Sensors
and
Actuators
B
162 (2012) 35–
42
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Sensors
and
Actuators
B:
Chemical
journa
l
h
o
mepage:
www.elsevier.com/locate/snb
Self-referenced
sensing
based
on
a
waveguide-coupled
surface
plasmon
resonance
structure
for
background-free
detection
Yuhang
Wan
a
,
Zheng
Zheng
a,∗
,
Zhiting
Lu
a
,
Jiansheng
Liu
a
,
Jinsong
Zhu
b
a
School
of
Electronic
and
Information
Engineering,
Beihang
University,
37
Xueyuan
Rd,
Beijing
100191,
China
b
National
Center
for
Nanoscience
and
Technology
of
China,
Zhongguancun
North
First
Street
No.
2,
Beijing
100190,
China
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
17
June
2011
Received
in
revised
form
2
November
2011
Accepted
10
December
2011
Available online 17 December 2011
Keywords:
Surface
plasmon
resonance
Self-referenced
sensing
Optical
sensor
Waveguide-coupled
surface
plasmon
resonance
Biosensor
a
b
s
t
r
a
c
t
A
novel
self-referenced
sensing
method
is
proposed
and
studied
using
a
waveguide-coupled
surface
plas-
mon
resonance
structure,
where
it
is
shown
that
two
modes
supported
by
this
structure
could
couple
to
the
surface
plasmon
wave
at
the
sensing
surface.
Due
to
the
different
modal
characteristics,
these
two
modes
could
possess
different
penetration
depths,
field
enhancements
and,
therefore,
different
sensitiv-
ities
to
the
surface
and
bulk
background
refractive
index
changes.
The
self-referenced
scheme
can
then
be
applied
to
differentiate
these
refractive
index
changes.
As
the
device
structure
affects
the
modal
prop-
erties,
its
parameters
can
be
optimized
to
achieve
the
lowest
accumulated
system
errors.
Our
analysis
reveals
that,
as
one
of
the
SPR
modes
gets
closer
to
be
cut
off,
the
capability
of
the
scheme
to
correct
the
background
interference
could
improve.
© 2011 Elsevier B.V. All rights reserved.
1.
Introduction
As
a
real-time,
label-free,
highly
sensitive
optical
sensing
tech-
nology,
surface
plasmon
resonance
(SPR)
biosensors
have
been
widely
accepted
as
one
of
key
enabling
technologies
for
the
kinet-
ics
analysis
of
biomolecular
interactions
and
detecting
biochemical
analytes.
The
binding
of
target
molecules
to
the
functionalized
sen-
sor
surface
leads
to
a
refractive
index
(RI)
change
near
the
surface.
The
propagation
characteristics
of
the
surface
plasmon
(SP)
wave
along
the
surface
are
perturbed
by
this
RI
change,
as
the
field
of
the
SP
wave
decays
exponentially
into
the
dielectric
region.
The
variation
in
the
SP
modal
property
is
then
monitored
and
recorded
through
measuring
the
resonance
angle
or
wavelength.
While
the
thickness
of
the
analyte
layer
attached
to
the
surface
is
between
several
nanometers
to
tens
of
nanometers
depending
on
the
size
of
the
analyte
molecule
and
its
orientation
when
bound,
the
penetra-
tion
depth,
i.e.
the
decay
distance
of
the
SP
wave,
in
the
dielectric
region,
is
normally
around
hundreds
of
nanometers.
Therefore,
the
modal
properties
of
the
SP
wave
are
also
affected
by
the
media
beyond
the
target
analyte
layer,
i.e.
the
‘background’,
often
consist-
ing
of
the
buffer
solution.
The
background
RI
changes
could
lead
to
perturbations
of
the
SPR
condition.
Distinguishing
the
interaction
of
interest
from
the
bulk
change
of
the
background
is
challenging,
∗
Corresponding
author.
Tel.:
+86
10
82317220;
fax:
+86
10
82317220.
E-mail
address:
zhengzheng@buaa.edu.cn
(Z.
Zheng).
as
the
observed
total
SPR
signal
is
sensitive
to
a
combination
of
the
surface-adsorbed
layer
(the
surface
RI
change)
and
the
background
(the
bulk
RI
change).
For
most
applications
such
as
medical
diag-
nostics,
environmental
monitoring,
and
proteomics
research,
the
background
RI
is
inevitably
affected
by
the
change
in
the
concen-
tration
of
the
sample
during
different
injections
and
is
often
time
varying
due
to
the
temperature
fluctuations.
The
SPR
signal
change
introduced
by
the
bulk
RI
change
can
be
comparable
to,
or
even
larger
than
that
by
the
target
analyte.
Various
remedies
have
been
proposed
to
suppress
the
adverse
impact
of
the
background
RI
changes.
Temperature
stabilization
can
suppress
the
bulk
RI
drift,
but
cannot
deal
with
the
concen-
tration
change.
Using
two
separate
channels
covered
by
receptors
with
and
without
affinity
to
the
analyte
and
taking
the
one
without
affinity
as
a
reference
channel
is
another
technique
that
is
widely
adopted
in
commercial
systems.
The
advantage
of
the
reference-
channel
method
is
that
it
can
compensate
both
the
background
variation
and
the
non-specific
binding.
However,
the
need
to
dou-
ble
the
number
of
sensing
channels
limits
its
potential
applications
in
high
throughput
systems,
and
perfectly
identical
reference
chan-
nels
are
hard
to
realize.
On
the
other
hand,
several
self-referenced
SPR
sensing
schemes
[1–5],
or
sometimes
called
two-plasmon
spectroscopy,
have
been
investigated
in
recent
years.
The
key
for
the
self-referenced
method
is
to
simultaneously
excite
two
types
of
SP’s
with
dif-
ferent
penetration
depths
and
leverage
the
different
sensitivities
of
the
SP’s
to
the
RI
changes.
By
measuring
and
analyzing
the
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matter ©
2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.snb.2011.12.019