ABSTRACT This paper theoretically presents an improved sensitive surface plasmon resonance (SPR) biosensor using multilayer graphene with angular modulation. Metal thin film functionalization with graphene leads to an enhanced sensitive biosensor. This is due to pi-stacking interaction between carbon-based hexagonal structure of graphene and carbon-based ring biomolecules which increase biomolecule adsorption in the graphene layers. In comparison to conventional SPR sensors this produces a large change in the local refractive index at the sensor surface. The light reflection coupled into a SPR mode propagating along a silver-graphene interface is calculated and compared to a conventional silver-based SPR biosensor. The comparison result shows the improvement in sensitivity of biosensor

Anthony Centeno

Hamid Toloue

Nano Ikohza

CiteSeerX

                            VOL. 10, NO. 16, SEPTEMBER 2015                                                                                                            ISSN 1819-6608            
ARPN Journal of Engineering and Applied Sciences 
 
©2006-2015 Asian Research Publishing Network (ARPN). All rights reserved.
 
www.arpnjournals.com 
 
 
7119
AN ENHANCED SENSITIVE GRAPHENE-BASED SPR BIOSENSOR 
WITH ANGULAR MODULATION 
 
Hamid Toloue A. T. and Anthony Centeno Nano Ikohza  
Malaysia- Japan International Institute of Technology Universiti Teknologi Malaysia Kuala Lumpur, Malaysia 
E-Mail: h.toloue@gmail.com 
 
ABSTRACT 
 This paper theoretically presents an improved sensitive surface plasmon resonance (SPR) biosensor using 
multilayer graphene with angular modulation. Metal thin film functionalization with graphene leads to an enhanced 
sensitive biosensor. This is due to pi-stacking interaction between carbon-based hexagonal structure of graphene and 
carbon-based ring biomolecules which increase biomolecule adsorption in the graphene layers. In comparison to 
conventional SPR sensors this produces a large change in the local refractive index at the sensor surface. The light 
reflection coupled into a SPR mode propagating along a silver-graphene interface is calculated and compared to a 
conventional silver-based SPR biosensor. The comparison result shows the improvement in sensitivity of biosensor. 
 
Keywords: surface plasmon resonance, biosensor, graphene, silver. 
 
INTRODUCTION  
 In the last two decades there has been much 
investigation and improvement of optical biosensors and 
biochips. Such instruments hold much potential for 
different types of application in areas such as proteomics, 
pharmacogenomics, medical diagnostics, environmental 
monitoring, food safety, agriculture and security 
demonstrated by recent scientific and technological 
advances. Consequently, a wide variety of biosensors 
based on different detection techniques has been studied 
[1-3]. 
A unique technology is presented by a kind of 
optical biosensors which is label free. It is possible to 
make direct observation of molecular interaction in real-
time. Binding-induced refractive index variations are 
measured by optical label free biosensors and they are 
typically based on metal-dielectric waveguides such as 
surface plasmon resonance (SPR) biosensor [4]. 
 SPR sensor is fundamentally based on surface 
plasmon (SP) waves. SP waves propagate along the 
surface of noble metals such as gold, copper and silver at 
the metal-dielectric interface in the visible range of light 
spectrum. In a conventional SPR sensor, a thin noble metal 
film is sandwiched between two dielectrics, as shown in 
Figure-1. Silver and copper surfaces generally oxidize 
quickly and gold is a weak biomolecule absorber. Weak 
molecular adsorptions of metal and oxidation layer on top 
of the metal surface are two main reasons which restrict 
the sensitivity of the sensor. 
SPR sensors can be classified by coupling 
wavelength, coupling angle, and intensity, phase, or 
polarization changes. A laser wave excites SP wave in the 
SPR sensors based on angular interrogation. The strength 
of coupling between the SP wave and the incident wave 
can be evaluated and measured for several angles of 
incident light. The strongest coupling of the angle of 
incident light which has minimum reflection is used as the 
output of sensor [5].   
 
 
Figure-1. Optical excitation of surface plasmon in 
dielectric-metal-dielectric structure. 
 
