Photoacoustic imaging has been widely studied as a deep biological tissue imaging modality combining
optical absorption and ultrasonic detection. It enables multi-scale high resolution imaging of optical absorbing
intrinsic molecules as well as exogenous molecules. Gold nanoparticles have the primary advantages
of large absorption cross section and bioconjugation capability for the imaging contrast agents. In
order to design the photoacoustic imaging agents for enhancing the contrast with high specificity to targeted
molecules and / or cell, we measured and analyzed time-of-flight photoacoustic signals of aqueous solutions
of various shapes and sizes of gold nanoparticles. The signal intensities were sensitive to the shapes
and sizes of the gold nanoparticles. We found a strong photoacoustic signal of the polyhedral gold nanoparticle
due to the localized surface plasmon resonance. The experimental results derive the strategy of designing
the optimum photoacoustic contrast agents.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3543

Hirasawa, T.

Ishihara, M.

Okawa, S

Sato, R.

Teranishi, T.

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 2 No 4, 04NABM12(3pp) (2013)   2304-1862/2013/2(4)04NABM12(3) 04NABM12-1  2013 Sumy State University Photoacoustic Signal Enhancement by Localized Surface Plasmon of Gold Nanoparticles  M. Ishihara1,*, S. Okawa1, R. Sato2, T. Hirasawa1, T. Teranishi2  1 Department of Medical Engineering, National Defense Medical College, 3-2, Namiki, 3598513 Tokorozawa, Japan 2 Institute for Chemical Research, Kyoto University, Gokasho, 6110011 Uji, Japan  (Received 03 June 2013; published online 31 August 2013)  Photoacoustic imaging has been widely studied as a deep biological tissue imaging modality combining optical absorption and ultrasonic detection. It enables multi-scale high resolution imaging of optical ab-sorbing intrinsic molecules as well as exogenous molecules. Gold nanoparticles have the primary ad-vantages of large absorption cross section and bioconjugation capability for the imaging contrast agents. In order to design the photoacoustic imaging agents for enhancing the contrast with high specificity to target-ed molecules and / or cell, we measured and analyzed time-of-flight photoacoustic signals of aqueous solu-tions of various shapes and sizes of gold nanoparticles. The signal intensities were sensitive to the shapes and sizes of the gold nanoparticles. We found a strong photoacoustic signal of the polyhedral gold nanopar-ticle due to the localized surface plasmon resonance. The experimental results derive the strategy of de-signing the optimum photoacoustic contrast agents.  Keywords: Photoacoustic, Gold nanoparticle, Polyhedron, Localized surface Plasmon resonance, Ultra-sound, Pulsed laser, Tomography.   PACS numbers: 73.20.Mf, 78.67.Bf, 81.70.Cv                                                           * miyaishi@ndmc.ac.jp 1. INTRODUCTION  Optical imaging promises to expand existing medi-cal imaging modalities beyond the typical visualization of anatomical features to incorporate functional and pathological information. Molecular imaging using op-tical technique has received great attention in biomedi-cine because of non-ionizing radiation and real-time imaging. With selected optical wavelength, a wide vari-ety of intrinsic or exogenous molecules can be visual-ized to reveal the anatomy, function, metabolism in biological system [1]. However, due to strong light scat-tering in tissue, optical imaging technique suffers from either shallow penetration depth or poor spatial resolu-tion. Photoacoustic (PA) imaging, which is based on opti-cal absorption and ultrasonic detection, has overcome the drawback of the optical imaging technique by tak-ing advantages of rich optical contrast and ultrasonic spatial resolution for deep imaging because ultrasonic waves are less scattered. Absorption of photons by opti-cal absorbing molecules (chromophores) thermoelas-tically induces pressure waves through PA effect. PA images forms images by detecting the induced pressure waves. The physical processes responsible for PA ef-fects are characterized by absorption of nanosecond pulsed light, optical excitation, non-radiative relaxa-tion, heating, and pressure wave generation. The PA imaging apparatus for small animal imaging has been offered commercially. Its technique now is ready to provide clinicians with three-dimensional microvascu-lar network using hemoglobin of different oxygenera-tion states as intrinsic chromophores. Not only intrinsic chromophores but also exogenous molecules have been actively studied as the PA imaging target. Metal nanoparticles as well as organic dyes and carbon nanotubes have been actively demonstrated as the exogenous contrast agents of PA imaging due to their unique optical properties arising from the surface plasmon resonance effect. The primary advantages of gold nanoparticles lie in their large absorption cross section with unique spectra due to the surface plasmon resonance effect and bioconjugation capability, which means that the gold nanoparticles can be specifically targeted to molecules and / or cells. For example, gold nanospheres [2], nanorods [3], nanoshells [4], nanocag-es [5], and nanobeacon [6] have been studied in PA im-aging [7]. In this study, we performed a comprehensive PA measurement of gold nanoparticles with various shapes and sizes in order to design exogenous PA imaging agent, which enabled to enhance the contrast for mo-lecular PA imaging.  