Subscriber access provided by UB + Fachbibliothek Chemie | (FU-Bibliothekssystem)
Article
Cavity-Coupled Plasmonic Device with Enhanced Sensitivity and Figure-of-Merit Mohsen Bahramipanah, Shourya Dutta-Gupta, Banafsheh Abasahl, and Olivier J.F. Martin ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.5b02977 • Publication Date (Web): 01 Jul 2015 Downloaded from http://pubs.acs.org on July 7, 2015
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Nano is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 40
ACS Nano
1 2 3 4 6
5
Cavity-Coupled Plasmonic Device with Enhanced 8
7 9 1
10
Sensitivity and Figure-of-Merit 12 13 14 16
15
Mohsen Bahramipanah,* Shourya Dutta-Gupta, Banafsheh Abasahl, and Olivier J. F. Martin 17 18 19
Nanophotonics and Metrology Laboratory (NAM), Swiss Federal Institute of Technology 20 2
21
Lausanne (EPFL), 1015 Lausanne, Switzerland 23 25
24
KEYWORDS: Plasmon, Fabry-Perot, nanoantennas, sensor, FDTD 26 27 29
28
ABSTRACT Using full-wafer processing, we demonstrate a sophisticated nanotechnology for 30 31
the realization of an ultra-high sensitive cavity-coupled plasmonic device that combines the 34
3
32
advantages of Fabry–Perot microcavities with those of metallic nanostructures. Coupling the 36
35
plasmonic nanostructures to a Fabry–Perot microcavity creates compound modes, which have 37 38
the characteristics of both Fabry–Perot and localized surface plasmon resonance (LSPR) modes, 41
40
39
boosting the sensitivity and figure-of-merit of the structure. The significant trait of the proposed 43
42
device is that the sample to be measured is located in the substrate region and is probed by the 4 46
45
compound modes. It is demonstrated that the sensitivity of the compound modes is much higher 48
47
than that of LSPR of plasmonic nanostructures or the pure Fabry-Perot modes of the optical 49 50
microcavity. The response of the device is also investigated numerically and the agreement 51 53
52
between measurements and calculations is excellent. The key features of the device introduced in 54 5 56 57 58 59 60 ACS Paragon Plus Environment
1
ACS Nano
Page 2 of 40
1 3
2
this work are applicable for the realization of ultra-high sensitive plasmonic devices for 5
4
biosensing, optoelectronics, and related technologies. 6 7 8 10
9
Recent developments in nanotechnology have led to the realization of new optical sensors that 1 12
can measure a broad range of analytes in both liquid and gaseous forms.1-10 Sensors based on 15
14
13
surface plasmon resonances have attracted significant attention for chemical and biological 17
16
sensing applications, thanks to their ability to confine light at the nanoscale well below the 18 19
diffraction limit, which provides record sensitivity and low noise.11 Plasmons supported by thin 2
21
20
films (excited via Otto or Kretschmann configuration),12-17 plasmonic resonators,18 24
23
nanocavities,19, 20 nanoparticles,21-26 nanocluster,27 nanopillars,28 nano-antennas,29 and nanorods30 25 27
26
are some of the numerous configurations for plasmonic sensors which have been suggested to 29
28
take advantage of the field localization in the sub-wavelength sensing region. All these devices 30 31
are designed to enhance the refractive index sensitivity, which is defined as the ratio of the shift 34
3
32
in resonance wavelength to the change in the refractive index of the analyte.31 The refractive 36
35
index sensitivity depends on the characteristics of the fields in the active regions of plasmonic 37 39
38
nanostructures and the perturbations of the fields caused by the interactions of the analytes 41
40
within those regions.32 However, localized surface plasmon resonance (LSPR) sensors are 43
42
characteristically insensitive to changes happening outside the active region of the structure and 4 46
45
their spatial sensing depth is accordingly constrained to a few nanometers around the 48
47
nanostructure.33-35 Furthermore, the overall figure-of-merit (FoM), which is defined as the 50
49
refractive index sensitivity divided by plasmon resonance linewidth,31 of the LSPR-based sensors 51 53
52
harshly suffers from the large plasmon resonance linewidth associated with the large intrinsic 5
54
absorption of metals at optical wavelengths.36-42 56 57 58 59 60 ACS Paragon Plus Environment
2
Page 3 of 40
ACS Nano
1 3
2
In order to increase the FoM, significant research efforts have been devoted to boosting the 5
4
sensitivity of metallic nanostructures by optimizing their shape.38, 43-45 Moreover, several designs 7
6
including plasmon hybridization,46 transformation optics,47 and subgroup decomposition,48 have 10
9
8
been suggested to narrow the resonance linewidth of plasmonic nanostructures. However, the 12
1
spectral linewidth of these resonances is still considerably larger than those of propagating 13 14
surface plasmons.14, 31, 49, 50 17
16
15
The most notable way of narrowing the linewidth is to couple the broad plasmon resonance of 19
18
plasmonic nanostructures to a narrow resonance system. It has been shown in the plasmonic 20 2
21
analogue of electromagnetically induced transparency that coupling a broad plasmon 24
23
superradiant mode to a narrow subradiant one leads to excitation of a sharp Fano lineshape 26
25
resonance.21, 27
27, 51-58
. The resulting resonance has superior refractive index sensing properties
29
28
thanks to the control of the radiative losses, compared to Lorentz-resonant systems.56 31
30
Additionally, compound modes generated because of the interaction between localized and 32 3
propagating plasmons in a periodic gold grating array placed close to a thin gold film have also 36
35
34
been investigated recently.59-62 These resonances exhibit both characteristics of localized and 38
37
propagating surface plasmons, which lead to a high sensitivity to the refractive index variations. 39 41
40
Alternatively, plasmon resonances can also be coupled to an optical microcavity to decrease 43
42
the resonance linewidth.63-68 The linewidth of such a cavity-coupled plasmon resonance is 45
4
determined by the cavity quality factor which modifies the radiative damping. The general 46 48
47
characteristic of cavity-coupled plasmonic sensors that have been reported so far is that the 50
49
sensing medium is localized outside the cavity and is probed by the localized field of the 51 52
plasmonic structure. Therefore, the dielectric microcavity just contributes to narrowing the 53 5
54
linewidth of the cavity-coupled plasmonic system and does not play a crucial role for sensing. To 56 57 58 59 60 ACS Paragon Plus Environment
3
ACS Nano
Page 4 of 40
1 3
2
the best of our knowledge, the only work on a cavity-coupled plasmonic structure that benefitted 5
4
from the cavity modes for sensing was the nanosensor platform proposed by Schmidt et al.68 6 7
They showed that the optical characteristics of the substrate on a nanoscale area could be 10
9
8
modified by photobleaching the cavity layer using ultraviolet light, thereby changing its 12
1
refractive index. However, as the material of the substrate cannot be changed once it has been 13 14
fabricated, the applications of this cavity-coupled plasmonic sensor are severely limited and in its 17
16
15
present form it cannot be applied for sensing analytes in liquid. 19
18
In this paper, we demonstrate that the coupling of the dipolar plasmon resonance of a two20 2
21
dimensional nanodisks array to the narrow resonances of an optical Fabry–Perot microcavity 24
23
creates compound modes, boosting both the sensitivity and FoM. It is shown that this cavity– 25 26
coupled plasmonic system excellently combines the advantages of Fabry–Perot microrcavities 27 29
28
with those of plasmonic nanostructures, providing exceptional features such as ultra-high 31
30
sensitivity and FoM, large spatial sensing depth and a strongly improved detection resolution. In 32 3
particular, we study the case where the cavity-coupled plasmonic device is fabricated with the 36
35
34
sensing medium inside the substrate region of the structure. We reveal the optical properties of 38
37
this device using bright-field optical microscopy and give a detailed explanation of the 39 41
40
underlying physics using finite-difference time-domain (FDTD) simulations. Finally, we discuss 43
42
the sensing properties of this structure and demonstrate them experimentally. Let us emphasize 45
4
that such a cavity-coupled plasmonic device benefits both from the LSP resonance and Fabry46 48
47
Perot modes, which respective contributions can be distinguished in the optical response of the 50
49
compound modes. Furthermore, having the sensing medium inside the substrate region makes 51 52
possible the joint utilization of both the LSP and the Fabry-Perot resonances for sensing the 53 5
54
refractive index variations. 56 57 58 59 60 ACS Paragon Plus Environment
4
Page 5 of 40
ACS Nano
1 3
2
Results and Discussion 4 6
5
Cavity-coupled plasmonic structure. In the optical system investigated here, the localized 7 8
surface plasmon resonance is supported by the subwavelength metallic nanodisks. Their 1
10
9
resonance wavelength can be tuned by changing the size of the nanodisks, the background, or the 13
12
metal. One of the major limitations of using such a LSPR structure as a refractive index sensor is 14 16
15
their large linewidth, which is caused by the large intrinsic losses of metals. Alternatively, Fabry18
17
Perot cavities have narrow linewidths which are more suitable for sensing applications;69-76 20
19
however, their field localization is very poor. Thus, we propose here to effectively reduce the 21 23
2
linewidth while maintaining the field localization by coupling the plasmonic structure to an 25
24
optical microcavity. 26 27
The cavity-coupled plasmonic structure studied here is shown in Figure 1a. It consists of two 28 30
29
