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Photothermal effect of Au nanoparticles and photothermal inactivation to saccharomycetes cell
Journal Pre-proof Photothermal effect of Au nanoparticles and photothermal inactivation to saccharomycetes cell Renxi Gao, Rongpeng Fu, Weiyan Jiao, Guanghua Fan, Chunyan Liang, Jinjing Chen, Huaibo Ren, Yingying Wang, Wenjun Liu, Shoutian Ren, Quanli Dong, Qifeng Wei, Xiulian Ren, Mingjian Sun, Weixin Liu
PII:
S0030-4026(19)31655-9
DOI:
https://doi.org/10.1016/j.ijleo.2019.163757
Reference:
IJLEO 163757
To appear in:
Optik
Received Date:
20 August 2019
Accepted Date:
7 November 2019
Please cite this article as: Gao R, Fu R, Jiao W, Fan G, Liang C, Chen J, Ren H, Wang Y, Liu W, Ren S, Dong Q, Wei Q, Ren X, Sun M, Liu W, Photothermal effect of Au nanoparticles and photothermal inactivation to saccharomycetes cell, Optik (2019), doi: https://doi.org/10.1016/j.ijleo.2019.163757
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Photothermal effect of Au nanoparticles and photothermal inactivation to saccharomycetes cell
Renxi Gaoa*, Rongpeng Fua, Weiyan Jiaoa, Guanghua Fana*, Chunyan Lianga, Jinjing Chena, Huaibo Rena, Yingying Wanga, Wenjun Liua, Shoutian Rena, Quanli Donga, Qifeng Weib, Xiulian Renb, and Mingjian Sunc, Weixin Liud
a
China, b
ro of
Department of Optoelectronic Science, Harbin Institute of Technology at Weihai, Weihai 264209,
School of Ocean, Harbin Institute of Technology at Weihai, Weihai 264209, China,
c
School of Information and Electrical Engineering, Harbin Institute of Technology at Weihai, Weihai 264209, China
d
-p
School of Space Science and Physics, Shandong University at Weihai, Weihai 264209, China
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*Corresponding authors: [email protected], [email protected].
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Abstract
Au nanoparticles (Au NPs) absorb light energy and convert it to thermal energy that transfers
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to environment. The temperature variation of Au NP and environment as well as photothermal conversion efficiency of Au NP are problems concerned by researchers. Herein the linear absorption of Au NP is simulated based on Mie theory, the surface plasmon resonance peak
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wavelength increases with increase of NP diameter, and the absorption reaches the maximum when the diameter is 70 nm. The heat transfer from an Au NP to water is simulated by finite
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element method, the thermal influence space is shown to be a sphere with radius of dozens of nanometers. The increase of Au NP temperature is fast in initial stage and slow in later stage of irradiation, the NP temperature saturates with elapse of irradiation time. The photothermal conversion efficiency is determined to be 0.7. Thermal effect of Au NPs to saccharomycetes cell is investigated through laser irradiation at 532 nm, the cell that adheres Au NPs are found to be killed by photothermal effect, which shows application of Au NPs in photothermal therapy.
1
Key words Au nanoparticles, surface plasmon resonance, photothermal effect, biological tissue, photothermal therapy.
1. Introduction Au nanoparticles (NPs) posses unique optical properties and chemical stability, which show potential applications in photoacoustic imaging, optothermal therapy, biomarker, nanometer thermal energy fluid, nano heat source, drug targeting transport
ro of
and so on[1-8]. Especially, the photothermal effect of Au NPs in the cancer therapy has became a research hotspot[2,3,7]. Optothermal therapy utilizes the photothermal effect
of Au NPs that bond the cancer cells, which kills cancer cell precisely and remains normal cells unacted.
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When the frequency of light is close to the resonant collective oscillating
frequency of the free electron gas of Au NP, a strong energy coupling occurs, through
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which the electron gas absorbs and scatters the light strongly[9]. The wavelength of resonant light is the surface plasmon resonant (SPR) absorption peak, which relates to
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size of Au NP and refractive index of environmental medium[10]. The photon energy at the SPR peak is absorbed effectively by Au NP and converts to thermal energy[11], the
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conversion takes place in time scale from dozens to hundreds of picoseconds[12]. For this conversion, the transfer efficiency from light to thermal energy as well as the time varying temperature of Au NP and environment is important problems that concerned
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by researchers. The transfer efficiency from light to thermal energy of Au NPs in water is investigated through time-resolved X-ray diffraction[13]. It is also reported
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that the photothermal effect of Au NPs is investigated by using a photothermal microscopic, where the gradient of refractive index of medium surrounding Au NPs is analyzed[14]. Because it is difficult to investigate the transfer efficiency from light to thermal energy of a single Au NP, so method that can deduce transfer efficiency from the light irradiated Au NPs solution is important. Roper and Jiang reported the related works[15,16]. However, this method is likely be affected by many experimental factors, so experimental measurement should be combined theoretical model. Herein a steady 2
state heat conduction model is established to simulate the experimental results of photothermal effect, through which the transfer efficiency is deduced. On the other hand, the effect range of heat transfer of a single Au NP irradiated by light is also an important problem that should be concerned[17,18], this relates to the range that Au NP can kill pathological cell and remains normal cells unacted. Herein the time varying temperature of Au NP and environment under laser irradiation are simulated detailedly by finite element method, it is found that, within dozens of nanoseconds, the range of temperature change is dozens of nanometers near the Au
ro of
NP. Accordingly, photothermal experiments of Au NPs to biological cells are performed, in which Au NPs are adhered to saccharomycetes cells, which is irradiated
by laser at 532 nm, the sterilization of saccharomycetes cells are investigated, the cell
2. The model and theoretical analysis
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2.1 The absorption of Au NPs
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can be killed by the photothermal effect of Au NPs precisely.
