Applied
Surface
Science
258 (2012) 5881–
5885
Contents
lists
available
at
SciVerse
ScienceDirect
Applied
Surface
Science
j
our
nal
ho
me
p
age:
www.elsevier.com/loc
ate/apsusc
Size-dependent
SERS
detection
of
R6G
by
silver
nanoparticles
immersion-plated
on
silicon
nanoporous
pillar
array
Yong
Qiang
Wang
a,b
,
Sheng
Ma
a
,
Qian
Qian
Yang
a
,
Xin
Jian
Li
a,∗
a
Department
of
Physics
and
Laboratory
of
Materials
Physics,
Zhengzhou
University,
Zhengzhou
450052,
China
b
School
of
Physics
and
Chemistry,
Henan
Polytechnic
University,
Jiaozuo
454003,
China
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
4
February
2012
Received
in
revised
form
24
February
2012
Accepted
25
February
2012
Available online 3 March 2012
Keywords:
Surface-enhanced
Raman
scattering
(SERS)
Silicon
nanoporous
pillar
array
(Si-NPA)
Ag/Si-NPA
Rhodamine
6G
(R6G)
a
b
s
t
r
a
c
t
A
series
of
silver/silicon
nanoporous
pillar
arrays
(Ag/Si-NPAs)
were
prepared
by
an
immersion-plating
method
through
controlling
the
immersing
times
and
their
surface-enhanced
Raman
scattering
(SERS)
behaviors
to
rhodamine
6G
(R6G)
were
contrastively
studied.
With
a
concentration
of
10
−15
M,
the
iden-
tification
of
R6G
could
be
performed
by
all
the
samples,
but
the
corresponding
peak
intensities
varied
largely.
This
phenomenon
was
attributed
to
the
size
difference
of
the
deposited
silver
nanoparticles,
and
the
optimal
size
range
for
obtaining
the
strongest
SERS
signal
was
determined
to
be
∼35–55
nm.
Ag/Si-NPA
might
be
an
effective
substrate
for
performing
highly
sensitive
SERS
detections.
© 2012 Elsevier B.V. All rights reserved.
1.
Introduction
As
a
powerful
detecting,
identifying
and
analyzing
mean
which
can
provide
ultrasensitive
characterizations
down
to
sin-
gle
molecule
level
[1,2],
surface-enhanced
Raman
scattering
(SERS)
technology
has
been
widely
used
in
the
field
of
molecule
struc-
tural
identifying,
bio-analysis
and
medical
detections
[3–7].
In
SERS
detections,
the
target
molecules
were
usually
adsorbed
on
roughened
metal
surfaces
or
metal
nanoparticles,
and
therefore
the
species,
surface
morphologies
and
feature
sizes
of
the
adopted
metal
would
play
key
roles
in
deciding
the
effect
and
the
sen-
sitivity
of
the
active
substrates
[8–10].
Among
various
newly
developed
SERS-active
substrates,
two
kinds
of
materials
aroused
much
attention
in
the
past
several
years.
One
was
prepared
by
growing
noble
metal
nanoparticles
on
nanostructure
arrays,
such
as
on
porous
alumina
or
TiO
2
nanotube
array
[11–15],
the
other
was
obtained
by
immersion-plating
noble
metal
nanoparticles
on
porous
silicon
(PS)
utilizing
its
big
specific
surface
area
and
strong
chemical
reducibility
[16–18].
Based
on
the
above
active
substrates,
a
lot
of
meaningful
results
have
been
obtained
both
in
obtaining
strong
SERS
effects
and
in
clarifying
the
underlying
mechanisms.
In
our
previous
study,
we
reported
that
a
silicon
micron/nanometer
hierarchical
structure,
silicon
nanoporous
∗
Corresponding
author.
Tel.:
+86
371
67766629;
fax:
+86
371
67766629.
E-mail
address:
lixj@zzu.edu.cn
(X.J.
Li).
pillar
array
(Si-NPA),
was
prepared
by
a
hydrothermal
etching
method
[19].
In
addition
to
the
nanoporous
structure
similar
to
traditional
PS,
the
surface
morphology
of
Si-NPA
was
character-
ized
by
the
presentation
of
large
quantities
of
regularly
arrayed,
nanoporous
silicon
pillars
[19].
As
a
combination
of
the
nanoporous
structure
and
the
regular
array,
such
a
patterned
surface
feature
might
be
conducive
for
preparing
uniform
SERS-active
substrates
with
high
measurement
reproducibility.
According
to
the
idea,
noble
metal
nanoparticles
(Au,
Ag
and
Cu)
were
deposited
on
Si-
NPA
through
immersion-plating
method
and
strong
SERS
effects
were
observed
in
as-prepared
metal/Si-NPA
systems
[20–22].
For
example,
by
using
Ag/Si-NPA
as
the
SERS-active
substrate
to
detect
low-concentration
adenine,
significantly
enhanced
Raman
signals
were
observed
and
the
adsorption
modes
of
adenine
molecules
on
silver
particles
were
identified
[21].
Nevertheless,
how
to
optimize
the
preparing
conditions
to
obtain
the
strongest
SERS
effect
and
how
to
clarify
the
factors
affecting
the
SERS
behaviors
were
still
problems
suspended.
In
this
study,
a
series
of
Ag/Si-NPAs
were
prepared
by
an
immersion-plating
method
through
controlling
the
immersing
times
and
their
SERS
behaviors
to
rhodamine
6G
(R6G)
were
studied
contrastively.
Mainly
through
investigating
the
correla-
tion
between
the
peak
intensities
of
the
SERS
spectra
and
the
deposited
silver
nanoparticles,
the
optimal
size
range
of
the
silver
nanoparticles
for
obtaining
the
strongest
SERS
effect
was
obtained.
These
results
might
be
meaningful
both
for
optimizing
the
prepa-
ration
conditions
of
the
SERS-active
substrates
and
for
clarifying
the
related
SERS
mechanism.
0169-4332/$
–
see
front
matter ©
2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.apsusc.2012.02.129