  The vast majority of the electromagnetic field of 
SPs is concentrated in the dielectric which plays the role 
of the sensing medium. The propagation constant of the 
SPs is highly sensitive to changes in the relative electric 
permittivity, or equivalently, the refractive index of 
dielectric.  
 The SPR biosensor is known as a very effective 
optical detection for absorption of biomolecules [6]. This 
is due to the great change in the excitation angle of SPs 
which made by local variation of refractive index in 
sensing medium near the sensor surface. 
Numerous techniques have been investigated to improve 
sensitivity in SPR biosensor such as metallic nanoslits, 
metal nanoholes and nanoparticles in buffered solution [7, 
8]. The accurate control of the optical properties and 
geometry of nanostructure still remains challenging. The 
surface plasmons properties can be changed by 
functionalizing of the metal surface with biomolecular 
recognition elements (BRE). This is an alternative to 
enhance biomolecule adsorption efficiency on the metal 
surface.   
 
 
 
                            VOL. 10, NO. 16, SEPTEMBER 2015                                                                                                            ISSN 1819-6608            
ARPN Journal of Engineering and Applied Sciences 
 
©2006-2015 Asian Research Publishing Network (ARPN). All rights reserved.
 
www.arpnjournals.com 
 
 
7120
Optical Properties of Graphene in Visible Spectrum 
 Two dimensional crystals and hybrids such as 
graphene are now rapidly developing from pure science to 
technology. Graphene is evolving as a possible alternative 
to conventional optoelectronic, plasmonic and 
nanophotonic materials. Graphene could play a significant 
role in new generation of multilayer optical devices 
consisting of almost all kinds of optical materials such as 
dielectrics, semiconductors, semimetals, metals [9]. A 
mixture of graphene with conventional plasmonic 
nanodevices may offer ultrasensitive chemical sensors and 
biosensors. It expects that graphene has very high quantum 
effectiveness for light–matter interactions. Furthermore, its 
optical and electrical properties can be altered by doping 
and gating in conventional plasmonics devices based on 
noble metals.  
 Recent studies on transmission of light through 
graphene membranes revealed a universal opacity constant 
of graphene (wavelength independent) [10]. By using the 
Fresnel coefficients calculation framework the refractive 
index in the visible spectrum is obtained from [11]: 
 
6
03 (1.8153 10 )Graphenen i        (1) 
 
where λ0 is the free space wavelength. 
Biosensing application could improve by several 
properties of graphene such as high adsorption of 
biomolecule due to π-stacking interactions, constant 
absorption in visible to the infrared (IR), SP with high 
field concentration in IR, low small molecule permeability 
offering passivation [12, 13]. 
 
THEORETICAL MODEL 
 In this study, a graphene sheet on top of the silver 
thin film is considered as a BRE which is a good molecule 
absorber and impermeable to molecules as small as 
helium. Impermeability of graphene is an important factor 
to prevent silver surface from oxidation. In recent years, 
graphene on Au and Ag has been fabricated and shows 
stable adsorption of biomolecule with carbon-based ring 
structures [14, 15]. In comparison with a conventional 
SPR sensor, graphene provides a greater change of 
refractive index near the metal surface. In addition a 
graphene coating on the silver surface improves the 
surface plasmon polariton (SPP) propagation constant. 
Considering the intensity of light reflected from a N-layer 
system shown in Figure-2 for a transverse-magnetic 
incident wave, the total reflection, R, is given by [16]. 
 
2
11 12 1 21 22
11 12 1 21 22
( ) ( )
( ) ( )
N N
N N
M M q q M M q
R
M M q q M M q
  

  
     (2) 
 
1
2
N
ij k
k ij
M M


 
  
 
  , , 1, 2i j        (3) 
 
 
 
Figure-2. Light reflection for N-layer system. 
 
cos sin /
sin cos
k k k
k
k k k
i q
M
iq
 
 
 
   
      (4) 
 
2 2
1 sink
k
k
n
q
 


        (5) 
 
2 2
1
2
sink k kd n
  

   
 
       (6) 
  