Mie theory is used to simulate the absorption and scattering of spherical Au
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NPs[19,20]. The diameter of Au NP is much smaller than the diameter of the laser beam, so the incident light at the Au NP can be viewed as plane wave. In Mie theory, Cabs
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and Csca is the absorption and scattering cross section of a particle, respectively. The extinction cross section is the sum of the absorption and scattering cross section,
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Cext Cabs Csca . Usually, extinction coefficient Q ext =C ext / a2 is used because this
dimensionless coefficient is convenient in calculation, which is the sum of absorption scattering
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and
coefficient
Q
ext
Q sca Qabs ,
where
Q abs =C abs / a 2
and
Q sca =C sca / a 2 is the absorption and scattering coefficient, respectively. In Mie
theory, the absorption and scattering coefficient is expressed as the formula Qext
2 (2n 1) Re(an bn ) x 2 n1
and 3
(1)
Qsca
2 2 2 (2n 1)( an bn ) 2 x n1
(2)
with an
n ( mx ) n ( x ) m n ( mx ) n ( x ) n ( mx ) n ( x ) m n ( mx ) n ( x )
(3)
and bn
m n ( mx ) n ( x ) n ( mx ) n ( x) m n ( mx ) n ( x ) n ( mx ) n ( x )
(4)
of
Au
NP,
respectively.
n z / 2 J n1/ 2 ( z) Yn1/ 2 ( z) with 1/ 2
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where m and is the relative complex refractive index and relative permeability
n z / 2 J n1/ 2 ( z ) 1/ 2
J n 1/ 2 and Yn1/ 2
,
Bessel functions,
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x 2 an f / and m nnano / n f , where nnano and n f are respectively the refractive
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index of Au NP and solvent.
The absorption cross section is the difference value of the extinction and
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absorption cross section Cabs Cext Csca . The energy absorbed by a NP is
Q Cabs F , where F is flux of light energy. The energy fluence that absorbed by Au
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NPs in unit time is expressed as S abs =C abs I , where I is incident laser power density. According to the formulas listed above, the absorption cross section and energy that
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absorbed by Au NPs can be obtained. Accordingly, relations between absorption efficiency and NP size as well as the light wavelength can be theoretically simulated.
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2.2 Temperature raising and thermal diffusion of Au NP The distance among Au NPs is much larger than the NP diameter for the solution
is dilute, it is reasonable to assume that the there is no interaction among NPs and only a single Au NP is needed to be analyzed. The light that irradiates into solution is absorbed by Au NPs, which is changed into thermal energy that heats NP to a high temperature, and the heated NP transfers thermal energy to water around the NP subsequently. Because the mass transfer in nanoscale is neglectable[17], so the transfer 4
of thermal energy can be described by heat conduction equations listed as follows
mcm
Tm K mTm Sabs / V t
for r a
( 6)
W cW
TW KW TW 0 t
for r a
(7)
and
where m and cm is the density and specific heat of Au NP, respectively. Tm is the temperature and K m is the thermal conductivity of Au NP. W and cW is the
ro of
density and specific heat of water, respectively. TW is the temperature and KW is the thermal conductivity of water. The equation (5) and (6) are applicative when the intensity is low and does not lead to vaporization of water.
2.3 The derivation of photothermal conversion efficiency of Au NP
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Figure 1 shows the schematic diagram of experimental setup that used to measure the transfer efficiency of Au NPs from light to thermal energy. A laser beam
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at wavelength of 532 nm irradiates vertically from top to bottom of Au NPs solution, a probe-typed thermocouple is used to measure the time-varying temperature of the
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solution. Based on this experimental setup, a model is established to deduce the photo-thermal transfer efficiency of Au NPs. Two hypotheses should be proposed
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before establishment of the model. The first one is that the time of photo-thermal transfer of Au NP is rather short and can be neglected, and thermal radiation can also be neglected. The second one is that the temperature of solution is nearly uniformly
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distributed. In fact, the photo-thermal transfer of Au NP accomplishes within several hundreds of picoseconds[15], and negligible thermal radiation in Au NPs solution can
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be confirmed in the experimental section, so the first hypothesis is true. For the second one, because there is a few solution in test tube, a nearly uniform distribution of temperature is easily accomplished, so the second hypothesis is also true.