2. MATERIALS AND METHOD  2.1 Photoacoustic Measurement  PA measurement apparatus consisted of nanosec-ond pulsed laser, ultrasound transducer, preamplifier, and digital oscilloscope. In this study, the excitation light was sourced from a second harmonic Q-switched neodymium-doped yttrium aluminum garnet (Nd : YAG) laser and a tunable optical parametric oscil-lator (OPO). The excitation pulsed light was coupled into a multi-mode optical fiber for the illumination. The pressure waves induced by the excitation light source were detected by our originally-fabricated ring-shaped ultrasound transducer consisting of a P(VdF / TrFE) film, which was characterized by broader frequency band than that of a piezoelectric ceramic PZT. The transducer was arranged coaxially with the optical fi-ber. Using this transducer, the PA signal was meas-ured with constant positional relation between the light excitation and the ultrasonic detection. In order to ac-quire a PA tomographic image, the ring-shaped ultra- M. ISHIHARA, S. OKAWA, R. SATO, T. HIRASAWA, T. TERANISHI  PROC. NAP 2, 04NABM12 (2013)   04NABM12-2 sound transducer with the optical fiber was mechani-cally scanned.   2.2 Gold Nanoparticles   Octahedral, cubic and spherical gold nanoparticles were used in this study. The cetyltrimethylammonium bromide-capped octahedral and cubic gold nanoparticles were synthesized using a slightly modified seed-mediated method reported previously by T. Teranishi [8]. The sizes of the particles were 55.5  1.3 nm (octa-hedron) and 56.1  2.6 nm (cube). The 50 nm spherical gold nanoparticles were purchased for the comparison. Aqueous solutions of the gold nanoparticles were pre-pared for the samples. Size and morphology of the particles were charac-terized by means of transmission electron microscopy (TEM). Vis-NIR extinction spectra of the aqueous solu-tions of the gold nanoparticles were measured with a spectrophotometer in the wavelength range of 400-700 nm.        Fig. 1 – TEM images of (a) octahedral, (b) cubic and (c) spherical gold nanoparticles employed in this study    Fig. 2 – Extinction spectra of aqueous solutions of gold nano-particles employed in this study  3. RESULTS AND DISCUSSION   Fig. 1 shows TEM images of the octahedral, cubic and spherical gold nanoparticles. These images indi-cate the characteristic shapes and uniform size. It is confirmed that the structure of each nanoparticle is controlled precisely. Fig. 2 shows extinction spectra of the aqueous solutions of gold nanoparticles. All of the nanoparticles exhibited localized surface plasmon res-onance peaks, which appear in the region of 500-600 nm region. The observed waveforms were the time-of-flight PA signals. The waveforms indicated the process of absorp-tion of photons by the aqueous solutions of gold nano-particles thermoelastically. The amplitudes of the PA signals, which corresponded to the brightness of PA image, showed strong dependence to the shapes of the nanoparticles.  The PA amplitudes of the polyhedral nanoparticles were significant higher than that of the spherical nanoparticles. The octahedral samples indi-cated the highest signal intensity. It is common knowledge that the plasmonic property of gold nanopar-ticle is dominated by particle shape. The plasmonic en-hancement of the polyhedral nanoparticles was stronger than that of the spherical nanoparticles as the strong plasmonic enhancement occurred at the sharp corners of the polyhedral nanoparticles. The PA amplitudes were also depended on the concentrations of the aqueous solu-tions and illuminating optical energy densities. The sta-bility of the PA signals, signal intensity change with the increase of the number of the laser pulse, also showed the shape dependence. This dependence might be related to thermodynamical stability of the structure.  4. CONCLUSIONS  We performed a comprehensive PA measurement of various shapes of gold nanoparticles. The strong PA sig-nal amplitudes were observed in the case of polyhedral nanoparticles. Especially, octahedral nanoparticles showed remarkable enhancement due to the localized surface plasmon resonance. The structure of a gold na-noparticle was found to be an important parameter to design the PA contrast agents. These insights suggested that it enabled to derive optimum design of exogenous contrast agents using gold nanoparticles.   AKNOWLEDGEMENTS  This study was partially supported by JST Collabo-rative Research Based on Industrial Demand (In vivo Molecular Imaging: Towards Biophotonics Innovations in Medicine). This work was also partially supported by the Collaborative Research Program of Institute for Chemical Research, Kyoto University (grant 2013-30).    b a c  PHOTOACOUSTIC SIGNAL ENHANCEMENT OF GOLD NANOPARTICLES PROC. NAP 2, 04NABM12 (2013)   04NABM12-3 REFERENCES  1. L.V. Wang, S. Hu, Science 335, 1458 (2012). 2. W. Lu, Q. Huang, G. Ku, X. Wen, M. Zhou, D. Guzatov, et al., Biomaterials 31, 2617 (2010). 3. S. Yang, F. Ye, D. Xing, Opt. Exp. 20, 10370 (2012). 4. L. Rouleau, R. Berti, V.W. Ng, C. Matteau-Pelletier, T. Lam, P. Saboural, et al., Contrast Media Mol. I. 8, 27 (2013). 5. K.H. Song, C. Kim, C.M. Cobley, Y. Xia, L.V. Wang, Nano Lett. 9, 183 (2009). 6. D. Pan, M. Pramanik, A. Senpan, S Ghosh, S.A. Wickline, L.V. Wang, et al., Biomaterials 31, 4088 (2010). 7. T. Kushibiki, M. Ishihara, J Anal. Oncol. 2, 81 (2013). 8. M. Eguchi, D. Mitsui, H.-L. Wu, R. Sato, T. Teranishi, Langmuir 28, 9021 (2012).  