The kth layer has local dielectric function εk and 
a thickness of dk where k is from 2 to N-1. In this study 
we considered a fixed wavelength of 633 nm which is for 
He-Ne laser. The calculations were carried out for the 
dielectric function of silver using a Drude-Lorentz model. 
The scenario considered uses a 56 nm silver thin film with 
multiple layers of graphene (d4) as the BRE. Thickness of 
each graphene layer is 0.34 nm. Biomolecule adsorption 
on sensor surface causes a small local change in water 
near to the sensor surface. This local change is modeled 
for 100 nm depth from sensor surface to the sensing 
medium. This binding layer assumed to have a refractive 
index of 1.335 in a water medium and the refractive index 
of water is 1.33. 
 The set up for silver-graphene SPR biosensor is 
illustrated in Figure-3, where the graphene layer covers a 
silver thin film. The other side of silver layer is in contact 
with titanium as an adhesive layer on top of the SF10 
glass. Thickness of the titanium layer is 3 nm and the 
refractive index of this layer is 2.7+i3.76. 
 The sensitivity (S) can be defined by relation 
between the sensor output, , angle of incidence light, and 
the moles of biomolecules in the water, M [17]: 
                            VOL. 10, NO. 16, SEPTEMBER 2015                                                                                                            ISSN 1819-6608            
ARPN Journal of Engineering and Applied Sciences 
 
©2006-2015 Asian Research Publishing Network (ARPN). All rights reserved.
 
www.arpnjournals.com 
 
 
7121
 
Figure-3. Schematic of silver-graphene SPR biosensor 
with an adhesive layer. 
 
n
n
S S E
M n M
   
   
  
     (6) 
 
Where Δn is the change in refractive index at the sensor 
surface.  
 The enhanced adsorption efficiency of 
biomolecules by using graphene is given by 
.Graphene conventionalE A E (where A>1).  We should notice 
the actual value of adsorption efficiency need to be 
derived from experimental result. The adsorption 
efficiency is increased by coating graphene on top of the 
silver surface.  
 By considering Eq. (7), the total sensitivity will 
be improved by increasing sensitivity to refractive index 
change (Sn) for silver-graphene substrate. The local change 
in refractive index near to sensor surface is assumed to be 
same (0.005 for 100 nm depth) in conventional and 
graphene-based structures. It means the sensitivity can be 
enhanced only if the shift in SPR angle by adding 
biomolecules on sensor surface in graphene-based is 
greater than conventional structure. 
 
RESULTS AND DISCUSSIONS 
 The numerically simulated SPR curves (red 
graphs) for the conventional biosensor based on silver 
(solid line) and gold (dashed line) before biomolecule 
adsorption are shown in Figure-4. The green curves on the 
other hand show the light absorption and blue graph 
indicates the transmission of light, respectively. A 
minimum reflection in red curve is due to the excitation of 
the SPP. As shown, the SPR occurred in total internal 
reflection. There is no transmission of light for all the 
incident angles bigger than 50.7 degree. SPR curve for 
silver substrate is sharper than gold substrate. 
Furthermore, the SPR angle and full width at half 
maximum (FWHM) for silver substrate is less than that of 
gold substrate. These make silver a much better and more 
responsive sensor than gold. 
 
 
 
Figure-4. Reflection (red), transmission (blue) and 
absorption (green) of incident light for gold (dashed line) 
and silver (solid line) thin films in SPR biosensor. 
 
Figure-5 shows the simulation result of six different SPR 
curves for the silver-based SPR biosensor with variation in 
thickness of silver thin film prior to biomolecules 
adsorption. Silver thickness ranging from 46nm to 59nm 
with the interval of 3nm in between was applied on the 
sensor. It was observed that the sharpest SPR curve with 
zero reflection in SPR angle was obtained for 56 nm of 
silver.   
 
 
 
Figure-5. Reflection of light in conventional silver SPR 
sensor based on Fresnel equation. 
 
By adding the biomolecules on top of the silver 
surface, refractive index of local area near to the silver 
surface will be changed causing a shift in the angle of the 
minima as shown in Figure-6. The incidence angles at 
minimum point are known as SPR angle. 
 