5
Figure 1. The schematic diagram of experimental setup
Based on the experimental setup and the hypotheses, a steady state heat conduction model is established to describe the photothermal conversion of Au NPs
C
dT Qi Qc Qr dt
(8)
where
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-p
C mAu C pAu mwC pw Qi I
ro of
solution[15,16]. The temperature of Au NPs solution can be expressed as
(10) (11)
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Qc B T Tamb
(9)
Where C is the equivalent heat capacity of solution, mAu and mw is the mass of Au
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NPs and water, C pAu and C pw is specific heat of Au NPs and water, respectively. Qi is thermal energy that converts from the laser energy that absorbed by Au NPs,
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which is expressed as Qi Sabs , where is pulse duration of laser. I is laser power,
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is photo-thermal transfer efficiency of Au NP. T is temperature of solution, Tamb is environment temperature. Qc and Qr is the energy that transfers from solution to external environment through heat conduction and thermal radiation, respectively. B is thermal conductivity coefficient from solution to external environment. Assuming that the thermal radiation of Au NPs during laser irradiation can be ignored, then by using equations (8) to (11), the time-varying temperature of solution can be expressed as 6
T Tamb
Bt I be C B
(12)
where b is a coefficient that can be obtained by analyzing the experimental results. If the pulse duration is long enough, then there is e
Bt C
0 , and the temperature of
solution reaches to a stabilized value T0 Tamb
I B
(13)
If the coefficient B can be obtained, the photo-thermal transfer efficiency can be
ro of
obtained accordingly by using equation (13). When the temperature of solution rises to a certain value and then ceases the laser irradiation, the temperature of solution declines as follows
k
(14)
-p
T Tamb e
Bt C
The coefficient B can be obtained by fitting the temperature of cooling process with
can be obtained.
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3. Results and discussions
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equation (14). According to the above analyses, the photo-thermal transfer efficiency
3.1 The optical absorption of Au NPs
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Figure 2 (a) shows the linear absorption spectra of Au NP in water based on Mie theory. It can be seen that with increase of diameter of Au NP, the peak wavelength of
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the SPR increases. With increase of diameter of Au NP, the absorption of Au NP increases firstly and decreases subsequently, the Au NP with diameter of 70 nm
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possesses the largest absorbance. Figure 2 (b) show the absorption cross section versus the diameter of Au NP. It can be seen that when the diameter of Au NP increases from 10 to 30 nm, the absorption cross section increases a little. However, when the diameter of Au NP increase from 50 to 200 nm, the absorption cross section increases remarkably, where there is a inflection point at 70 nm. The reason is that the absorption cross section is the product of absorbance and cross section, i.e.
Cabs Qabs a2 , although Au NP with diameter of 70 nm possesses the largest 7
absorbance, the cross section of NP increases quadratically with the diameter, so the
3.0 2.5 2.0 1.5 1.0 0.5 450
500
550
600
650
700
40 35
(b)
30 25 20 15 10
0.0 400
14
150nm 100nm 90nm 80nm 70nm 60nm 50nm 40nm 30nm 20nm
2
(a)
3.5
Absorbace of Au NP (a.u.)
4.0
Absorption cross section (m x10 )
absorption cross section increases monotonically and exhibits an inflection point.
750
5 0 -5 0
50
100
150
200
Diameter of Au NP (nm)
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Wavelength (nm)
Figure 2 (a) The linear absorption of Au NPs with different diameters. (b) The absorption cross section of Au NP versus diameter of Au NP.
3.2 The change of temperature of Au NP and surrounding water
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Figure 3 (a) shows time-varying temperature of Au NP and the surrounding water, the NP diameter is 20 nm and the laser intensity is 5.0×109 W/m2. It can be seen that
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from 0 to 4 ns, the temperature of Au NP increases rapidly, and then, from 6 to 10 ns, the temperature of Au NP increases slowly. The reveals that the laser energy absorbed
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by Au NP is converted into thermal energy that heats NP, subsequently, the heated NP starts to transfer thermal energy to surrounding water. When the laser irradiation
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persists 10 ns, the temperature of Au NP rises from 20 ℃ (indoor temperature) to 40.5 ℃. When the irradiation of laser persists 20 ns, the temperature of Au NP rises to 41.7 ℃. And when the irradiation of laser persists 100 ns, the temperature of Au NP
ur
rises to 43.4 ℃. These reveal that, with the persistence of laser irradiation at low intensity, the temperature of Au NP increases slowly and reaches to a saturated value.
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Figure 3 (b) shows time-varying temperature of water around an Au NP with diameter of 20 nm. Because the temperature of NP does not exceed the temperature of phase transition of water (100 ℃), so the temperature at interface of NP and water is continuously distributed. The temperature at 10 nm is the temperature at the surface of Au NP, or the temperature of Au NP itself. It can be seen that, after irradiation of 100 ns, at 3 nm away from Au NP (i.e. r=13 nm), the temperature rises to 37.2 ℃; at 8 nm 8
away from Au NP (i.e. r=18 nm), the temperature rises to 32.4 ℃; at 15 nm away from Au NP (i.e. r=25 nm), the temperature rises to 28.8 ℃; at 80 nm away from Au NP (i.e. r=90 nm), the temperature rises to 22.6 ℃. At the position 100 nm away from the surface of NP, the temperature of water is nearly the same as the indoor temperature (20 ℃). These indicate that the photothermal effects of Au NP is limited
2
8
32
128
0ns 1ns 2ns 3ns 4ns 5ns 6ns 7ns 8ns 9ns 10ns 12ns 15ns 20ns 30ns 40ns 60ns 80ns 100ns
10nm 13nm 18nm 25nm 34nm 47nm 65nm 90nm 126nm 174nm
40 35 30 25 20
512
Radius from the center of Au NP (nm)
(b)
Radius from the center of Au NP (nm)
45
0
20
40
ro of
(a)
o
44 42 40 38 36 34 32 30 28 26 24 22 20 0.5
Temperature of surrounding water( C)
o
Temperature of Au NP and water ( C)
to a range of dozens of nanometers.
