of 12
Aluminum Metasurface With Hybrid Multipolar
Plasmons for 1000
-
Fold Broadband Visible Fluorescence
Enhancement and Multiplexed Biosensing
Radwanul H
asan
Siddique
1,
3
,
Shailabh Kumar
1,†
,
Vinayak Narasimhan
1
,
Hyounghan Kwon
1
,
and
Hyuck Choo
1,2,
3
*
1
Department of Medical Engineering, California Institute of Technology, 1200 E. California Blvd.,
MC 136
-
93, Pasadena, California 91125, USA.
2
Department of Electrical Engineering, California Insti
tute of Technology,
1200 E. California
Blvd., MC 136
-
93,
Pasadena, California 91125, USA.
3
S
amsung Advanced Institute of Technologies, Samsung Electronics, 130 Samseong
-
ro, Maetan
-
dong, Yeongtong
-
gu, Suwon, Gyeonggi
-
do, 16678, South Korea
.
These authors c
ontributed equally to this work.
E
-
mail:
hyuck.choo@samsung.com
; hchoo@caltech.edu
Supplementary Information
Section
S1: Enhancement factors
S1.1
Enhancement factor calculations
Experimental
fluorescence enhancement factors were calculated by comparing the ratio
of
molecular fluorescence obtained from
diffusing molecules on
the
nDISC
regions
as compared to
on a control non
-
enhancing substrate
. Using the equation
:
1
-
2
퐸퐹
=
1
×
2
2
×
1
Where I1 is the integrated fluorescence intensity from N1 number of molecules
at the
nDISC
region
, and I2 is the total fluorescence intensity from N2 number of
molecules on a
nontextured
glass
surface. Since, the
same
concentration of molecules
was added to both substrates
, we
assume
the volumetric
density of molecules, η. Then the number of molecules
near the hotspot for the
nDISC surfaces can be represented as:
1
=
×
1
where
V1
is the ef
fective hotspot volume at
the dielectric between Al layers. FDTD simulations were consulted to calculate an effective
distance from the hotspot where the molecule
can experience a significant electromagnetic field
enhancement. An effective distance of 25 nm and dielectric thickness of 5 nm were used. For the
nonstructured
control
surface, number of molecules can be represented
as
2
=
×
2
,
where
V2
is
the confo
cal volume near a flat surface used as control
.
The effective focal depth of field for
the microscope
and the substrate
was
estimated
as
0.285 μm.
Fluorescence intensities I1 and I2
were obtained from the images after background subtraction. Average intens
ities were calculated
around the hotspots for
I1 and over control surfaces for I2, for EF calculation.
S1.2
Normalized Enhancement factor:
The quantum yield (QE) enhancements were calculated
at the respective wavelengths for the three fluorophores using th
e equation
:
3
=
0
(
1
0
)
+
0
+
푛푟
0
These calculated QE enhancements are shown in table S1 and were used to normalize the absolute
enhancement factors calculated previously. The normalized EF is thus independent o
f
any quantum
yield enhancement and solely represents locali
zed electromagnetic and molecular enhancement at
the hotspot.
Figure
S1
.
Experimental
scattering of nDISC nanoantenna.
Dark field scattering
measurement
of
FIB
-
milled 500 nm nDISC antenna
shows
a scattering peak at 507 nm with a quality factor of
4.15.
Figure
S2
.
Simulated scattering
spectra of
lone
Al nanodisks inside a dielectric cavity.
Figure
S3
.
Simulated scattering of Al nDISC nanoantenna with different diameter
.
Calculated quality factors of hybrid
multipolar
scattering
peaks
and their corresponding
out
-
of
-
plane field component
E
z
show the superior plasmon properties of
larger
nDISC
nanoantenna.
Figure
S4
.
FDTD
Simulation of radiative and non
-
radiative enhancements
spectra for a dipole
placed
2.5 nm above the metal disk and 2.5 nm to the side
in a 500 nm Al nDISC and nanodisk.
nDISC show
s
almost threefold increase in the radiative enhancement over non
-
radiative
enhancement. Whereas, radiative enhancements of nanodisk is
largely
dominated by non
-
radiative
enhancements demonstrating nanodisk’s poor performance on dipole
’s emission enhancement.
