This document discusses optical nanoantennas and their potential applications. It describes how nanoantennas can interact with and enhance light at the nanoscale via localized surface plasmon resonance. Various fabrication methods are discussed for creating nanoantennas, including electron beam lithography. Different antenna geometries and their effects are presented. Applications explored include biological and biomedical uses like biosensing, biomedical imaging, and tumor ablation through photothermal heating. Simulations of bowtie nanoantennas using software show optimization of parameters like frequency, gap size, and arm length for thermal ablation applications.

1. Optical nanoantennas
Studenti:
Federico Zavanella
Betis Zeneli
Antonella Zito
Bio micro and nano systems
POLITECNICO DI TORINO
CORSO DI LAURA MAGISTRALE IN
INGEGNERIA BIOMEDICA

2. Overview
INTRODUCTION
WORKING PRINCIPLES
FABRICATION METHODS:  Electron-beam lithography
 Focused ion-beam milling
 Nanoimprint lithography
GEOMETRIES
APPLICATIONS:  Biological and biomedical applications
 Exemplifying application for tumor ablation
 Self and AFM based assembly
SIMULATIONS:  Coventor
 Comsol
 Results
CONCLUSIONS AND COMMENTS

3. Working Principle
 Traditoinal antennas can
EXCHANGE ENERGY WITH
ITS SURROUNDINGS as well
as information by means of EM
fields
 Shrinking dimensions to NANOSCALE allows enhenced
interaction between IR or visible light and nanoscale matter,
enabling several kind of applications

4. Working Principle
 LOCALIZED SURFACE PLASMON RESONANCE
 For certain
materials, such as
gold and silver, it
happens to appear
close to the visible
spectral range
 Thanks to LSPR we
can consider
plasmonic
nanostructures as
nanoantennas

5. Fabrication Methods
 The resonance of optical antennas strongly depends on the
exact geometry and dimensions. In order to obtain high-
definition nanostructures (required <10nm), a combination of
both TOP-DOWN and BOTTOM-UP approaches can be used.
Some of the most popular techniques to fabricate nano
antennas:
 Electron-beam lithography (EBL)
 Focused ion-beam milling (FIB)
 Nanoimprint lithography (NIL)
 Self and AFM based assembly

6. Fabrication Methods
 Direct patterning by a focused beam
on flat surfaces covered with an
electron sensitive material (i.e.
PMMA)
 Resolutions below 5nm
 Adhesion layer required
 Low throughput and high costs
 ELECTRON-BEAM LITHOGRAPHY

7. Fabrication Methods
 Localized sputtering of conductive
material (by means of a focused Ga
ion beam) for a direct pattern
 Resolution: 10-15 nm
 Sputtered material contamination
and ion implantation issues
 FOCUSED ION-BEAM MILLING

8. Fabrication Methods
 Pattern created by
mechanically deformed
resist layer
 Resolution:
10 up to 5 nm
 Variations:
UV nanoimprinting
lithography and soft
nanoimprinting
techniques
 NANOIMPRINTING LITHOGRAPHY
 High throughput and low cost, suitable for large areas

9. Fabrication Methods
 Chemically grown
nanostructures: controlled
shape, purity and
cristallinity
 Pattern obtained by
(AFM)nanomanipulation,
electrophoresis, fluidic
alignment or micro-
contact printing
 SELF AND AFM BASED ASSEMBLY
 Less perfect than lithographed strucures, but narrow (1nm) gaps
can be achieved, depending on the surfactant layer used
 High throughput

10. Geometries
 Since the aim is to exploit plasmon resonance effects, size,
shape and surface properties must be well defined
 The geometry strongly influence antennas’ characteristics
 Several designs are being analyzed in order to optimize its
characteristics

11. Geometries
 A much intense near field can be obteined by coupling these
elementary shapes into nanospheres and nanorods DIMERS.
 In the most simple case, a SINGLE METAL NANOSPHERE
can constitute a nanoantenna
 An elongated particles (NANORODS) may enhance the e.f.
near its ends.

12. Geometries
 Losses issues related to the volume.
 BOW-TIE nanoantennas possess
broad band width and high field
enhancement in the gap
 the radius of curvature at the apex
strongly influences its behavior
 YAGI-UDA structures, whose
parameters are designed as in their
RF counterparts

13. Geometries
 Better field localization
 CROSS nanoantennas consist of two
perpendicular dipole sharing a common
gap
 The two field components coherently add
up in the gap region

14. Applications
Lots of possible applications can take advantage of optical
antennas properties:
 Optical DETECTORS
 SOLAR CELLS
 …
 BIOLOGICAL and BIOMEDICAL applications NEXT>

15. Applications

16. Applications
 LSPR depends on the
dielectric constant of the
surrounding medium
 Varying Ɛm, the SPR
wavelength changes
 Nanoparticles can be
detected as an Ɛm
variation
 Thanks to their high
value shape factor, gold
NANORODS are suited
for this application
 BIOSENSING

17. Applications
 Nanoantennas could be exploited as imaging probes or
contrast agents due to their optical, elecrtronic, magnetic and
structural properties
 MRI, MSR, PET and SPECT could be enhanced, as well as
fluorescent emission and Raman spectroscopy
 An example shows targeted molecules within the cell
enviroment:
 BIOMOLECULES IMAGING

18. Applications
 An example: array of gold
nanoantennas laced into
an artificial membrane
enhances the fluorescence
intensity of three different
molecules (blue, green
and red flashes)
 This minimally invasive
technique allows to
observe molecule’s
movements and
interaction within the
cellular environment
 BIOMOLECULES IMAGING

19. Applications
 An example: array of gold
nanoantennas laced into
an artificial membrane
enhances the fluorescence
intensity of three different
molecules (blue, green
and red flashes)
 This minimally invasive
technique allows to
observe molecule’s
movements and
interaction within the
cellular environment
 BIOMOLECULES IMAGING