60
80
100
120
Persist time of laser irradiation (ns)
-p
Figure 3 Under laser irradiation intensity of 5.0×109 W/m2, (a) the time-varying temperature of Au NP with diameter of 20 nm and the surrounding water, (b) the time-varying temperature of water
re
around an Au NP with diameter of 20 nm, where r=10 nm is the surface of Au NP.
Figure 4 (a) shows the saturated temperature of Au NP with diameter of 20 nm
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under irradiation of different laser intensity. The saturated temperature is shown to increase with increase of intensity (the maximum temperature is below 100 ℃).
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Figure 4 (b) shows that, under irradiation of different laser intensity, the temperature of Au NP is saturated when irradiation time persists 20 ns, this is the theoretical foundation for the application of photothermal therapy based on Au NP. Specifically
ur
speaking, under irradiation of 1.0×1010 W/m2, when the irradiation time persists 100 ns, the temperature of Au NP rises to 65.7 ℃, under this circumstances the water
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around Au NP is still liquid state, which can kill the cell that contacts Au NP and does not affect the cell dozens of nanometers away from Au NP.
9
Increasing of temperature( C)
o
(a)
(b)
o
Increasing temperature ( C)
50 40 30 20 10 0 6
4
2
0
9
8
2
10
(b)
50 45 40 35 30 25 20 15 10 5 0
9
2
10x10 W/m 2 9 9x10 W/m 2 9 8x10 W/m 2 9 7x10 W/m 2 9 6x10 W/m 2 9 5x10 W/m 2 9 4x10 W/m 2 9 3x10 W/m 2 9 2x10 W/m 2 9 1x10 W/m
0
20
Optical intensity (10 W/m )
40
60
80
100 120 140
Irradiation time (ns)
Figure 4 (a) The saturated temperature of Au NP with diameter of 20 nm under irradiation of
ro of
different laser intensity. (b) The saturation of temperature of Au NP under irradiation of different laser intensity.
Figure 5 (a) shows time-varying temperature of Au NPs with different diameter
under irradiation of 5.0×109 W/m2. It can be seen that, with increase of diameter, the
-p
time that reaches the saturated temperature of Au NP increases. Figure 5 (b) shows the temperature of Au NPs with different diameter under the irradiation of intensity of
re
5.0×109 W/m2, the irradiation time is 100 ns. It can be seen that with the diameter increases from 10 to 60 nm, the saturated temperature of Au NP rises remarkably. And
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with the diameter of NP increases from 80 to 200 nm the saturated temperature of Au NP decreases. The NP with diameter of 80 nm possesses the highest saturated temperature. These indicate that there is Au NP with the optimum diameter (≈80 nm),
na 9
2
200nm 150nm 100nm 90nm 80nm 70nm 60nm 50nm 40nm 30nm 20nm 10nm
ur 0
20
40
60
250
(a)
I0=5X10 W/m
80
Increasing temperature(K)
275 250 225 200 175 150 125 100 75 50 25 0
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o
Temperature of Au NP ( C)
which possesses the highest photothermal conversion efficiency.
100
(b)
200 150 100
120
50 0 0
Irradiation time (ns)
25
50
75 100 125 150 175 200
Diamter of Au NP (nm)
Figure 5 (a) Time-varying temperature of Au NPs with different diameter under irradiation of 5.0×109 W/m2. (b) The saturated temperature of Au NPs with different diameter under irradiation of 5.0×109 W/m2, the irradiation time is 100 ns. 10
3.3 The measurement of photothermal conversion efficiency of Au NP Figure 6 (a) shows the Au NP solution fabricated through the reduction of Au3+ of HAuCl4 by sodium citrate. Figure 6 (b) shows the transmission electron microscope image of the Au NPs, it can be seen that the average diameter of these NPs is 20 nm. Figure 6 (c) shows optical extinction spectrum of the Au NPs solution, the SPR peak locates at 532 nm, where there are strong absorption and scattering of light when the wavelength of incident light is close to this peak. (b)
4.0
(c)
Optical extinction (a.u)
(a)
3.5 2.5 2.0 1.5 1.0 0.5 0.0 300
ro of
Au NP with diameter of 20 nm
3.0
400
500
600
700
800
900
Wavelength (nm)
-p
Figure 6 (a) Au NP solution. (b) Transmission electron microscope image of Au NPs. (c) The optical extinction spectrum of Au NP solution, the average diameter of Au NPs is 20 nm.