                            VOL. 10, NO. 16, SEPTEMBER 2015                                                                                                            ISSN 1819-6608            
ARPN Journal of Engineering and Applied Sciences 
 
©2006-2015 Asian Research Publishing Network (ARPN). All rights reserved.
 
www.arpnjournals.com 
 
 
7122
 
Figure-6.  SPR curve before (solid line) and after (dashed 
line) adding biomolecules in conventional silver-based 
structure. 
 
 It is observed the change in refractive index only 
causes the shift in SPR angle to the right side of the graph. 
There are not any other changes in light reflection curve 
after adding biomolecules because the refractive index of 
sensing medium is a real number and does not have any 
imaginary part. 
 The effect of multilayer graphene in SPR curve is 
calculated, based on transfer matrix for N-layer Fresnel 
equation, as shown in Figure-7. It is clearly illustrated that 
by adding more graphene layers on top of the silver 
surface, the SPR curve will be broaden, resulting in less 
sensitivity [18]. Therefore the maximum thickness of the 
graphene layer to get the desired output should be noticed. 
The results summarized in Figure-8 shows that the 
sensitivity to refractive index change enhanced with an 
increase in number of graphene layers. This is due to 
greater shift of resonance angle by increasing graphene 
layers. It occurred because of the larger change in 
refractive index at sensing medium near to the graphene 
surface. 
 
 
 
Figure-7. SPR curves for conventional structure and 
multilayer graphene-based structure. 
 
 
 
Figure-8. Enhancement in sensitivity to refractive index 
change for multilayer graphene based SPR biosensor. 
 
The calculations indicated that the sensitivity to 
refractive index is enhanced by 22.5% for 10 layer of 
graphene. The sensitivity to local variation in refractive 
index near to sensor surface can be obtained by the 
following equation 1 0.0204 ,nS N   where N is the 
number of graphene layers. The equation is only valid up 
to 5 layers of graphene. This is due to linearly increment 
as observed in Figure-8. 
  
CONCLUSIONS 
 Simulations of the sensitivity for a silver-
graphene SPR biosensor have been presented by using 
MATLAB. The results showed that by adding a graphene 
layer on silver surface in a SPR biosensor the sensitivity 
enhanced as compared to that of conventional sensor. This 
is due to a better adsorption efficiency of graphene and 
greater change in refractive index of water near the sensor 
surface after biomolecule adsorption. The model suggested 
that the total sensitivity increases with the number of 
graphene layers used. 
 
REFERENCES 
 
[1] Garaj S., Hubbard W., Reina A., Kong J., Branton D. 
and Golovchenko J.A. 2010. ‘Graphene as a 
subnanometre trans-electrode membrane’, Nature, 
Vol. 467, No. 7312, pp. 190-U173. 
 
[2] Anker J.N., Hall W.P., Lyandres O., Shah N.C., Zhao 
J. and Van Duyne R.P. 2008. “Biosensing with 
plasmonic nanosensors’, Nature Materials, Vol. 7, No. 
6, pp. 442-453. 
 
[3] Homola J. 2008. ‘Surface plasmon resonance sensors 
for detection of chemical and biological species’, 
Chemical Reviews, Vol. 108, No. 2, pp. 462-493. 
 
[4] Maier S.A. and Atwater H.A. 2005. ‘Plasmonics: 
Localization and guiding of electromagnetic energy in 
metal/dielectric structures’, Journal of Applied 
Physics, Vol. 98, No. 1. 
 
                            VOL. 10, NO. 16, SEPTEMBER 2015                                                                                                            ISSN 1819-6608            
ARPN Journal of Engineering and Applied Sciences 
 
©2006-2015 Asian Research Publishing Network (ARPN). All rights reserved.
 
www.arpnjournals.com 
 
 
7123
[5] Homola J. 2003. “Present and future of surface 
plasmon resonance biosensors’, Analytical and 
Bioanalytical Chemistry, Vol. 377, No. 3, pp. 528-
539. 
 