functional layers: the top layer with a two-dimensional gold nanodisks array placed on top of an 32
31
ITO-coated glass substrate and the bottom layer made up of a 200 nm-thick gold metallic plane 3 34
deposited on a SiO2-coated silicon substrate, which acts as a back reflector. A 200 nm-thick SiO2 37
36
35
film is also deposited on top of the gold reflective film as protective layer. Parylene is used as 39
38
spacer between these two functional layers to create a microcavity with desired thickness. An 40 42
41
ITO-coated glass substrate is placed upside down on the parylene spacer to form a Fabry-Perot 4
43
resonant cavity, Figure 1a. 45 46 47 48 49 50 51 52 53 54 5 56 57 58 59 60 ACS Paragon Plus Environment
5
ACS Nano
Page 6 of 40
1 2 3 4 5 6 7 8 9 10 1 12 13 14 15 16 17 18 19 20 2
21
Figure 1. (a) Schematic of the cavity-coupled plasmonic structure and (b) light paths through the 23 25
24
structure. 26 28
27
Simulations are performed with a home-made three-dimensional FDTD code. The structure is 30
29
excited by a transverse magnetic (TM) polarized Gaussian modulated (in time) pulse source 31 32
centered around the frequency of interest, with a plane wave spatial distribution and a normal 35
34
3
incidence. The plane wave propagates in the glass region along z-direction with the electric field 37
36
polarized along x-direction, Figure 1a. To have a dominant dipolar plasmon resonance in the 38 40
39
investigated spectral range between 600 and 1000 nm, the diameter, thickness and period of the 42
41
nanodisks array are fixed at 210 nm, 50 nm and 300 nm, respectively, unless stated otherwise. 43 4
Further details on the simulation method are presented in the Supporting Information. 45 47
46
When the structure is illuminated from the glass side, some of the light is reflected back from 49
48
the nanodisks array, with a phase change of 1, and some of the light is transmitted into the 50 52
51
microcavity, as illustrated in Figure 1b. During one round-trip inside the Fabry-Perot cavity, the 54
53
light is partly reflected back from the nanodisks array into the cavity and partly transmitted out 56
5
of the cavity with a 2 phase change. When the geometrical parameters of the nanodisks array 58
57 59 60
ACS Paragon Plus Environment
6
Page 7 of 40
ACS Nano
1 3
2
and Fabry-Perot cavity are properly chosen, the transmitted light from inside the cavity will have 5
4
an odd multiple of phase difference with the light reflected back from the nanodisks array, i.e., 6 8
7
2 - 1 = (2k-1), with k an integer, and destructive interference for the total reflection from 10
9
the structure will be achieved. In this case, a net absorption of 1 at the corresponding 12
1
wavelengths can be observed, i.e., perfect absorption.77 However, when the Fabry-Perot 15
14
13
resonances coincide with the LSPR mode of the nanodisks array, the transmitted light from the 17
16
cavity will have an even multiple of phase difference with the light reflected back from the 18 20
19
nanodisks array, i.e., 2 - 1 = (2k), and constructive interference for the total reflection will 2
21
be achieved, which leads to a near unity reflection. 23 25
24
First, we study the effect of the cavity length on the optical response of the system. For the 27
26
time being, the material inside the cavity is assumed to be air (=1). The normalized reflectance 28 29
and the phase difference between the transmitted light from the cavity and the reflected light 32
31
30
from the nanodisks array are shown as a function of the wavelength and of the cavity length in 34
3
Figures 2a and 2b. Figure 2a clearly shows the Fabry-Perot modes and their mode number N. In 35 37
36
the vicinity of these Fabry-Perot resonances, phase differences between the transmitted light 39
38
from the cavity and the reflected light from the nanodisks array exhibit strong variations within 40 41
its value of ±Figure 2b. In this case, destructive interference for the reflection is achieved. As 4
43
42
can be seen in Figures 2a and 2b, for a fixed wavelength, the higher order modes of the cavity46
45
coupled plasmonic structure exhibit the Fabry-Perot resonance condition with increasing 47 49
48
microcavity length. The corresponding microcavity lengths, which satisfy the condition of 51
50
destructive interference for the reflected light, and the corresponding reflection efficiencies are 53
52
given in Table 1 (white rows). Moreover, there is one region in Figures 2a and 2b where the 54 56
5
Fabry-Perot dips vanish, such that near unity reflection is achieved. This region, highlighted by a 57 58 59 60 ACS Paragon Plus Environment
7
ACS Nano
Page 8 of 40
1 3
2
horizontal white dashed line, corresponds to the LSPR mode. We observe that when the Fabry5
4
Perot resonances coincide with the LSPR mode of the nanodisks array, the transmitted light from 6 7
the cavity is in-phase with the reflected light from the nanodisks array and constructive 10
9
8
interference of the reflected planewaves leads to near unity reflection. When the cavity length is 12
1
varied, this interaction with the plasmon mode occurs whenever the Fabry-Perot resonance is 13 14
equal to the LSPR resonance. Vertical black arrows in Figures 2a and 2b indicate these resonant 17
16
15
modes. It is obvious from the phase distribution that the constructive interference condition 19
18
highly depends on the cavity length. In fact, a small variation in the cavity length can jeopardize 20 2
21
the constructive interference condition. The corresponding microcavity lengths, which lead to 24
23
constructive interference for the reflection, are also depicted in Table 1 (gray shaded rows). For a 25 26
meaningful comparison, the normalized reflectance as a function of the wavelength and cavity 27 29
28
length for a conventional Fabry-Perot cavity with a 50 nm thin gold layer instead of the two31
30
dimensional nanodisks array is shown in Figure S2a. This figure exhibits the conventional Fabry32 3
Perot resonant modes. However, since the top boundary does not support any LSPR modes due 36
35
34
to the absence of nanostructures, the near unity reflection peak cannot be achieved and instead 38
37
we can see a dip. 39 41
40
Cuts through Figures 2a (blue solid line) and 2b (red dotted line) for the cavity length of 1830 43
42
nm are shown in Figure 2c. For comparison, a cut through Figure S2a for the same cavity length 45
4
of 1830 nm is also shown in Figure S2b. As can be seen in the reflection spectrum of the cavity46 48
47
coupled plasmonic structure, a nearly perfect destructive interference in the reflection spectrum 50
49
and correspondingly near unity absorption at = 624.7 nm can be achieved. The phase 51 52
difference between the transmitted light from the cavity and the reflected light from the 5
54
53
nanodisks array is almost . The absorption efficiency is about 97.18% at this wavelength. On 56 57 58 59 60 ACS Paragon Plus Environment
8
Page 9 of 40
ACS Nano
1 3
2
the other hand, perfect constructive interference for the reflection (phase difference of zero) and 5
4
correspondingly near unity reflection, with a reflection efficiency of about 93.87%, at = 725 6 8
7
nm is also achieved. Moreover, we can see another mode at = 864.5 nm with an absorption 10
9
efficiency of about 61.4%, for which neither perfect constructive or destructive interference 1 12
occur. For comparison and qualitative analysis, the normalized reflection spectrum of a bare two15
14
13
dimensional gold nanodisks array on top of the ITO coated glass substrate, without the presence 17
16
of the underlying cavity, is also shown in Figure 2c (blue dashed line), from which we can see 18 19
the dipolar resonance at the wavelength of = 725 nm. The reflection efficiency is about 82.12% 2
21
20
at this wavelength. Despite some minor similarities in the peak resonance wavelength, the 23 24
reflection spectra for the cavity and no–cavity systems are significantly different, indicating that 27
26
25
the cavity has an important impact on the optical response of the structure. The large linewidth of 29
28
the dipolar resonance peak of the bare two-dimensional nanodisks array structure is 432.8 nm 30 32
31
(full-width at half maximum, FWHM). On the other hand, the linewidths of the resonance dips 34
3
and peak for the cavity-coupled plasmonic structure are 11.1 nm, 3 nm, 12.5 nm at their 36
35
corresponding resonance wavelength = 624.7 nm (third mode), = 725 nm (second mode), 37 39
38
= 864.8 nm (first mode), respectively. This very significant narrowing in the linewidth of the 41
40
cavity-coupled plasmonic structure arises from the high quality factor of the microcavity and has 42 43
a positive influence on the sensing capabilities of the structure, as will be shown later. For 46
45
4
comparison, the linewidths of the conventional Fabry-Perot cavity modes, shown in Figure S2b, 47 48
are 2.4 nm, 3.4 nm and 4.7 nm, respectively; note that the second hybrid mode is slightly 49 51
50
narrower than the corresponding mode of the conventional Fabry-Perot cavity. 53
52
Let us now consider the effect of detuning the LSPR wavelength with respect to the Fabry54 5
Perot mode on the peak observed in the spectral response. Figure 2d shows the influence of the 56 57 58 59 60 ACS Paragon Plus Environment
9
ACS Nano
Page 10 of 40
1 3
2
nanodisks size on the LSPR wavelength for a bare two-dimensional nanodisks array (blue dashed 5
4
line) in addition to the Fabry-Perot mode (blue solid line). As the size of the nanodisks is 6 7
increased from 160 nm to 250 nm, a red shift of the plasmon resonance is observed from 691 nm 10
9
8
to 753 nm, as expected.78 The intersection of these two lines determines the exact dimension of 12
1
the nanodisks at which constructive interference can be achieved. Furthermore, the normalized 13 14
reflectance of the second mode as a function of the size of the nanodisks for the complex cavity17