re
To verify the hypothesis that the thermal radiation of Au NPs can be neglected in the first hypothesis, the Au NP solution is divided into two parts, one part of Au NPs
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solution is filled in a test tube where there is silver plating on the wall, and the other part of Au NPs solution is filled in a test tube where there is no silver plating on the
na
wall, both the test tubes are wrapped with degreasing cotton to prevent heat conduction from the tubes to external environment. Figure 7 (a) and (b) shows the test tube with and without silver plating on the wall, which is wrapped with degreasing
ur
cotton, respectively. A continuous wave laser with wavelength of 532 nm and power of 200 mW is used to irradiate vertically from top to bottom of Au NPs solution, the
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volume of the solution is 5 mL (the diameter of the test tube is 20 mm). The time-varying temperature of Au NPs solution is measured by a probe-typed thermocouple. Figure 7 (c) shows the heating curve of the temperature of Au NPs solution filled in the test tube with and without silver plating on the wall, respectively. It can be seen that the heating curves of Au NPs solution with and without silver plating on the wall are almost the same, which reveals that the thermal radiation from Au NPs solution to external environment is insignificant. 11
Temperature of Au NP solution (℃)
14
(a)
(b)
(c)
12 10 8 6 4 2
With silver plating on tube wall Without silver plating on tube wall
0 0
1000
2000
3000
4000
Irradiation time (s)
Figure 7 (a) Test tube with silver plating on the wall, (b) test tube without silver plating on the wall, both tubes are wrapped with degreasing cotton. (c) Heating curves of the temperature of Au NPs solution filled in the test tube with and without silver plating on the wall.
ro of
To investigate the effect of Au NP concentration to photothermal conversion efficiency, the as-produced Au NPs solution is diluted to a half and a quarter of the
original concentration, respectively. Each solution is irradiated by laser at 532 nm
-p
with power of 200 mw, when the temperature of solution is saturated, the laser
irradiation is stopped and the cooling process starts. The time-varying temperature of
re
heating and cooling process of the solution with original concentration, a half and a
(a)
Temperature variation of solution (K)
h=0.6290
B=0.0196 W/K
h=0.6546
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B=0.0241 W/K
5
6
(b)
5
4
4
3
3
2
na
2
1
1
Experimental result Theoretical fitting of heat up Theoretical fitting of heat release
0 0
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6
B=0.0222 W/K
Experimental result Theoretical fitting of heat up Theoretical fitting of heat release
0
1000 2000 3000 4000 5000 6000 Heating and cooling time (s)
Temperature variation of solution (K)
6
ur
Temperature variation of solution (K)
quarter of the original concentration is shown in figure 8 (a), (b), and (c), respectively.
0
h=0.6911
1000 2000 3000 4000 5000 6000 Heating and cooling time (s)
(c)
5 4 3 2 1
Experimental result Theoretical fitting of heat up Theoretical fitting of heat release
0 0
1000 2000 3000 4000 5000 6000 Heating and cooling time (s)
Figure 8 Time-varying temperature of heating and cooling process of solution with (a) original concentration, (b) a half of original concentration, and (c) a quarter of original concentration. 12
The heating and cooling curve can be well fitted with formula (12) and (14), respectively. All these indicate that the proposed model in this work is reasonable. The coefficient B and photo-thermal transfer efficiency can be obtained accordingly. Specifically speaking, for the solution with original concentration, a half and a quarter of original concentration, is 0.629, 0.655, an 0.691, respectively. Theoretically, from formula (12), it can be seen that the saturated temperature T0 directly relates to the photo-thermal transfer efficiency through the relation =B （T0 -Tamb ) / I . However,
ro of
in a specific experiment, the measured temperature may not be the theoretically defined saturated temperature. A reason is that the intensity of a laser beam attenuates
according to the Lambert law, and the other is that the Gaussian laser intensity is
-p
non-uniformly distributed, which lead to temperature gradient in the solution, so the temperature measured by thermocouple is lower than the saturated temperature that
re
locates at the center of the laser beam. Accordingly, there are deviations between the experimental results and theoretical curves, therefore it is understandable that there
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are deviations in the obtained .
3.3 The thermal effect of Au NPs to saccharomycetes cell
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To investigate the thermal effect of Au NPs to biological cell, saccharomycetes cells are attached with Au NPs in water, which are irradiated with laser at 532 nm. Figure 9 shows the time-varying temperature of heating and cooling curves of
ur
saccharomycetes cells with and without Au NPs, where the intensity of laser is 340 mW/cm2, the horizontal line denotes that the saccharomycetes cells cannot survive
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when the temperature exceeds 55 ℃. It can be seen that when the irradiance of laser persists 10 minutes, the temperature of saccharomycetes cells attached with Au NPs exceeds 72 ℃, whereas the temperature of saccharomycetes cells without Au NPs is 49 ℃.
13
℃
Time-varying temperature( )
80 70 60
55 centigrade
50 40 30 Saccharomycetes cells with Au NPs Saccharomycetes cells without Au NPs Inactive temperature of cells, 55
20
℃
0
5
10
15
20
Heating an cooling time (min)
Figure 9 Time-varying temperature of heating and cooling curves of the saccharomycetes cells with and without Au NPs, the intensity is 340 mW/cm2, the horizontal line denotes that the
ro of
saccharomycetes cells cannot survive when the temperature exceeds 55 ℃.
