissuccessfulonsensorsbasedonan
intensitymodulationschemedowntoasensitivityof10
-6
RIU
Twolightsourceswithdifferentwavelengthhelptoimprove
thesensitivitywithintensitymodulation
Typicalsensitivity-
15000%
��??????

8. ▪Surfaceplasmonexcitationbyshiftinphaseofthelightwaveataincidenceangleandwavelength
▪ExplicitlyusedforthecoherentmonochromaticlightsourceinSPRinstrumentation
▪Itneedsphaseshiftequipmentsuchasalockinamplifier
where ∆ϕ is the differential phase changes corresponding to ∆n
The phase sensitivity which is defined as
��
??????=�
2−�
1
Phase or polarization Modulation P
a
S
n



=
Other than sensitivity the figure of merit (FOM) is another important parameter to characterize sensor performance
FWHM contains information on light absorption by the binding molecules
??????????????????=
�
????????????�??????
Where S denotes Sensitivity

9. LSPR sensor SPR sensor
Resonanceconditionsaresimpler Theenergyandmomentummatching
conditionsshouldbesatisfied
Smallsizeofplasmafield(20-40nm)
Marginalbulkeffect
Largerplasmafield(200-1000nm)
LargeBulkeffect
complexityresidesinthesurfaceofthe
chip
complexityresidesin the
instrumentationsetuptoexciteSPR
andreaditaccurately.
Temperatureindependent Moresensitivetothermalvariation
Instrumentallysimple Instrumentallycomplex
Localizedsurfaceplasmonresonance(LSPR)sensors
▪Alabel-freeandpowerfulsurfacesensingplatform
withhighersensitivity,simplefabricationand
measurementequipment
▪Theextremechemicalsensitivityofmetal
nanoparticlestominutechangesinthelocaldielectric
environment,isrevealedasadiscretechangetotheir
opticalresponseduetosurfaceadsorption
▪InLSPRsensor,lightpassesthroughthesample
solutionareaffectedbyabsorptionorscatteringofthe
sample
▪Requiresasimpleopticalconfigurationwithouta
prism
▪Cost-effectiveandsuitableforminiaturization

10. Analyte
Metal grating
Reflected light
P-polarized
Incident light
Grating period
SPR sensors using diffraction gratings
Incident light2
sin
za
kn



=
Diffracted wave vector22
sin
zm a
k n m



=+

At resonance SPP zm
kk = 2 2 2
sin
md
a
md
nm
  

   
+=
+
After Simplification sin
md
a
md
nm



+=
+
Atresonancecondition2
2
sin
mr a
a
mr a
n
nm
n



+ = 
+ 2
22
3
3
2
2
2
a mr
mr amr a
a mra
mrmr a
nm
na n n
nmn
n





+
+ +
=
+

+ 3
2
2
1
sin( )
cos( )
mr
a a mr a
n n n


  


=  − 
 +


Angular Modulation
Wave length Modulation
▪Themomentummismatchiscompensatedbydiffractionusingametallicdiffractiongrating
▪TheresonanttransferofopticalenergyintoanSPPisobservedasadipintheangularorwavelengthspectrumofreflectedlight
▪Lightpropagatesintothecorethroughtotalinternal
reflectionandgeneratesanevanescentfieldinthe
vicinityofthewaveguideboundary,whichinducesSPR
attheinterfacebetweenthemetalfilmandthesensing
medium
▪Provideshighlyintegrated,multichannel,androbust
sensingdevices
Theexpressionforthesensitivityisobtainedbydifferentiating
resonantconditionwithrespectto,andn
a
-grating period
Wave guide-based sensor
▪Planar waveguide configuration -unable to
interrogate the incident angle scanning
▪Wavelength interrogation is the only option for the
signal acquisition technique

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References

12. Thankyou