16
15
coupled plasmonic structure is also depicted (red dotted line). A strong variation of the 19
18
reflectance is clearly seen. For example, for the size of 160 nm a reflectance of 2.52% is obtained 20 2
21
which increases to 93.87% for the nanodisks size of 210 nm. Further increase in the nanodisks 24
23
size results in a decrease in the reflectance. This indicates that the peak observed in the spectrum 25 26
for 210 nm is due to the constructive interference and deviations of the LSPR from the Fabry27 29
28
Perot mode result in a change in the interference condition which transforms the peak into a dip. 30 31 32 3 34 35 36 37 38 39 40 41 42 43 4 45 46 47 48 49 50 51 52 53 54 5 56 57 58 59 60 ACS Paragon Plus Environment
10
Page 11 of 40
ACS Nano
1 2 3 4 5 6 7 8 9 10 1 12 13 14 15 16 17 18 19 20 21 2 23 24 25 26 27 28 29 30 31 3
32
Figure 2. Colormaps of (a) normalized reflectance and (b) phase difference as a function of the 35
34
wavelength and cavity length for cavity-coupled plasmonic structures shown in Figure 1. (c) 36 37
Normalized reflection spectra (blue solid line) and phase difference (red dotted line) for a cavity40
39
38
coupled plasmonic structure for 1830 nm cavity length. The reflection spectrum for a bare two42
41
dimensional gold nanodisks array without the underlying Fabry-Perot cavity is also shown as 43 4
blue dashed line. (d) LSPR wavelength for a bare two-dimensional nanodisks array (blue dashed 47
46
45
line) and the normalized reflectance (red dotted line) for the second mode of the proposed cavity49
48
coupled plasmonic structure as a function of the size of the nanodisks. For clarity, the 50 52
51
corresponding Fabry-Perot mode, which results in constructive interference, is also shown (blue 54
53
solid line). For the phase plots, the phase difference of the transmitted light outside the cavity 5 56
with the reflected light from the nanodisks array are calculated and shown. 57 58 59 60 ACS Paragon Plus Environment
11
ACS Nano
Page 12 of 40
1 3
2
Table 1. Resonant mode number, resonance wavelength, and normalized reflectance for the 5
4
resonant modes and their corresponding microcavity length. Gray and white rows indicate the 6 7
constructive and destructive interference cases, respectively. 9
8
1
10 d (nm)
12
1100 1220 1280 1460 1600 1830 1930 1990 2
21
20
19
18
17
16
15
14
13
Resonant mode number (N)
Resonance Wavelength
(nm)
Normalized Reflectance
(%)
4 4 5 5 5–6 6 7 6
725 776 652 725 775 – 652 725 651 776
94.5 0.04 0.3 94.2 0.1 – 0.3 93.9 0.4 0.02
23 25
24
For better understanding of the physics behind the proposed cavity-coupled plasmonic 26 28
27
structure, FDTD simulations of the total electric field amplitude distributions (absolute value) at 30
29
the resonance wavelengths of = 624.7 nm, Figures 3a and 3b, = 725 nm, Figures 3c and 3d, 31 32
and = 864.8 nm, Figures 3e and 3f, are compared with the electric field amplitude distribution 35
34
3
of the plasmon mode of the bare two-dimensional nanodisks array, Figures 3g and 3h. In 36 37
particular, the left panel shows the local electric field distributions in the xy plane, 5 nm above 38 40
39
the nanodisk inside the cavity, and the right panel illustrates the electric field distributions in the 42
41
xz plane cut through the center of the gold nanodisks. To ease interpretation of the presented 43 4
field distributions, we note that the structures are illuminated by a plane wave which is polarized 47
46
45
in such a way as to contain only the Ex component of the electric field, black arrow in Figure 3a. 48 49 50 51 52 53 54 5 56 57 58 59 60 ACS Paragon Plus Environment
12
Page 13 of 40
ACS Nano
1 2 3 4 5 6 7 8 9 10 1 12 13 14 15 16 17 18 19 20 21 2 23 24 25 26 27 28 29 30 31 32 3 34 35 36
Figure 3. Total electric field amplitude distributions, at the resonance wavelengths of (a-b) = 39
38
37
624.7 nm, (c-d) = 725 nm, and (e-f) = 864.8 nm for cavity-coupled plasmonic structure and 40 41
(g-h) at = 725 nm for the bare two-dimensional gold nanodisks array. The left panel shows the 4
43
42
local electric filed distributions in the xy plane and the right panel gives the electric field 45 46
distributions in the xz plane cut through the center of the gold nanodisks. 47 48 50
49
The field plots corresponding to the third mode at = 624.7 nm, Figures 3a and 3b, clearly 52
51
show that the electric field is strongly enhanced not only at the edges of the nanodisk but also 53 54
inside the Fabry-Perot cavity because of destructive interference. From the xy field distribution, 57
56
5
Figure 3a, it is obvious that the dipolar plasmon resonance cannot be effectively exited and the 58 59 60 ACS Paragon Plus Environment
13
ACS Nano
Page 14 of 40
1 3
2
Fabry-Perot component dominates in this compound mode. Furthermore, the field in the xz plane 5
4
shows a standing wave pattern within the cavity, characteristic of a Fabry-Perot kind of 6 7
resonance. From the same plot, it can be observed that the strong fields associated with the 10
9
8
nanodisks are located primarily in the ITO layer, indicated by pink lines in Figure 3b. The 12
1
absence of strong standing wave pattern outside the structure also provides additional proof of 13 14
destructive interference. In contrast to the third mode at which almost destructive interference is 17
16
15
obtained, the second mode at = 725 nm exhibits constructive interference and hence 18 19
completely different field distributions. Standing wave patterns can be observed both inside and 2
21
20
outside the cavity, Figure 3d. However, the field intensities for the second mode inside the cavity 24
23
are lower as compared to the fields observed for the third mode at identical spatial locations, 25 26
Figure 3b and Figure 3d. In case of this mode, the fields associated with the nanodisks are 29
28
27
predominantly localized in the cavity region as opposed to the ITO layer. Even though the field 31
30
localizations due to the nanodisks are different for the third and the second modes, the maximum 32 34
3
intensities observed are very similar. The xy field plot of the second mode, Figure 3c, clearly 36
35
shows the excitation of the dipolar plasmon resonance associated with the nanodisks. This is in 37 38
contrast with the fields observed on a similar plane for the third mode, Figure 3a. Therefore, in 39 41
40
case of the second mode, both the Fabry-Perot and LSPR modes play a crucial role for creating 43
42
the compound mode. The field distributions for the first mode, = 864.8 nm, which exhibits 4 46
45
neither perfect constructive or perfect destructive interference of the reflected light is shown in 48
47
Figures 3e and 3f. In this case the electric field is localized at both the edges of the nanodisk as 50
49
well as inside the Fabry-Perot cavity. The maximum intensities observed for this mode are 51 53
52
higher as compared to the other two modes. Figure 3e shows the xy field plot elucidating the 5
54
excitation of a dipolar plasmon resonance, similar to the one associated with the second mode. 56 57 58 59 60 ACS Paragon Plus Environment
14
Page 15 of 40
ACS Nano
1 3
2
Additionally, the electric field associated with the nanodisks is localized in both the cavity region 5
4
as well as in the ITO layer, Figure 3f. For completeness, we also present the electric fields for 6 7
nanodisks in the absence of the cavity in both the xy and xz planes, Figures 3g and 3h. The 10
9
8
electric field in this case is just localized at the edges of the nanodisk. As can be seen, the field 12
1
distribution of the dipolar mode matches quite well with the field distributions computed for the 13 14
second mode of the cavity-coupled plasmonic structure, Figures 3c and 3d. 17
16
15
As discussed before, the second mode of the cavity-coupled plasmonic structure is much 18 19
narrower than the first and third modes. The physical principle of this line narrowing can be 20 2
21
evaluated from the loss mechanisms in play within the cavity-coupled plasmonic structure. From 24
23
Figures 3b and 3f it is clearly seen that the light is mostly concentrated inside the cavity. Since 25 27
26
the main source for losses in the system is the plasmonic nanostructures, the concentrated light 29
28
inside the cavity would face higher losses when compared to the second mode, in which most of 31
30
the light is concentrated outside the cavity, Figure 3d. Therefore, the higher rate of energy loss 32 34
3
relative to the stored energy inside the cavity for the first and third modes results in a lower 36
35
quality factor and broadening of the linewidths. 38
37
The aforementioned numerical analysis demonstrates that the various interactions between the 39 41
40
Fabry-Perot and the LSPR resonances can be used for constructing compound resonances with 43
42
narrow linewidths. In the subsequent sections, we detail the various steps used for realizing the 45
4
cavity-coupled structures and the experimental validation of their sensitivity for bulk refractive 46 48
47
index sensing. 50
49
Nanofabrication: To experimentally realize the proposed cavity-coupled plasmonic device, 51 52
we have combined electron beam lithography with UV-lithography to fabricate metallic 53 5
54
nanostructures and the microfluidic chamber defining the optical Fabry-Perot cavity. Although 56 57 58 59 60 ACS Paragon Plus Environment
15
ACS Nano
Page 16 of 40
1 3
2
the fabrication is quite intricate, this geometry enables the sensing medium to be inside the 5
4
substrate, in direct interaction with the plasmonic nanostructures. The fabrication process is 6 7
illustrated in Figure 4. 9
8 10 1 12 13 14 15 16 17 18 19 20 21 2 23 24 25 26 27 28 29 30 31 32 3 34 35 36 37 38 39 40 41 42 43 4 45 46 47 49
48
Figure 4. Process flow for the fabrication of (a-f) microcavities; (g-i) two-dimensional gold 50 51
nanodisks array; (j) final chip bonding. 52 53 54 5 56 57 58 59 60 ACS Paragon Plus Environment