Photoacoustic Signal Enhancement by Localized Surface Plasmon of Gold Nanoparticles

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 2 No 4, 04NABM12(3pp) (2013) 
 
 
2304-1862/2013/2(4)04NABM12(3) 04NABM12-1  2013 Sumy State University 
Photoacoustic Signal Enhancement by Localized Surface Plasmon of Gold Nanoparticles 
 
M. Ishihara1,*, S. Okawa1, R. Sato2, T. Hirasawa1, T. Teranishi2 
 
1 Department of Medical Engineering, National Defense Medical College, 3-2, Namiki, 3598513 Tokorozawa, Japan 
2 Institute for Chemical Research, Kyoto University, Gokasho, 6110011 Uji, Japan 
 
(Received 03 June 2013; published online 31 August 2013) 
 
Photoacoustic imaging has been widely studied as a deep biological tissue imaging modality combining 
optical absorption and ultrasonic detection. It enables multi-scale high resolution imaging of optical ab-
sorbing intrinsic molecules as well as exogenous molecules. Gold nanoparticles have the primary ad-
vantages of large absorption cross section and bioconjugation capability for the imaging contrast agents. In 
order to design the photoacoustic imaging agents for enhancing the contrast with high specificity to target-
ed molecules and / or cell, we measured and analyzed time-of-flight photoacoustic signals of aqueous solu-
tions of various shapes and sizes of gold nanoparticles. The signal intensities were sensitive to the shapes 
and sizes of the gold nanoparticles. We found a strong photoacoustic signal of the polyhedral gold nanopar-
ticle due to the localized surface plasmon resonance. The experimental results derive the strategy of de-
signing the optimum photoacoustic contrast agents. 
 
Keywords: Photoacoustic, Gold nanoparticle, Polyhedron, Localized surface Plasmon resonance, Ultra-
sound, Pulsed laser, Tomography. 
 