S
imulations of emission profiles of a dipole
on
both plasmonic Al nDISC and single nanodisk
antennae
at emission wavelength of 568 nm is shown in the right
panel confirming the enhanced
coupling of emitter’s radiation to LDOS modes of nDISC.
Figure
S
5
.
DNA adsorption on fabricated PMMA vs silica
.
Cy3
-
tagged aptamers were added to
PMMA submicron cavities prepared using the phase
-
separation method, standard glass slides
and silicon pieces with native SiO
2
.
Higher fluorescence intensity was observed on PMMA
substrates indicating enhanced surface adhe
sion of the diffusing single
-
stranded DNA.
Fluorophore
QE enhancement
FAM
0.831
Cy3
7.282
Cy5
2.620
Table
S
1
.
Quantum efficiency enhancement
calculated at the respective excitation wavelengths
for three fluorophores on th
e nDISC nanoantenna
metasurface.
Figure S6.
Figure shows normalized fluorescence image of a nDISC with PMMA nanoring with
respect to a PMMA submicron cavity surface (DNA tagged with FAM). The
color bar
represents
the raw intensity enhancement of the nDISC with respect to the PMMA submicron cavities.
Figure
S
7
.
Normalize
d broadband enhancement factors.
Enhancement of fluorescence
normalized with respect to dye quantum yield for three visible waveleng
ths on the Al nDISC
substrate
with PMMA nanoring
. This factor eliminates the effect of varying fluorophore
quantum efficiencies
. E
lectromagnetic field enhancement
and enhanced molecular capture due to
the PMMA nanoring as compared to control glass slide su
bstrates are taken into account.
Figure
S8
.
Fluorescence comparison of nDISC nanoantenna metasurfaces with different metal
s
.
Flu
orescence response of nDISC metasurfaces without any change in substrate geometry, while
changing the metal using
Cy3
-
tagged aptamers.
Figure S9.
Emission intensity in the direction (θ, φ) for emission into the back
-
ward half
-
space
(left) and into the forward substrate half
-
space (right) from the electric dipole inside nDISC
cavity (top), on single Al nanodisk (mi
ddle) and on the flat glass (bottom). All calculated far
-
field patterns are normalized with respect to the same global maximum emission.
Figure S10
.
Time
-
lapse
analysis of mean fluorescence obtained from a single
nDISC
at two
different concentrations (
a) 1 μ
M and (b) 10 nM. At high concentrations, we see higher intensity
but also photobleaching of the signal over time, indicating that molecules are already bound on
the PMMA nanoring surface. At
100
-
fold
lower concentration,
we do not observe decrease in
signal over time, indicating
that
the photobleaching is countered by arrival of
unbound
molecules
or most of the signal is from yet unbound molecules diffusing near the hotspot
.
Figure S1
1
. Plot showing obtained fluorescence from fluorophore
-
linked
aptamers (1 μM) for
laser powers ranging from 1
-
3% and fluorophores including (a) FAM (b) Cy3 and (c) Cy5. We
used 2% laser power for all the measurements made in the manuscript
(FAM and Cy3
-
0.2 mW,
Cy5
-
0.1 mW
)
. The results indicate a linear response b
etween laser power and fluorophores in
the target range.
References:
1.
Cai, W.; Ren, B.; Li, X.; She, C.; Liu, F.; Cai, X.; Tian, Z.
-
Q., Investigation
o
f Surface
-
Enhanced Raman Scattering
f
rom Platinum Electrodes
u
sing
a
Confocal Raman
Microscope: Dependence
o
f Surface Roughening Pretreatment.
Surf. Sci.
1998,
406
, 9
-
22.
2.
Smythe, E. J.; Dickey, M. D.; Bao, J.; Whitesides, G. M.; Capasso, F.,
Optical Antenna
Arrays on a Fiber Facet for
In Situ
Surface
-
Enhanced Raman Scat
tering Detection
.
Nano
Lett.
2009,
9
, 1132
-
1138.
3.
Mack, D. L.; Cortés, E.; Giannini, V.; Török, P.; Roschuk, T.; Maier, S. A.,
Decoupling
Absorption and Emission Processes in Super
-
Resolution Localization of Emitters in a
Plasmonic Hotspot.
Nat. Commun.
2017,
8
, 14513.