16
Page 17 of 40
ACS Nano
1 3
2
First, a standard 4ʺ crystalline silicon wafer (545 m thickness, specification 100/P/SS/01-100) 5
4
was cleaned in piranha solution (96% Sulphuric acid, H2SO4, and 30% Peroxide, H2O2) for 10 6 8
7
min at 100 ºC to remove organic residue on the wafer surface. A continuous 500 nm SiO2 layer 10
9
was deposited using e-beam evaporation (Leybold Optics LAB 600H). Then, a 200-nm-thick 12
1
layer of gold with a chromium adhesion layer of 2 nm was deposited on the SiO2 layer; this layer 13 15
14
acts as the mirror for the cavity-coupled plasmonic structure. A 200 nm-thick SiO2 film was also 17
16
deposited on top of the gold film, with a chromium adhesion layer of 2 nm, to facilitate the 18 19
adhesion of parylene in the next step and also as a protective layer for the gold mirror, Figure 4a. 2
21
20
It is well-known that bonding glass to silicon wafers with polymer glue as the intermediate 24
23
layer is possible, since the polymer layer is elastic and can be effectively heated above its glass 25 26
transition temperature.79 Among different polymers utilized to perform polymer bonding, 29
28
27
parylene-C was used in this work both to form the microcavity and to perform the bonding 31
30
operation. An advantage of parylene-C is that it is bio-compatible and can be deposited at room 32 34
3
temperature; furthermore, it does not requires thermal annealing or baking cycles during 36
35
deposition.79 Therefore, 1830 nm parylene-C was deposited on the sample using a Comelec C37 38
30-S parylene deposition system, Figure 4b. 39 41
40
UV-lithography technique was used to create the microcavity in parylene. The batch priming 43
42
of the substrate was done in a YES III, HMDS primer oven (BITA BeNeLux) for 10s at 125 ºC 4 45
to enhance adhesion of the positive photoresist. Before coating the substrate with the photoresist, 48
47
46
the dehydration baking step was performed on a hot plate for 4 min at 160 ºC. This step has a 50
49
substantial impact on adhesion of positive photoresist to the substrate. Then, a 5 m thick layer 51 53
52
of AZ9260 positive photoresist (AZ Electronic Materials) was spin-coated on the top of the 5
54
parylene film using EVG150 coater and developer system for positive resist (EV Group). Soft 56 57 58 59 60 ACS Paragon Plus Environment
17
ACS Nano
Page 18 of 40
1 3
2
baking of the substrate was then carried out on a hot plate at 115 ºC for 4 min, followed by 8 min 5
4
relaxation at 25 ºC. Then, a chrome coated glass mask was used to transfer the patterns of the 7
6
microcavities into the photoresist. The mask consists of square features (1×1 mm2) with the pitch 10
9
8
size of 2 mm. UV-Lithography was performed with a Karl Suss MA6 double side mask aligner 12
1
(Karl Suss Inc.) in the hard contact mode between the wafer and the mask with a 10 mW/cm2 13 14
mercury light source, and 17s exposure time, corresponding to a dose of approximately 170 17
16
15
mJ/cm2. Then the exposed areas were removed with a solvent (AZ 400K:DI 1:4) during the 19
18
development process. Using the photoresist as a mask, parylene was then successfully etched 20 2
21
with Surface Technology Systems (STS) Multiplex ICP (RF power 800 W, platen power 150 W, 24
23
O2 flow 20 sccm, pressure 95 mTorr, time 2 min), Figure 4c. Any remaining photoresist was 25 26
striped by bathing the wafer in Shipley 1165 for 10 min followed by fine rinsing with de-ionized 27 29
28
(DI) water and drying with N2 gas. The SEM image of the parylene wall of the microcavity is 31
30
shown in Figure 5a. To fabricate the inlet and outlet holes inside the cavity, the wafer was spin32 3
coated with 8 m thick layer of AZ9260 photoresist after batch priming of the substrate in YES 36
35
34
III, HMDS primer oven for 10s at 125 ºC and a dehydration bake step for 4 min at 160 ºC. After 37 38
soft baking the photoresist layer at 115 ºC for 4 min and 20 min relaxation at 25 ºC, another 39 41
40
chrome coated glass mask with array of holes (200 m in diameter) was used to transfer the 43
42
patterns precisely inside the previously fabricated cavities. The exposure was performed for 24s, 4 45
corresponding to a dose of approximately 240 mJ/cm2, after precise alignment of the second 48
47
46
mask with the previous microcavity patterns in the parylene layer. These exposures have been 50
49
tuned according to the substrate material and the layers reflectivity in order to elude immoderate 51 53
52
stress, failure in the adhesion, or undesired pattern dimensional changes. Similar to the previous 5
54
step, the exposed areas were removed with a solvent (AZ 400K:DI 1:4) during the development 56 57 58 59 60 ACS Paragon Plus Environment
18
Page 19 of 40
ACS Nano
1 3
2
step by developer. Using the patterned AZ9260 photoresist as a mask, the 200 nm SiO2, 200 nm 5
4
gold, and 500 nm SiO2 layers were then etched by Argon ions using Nexus IBE350, broad-beam 6 7
ion etcher, Figure 4d. The etch rates for SiO2 and gold were found to be 88 nm/min and 100 10
9
8
nm/min, respectively, for low ion damage with energy range of about 50 V. Then deep reactive 12
1
ion etching (DRIE) of Si was performed, using the same AZ9260 photoresist mask, on Adixen 13 14
AMS200 etcher with SF6 plasma for 1 hour with a vertical etch rate of 5 m/min to etch 300 m 17
16
15
of Si wafer inside the holes, Figure 4e. The wafer was then thinned down from the backside 18 19
using a DAG810 automatic surface grinder, until the paths to the holes were opened, Figure 4f. 2
21
20
At last, any remaining photoresist was striped by bathing the wafer in Shipley 1165 for 10 min 24
23
followed by rinsing with DI water and drying with N2 gas. The SEM image of the microcavity 25 26
with the two holes inside, and the magnified image of the microhole are shown in Figures 5b and 29
28
27
5c. 31
30
On the other hand, 100 nm ITO was deposited using e-beam evaporation (Leybold Optics LAB 32 34
3
600H) on a glass wafer (540 m thickness), Figure 4g. Then, the two-dimensional gold 36
35
nanodisks array was fabricated on the ITO-coated glass wafer using electron-beam lithography, 37 38
gold evaporation and subsequent lift-off, as shown in Figures 4h and 4i. The SEM image of the 41
40
39
nanodisks array is shown in Figure 5d. 42 43 4 45 46 47 48 49 50 51 52 53 54 5 56 57 58 59 60 ACS Paragon Plus Environment
19
ACS Nano
Page 20 of 40
1 2 3 4 5 6 7 8 9 10 1 12 13 14 15 16 18
17
Figure 5. SEM images of the fabricated sample: (a) parylene-edge of the cavity after plasma 19 20
etching; (b) cavity part of the structure with two holes as inlet and outlet; (c) microhole channel 21 23
2
for injecting analyte inside the cavity; and (d) two-dimensional array of gold nanodisks on ITO25
24
coated glass substrate. 26 27 28
In order to bond these two wafers together to form the cavity-coupled plasmonic structure, the 29 31
30
wafers were diced in 1.5×2 cm2 rectangles and were then treated with O2 plasma at 150 W during 3
32
10s for surface activation using a Tepla 300 plasma stripper under 400 ml/min O2 flow. Next, 34 35
wafers were bond at 100 ºC during 4 hours with a pressure of 3000 mbar using Thermal 38
37
36
Nanoimprinter EHN-3250, Figure 4j. 40
39
Figure 6 shows a photograph of the fabricated sample before the bonding process. For each 41 42
chip, there are 60 microcavities with 1×1 mm2 dimensions and two 200 m circular holes in each 45
4
43
microcavity as inlet and outlet. This wafer-scale fabrication technology yields a total number of 46 47
540 individual devices on a 4ʺ wafer; each device can be used separately for different sensing 50
49
48
applications. 51 52 53 54 5 56 57 58 59 60 ACS Paragon Plus Environment
20
Page 21 of 40
ACS Nano
1 2 3 4 5 6 7 8 9 10 1 12 13 14 15 17
16
Figure 6. Photograph of the fabricated superchip containing 60 microcavities. 18 19 20
The specific fabrication steps can be replaced by more low-cost fabrication techniques, such as 21 23
2
nanoimprint lithography for the fabrication of nanostructure or injection-molding for realizing 25
24
the microcavity to reduce the fabrication costs.80, 81 26 27
Ultra-high sensitive cavity-coupled plasmonic biochemical sensor. In this section, the 30
29
28
performance of the proposed cavity-coupled plasmonic device as a biochemical sensor is 32
31
evaluated. Since the reflection peak and dips, Figure 2c, of the cavity-coupled plasmonic 3 35
34
structure are spectrally much narrower than the LSPR mode of the bare nanodisks array, they are 37
36
employed to probe bulk refractive index changes with a very high resolution. The interaction of 39
38
the analyte with the compound modes of the device changes the effective index of the modes and 40 42
41
thus the resonance wavelengths of the structure and the detection can be made by monitoring the 4
43
shift in the reflection peak/dips wavelengths. 45 46
In the realized device, the microcavity can be filled via standard microfluidic pumps or via 47 49
48
mere capillary forces. For the current study, we use the latter technique for filling the cavity. 51
50
Putting a drop of analyte on top of one hole results in a self-filling procedure via capillary forces 52 53
only, which ensures a bubble-free filling for the microcavity. The filling process is demonstrated 56
5
54
in Figure 7 to illustrate the temporal development of the filling. In particular, this figure shows 57 58 59 60 ACS Paragon Plus Environment
21
ACS Nano
Page 22 of 40
1 3
2
the snapshots of the cavity as visualized under a microscope at two different time points (10s and 5
4
60s) after the addition of the drop. No additional external pressure was introduced to the inlet. 6 7
For the case of 10s, the liquid/air interface is clearly visible (indicated by the dashed blue line). 10
9
8
Driven by capillary forces, the solution automatically flows from the inlet into the microcavity 12
1