The dead saccharomycetes cell can be dyed with trypan blue whereas the survived saccharomycetes cell cannot be dyed with trypan blue. All the irradiated
-p
saccharomycetes cells are dyed with trypan blue, which are then examined by using a microscope to stat the survival rate of the cells, the images are shown in figure 10,
re
where the dyed calls are black and the un-dyed cells are transparent. Figure 10 (a) shows the image of saccharomycetes cells attached with Au NPs, it can be seen that
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the survival rate of these cells exceeds 96%, which indicates that Au NPs cannot kill saccharomycetes cells. Figure 10 (b) shows the image of the irradiated saccharomycetes cells without Au NPs, the irradiance time is 10 minutes. It can be
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seen that the survival rate of these cells exceeds 92%, which indicates that the photothermal effect of saccharomycetes cells is not enough to kill the cells. Figure 10
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(c) shows the image of the irradiated saccharomycetes cells that attached with Au NPs (the volume ratio of cell solution versus NPs solution is 1:1), the irradiance time is 10
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minutes. It can be seen that the survival rate of these cells is less than 33%, which indicates that the photothermal effect of Au NPs kills the cells effectively. Figure 10 (d) shows the image of the irradiated saccharomycetes cells that attached with Au NPs (the volume ratio of cell solution versus NPs solution is 1:2), the irradiance time is 10 minutes. It can be seen that the survival rate of these cells is less than 30%, which also indicates that the photothermal effect of Au NPs kills the cells effectively. The experimental resuls in figure 10 (c) and (d) reveal that the volume ratio of cell 14
solution versus NPs solution is not the dominant factor that kills the cells, in fact, the dominant factor is that the photo-thermal effect of the attached Au NPs on the cells. Figure 10 (e) shows the image of the irradiated saccharomycetes cells that attached with Au NPs (the volume ratio of cell solution versus NPs solution is 1:1), the irradiance time is 10 minutes and the intensity of laser is decreased to 170 mW/cm2. It can be seen that the survival rate of these cells is about 100%, which indicates that the photothermal effect of Au NPs is not enough to kill the cells.
(a)
-p
ro of
(b)
(d)
(e)
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na
lP
re
(c)
Figure 9 The images of saccharomycetes cells. (a) Cells attached with Au NPs. (b) Cells without
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Au NPs. (c) Irradiated cells attached with Au NPs. (d) Irradiated cells attached with Au NPs, the
volume ratio of cell solution versus NPs solution is 1:2. (e) Irradiated cells attached with Au NPs, the volume ratio of cell solution versus NPs solution is 1:1.
Conclusion Au NPs are important nanomaterials for their application in the photo-thermal therapy. In this work, the linear optical properties of Au NPs are investigated through theoretical simulations according to Mie theory. It is found that the absorption peak 15
wavelength increases with increase of the diameter of Au NP. The NP with diameter of 70 nm exhibits the strongest absorption. The time-varying temperatures of a single Au NP and the surrounding water are simulated based on the classics heat conduction model. It is found that, at the initial stage of the laser irradiation, the increase of temperature of Au NP is fast, and then with persistence of the laser irradiation, the increase of temperature of Au NP slows down, ultimately, the temperature tends to be a saturate value. The time-varying temperature of water is similar to that of Au NP, the range of the temperature changing is limited to be dozens of nanometers from the
ro of
surface of Au NP. Because it is difficult to investigate the transfer efficiency from photo energy to thermal energy of a single Au NP, so in this paper the steady state
heat conduction model is established and the corresponding experiment is formulated. In the corresponding experiments, the time-varying temperature of Au NPs solution is
-p
measured, by fitting the time-varying temperature of heating curves and cooling curves, the transfer efficiency is deduced to be about 0.7. The photo-thermal effect of
re
Au NPs to saccharomycetes cells are investigated, it is found that saccharomycetes cells can be killed only if Au NPs are attached to the cells. This is a reference for the
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Acknowledgements
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photothermal therapy of Au NPs.
This work is financially supported by the National Science Foundation of China
ur
(NSFC Grant No. 11574064); the National Key R&D Program of China (Grant No. 2017YFE0121000 and 2018YFC0114800); the key research and development project
Jo
of Shandong Province (Grant No. 2017CXGC1002), Shandong Provincial Natural Science Foundation,
(Grant
No.
ZR2017MF041
and
ZR2018MF026),
and
HITWH-Weihai City Co-construction Project (Grant No. ITGAZMZ001702 and ITGAZMZ001803).
16
References
[1] Khlebtsov N G, Dykman L A. Optical properties and biomedical applications of plasmonic nanoparticles[J]. Journal of Quantitative Spectroscopy and Radiative Transfer, 2010, 111(1): 1-35. [2] Peng Huang, Jing Lin, Wanwan Li, Pengfei Rong, Zhe Wang, Shouju Wang, Xiaoping Wang, Xiaolian Sun, Maria Aronova, Gang Niu, Richard D. Leapman, Zhihong Nie, and Xiaoyuan
ro of
Chen, Biodegradable gold nanovesicles with an ultrastrong plasmonic coupling effect for photoacoustic imaging and photothermal therapy[J], Angew. Chem. Int. Ed. 2013, 52: 13958-13964.