20. Applications
Nanoparticles like nanosphere, nanorods and nanoshells can
improve the SPECIFICITY of traditional cancer ablation
practices:
 PHOTO-THERMAL THERAPY
Tumors can be TARGETED by a remote control process
NIR light is absorbed by the antennas
SPR allows efficient photo-thermal conversion to HEAT

21. Exemplifying Application
 Gold nanorods
coated with
PEG for
biocompatibility
and drug
release
 Tumors were induced in mice
 and PEG-NRs injected into them
 PEG-NRs behavior was analized during the study

22.  Photo thermal theraphy was delivered
 Nanoshalls and Nanorods was compared, then the latters were
optimazed for near IR plasmon resonance
Exemplifying Application

23.  Irradiation regimens was arranged by investigating the ability of
PEG-NRs to act as X-ray absorbing agents (X-ray contrast ∝ NR
concentration)
RESULTS depends on:
 Material characteristics and external parameters
 Shape of nanoparticles, which gives absorption efficacy and
circulation times (for nanoparticle accumulation in tumor)
 Irradiation protocol and nanoantenna dosing regimen
Exemplifying Application

24. Quantitative bio-
distribution data,
incorporated into
COMPUTATIONAL
MODELING could
provide a priori
personalization of
irradiation regimens,
thanks to a rapid photo
thermal temperature
gradients calculation.
Exemplifying Application

25. Simulations
 In COVENTOR
 In COMSOL 4.3

26. Simulations
 BOW-TIE NANOANTENNA MODEL in COVENTOR:

27. Simulations
 BOW-TIE NANOANTENNA MODEL in COVENTOR:
Start from a 100 nm of silica substrate as bottom layer
Phisical vapour deposition of a 70 nm layer of ITO
90 nm PMMA resist layer by spin casting and soft baking
PRODUCTION STEPS:
EBL patterning
Resist development in MIBK:IPA for 70’’ and rinse with IPA
PVD of 50 nm golden film
Lift off in ultrasonic acetone bath for approx. 3’

28. Simulations
 antenna designed in terms of gap
size, flare angle, height of the arms
 supposed to be done in perfect
electric conductor on FR4 substrate
 BOW-TIE NANOANTENNA MODEL in COMSOL:
 Analysis conducted thanks to the
radio-frequency and heat transfer
modules provided infos about :
Behavior of EM waves
Bioheat transfer in human tissues

29. Simulations
 A sphere of uman tissue around the
anntenna were considered, phisical
properties of human liver follows:
Electrical cond. σ 0.333 S/m
Thermal cond. k 0.512 W/(m*K)
Density ρ 1060 kg/m³
Heat cap. Cp 3600 J/(kg*K)
Rel. Permitt. 1
Rel. Permeab. μ 1
 BOW-TIE NANOANTENNA MODEL in COMSOL:

30. Simulations
Exitation frequency 250-350 GHz
Gap size 1-10 μm
Flare angle 30-90°
Antenna height 100-500 μm
Time of exposure 60 s
 The blood flow effects
have been considerated
throw the following
parameters:
Blood Temp. 37°C
B. Specific Heat 4180 J/(kg*K)
B. Perfusion rate 6.4*10
B. Density 1000kg/m³
 So the best values for
antenna’s parameters
were figured out starting
from these ranges:
 BOW-TIE NANOANTENNA MODEL in COMSOL:

31. Results
 THERMAL BEHAVIOR of the system (HEATING exploited as
tumor ablation technique requires T > 45°C/50°C)
 EMISSION PATTERNS

32. Results
 TEMPERATURE Vs TIME

33. Results
0.01 s 1 s 30 s
 TEMPERATURE Vs TIME
ISOTHERMAL SURFACE: 50°C

34. Results
 TEMPERATURE as a function of FREQUENCY
f0

35. Results
 TEMPERATURE as a function of FREQUENCY
T Vs fo

36. Results
 TEMPERATURE as a function of FREQUENCY

37. Results
 TEMPERATURE as a function of GAP
Gap size

38. Results
 TEMPERATURE as a function of GAP
T Vs Gap size

39. Results
 TEMPERATURE as a function of FREQUENCY

40. Results
 TEMPERATURE as a function of the ARM LENGTH
T Vs arm length

41. Results
 TEMPERATURE as a function of the FLARE ANGLE
T Vs θ
θ

42. Results
 EMISSION PATTERNS
Electric field Vs fo

43. Results
 EMISSION PATTERNS
Electric field Vs gap size

44. Results
 EMISSION PATTERNS
Electric field Vs
arm length

45. Results
 EMISSION PATTERNS
Electric field Vs
flare angle

46. Results
 EMISSION PATTERNS

47. Results
 OPTIMIZATION OF THE VARIABLES
fo 300 GHz
Gap 5 μm
θ 70°
ho 350 μm
TEMPERATURE Vs TIME

48. Results
 OPTIMIZATION OF THE VARIABLES
Isosurface at 50°C Temperature distribution
- THERMAL BEHAVIOR -

49. Results
 OPTIMIZATION OF THE VARIABLES
- EMISSION PATTERN -
Electric field

50. Conclusion and comments
 At 200 GHz
resonation
occurs, for a
λ = 1.5 mm
(comparable with
device’s length)

51. Conclusion and comments
 A 300 GHz wave successfully induces an electric field strongly
localized in the gap, which in turn produce heat, warming up
the tissue above 50° C
 A temperature above 50°C is enough to cause cells
apoptosis, especially in tumors, due to their disorganized
vascular system
 A compromise was necessary to be found for the frequency
value, taking into consideration required heating and
interaction with tissues

52. Thankyou for the attention