and within 60s the whole cavity is filled with the sensing solution without trapping any visible 13 14
air bubbles. Filling via capillary forces is handy for simple and rapid tests of analytes and does 17
16
15
not require any extraneous microfluidic equipment. However, since the proposed device is 19
18
microfluidic compatible, it can always be coupled either to needles or pumps and valves to 20 2
21
develop more sophisticated assays. Note that microfluidics also enables real-time handling of 24
23
analytes. 25 26 27 28 29 30 31 32 3 34 35 36 37 38 39 40 41 42 43 45
4
Figure 7. Microscopic images of the cavity filling with D-Glucose solution after (a) 10 and (b) 46 47
60 seconds. The blue dashed line shows the liquid/air interface which flows from the inlet into 50
49
48
the microcavity. The green dashed line in the middle of the structure indicates the gold nanodisks 52
51
array. 53 54 5 56 57 58 59 60 ACS Paragon Plus Environment
22
Page 23 of 40
ACS Nano
1 3
2
Let us now perform bulk biochemical sensing experiments to demonstrate the sensing 5
4
capability of the device. Deionized (DI) water is injected through the inlet and the reflection 6 7
spectrum is measured. Subsequently, D-Glucose (C6H12O6) solutions with different 10
9
8
concentrations are injected through the inlet, and the shifts of the modes are measured with 12
1
respect to the wavelengths of the modes for DI water. After each sensing step, the cavity is 13 14
completely washed with DI water and Isopropanol followed by drying with N2 gas to make sure 17
16
15
that no residue of glucose is left inside the cavity or on the nanostructures, and that the sensor 19
18
response is back to that of the DI water. The experimentally measured reflection spectra as a 20 2
21
function of the wavelength and concentration and corresponding refractive index of the D24
23
Glucose solution are shown in Figure 8a. For comparison, we also perform bulk biochemical 25 26
sensing simulations. It is assumed that the cavity is filled with D-Glucose solutions in DI water 27 29
28
with mass concentrations of 0–22%. A sensing analysis is then simulated as a uniform medium 31
30
whose refractive index is changed from its original refractive index 1.33 up to 1.37 32 3
(n=4×10−2).82 The simulated reflection spectra as a function of the wavelength and 36
35
34
concentration and corresponding refractive index of the D-Glucose solution are illustrated in 37 38
Figure 8b. As can be seen, the simulation results agree well with the experimental data. Based on 39 41
40
the measurement results, the resonance wavelengths of the compound modes redshift almost 43
42
linearly from 912 nm to 932.3 nm for the first mode, from 797.4 nm to 819.3 nm for the second 4 45
mode, and from 707.4 nm to 724.9 nm for the third mode when the D-Glucose solution 48
47
46
concentration varies from 0 to 22 % with a corresponding variation of its refractive index from 50
49
1.33 to 1.37. 51 52
The experimentally derived detection sensitivities, defined as the derivative of the peak 5
54
53
wavelength versus the refractive index of the analyte, are 507.5 nm/RIU, 547.5 nm/RIU and 56 57 58 59 60 ACS Paragon Plus Environment
23
ACS Nano
Page 24 of 40
1 3
2
437.5 nm/RIU for the first, second and third mode, respectively. By utilizing a commercial high5
4
performance optical spectrum analyzer (Agilent 86146B) with 10 pm wavelength resolution, the 7
6
minimum detection limit for bulk sensing is as low as 1.970× 10−5 RIU, 1.826× 10−5 RIU and 10
9
8
2.285 × 10−5 RIU for the first, second and third modes, respectively. The sensitivity of the first 12
1
mode is higher than the sensitivity of the third mode which is related to the spectral position of 13 14
the resonance. Indeed, when the resonance wavelength is shifted to the red, a higher sensitivity 17
16
15
can be achieved upon index changes. This is so because a larger fraction of the spatial region 19
18
with enhanced electric fields is exposed to the material under sensing.83 On the other hand, the 20 2
21
sensitivity of the second mode is higher than those of the first and the third modes, since this 24
23
resonance is caused by the constructive interference, i.e. the Fabry-Perot mode coincides with the 25 26
LSPR mode of the nanodisks array and we can benefit from both the characteristics of Fabry27 29
28
Perot mode of the cavity and the LSPR mode of the nanostructures. However, this is a bit 31
30
counterintuitive since, at the wavelength where we obtain constructive interference (second 32 3
mode), the net field enhancement is lower as compared to the two other modes, Figure 3. 36
35
34
Therefore, we would naturally expect the first and the third modes to exhibit a higher sensitivity, 38
37
which is clearly not the case. A possible origin of this anomalous higher sensitivity of the second 39 41
40
mode as compared to the other two modes could be related to the actual field distributions 43
42
supported by the structure. Specifically, in case of the second mode, the majority of the fields 45
4
associated with the nanodisks are contained into the cavity, with the sensing medium. Whereas, 46 48
47
in the cases of the first and the third modes, the reverse holds true, i.e. the fields are mainly 50
49
contained in the ITO and the substrate. Hence, higher sensitivity can be achieved for the second 51 52
mode compared with the two other modes in which the Fabry-Perot resonances are dominant. 53 54 5 56 57 58 59 60 ACS Paragon Plus Environment
24
Page 25 of 40
ACS Nano
1 3
2
The experimentally measured FWHM of the resonant modes are 23.4 nm, 9.3 nm and 19.8 nm 5
4
for the first, second and third mode, respectively, Figure 8a. Hence, our system shows a 6 7
remarkably high FoM, with values of 21.68, 58.87, and 22.09 for the first, second and third 10
9
8
modes, respectively. The high FoM of 58.87 of the realized device greatly exceeds those of the 12
1
plasmonic sensors in the case of a semi-infinite substrate, where typical FoM values are 0.6-17 13 14
for LSPR sensors without the occurrence of Fano resonance, and 2.9-21 for LSPR sensors with 17
16
15
Fano resonance. Moreover, it is much higher than those of the SPP sensors without the 19
18
occurrence of Fano resonance, in which the typical FoM values are as high as 31. However, it is 20 2
21
almost lower than those of SPP sensors with Fano resonance, in which the typical FoM values 24
23
are 48-252. A detailed summary of the resonance wavelengths, FWHMs, refractive index 25 26
sensitivities and FoM values of different plasmonic metal nanostructures along with the 27 29
28
references are provided in Tables S1 of the Supporting Information. As expected, the smallest 31
30
linewidth – corresponding to the largest FoM – is achieved in the constructive interference 32 3
region. Hence, this cavity-coupled plasmonic device is especially well suited for boosting the 36
35
34
sensing performances of localized plasmonic systems. 38
37
For quantitative comparison and to demonstrate the improved sensitivity with the proposed 39 41
40
cavity-coupled plasmonic structure, the experimental and simulated reflection spectra for a bare 43
42
two-dimensional array of gold nanodisks without the underlying cavity are shown in Figures 8c 45
4
and 8d as a function of wavelength and D-Glucose concentration, as well as the corresponding 46 48
47
refractive index. We can see a good agreement between the simulation results and the 50
49
experimental data. The LSPR peak wavelength redshifts almost linearly from 801 nm to 809 nm, 51 52
when the D-Glucose solution concentration varies from 0 to 22.0 %, corresponding to a variation 53 5
54
of its refractive index from 1.33 to 1.37. Based on the measurement results, the experimental 56 57 58 59 60 ACS Paragon Plus Environment
25
ACS Nano
Page 26 of 40
1 3
2
detection sensitivity is calculated to be 200 nm/RIU which is almost 2.7 times lower than that for 5
4
the second mode of the cavity-coupled plasmonic structure. Moreover, the FWHM of the 6 7
reflection peak is 498 nm, which is much larger than those for the cavity-coupled plasmonic 10
9
8
structure. Hence, the FoM of the bare two-dimensional nanodisks array structure is calculated to 12
1
be 0.4 which is almost 147 times lower than that of the cavity-coupled plasmonic sensor. 13 14 15 16 17 18 19 20 21 2 23 24 25 26 27 28 29 30 31 32 3 34 35 36 37 38 39 40 41 42 43 4 45 46 47 48 49 51
50
Figure 8. Colormap of the reflection spectra as a function of the wavelength and D-Glucose 52 54
53
solution refractive index; the corresponding solution concentration is also indicated. (a) 56
5
Measurements and (b) numerical simulation results for the cavity-coupled plasmonic structure. 57 58 59 60 ACS Paragon Plus Environment
26
Page 27 of 40
ACS Nano
1 3
2
(c) Measurements and (d) numerical simulation results for a bare two-dimensional gold 5
4
nanodisks array. 6 8
7
In Figure 9, we summarize the measurement results for the reflection peak/dips wavelengths of 9 1
10
the proposed cavity-coupled plasmonic device as a function of the concentration and the 13
12
corresponding D-Glucose solution refractive index; these data are also compared with those of 14 15
the bare nanodisks array. Linear relationships can be seen between the resonance wavelengths 16 18
17
and the D-Glucose solution concentration. Moreover, larger shifts are achieved for the compound 20
19
modes of the cavity-coupled plasmonic device and the highest sensitivity corresponds to the 21 2
second mode, which represents the constructive interference region where the LSPR mode 25
24
23
coincides with the Fabry-Perot mode of the cavity. 26 27 28 29 30 31 32 3 34 35 36 37 38 39 40 41 42 43 4 45 46 47 48
Figure 9. Experimental results for the shift in the resonance wavelengths as a function of the D49 51
50
Glucose solution refractive index for the cavity-coupled plasmonic structure and a bare two53
52
