Enhancing Performance of SPR Sensor through Electric field Intensity Enhancement using Graphene Pradeep Kumar Maharana and Rajan Jha School of Basic Sciences lIT Bhubaneswar Bhubaneswar, India pkm1
[email protected],
[email protected]/
[email protected]
Abstract-
An ultra-stable high performance SPR sensor
based on graphene on Ag
configuration is
proposed.
The
proposed sensor shows enhanced performance as compared to widely reported Au on Ag configuration.
Keywords- surface-plasmon-resonance; enhancement factor; imaging sensitivity.
graphene;
field
INTRODUCTION
I.
Surface-plasmon-resonance (SPR) based sensors have gained tremendous
interest
in
the
past
decade,
both
from
fundamental-physics perspective, simplicity in design and as high sensitive sensors for high precession, label free optical detection of chemicals and bio chemicals [1-2]. Although SPR
F ig.l. Proposed sensor setup
sensors exhibit the high sensitivity among the sensors based on the evanescent waves sensing principle, many works have been proposed further to improve the sensitivity and detection accuracy limit of sensors for high precession sensing [3-11].
Ill.
However, maximizing the electric field at the sensing layer interface seems to be a credible method for enhancing the performance of SPR sensor. In this work we have considered graphene as dielectric over layer on SPR active metal Ag in the optimized Kretschmann's configuration for enhancing electric field at the sensing layer interface. Our study shows enhanced performance over a broad sensing layer refractive index range. 11.
EM-field distribution of SPs is important for SPR-sensors because the interaction of evanescent field with molecules in the sensing region is crucial. Mathematically, the interaction is represented by an overlap integral between the evanescent field of SPs constant (cJ i» space
PROPOSED SENSOR DESIGN AND RELATED THEORY
RESULTS AND DISCUSSION
(F(;»
and spatial distribution of dielectric
of the sensing region in three dimensional
[13]. Depending upon the interactions the overlap
integrals are different and accordingly the sensitivity of thin film based SPR sensor is proportional to overlap integral. In order to increase the numerical value of overlap integral
The proposed sensor set-up (shown in Fig. I) is a four layer structure consisting of a tunable laser (632.8
)
nm ,
polarizer,
(Ep =2.29549) on a high precision rotary stage, Ag (Eg = 5.3300 + 7.5600i) liquid as biosensing layer (nd = 1.330-1.370). and
BK7 prism
(Em =
-17.81 +0.676i) [11], graphene
[12] and
photo detector. We have considered the N-layer model [7] for theoretical calculation of reflectivity of the p-polarized light in the proposed structure.
through field enhancement, we carried out the study of electric field enhancement factor (FIEF) [11] at graphene-sensing layer interface and compared the FIEF with the one for bimetallic Ag-Au configuration. Fig. 2 shows the variation of FIEF with the distance from the graphene (or metal)-sensing layer interface
for
optimized
thickness
of
Ag
with
different
graphene layers and Ag-Au. We found that the values of FIEF at the interface are 42.91 for graphene (L=I) on Ag, and 33.21 for Au -Ag. FIEF for graphene monolayer over Ag is 30 % higher than bimetallic Ag-Au counterpart which can enhance the performance and prevent Ag from oxidation in SPR sensor. For other combinations of graphene layers on Ag, the FIEF is either comparable or less than the bimetallic
50.-Ag+L(=l) ----�--�---r--_,--_.
REFERENCES
-Ag+L(=2) ---Ag+L(=3)
[I]
·····Ag+L(=4) _.-
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Ag+L(=5)
doi: 10.1080102726340801921650.
"---A +Au
[2] H. Raether, "Surface Plasmons on Smooth and Rough Surfaces and on Gratings", Springer-Verlag, Berlin, pp. 4-18, 125-126,1988. [3] A K. Sharma and B. D. Gupta, "On the performance of different bimetallic combinations in surface plasmon resonance based fiber optic sensors", J
1
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6
5
4
3
Distance from graphene(or metal)-sensing layer interface(x
tOOk)
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Fig.2. Variation of FIEF with distance from graphene-sensing layer
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for
Ag
with
L=I,
2,3,4
and
5
and
Ag-Au
bimetallic
configuration
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based surface plasmon resonance affinity biosensor for high performance"
of sensitivity, so with a view to study the sensitivity of the
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proposed configuration, in Fig.3 we plot variation of imaging sensitivity [8] and FWHM as a function of sensing layer
[6] R. Jha and A. Sharma, "High-performance sensor based on surface plasmon resonance with chalcogenide prism and aluminum for detection in
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infrared," Opt. Lett., vol. 34, no. 6, pp. 749-751, Mar. 2009. [7] T. Srivastava, R. Jha and R. Das, "High-Performance Bimetallic SPR Based on Periodic-Multilayer-Waveguides" IEEE Photonics Technology Letters, vo1.23, no.20,pp.1448-1450,Oct.2011.
Sensor
92 -==--�--.--�-�=---�-�--�-----,o.5 701
-J=.5401 �
�--�-f-+-�
89
___
';' Au on Ag oi 86 � -Graphene on Ag :� 83 Au on Ag § Graphene on Ag :, 80
.5101
-_.
.4501
17 e
·····
.4201
i:l �
_.
_._
-'
.
-
•.•. - ".
'�77 �
::
0)
_.-
'_'
"
5"n
.48012-
-- --- --
1.33
- --
1.335
-
.,........ ......
.3901 c
� :: :�:: = :�:: ::=�: � --
1.34
-
1.345
-
-
135
-
1,355
0
\ .36:� :c:�,,�'_
-
Sensing layer refractive tnd",, (nd
_
:
:: : ]
Fig.3. Variation of imaging sensitivity and Detection accuracy with sensing layer refractive index for graphene over Ag and Ag-Au bimetallic configuration
One can observe that our proposed configuration shows 22% higher as compared to bimetallic counterpart (dashed blue curve) for a broad sensing layer refractive index range
=
0.040 RlU. Moreover our proposed sensor shows 38%
higher detection accuracy (dotted green curve) compared to bimetallic configuration (dash-dotted green curve) over the same L1nd. The proposed sensor shows more than 50% imaging sensitivity and 100% increase in detection accuracy in infrared as compared to visible. We believe the propose sensor will open a new window in high performance sensing.
ACKNOWLEDGMENT The present work is partially supported by the Department of
Science
and
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sensor
based
on
graphene
and
silicon",
Technology Letters, Vo1.25, no.2,ppI22-125,Jan.2013.
IEEE Photonics
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Biow Hiem Ong, Xiaocong Yuan, Swee Chuan Tjin, Jingwen Zhang,
Hui Min Ng,"Optimised film thickness for maximum evanescent field enhancement of a bimetallic film surface plasmon resonance biosensor",
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enhanced imaging sensitivity (solid blue curve» by more than
L1nd
[8]
Technology
(DST),
India
under
project
SRiFTP/PS-086/2010. Pradeep K. Maharana is thankful to llT Bhubaneswar for providing fellowship
[12] J.W. Weber, VE. Calado, M.C.M. van de Sanden, "Optical constants of graphene
measured
by
spectroscopic
ellipsometry",
Letters, Vo1.97, pp.091904-091906, Aug. 2010.
Applied Physics
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