[3] Xiaohua Huang, Prashant K. Jain, Ivan H. El-Sayed, Mostafa A. El-Sayed, Plasmonic
-p
photothermal therapy (PPTT) using gold nanoparticles[J], Lasers Med Sci., 2008, 23: 217-228.
re
[4] Jibin Song, Zheng Fang, Chenxu Wang, Jiajing Zhou, Bo Duan, Lu Pu and Hongwei Duan, Photolabile plasmonic vesicles assembled from amphiphilic gold nanoparticles for
lP
remote-controlled traceable drug delivery[J], Nanoscale, 2013, 5: 5816-5824. [5] Haichuan Jin, Guiping Lin, Lizhan Bai, Aimen Zeiny, Dongsheng Wen,
Steam generation
in a nanoparticle-based solar receiver[J], Nano Energy, 2016, 28: 397-406.
na
[6] Alexander O. Govorov and Hugh H. Richardson, Generating heat with metal nanoparticles[J], Nanotoday, 2007, 2(1): 30-38.
ur
[7] Jing-Liang Li and Min Gu, Gold-Nanoparticle-Enhanced Cancer Photothermal Therapy[J], IEEE Journal of Selected Topics in Quantum Electronics, 2010, 16(4): 989-996.
Jo
[8] Yeonee Seol, Amanda E. Carpenter, Thomas T. Perkins, Gold nanoparticles: enhanced optical trapping and sensitivity coupled with significant heating[J], 2006, 31(16): 2429-2431.
[9] Vincenzo Amendola, Roberto Pilot, Marco Frasconi, Onofrio M Maragò, Maria Antonia Iatì, Surface plasmon resonance in gold nanoparticles: a review[J], Journal of Physics: Condens. Matter, 2017, 29: 203002-1-48. [10] Xiong Liu, Mark Atwater, Jinhai Wang, Qun Huo ， Extinction coefficient of gold nanoparticles with different sizes and different capping ligands[J], Colloids and Surfaces B: 17
Biointerfaces, 2007, 58: 3-7. [11] Min Hu and Gregory V. Hartland, Heat Dissipation for Au Particles in Aqueous Solution: Relaxation Time versus Size[J], J. Phys. Chem. B 2002, 106: 7029-7033. [12] Voisin C, Christofilos D, Loukakos P A, et al. Ultrafast electron-electron scattering and energy exchanges in noble-metal nanoparticles[J]. Physical Review B, 2004, 69(19): 195416. [13] Comaschi T, Balerna A, Mobilio S. Temperature dependence of the structural parameters of gold nanoparticles investigated with EXAFS[J]. Physical Review B, 2008, 77(7): 075432-1-10.
ro of
[14] Poul M. Bendix, S. Nader S. Reihani, and Lene B. Oddershede, Direct Measurements of Heating by Electromagnetically Trapped Gold Nanoparticles on Supported Lipid Bilayers[J], ACS Nano, 2010, 4(4): 2256-2262.
[15] D. Keith Roper, W. Ahn, and M. Hoepfner, Microscale heat transfer transduced by surface
-p
plasmon resonant gold nanoparticles[J]. The Journal of Physical Chemistry. C, Nanomaterials and Interfaces, 2007, 111(9): 3636-3641.
re
[16] Ke Jiang, David A. Smith, and Anatoliy Pinchuk, Size-Dependent Photothermal Conversion
27073-27080.
lP
Efficiencies of Plasmonically Heated Gold Nanoparticles[J], J. Phys. Chem. C, 2013, 117:
[17] E Sassaroli, K C P Li and B E O’Neill, Numerical investigation of heating of a gold
na
nanoparticle and the surrounding microenvironment by nanosecond laser pulses for nanomedicine applications[J], Phys. Med. Biol. 2009, 54: 5541–5560. [18] Thomas Grosges, and Dominique Barchiesi, Gold Nanoparticles as a Photothermal Agent in
ur
Cancer Therapy: The Thermal Ablation Characteristic Length[J], Molecules, 2018, 23: 1316-1-13.
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[19] G. Mie, Beiträge zur Optik trüber Medien, speziell kolloidaler Metallösungen[J], Annals of Physics, 1908, 25: 377-445.
[20] Lentz W J. Generating Bessel functions in Mie scattering calculations using continued fractions[J], Applied Optics, 1976, 15(3): 668-671.
18
PII:
S0030-4026(19)31655-9
DOI:
https://doi.org/10.1016/j.ijleo.2019.163757
Reference:
IJLEO 163757
To appear in:
Optik
Received Date:
20 August 2019
Accepted Date:
7 November 2019
Please cite this article as: Gao R, Fu R, Jiao W, Fan G, Liang C, Chen J, Ren H, Wang Y, Liu W, Ren S, Dong Q, Wei Q, Ren X, Sun M, Liu W, Photothermal effect of Au nanoparticles and photothermal inactivation to saccharomycetes cell, Optik (2019), doi: https://doi.org/10.1016/j.ijleo.2019.163757
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.
Photothermal effect of Au nanoparticles and photothermal inactivation to saccharomycetes cell
Renxi Gaoa*, Rongpeng Fua, Weiyan Jiaoa, Guanghua Fana*, Chunyan Lianga, Jinjing Chena, Huaibo Rena, Yingying Wanga, Wenjun Liua, Shoutian Rena, Quanli Donga, Qifeng Weib, Xiulian Renb, and Mingjian Sunc, Weixin Liud
a
China, b
ro of
Department of Optoelectronic Science, Harbin Institute of Technology at Weihai, Weihai 264209,
School of Ocean, Harbin Institute of Technology at Weihai, Weihai 264209, China,
c
School of Information and Electrical Engineering, Harbin Institute of Technology at Weihai, Weihai 264209, China
d
-p
School of Space Science and Physics, Shandong University at Weihai, Weihai 264209, China
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*Corresponding authors: [email protected], [email protected].