dimensional nanodisks array. 54 5 56 57 58 59 60 ACS Paragon Plus Environment
27
ACS Nano
Page 28 of 40
1 3
2
The cavity-coupled plasmonic structure has a higher refractive index sensitivity than the 5
4
conventional Fabry-Perot cavity. Figure S3 shows the resonance wavelength shift for the first, 6 8
7
second and third modes of the conventional Fabry-Perot cavity as a function of D-Glucose 10
9
concentration and corresponding refractive index. The shifts are 19.4 nm, 17 nm, and 15 nm for 1 12
the conventional Fabry-Perot cavity, while they are 20.3 nm, 21.9 nm, and 17.5 nm for the 13 15
14
cavity-coupled structure, leading to a significant sensitivity improvement, up to almost 30%, for 17
16
the cavity-coupled structure. 19
18
Moreover, we have mentioned that an interesting feature of the proposed structure is that the 20 2
21
analyte is in the substrate region in direct contact with the plasmonic nanostructures, as opposed 24
23
to other cavity-coupled plasmonic systems, where the sensing medium is outside the cavity.64 25 26
Here, we compare these two configurations and focus on the constructive interference region in 27 29
28
which near unity reflection and highest sensitivity can be achieved. Figure 10 shows the 31
30
simulated resonant peak wavelength shifts as a function of the D-Glucose solution refractive 32 3
index for both geometries. In the case of the nanodisks outside the cavity, it is assumed that the 36
35
34
cavity is filled with SiO2. Since the Fabry-Perot mode redshifts in the presence of a SiO2, the size 38
37
of the nanodisks must be adjusted to 250 nm in order to have constructive interference. For this 39 41
40
configuration, the shift of the resonance wavelength for a 22% D-Glucose concentration is only 43
42
about 1.5 nm, blue solid line in Figure 10, while for the previously discussed configuration with 45
4
the analyte inside the cavity, the shift is about 21 nm which is about 14 times larger, red dashed 46 48
47
line in Figure 10. This small shift of 1.5 nm in the resonance wavelength of the cavity-coupled 50
49
plasmonic structure with the sensing medium outside the cavity, even in compare to the bare 51 52
two-dimensional array of gold nanodisks array is also observed in previous researches on cavity53 5
54
coupled plasmonic structures.64 56 57 58 59 60 ACS Paragon Plus Environment
28
Page 29 of 40
ACS Nano
1 2 3 4 5 6 7 8 9 10 1 12 13 14 15 16 17 18 19 20 21 23
2
Figure 10. Resonance wavelength shifts as a function of D-Glucose refractive index for the 25
24
porposed cavity-coupled plasmonic structure with the sensing medium (white area) inside the 26 27
cavity (red dashed line) and for the cavity-coupled plasmonic structure with the sensing medium 28 30
29
outside the cavity (blue solid line). 31 3
32
CONCLUSIONS In summary, we have introduced a novel approach to realize an ultra-high 34 35
sensitive cavity-coupled plasmonic device, using full-wafer level processing, which combines 36 38
37
the advantages of Fabry–Perot microcavities with those of plasmonic nanostructures to boost the 40
39
sensitivity and figure-of-merit. Detailed characteristics of the device are studied by FDTD 41 42
numerical simulations to demonstrate the feasibility of this concept. The role played by the 45
4
43
compound resonances arising from the constructive and destructive interference has been 47
46
discussed in detail. The experimental results demonstrate that the resonant compound mode of 48 49
the device has a sensitivity of 547.5 nm/RIU, a resolution of 1.826× 10−5 RIU, a FWHM of 9.3 52
51
50
nm, and a FoM of 58.87 at an optical wavelength of around 800 nm. The special feature of the 54
53
proposed device is that the sample to be measured is localized in the substrate region and is 5 57
56
probed by the compound modes. Another distinct advantage is the convenient self-filling of the 58 59 60 ACS Paragon Plus Environment
29
ACS Nano
Page 30 of 40
1 3
2
microcavity employing only capillary forces, without needing any additional microfluidic 5
4
structures. Furthermore, the proposed cavity-coupled plasmonic device technology is particularly 6 7
promising for biomedical and biochemical applications. This combination sets ground for 10
9
8
developing hybrid sensors that can be fully integrated into lab-on-chip solutions. 12
1
METHODS 13 14
Reflection measurement. The normal incidence reflection measurements were performed 17
16
15
using an inverted optical microscope (Olympus IX-71) coupled to a spectrometer (Jobin Yvon 19
18
Horiba Triax 550). The sample was illuminated using a halogen light source focused onto the 20 2
21
sample using a 10x objective (NA 0.25). The reflected light was collected using the same 24
23
objective and analyzed using a spectrometer. The reflected intensity was normalized to the 25 26
reflection from a silver mirror. 27 29
28
Conflict of Interest: The authors declare no competing financial interest. 30 32
31
ACKNOWLEDGMENT It is a pleasure to acknowledge Dr. C. Santschi and Dr. C. Hibert for 34
3
their support with the fabrication of the cavity-coupled plasmonic devices. This work was 35 37
36
supported by the Swiss National Science Foundation (project CR23I2_147279). 38 40
39
Supporting Information Available: A detailed description of the numerical method; additional 42
41
figures explaining the reflection spectrum and the sensitivity of a conventional Fabry-Perot 43 45
4
cavity; summary of the resonance wavelengths, FWHMs, refractive index sensitivities and FoM 47
46
values of plasmonic metal nanostructures for different types of resonances along with all the 48 49
references. This material is available free of charge via the Internet at http://pubs.acs.org. 50 51 53
52
Corresponding Author 5
54
Mohsen Bahramipanah (
[email protected]) 56 57 58 59 60 ACS Paragon Plus Environment
30
Page 31 of 40
ACS Nano
1 3
2
Present Addresses 5
4
Nanophotonics and Metrology Laboratory (NAM), Swiss Federal Institute of Technology 6 8
7
Lausanne (EPFL), 1015 Lausanne, Switzerland. 9 10 1 12 13
REFERENCES 14 16
15
1. 18
17
Kang, C.; Weiss, S. M. Photonic Crystal with Multiple-Hole Defect for Sensor
Applications. Opt. Express 2008, 16, 18188-18193. 19 21
20
2. 23
2
Vincenti, M. A.; Trevisi, S.; De Sario, M.; Petruzzelli, V.; D’Orazio, A.; Prudenzano, F.;
Cioffi, N.; de Ceglia, D.; Scalora, M. Theoretical Analysis of a Palladium-Based One25
24
Dimensional Metallo-Dielectric Photonic Band Gap Structure for Applications to H2 Sensors. J. 26 28
27
Appl. Phys. 2008, 103, 064507. 30
29
3. 31
Lahiri, B.; Khokhar, A. Z.; De La Rue, R. M.; McMeekin, S. G.; Johnson, N. P.
32
Asymmetric Split Ring Resonators for Optical Sensing of Organic Materials. Opt. Express 2009, 3 35
34
17, 1107-1115. 37
36
4. 38
Claes, T.; Molera, J. G.; De Vos, K.; Schachtb, E.; Baets, R.; Bienstman, P. Label-Free
39
Biosensing With a Slot-Waveguide-Based Ring Resonator in Silicon on Insulator. IEEE 42
41
40
Photonics J. 2009, 1, 197-204. 4
43
5. 45
Schartner, E. P.; Ebendorff-Heidepriem, H.; Warren-Smith, S. C.; White, R. T.; Monro,
47
46
T. M. Driving Down the Detection Limit in Microstructured Fiber-Based Chemical Dip Sensors. 49
48
Sensors 2011, 11, 2961-2971. 51
50
6. 52
Suárez, G.; Santschi, C.; Plateel, G.; Martin, O. J. F.; Riediker, M. Absorbance
54
53
Enhancement in Microplate Wells for Improved-Sensitivity Biosensors. Biosens. Bioelectron. 56
5
2014, 56, 198-203. 57 58 59 60 ACS Paragon Plus Environment
31
ACS Nano
Page 32 of 40
1 3
2
7. 5
4
Jalkanen, T.; Torres-Costa, V.; Makila, E.; Kaasalainen, M.; Koda, R.; Sakka, T.; Ogata,
Y. H.; Salonen, J. Selective Optical Response of Hydrolytically Stable Stratified Si Rugate 6 7
Mirrors to Liquid Infiltration. ACS Appl. Mater. Interfaces 2014, 6, 2884-2892. 10
9
8
8. 12
1
Kangwen, L.; Xunpeng, M.; Zuyin, Z.; Jiakun, S.; Yun, X.; Guofeng, S. Sensitive
Refractive Index Sensing with Tunable Sensing Range and Good Operation Angle-Polarization13 14
Tolerance using Graphene Concentric Ring Arrays. J. Phys. D: Appl. Phys. 2014, 47, 405101. 17
16
15
9. 19
18
Bonnot, K.; Cuesta-Soto, F.; Rodrigo, M.; Varriale, A.; Sanchez, N.; D’Auria, S.; Spitzer,
D.; Lopez-Royo, F. Biophotonic Ring Resonator for Ultrasensitive Detection of DMMP As a 20 2
21
Simulant for Organophosphorus Agents. Anal. Chem. 2014, 86, 5125-5130. 24
23
10. 25
Baker, J. E.; Sriram, R.; Miller, B. L. Two-Dimensional Photonic Crystals for Sensitive
26
Microscale Chemical and Biochemical Sensing. Lab Chip 2015, 15, 971-990. 27 29
28
11. 31
30
Agranovich, V. M.; Mills, D. L. Surface Polaritons. North Holland Publishing Company:
Amsterdam, 1982. 32 3
12. 36
35
34
Slavik, R.; Homola, J.; Vaisocherova, H. Advanced Biosensing using Simultaneous
Excitation of Short and Long Range Surface Plasmons. Meas. Sci. Technol. 2006, 17, 932-938. 39
38
37
13.
Homola, J. Surface Plasmon Resonance based Sensors. Springer: 2006.
43
42
41
14.
Homola, J. Surface Plasmon Resonance Sensors for Detection of Chemical and
40
Biological Species. Chem. Rev. 2008, 108, 462-493. 45
4
15. 46
Dutta-Gupta, S.; Martin, O. J. F. Strongly Coupled Bio-Plasmonic System: Application to
48
47
Oxygen Sensing. J. Appl. Phys. 2011, 110, 044701. 50
49
16. 51
Kvasnika, P.; Chadt, K.; Vala, M.; Bockova, M.; Homola, J. Toward Single-Molecule
52
Detection with Sensors Based on Propagating Surface Plasmons. Opt. Lett. 2012, 37, 163-165. 53 54 5 56 57 58 59 60 ACS Paragon Plus Environment
32
Page 33 of 40
ACS Nano
1 3
2
17. 5
4
Sipova, H.; Vrba, D.; Homola, J. Analytical Value of Detecting an Individual Molecular
Binding Event: The Case of the Surface Plasmon Resonance Biosensor. Anal. Chem. 2012, 84, 6 7
30-33. 10
9
8
18. 12
1
Unger, A.; Kreiter, M. Analyzing the Performance of Plasmonic Resonators for
Dielectric Sensing. J. Phys. Chem. C 2009, 113, 12243-12251. 13 14
19. 17
16
15
Hao, F.; Sonnefraud, Y.; Dorpe, P. V.; Maier, S. A.; Halas, N. J.; Nordlander, P.