 PACS numbers: 73.20.Mf, 78.67.Bf, 81.70.Cv 
 
 
                                                        
* miyaishi@ndmc.ac.jp 
1. INTRODUCTION 
 
Optical imaging promises to expand existing medi-
cal imaging modalities beyond the typical visualization 
of anatomical features to incorporate functional and 
pathological information. Molecular imaging using op-
tical technique has received great attention in biomedi-
cine because of non-ionizing radiation and real-time 
imaging. With selected optical wavelength, a wide vari-
ety of intrinsic or exogenous molecules can be visual-
ized to reveal the anatomy, function, metabolism in 
biological system [1]. However, due to strong light scat-
tering in tissue, optical imaging technique suffers from 
either shallow penetration depth or poor spatial resolu-
tion. 
Photoacoustic (PA) imaging, which is based on opti-
cal absorption and ultrasonic detection, has overcome 
the drawback of the optical imaging technique by tak-
ing advantages of rich optical contrast and ultrasonic 
spatial resolution for deep imaging because ultrasonic 
waves are less scattered. Absorption of photons by opti-
cal absorbing molecules (chromophores) thermoelas-
tically induces pressure waves through PA effect. PA 
images forms images by detecting the induced pressure 
waves. The physical processes responsible for PA ef-
fects are characterized by absorption of nanosecond 
pulsed light, optical excitation, non-radiative relaxa-
tion, heating, and pressure wave generation. The PA 
imaging apparatus for small animal imaging has been 
offered commercially. Its technique now is ready to 
provide clinicians with three-dimensional microvascu-
lar network using hemoglobin of different oxygenera-
tion states as intrinsic chromophores. Not only intrinsic 
chromophores but also exogenous molecules have been 
actively studied as the PA imaging target. 
Metal nanoparticles as well as organic dyes and 
carbon nanotubes have been actively demonstrated as 
the exogenous contrast agents of PA imaging due to 
their unique optical properties arising from the surface 
plasmon resonance effect. The primary advantages of 
gold nanoparticles lie in their large absorption cross 
section with unique spectra due to the surface plasmon 
resonance effect and bioconjugation capability, which 
means that the gold nanoparticles can be specifically 
targeted to molecules and / or cells. For example, gold 
nanospheres [2], nanorods [3], nanoshells [4], nanocag-
es [5], and nanobeacon [6] have been studied in PA im-
aging [7]. 
In this study, we performed a comprehensive PA 
measurement of gold nanoparticles with various shapes 
and sizes in order to design exogenous PA imaging 
agent, which enabled to enhance the contrast for mo-
lecular PA imaging. 
 
2. MATERIALS AND METHOD 
 
2.1 Photoacoustic Measurement 
 
PA measurement apparatus consisted of nanosec-
ond pulsed laser, ultrasound transducer, preamplifier, 
and digital oscilloscope. In this study, the excitation 
light was sourced from a second harmonic Q-switched 
neodymium-doped yttrium aluminum garnet 
(Nd : YAG) laser and a tunable optical parametric oscil-
lator (OPO). The excitation pulsed light was coupled 
into a multi-mode optical fiber for the illumination. The 
pressure waves induced by the excitation light source 
were detected by our originally-fabricated ring-shaped 
ultrasound transducer consisting of a P(VdF / TrFE) 
film, which was characterized by broader frequency 
band than that of a piezoelectric ceramic PZT. The 
transducer was arranged coaxially with the optical fi-
ber. Using this transducer, the PA signal was meas-
ured with constant positional relation between the light 
excitation and the ultrasonic detection. In order to ac-
quire a PA tomographic image, the ring-shaped ultra-
 M. ISHIHARA, S. OKAWA, R. SATO, T. HIRASAWA, T. TERANISHI  PROC. NAP 2, 04NABM12 (2013) 
 
 
04NABM12-2 
sound transducer with the optical fiber was mechani-
cally scanned.  
 
2.2 Gold Nanoparticles  
 
Octahedral, cubic and spherical gold nanoparticles 
were used in this study. The cetyltrimethylammonium 
bromide-capped octahedral and cubic gold nanoparticles 
were synthesized using a slightly modified seed-
mediated method reported previously by T. Teranishi 
[8]. The sizes of the particles were 55.5  1.3 nm (octa-
hedron) and 56.1  2.6 nm (cube). The 50 nm spherical 
gold nanoparticles were purchased for the comparison. 
Aqueous solutions of the gold nanoparticles were pre-
pared for the samples. 
Size and morphology of the particles were charac-
terized by means of transmission electron microscopy 
(TEM). Vis-NIR extinction spectra of the aqueous solu-
tions of the gold nanoparticles were measured with a 
spectrophotometer in the wavelength range of 400-
700 nm. 
 