[6] Piliarik M., Sipova H., Kvasnicka P., Galler N., Krenn 
J.R. and Homola J. 2012. ‘High-resolution biosensor 
based on localized surface plasmons’, Optics Express, 
Vol. 20, No. 1, pp. 672-680. 
 
[7] Blanchard-Dionne, A.P., Guyot L., Patskovsky S., 
Gordon R. and Meunier M. 2011. ‘Intensity based 
surface plasmon resonance sensor using a nanohole 
rectangular array’, Optics Express, Vol. 19, No. 16, 
pp. 15041-15046. 
 
[8] Jia S., Wu Y.M., Wang X.H. and Wang N. 2014. “A 
Subwavelength Focusing Structure Composite of 
Nanoscale Metallic Slits Array With Patterned 
Dielectric Substrate’, IEEE Photonics Journal, Vol. 6, 
No. 1. 
 
[9] Grigorenko A.N., Polini M. and Novoselov K.S. 
2012. ‘Graphene plasmonics’, Nat Photon, Vol. 6, No. 
11, pp. 749-758. 
 
[10] Kravets V.G., Nair R.R., Blake P., Ponomarenko 
L.A., Riaz I., Jalil R., Anisimova S., Grigorenko A.N., 
Novoselov K.S. and Geim A.K. 2011. ‘Optics of Flat 
Carbon - Spectroscopic Ellipsometry of Graphene 
Flakes’, Nato Sec Sci B Phys, pp. 3-9. 
 
[11] Bruna M. and Borini S. 2009. ‘Optical constants of 
graphene layers in the visible range’, Applied Physics 
Letters, Vol. 94, No. 3. 
 
[12] Szunerits S., Maalouli N., Wijaya E., Vilcot J.P. and 
Boukherroub R. 2013. ‘Recent advances in the 
development of graphene-based surface plasmon 
resonance (SPR) interfaces’, Analytical and 
Bioanalytical Chemistry, Vol. 405, No. 5, pp. 1435-
1443. 
 
[13] Tang Z.W., Wu H., Cort J.R., Buchko G.W., Zhang 
Y.Y., Shao Y.Y., Aksay I.A., Liu J. and Lin Y.H. 
2010. ‘Constraint of DNA on Functionalized 
Graphene Improves its Biostability and Specificity’, 
Small, Vol. 6, No. 11, pp. 1205-1209. 
 
[14] Song B., Li D., Qi W., Elstner M., Fan C. and Fang H. 
2010. “Graphene on Au(111): A Highly Conductive 
Material with Excellent Adsorption Properties for 
High-Resolution Bio/Nanodetection and 
Identification’, Chemphyschem, Vol. 11, No. 3, pp. 
585-589. 
 
[15] Kiraly B., Iski E.V., Mannix A.J., Fisher B.L., 
Hersam M.C. and Guisinger N.P. 2013. ‘Solid-source 
growth and atomic-scale characterization of graphene 
on Ag(111)’, Nat Commun, Vol. 4. 
 
[16] Yamamoto M. 2002. ‘Surface plasmon resonance 
(SPR) theory: tutorial’, Review of Polarography, 48, 
(209). 
 
[17] Wu L., Chu H.S., Koh W.S. and Li E.P. 2010. ‘Highly 
sensitive graphene biosensors based on surface 
plasmon resonance’, Optics Express, Vol. 18, No. 14, 
pp. 14395-14400. 
 
[18] Choi S.H., Kim Y.L. and Byun K.M. 2011. 
‘Graphene-on-silver substrates for sensitive surface 
plasmon resonance imaging biosensors’, Optics 
Express, Vol. 19, No. 2, pp. 458-466. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 


AN ENHANCED SENSITIVE GRAPHENE-BASED SPR BIOSENSOR WITH ANGULAR MODULATION

http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=E40885824C32D7AD0F41C2349DA24A16?doi=10.1.1.1040.106&rep=rep1&type=pdf

AN ENHANCED SENSITIVE GRAPHENE-BASED SPR BIOSENSOR WITH ANGULAR MODULATION

Abstract

Similar works

Full text

Available Versions

CiteSeerX