Symmetry Breaking in Plasmonic Nanocavities: Subradiant LSPR Sensing and a Tunable Fano 19
18
Resonance. Nano Lett. 2008, 8, 3983-3988. 20 2
21
20. 24
23
Sonnefraud, Y.; Verellen, N.; Sobhani, H.; Vandenbosch, G. A. E.; Moshchalkov, V. V.;
Van Dorpe, P.; Nordlander, P.; Maier, S. A. Experimental Realization of Subradiant, 25 26
Superradiant, and Fano Resonances in Ring/Disk Plasmonic Nanocavities. ACS Nano 2010, 4, 7. 27 29
28
21. 31
30
Baciu, C. L.; Becker, J.; Janshoff, A.; Sonnichsen, C. Protein-Membrane Interaction
Probed by Single Plasmonic Nanoparticles. Nano Lett. 2008, 8, 1724-1728. 32 3
22. 36
35
34
Stewart, M. E.; Anderton, C. R.; Thompson, L. B.; Maria, J.; Gray, S. K.; Rogers, J. A.;
Nuzzo, R. G. Nanostructured Plasmonic Sensors. Chem. Rev. 2008, 108, 494-521. 38
37
23. 39
Zhang, J.; Atay, T.; Nurmikko, A. V. Optical Detection of Brain Cell Activity Using
41
40
Plasmonic Gold Nanoparticles. Nano Lett. 2009, 9, 519-524. 43
42
24. 45
4
Unger, A.; Rietzler, U.; Berger, R.; Kreiter, M. Sensitivity of Crescent-Shaped Metal
Nanoparticles to Attachment of Dielectric Colloids. Nano Lett. 2009, 9, 2311-2315. 46 48
47
25. 50
49
Chen, J. I. L.; Chen, Y.; Ginger, D. S. Plasmonic Nanoparticle Dimers for Optical
Sensing of DNA in Complex Media. J. Am. Chem. Soc. 2010, 132, 9600-9601. 51 52 53 54 5 56 57 58 59 60 ACS Paragon Plus Environment
33
ACS Nano
Page 34 of 40
1 3
2
26. 5
4
Kuznetsov, A. I.; Evlyukhin, A. B.; Goncalves, M. R.; Reinhardt, C.; Koroleva, A.;
Arnedillo, M. L.; Kiyan, R.; Marti, O.; Chichkov, B. N. Laser Fabrication of Large-Scale 6 7
Nanoparticle Arrays for Sensing Applications. ACS Nano 2011, 5, 4843-4849. 10
9
8
27. 12
1
Lassiter, J. B.; Sobhani, H.; Fan, J. A.; Kundu, J.; Capasso, F.; Nordlander, P.; Halas, N.
J. Fano Resonances in Plasmonic Nanoclusters: Geometrical and Chemical Tunability. Nano 13 14
Lett. 2010, 10, 3184-3189. 17
16
15
28. 19
18
Kubo, W.; Fujikawa, S. Au Double Nanopillars with Nanogap for Plasmonic Sensor.
Nano Lett. 2011, 11, 8-15. 20 2
21
29. 24
23
Zhang, W.; Huang, L.; Santschi, C.; Martin, O. J. F. Trapping and Sensing 10 nm Metal
Nanoparticles Using Plasmonic Dipole Antennas. Nano Lett. 2010, 10, 1006-1011. 25 26
30. 27
Nusz, G. J.; Curry, A. C.; Marinakos, S. M.; Wax, A.; Chilkoti, A. Rational Selection of
29
28
Gold Nanorod Geometry for Label-Free Plasmonic Biosensors. ACS Nano 2009, 3, 795-806. 31
30
31. 32
Bahramipanah, M.; Abrishamian, M. S.; Mirtaheri, S. A.; Liu, J. M. Ultracompact
3
Plasmonic Loop–Stub Notch Filter and Sensor. Sens. Actuators, B 2014, 194, 311-318. 36
35
34
32. 38
37
Zhang, W.; Martin, O. J. F. A Universal Law for Plasmon Resonance Shift in Biosensing.
ACS Photonics 2015, 2, 144-150. 39 41
40
33. 43
42
Mayer, K. M.; Hafner, J. H. Localized Surface Plasmon Resonance Sensors. Chem. Rev.
2011, 111, 3828-3857. 45
4
34. 46
Anker, J. N.; Hall, W. P.; Lyandres, O.; Shah, N. C.; Zhao, J.; Van Duyne, R. P.
48
47
Biosensing with Plasmonic Nanosensors. Nat. Mater. 2008, 7, 442-453. 51
50
49
35.
Brolo, A. G. Plasmonics for Future Biosensors. Nat. Photonics 2012, 6, 709-713.
53
36.
Wang, H.; Brandl, D. W.; Le, F.; Nordlander, P.; Halas, N. J. Nanorice: A Hybrid
52
5
54
Plasmonic Nanostructure. Nano Lett. 2006, 6, 827-832. 56 57 58 59 60 ACS Paragon Plus Environment
34
Page 35 of 40
ACS Nano
1 3
2
37. 5
4
Nehl, C. L.; Liao, H.; Hafner, J. H. Optical Properties of Star-Shaped Gold Nanoparticles.
Nano Lett. 2006, 6, 683-688. 6 7
38. 10
9
8
Chen, H. J.; Kou, X. S.; Yang, Z.; Ni, W. H.; Wang, J. F. Shape- and Size-Dependent
Refractive Index Sensitivity of Gold Nanoparticles. Langmuir 2008, 24, 5233-5237. 12
1
39. 13
Cao, J.; Sun, T.; Grattan, K. T. V. Gold Nanorod-Based Localized Surface Plasmon
14
Resonance Biosensors: A review. Sens. Actuators, B 2014, 195, 332-351. 17
16
15
40. 19
18
Estevez, M. C.; Otte, M. A.; Sepulveda, B.; Lechuga, L. M. Trends and Challenges of
Refractometric Nanoplasmonic Biosensors: A review. Anal. Chim. Acta 2014, 806, 55-73. 20 2
21
41. 24
23
Prasad, J.; Zins, I.; Branscheid, R.; Becker, J.; Koch, A. H. R.; Fytas, G.; Kolb, U.;
Sonnichsen, C. Plasmonic Core–Satellite Assemblies as Highly Sensitive Refractive Index 25 26
Sensors. J. Phys. Chem. C 2015, 119, 5577–5582. 27 29
28
42. 31
30
Soler, M.; Mesa-Antunez, P.; Estevez, M. C.; Ruiz-Sanchez, A. J.; Otte, M. A.;
Sepulveda, B.; Collado, D.; Mayorga, C.; Torres, M. J.; Perez-Inestrosa, E.; et al. Highly 32 3
Sensitive Dendrimer-Based Nanoplasmonic Biosensor for Drug Allergy Diagnosis. Biosens. 36
35
34
Bioelectron. 2015, 66, 115-123. 38
37
43. 39
Lee, K.-S.; El-Sayed, M. A. Gold and Silver Nanoparticles in Sensing and Imaging:
41
40
Sensitivity of Plasmon Response to Size, Shape, and Metal Composition. J. Phys. Chem. B 2006, 43
42
110, 19220-19225. 45
4
44. 46
Willets, K. A.; Van Duyne, R. P. Localized Surface Plasmon Resonance Spectroscopy
48
47
and Sensing. Annu. Rev. Phys. Chem. 2007, 58, 267-297. 50
49
45. 51
Abasahl, B.; Dutta-Gupta, S.; Santschi, C.; Martin, O. J. F. Coupling Strength Can
52
Control the Polarization Twist of a Plasmonic Antenna. Nano Lett. 2013, 13, 4575-4579. 53 54 5 56 57 58 59 60 ACS Paragon Plus Environment
35
ACS Nano
Page 36 of 40
1 3
2
46. 5
4
Prodan, E.; Radloff, C.; Halas, N. J.; Nordlander, P. A Hybridization Model for the
Plasmon Response of Complex Nanostructures. Science 2003, 302, 419-422. 6 7
47. 10
9
8
Aubry, A.; Lei, D. Y.; Maier, S. A.; Pendry, J. B. Interaction between Plasmonic
Nanoparticles Revisited with Transformation Optics. Phys. Rev. Lett. 2010, 105, 233901. 12
1
48. 13
Rahmani, M.; Lei, D. Y.; Giannini, V.; Lukiyanchuk, B.; Ranjbar, M.; Liew, T. Y. F.;
14
Hong, M.; Maier, S. A. Subgroup Decomposition of Plasmonic Resonances in Hybrid 17
16
15
Oligomers: Modeling the Resonance Lineshape. Nano Lett. 2012, 12, 2101-2106. 19
18
49. 20
Bolduc, O. R.; Live, L. S.; Masson, J. F. High-Resolution Surface Plasmon Resonance
2
21
Sensors based on a Dove Prism. Talanta 2009, 77, 1680-1687. 24
23
50. 25
Lee, D. E.; Lee, T.-W.; Kwon, S.-H. Spatial Mapping of Refractive Index based on a
26
Plasmonic Tapered Channel Waveguide. Opt. Express 2015, 23, 5907-5914. 27 29
28
51. 31
30
Christ, A.; Ekinci, Y.; Solak, H. H.; Gippius, N. A.; Tikhodeev, S. G.; Martin, O. J. F.
Controlling the Fano Interference in a Plasmonic Lattice. Phys. Rev. B 2007, 76, 201405. 32 3
52. 36
35
34
Liu, N.; Langguth, L.; Weiss, T.; Kastel, J.; Fleischhauer, M.; Pfau, T.; Giessen, H.