     
 
Fig. 1 – TEM images of (a) octahedral, (b) cubic and (c) spherical gold nanoparticles employed in this study 
 
 
 
Fig. 2 – Extinction spectra of aqueous solutions of gold nano-
particles employed in this study 
 
3. RESULTS AND DISCUSSION  
 
Fig. 1 shows TEM images of the octahedral, cubic 
and spherical gold nanoparticles. These images indi-
cate the characteristic shapes and uniform size. It is 
confirmed that the structure of each nanoparticle is 
controlled precisely. Fig. 2 shows extinction spectra of 
the aqueous solutions of gold nanoparticles. All of the 
nanoparticles exhibited localized surface plasmon res-
onance peaks, which appear in the region of 500-
600 nm region. 
The observed waveforms were the time-of-flight PA 
signals. The waveforms indicated the process of absorp-
tion of photons by the aqueous solutions of gold nano-
particles thermoelastically. The amplitudes of the PA 
signals, which corresponded to the brightness of PA 
image, showed strong dependence to the shapes of the 
nanoparticles.  The PA amplitudes of the polyhedral 
nanoparticles were significant higher than that of the 
spherical nanoparticles. The octahedral samples indi-
cated the highest signal intensity. It is common 
knowledge that the plasmonic property of gold nanopar-
ticle is dominated by particle shape. The plasmonic en-
hancement of the polyhedral nanoparticles was stronger 
than that of the spherical nanoparticles as the strong 
plasmonic enhancement occurred at the sharp corners of 
the polyhedral nanoparticles. The PA amplitudes were 
also depended on the concentrations of the aqueous solu-
tions and illuminating optical energy densities. The sta-
bility of the PA signals, signal intensity change with the 
increase of the number of the laser pulse, also showed 
the shape dependence. This dependence might be related 
to thermodynamical stability of the structure. 
 
4. CONCLUSIONS 
 
We performed a comprehensive PA measurement of 
various shapes of gold nanoparticles. The strong PA sig-
nal amplitudes were observed in the case of polyhedral 
nanoparticles. Especially, octahedral nanoparticles 
showed remarkable enhancement due to the localized 
surface plasmon resonance. The structure of a gold na-
noparticle was found to be an important parameter to 
design the PA contrast agents. These insights suggested 
that it enabled to derive optimum design of exogenous 
contrast agents using gold nanoparticles.  
 
AKNOWLEDGEMENTS 
 
This study was partially supported by JST Collabo-
rative Research Based on Industrial Demand (In vivo 
Molecular Imaging: Towards Biophotonics Innovations 
in Medicine). This work was also partially supported by 
the Collaborative Research Program of Institute for 
Chemical Research, Kyoto University (grant 2013-30). 
 
 
 
b a c 
 PHOTOACOUSTIC SIGNAL ENHANCEMENT OF GOLD NANOPARTICLES PROC. NAP 2, 04NABM12 (2013) 
 
 
04NABM12-3 
REFERENCES 
 
1. L.V. Wang, S. Hu, Science 335, 1458 (2012). 
2. W. Lu, Q. Huang, G. Ku, X. Wen, M. Zhou, D. Guzatov, et 
al., Biomaterials 31, 2617 (2010). 
3. S. Yang, F. Ye, D. Xing, Opt. Exp. 20, 10370 (2012). 
4. L. Rouleau, R. Berti, V.W. Ng, C. Matteau-Pelletier, 
T. Lam, P. Saboural, et al., Contrast Media Mol. I. 8, 27 
(2013). 
5. K.H. Song, C. Kim, C.M. Cobley, Y. Xia, L.V. Wang, Nano 
Lett. 9, 183 (2009). 
6. D. Pan, M. Pramanik, A. Senpan, S Ghosh, S.A. Wickline, 
L.V. Wang, et al., Biomaterials 31, 4088 (2010). 
7. T. Kushibiki, M. Ishihara, J Anal. Oncol. 2, 81 (2013). 
8. M. Eguchi, D. Mitsui, H.-L. Wu, R. Sato, T. Teranishi, 
Langmuir 28, 9021 (2012). 
 


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Photoacoustic Signal Enhancement by Localized Surface Plasmon of Gold Nanoparticles

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