Plasmonic Analogue of Electromagnetically Induced Transparency at the Drude Damping Limit. 38
37
Nat. Mater. 2009, 8, 758-762. 39 41
40
53. 43
42
Gallinet, B.; Martin, O. J. F. Influence of Electromagnetic Interactions on the Line Shape
of Plasmonic Fano Resonances. ACS Nano 2011, 5, 8999-9008. 45
4
54. 46
Gallinet, B.; Martin, O. J. F. Relation between Nearfield and Farfield Properties of
48
47
Plasmonic Fano Resonances. Opt. Express 2011, 19, 22167-22175. 50
49
55. 51
Gallinet, B.; Martin, O. J. F. Ab Initio Theory of Fano Resonances in Plasmonic
52
Nanostructures and Metamaterials. Phys. Rev. B 2011, 83, 235427. 53 54 5 56 57 58 59 60 ACS Paragon Plus Environment
36
Page 37 of 40
ACS Nano
1 3
2
56. 5
4
Gallinet, B.; Martin, O. J. F. Refractive Index Sensing with Subradiant Modes: A
Framework To Reduce Losses in Plasmonic Nanostructures. ACS Nano 2013, 7, 6978-6987. 6 7
57. 10
9
8
Lovera, A.; Gallinet, B.; Nordlander, P.; Martin, O. J. F. Mechanisms of Fano
Resonances in Coupled Plasmonic Systems. ACS Nano 2013, 7, 4527-4536. 12
1
58. 13
Yan, C.; Martin, O. J. F. Periodicity-Induced Symmetry Breaking in a Fano Lattice:
14
Hybridization and Tight-Binding Regimes. ACS Nano 2014, 8, 11860-11868. 17
16
15
59. 19
18
Leveque, G.; Martin, O. J. F. Tunable Composite Nanoparticle for Plasmonics. Opt. Lett.
2006, 31, 2750-2752. 20 2
21
60. 24
23
Farhang, A.; Ramakrishna, S. A.; Martin, O. J. F. Compound Resonance-Induced
Coupling Effects in Composite Plasmonic Metamaterials. Opt. Express 2012, 20, 29447-29456. 25 26
61. 27
Farhang, A.; Bigler, N.; Martin, O. J. F. Coupling of Multiple LSP and SPP Resonances:
29
28
Interactions between an Elongated Nanoparticle and a Thin Metallic Film. Opt. Lett. 2013, 38, 31
30
4758-4761. 32 3
62. 36
35
34
Farhang, A.; Siegfried, T.; Ekinci, Y.; Sigg, H.; Martin, O. J. F. Large-Scale Sub-100 nm
Compound Plasmonic Grating Arrays to Control the Interaction Between Localized and 38
37
Propagating Plasmons. J. Nanophotonics 2014, 8, 083897. 39 41
40
63. 43
42
Artar, A.; Yanik, A. A.; Altug, H. Fabry–Perot Nanocavities in Multilayered Plasmonic
Crystals for Enhanced Biosensing. Appl. Phys. Lett. 2009, 95, 051105. 45
4
64. 46
Ameling, R.; Langguth, L.; Hentschel, M.; Mesch, M.; Braun, P. V.; Giessen, H. Cavity-
48
47
Enhanced Localized Plasmon Resonance Sensing. Appl. Phys. Lett. 2010, 97, 253116. 50
49
65. 51
Chanda, D.; Shigeta, K.; Truong, T.; Lui, E.; Mihi, A.; Schulmerich, M.; Braun, P. V.;
52
Bhargava, R.; Rogers, J. A. Coupling of Plasmonic and Optical Cavity Modes in Quasi-Three53 5
54
Dimensional Plasmonic Crystals. Nat. Commun. 2011, 2, 479. 56 57 58 59 60 ACS Paragon Plus Environment
37
ACS Nano
Page 38 of 40
1 3
2
66. 5
4
Xu, J.; Guan, P.; Kvasnička, P.; Gong, H.; Homola, J.; Yu, Q. Light Transmission and
Surface-Enhanced Raman Scattering of Quasi-3D Plasmonic Nanostructure Arrays with Deep 6 7
and Shallow Fabry-Perot Nanocavities. J. Phys. Chem. C 2011, 115, 10996-11002. 10
9
8
67. 12
1
Saison-Francioso, O.; Leveque, G.; Akjouj, A.; Pennec, Y.; Djafari-Rouhani, B.;
Szunerits, S.; Boukherroub, R. Plasmonic Nanoparticles Array for High-Sensitivity Sensing: A 13 14
Theoretical Investigation. J. Phys. Chem. C 2012, 116, 17819-17827. 17
16
15
68. 19
18
Schmidt, M. A.; Lei, D. Y.; Wondraczek, L.; Nazabal, V.; Maier, S. A. Hybrid
Nanoparticle–Microcavity-Based Plasmonic Nanosensors with Improved Detection Resolution 20 2
21
and Extended Remote-Sensing Ability. Nat. Commun. 2012, 3, 1108. 24
23
69. 25
Melamud, R.; Davenport, A. A.; Hill, G. C.; Chan, I. H.; Declercq, F.; Hartwell, P. G.;
26
Pruitt, B. L. In Development of an SU-8 Fabry-Perot Blood Pressure Sensor. IEEE Int. Conf. 27 29
28
MEMS 2005, 810-813. 31
30
70. 32
Yan, Z.; Xiaopei, C.; Yongxin, W.; Cooper, K. L.; Anbo, W. Microgap Multicavity Fabry
3
Perot Biosensor. J. Lightwave Technol. 2007, 25, 1797-1804. 36
35
34
71. 38
37
St-Gelais, R.; Masson, J.; Peter, Y.-A. All-Silicon Integrated Fabry–Perot Cavity for
Volume Refractive Index Measurement in Microfluidic Systems. Appl. Phys. Lett. 2009, 94, 39 41
40
243905. 43
42
72. 45
4
Lu, G.; Hupp, J. T. Metal−Organic Frameworks as Sensors: A ZIF-8 Based Fabry−Perot
Device as a Selective Sensor for Chemical Vapors and Gases. J. Am. Chem. Soc. 2010, 132, 46 48
47
7832-7833. 50
49
73. 51
Li Han, C.; Xiu Min, A.; Chi Chiu, C.; Shaillender, M.; Neu, B.; Wei Chang, W.; Peng,
52
Z.; Kam Chew, L. Layer-By-Layer (Chitosan/Polystyrene Sulfonate) Membrane-Based Fabry53 54 5 56 57 58 59 60 ACS Paragon Plus Environment
38
Page 39 of 40
ACS Nano
1 3
2
Perot Interferometric Fiber Optic Biosensor. IEEE J. Sel. Top. Quantum Electron. 2012, 18, 5
4
1457-1464. 6 7
74. 10
9
8
Wu, H.; Huang, H.; Bai, M.; Liu, P.; Chao, M.; Hu, J.; Hao, J.; Cao, T. An Ultra-Low
Detection-Limit Optofluidic Biosensor Based on All Glass Fabry-Perot Cavity. Opt. Express 12
1
2014, 22, 31977-31983. 13 14
75. 17
16
15
Pengbo, L.; Hui, H.; Tun, C.; Min, B.; Haibo, W.; Xueyu, L.; Zhenan, T. An Ultra-Low
Detection-Limit Optofluidic Biosensor Based on Fabry-Perot Cavity, IEEE Int. Conf. Control 19
18
Autom. 2014, 1264-1268. 20 2
21
76. 24
23
Yuan, G.; Gao, L.; Chen, Y.; Wang, J.; Ren, P.; Wang, Z. Efficient Optical Biochemical
Sensor with Slotted Bragg-Grating-Based Fabry–Perot Resonator Structure in Silicon-on25 26
Insulator Platform. Opt. Quantum Electron. 2015, 47, 247-255. 27 29
28
77. 31
30
Subimal, D.; Shourya Dutta, G.; Banerji, J.; Gupta, S. D. Critical Coupling at Oblique
Incidence. J. Opt. A: Pure Appl. Opt. 2007, 9, 555. 32 3
78. 36
35
34
Langhammer, C.; Schwind, M.; Kasemo, B.; Zoric, I. Localized Surface Plasmon
Resonances in Aluminum Nanodisks. Nano Lett. 2008, 8, 1461-1471. 38
37
79. 39
Ciftlik, A. T.; Gijs, M. A. M. A Low-Temperature Parylene-to-Silicon Dioxide Bonding
41
40
Technique for High-Pressure Microfluidics. J. Micromech. Microeng. 2011, 21, 035011. 43
42
80. 45
4
Auzelyte, V.; Gallinet, B.; Flauraud, V.; Santschi, C.; Dutta-Gupta, S.; Martin, O. J. F.;
Brugger, J. Large-Area Gold/Parylene Plasmonic Nanostructures Fabricated by Direct 46 48
47
Nanocutting. Adv. Opt. Mater. 2013, 1, 50-54. 50
49
81. 51
Piotter, V.; Hanemann, T.; Ruprecht, R.; Haußelt, J. Injection Molding and Related
52
Techniques for Fabrication of Microstructures. Microsyst. Technol. 1997, 3, 129-133. 53 5
54
82. 56
Sacks, O. CRC Handbook of Chemistry and Physics. CRC Press: 2004.
57 58 59 60 ACS Paragon Plus Environment
39
ACS Nano
Page 40 of 40
1 3
2
83. 5
4
Fischer, H.; Martin, O. J. F. Engineering the Optical Response of Plasmonic
Nanoantennas. Opt. Express 2008, 16, 9144-9154. 6 7 8 9 10 1 13
12
TOC 14 15 16 17 18 19 20 21 2 23 24 25 26 27 28 29 30 31 32 3 34 35 36 37 38 39 40 41 42 43 4 45 46 47 48 49 50 51 52 53 54 5 56 57 58 59 60 ACS Paragon Plus Environment
40