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Abstract
Au nanoparticles (Au NPs) absorb light energy and convert it to thermal energy that transfers
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to environment. The temperature variation of Au NP and environment as well as photothermal conversion efficiency of Au NP are problems concerned by researchers. Herein the linear absorption of Au NP is simulated based on Mie theory, the surface plasmon resonance peak
ur
wavelength increases with increase of NP diameter, and the absorption reaches the maximum when the diameter is 70 nm. The heat transfer from an Au NP to water is simulated by finite
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element method, the thermal influence space is shown to be a sphere with radius of dozens of nanometers. The increase of Au NP temperature is fast in initial stage and slow in later stage of irradiation, the NP temperature saturates with elapse of irradiation time. The photothermal conversion efficiency is determined to be 0.7. Thermal effect of Au NPs to saccharomycetes cell is investigated through laser irradiation at 532 nm, the cell that adheres Au NPs are found to be killed by photothermal effect, which shows application of Au NPs in photothermal therapy.
1
Key words Au nanoparticles, surface plasmon resonance, photothermal effect, biological tissue, photothermal therapy.
1. Introduction Au nanoparticles (NPs) posses unique optical properties and chemical stability, which show potential applications in photoacoustic imaging, optothermal therapy, biomarker, nanometer thermal energy fluid, nano heat source, drug targeting transport
ro of
and so on[1-8]. Especially, the photothermal effect of Au NPs in the cancer therapy has became a research hotspot[2,3,7]. Optothermal therapy utilizes the photothermal effect
of Au NPs that bond the cancer cells, which kills cancer cell precisely and remains normal cells unacted.
-p
When the frequency of light is close to the resonant collective oscillating
frequency of the free electron gas of Au NP, a strong energy coupling occurs, through
re
which the electron gas absorbs and scatters the light strongly[9]. The wavelength of resonant light is the surface plasmon resonant (SPR) absorption peak, which relates to
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size of Au NP and refractive index of environmental medium[10]. The photon energy at the SPR peak is absorbed effectively by Au NP and converts to thermal energy[11], the
na
conversion takes place in time scale from dozens to hundreds of picoseconds[12]. For this conversion, the transfer efficiency from light to thermal energy as well as the time varying temperature of Au NP and environment is important problems that concerned
ur
by researchers. The transfer efficiency from light to thermal energy of Au NPs in water is investigated through time-resolved X-ray diffraction[13]. It is also reported
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that the photothermal effect of Au NPs is investigated by using a photothermal microscopic, where the gradient of refractive index of medium surrounding Au NPs is analyzed[14]. Because it is difficult to investigate the transfer efficiency from light to thermal energy of a single Au NP, so method that can deduce transfer efficiency from the light irradiated Au NPs solution is important. Roper and Jiang reported the related works[15,16]. However, this method is likely be affected by many experimental factors, so experimental measurement should be combined theoretical model. Herein a steady 2
state heat conduction model is established to simulate the experimental results of photothermal effect, through which the transfer efficiency is deduced. On the other hand, the effect range of heat transfer of a single Au NP irradiated by light is also an important problem that should be concerned[17,18], this relates to the range that Au NP can kill pathological cell and remains normal cells unacted. Herein the time varying temperature of Au NP and environment under laser irradiation are simulated detailedly by finite element method, it is found that, within dozens of nanoseconds, the range of temperature change is dozens of nanometers near the Au
ro of
NP. Accordingly, photothermal experiments of Au NPs to biological cells are performed, in which Au NPs are adhered to saccharomycetes cells, which is irradiated
by laser at 532 nm, the sterilization of saccharomycetes cells are investigated, the cell
2. The model and theoretical analysis
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2.1 The absorption of Au NPs
-p
can be killed by the photothermal effect of Au NPs precisely.
Mie theory is used to simulate the absorption and scattering of spherical Au
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NPs[19,20]. The diameter of Au NP is much smaller than the diameter of the laser beam, so the incident light at the Au NP can be viewed as plane wave. In Mie theory, Cabs
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and Csca is the absorption and scattering cross section of a particle, respectively. The extinction cross section is the sum of the absorption and scattering cross section,
ur
Cext Cabs Csca . Usually, extinction coefficient Q ext =C ext / a2 is used because this
dimensionless coefficient is convenient in calculation, which is the sum of absorption scattering
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and
coefficient
Q
ext
Q sca Qabs ,
where
Q abs =C abs / a 2
and
Q sca =C sca / a 2 is the absorption and scattering coefficient, respectively. In Mie
theory, the absorption and scattering coefficient is expressed as the formula Qext
2 (2n 1) Re(an bn ) x 2 n1
and 3
(1)
Qsca
2 2 2 (2n 1)( an bn ) 2 x n1
(2)
with an
n ( mx ) n ( x ) m n ( mx ) n ( x ) n ( mx ) n ( x ) m n ( mx ) n ( x )
(3)
and bn
m n ( mx ) n ( x ) n ( mx ) n ( x) m n ( mx ) n ( x ) n ( mx ) n ( x )
(4)
of
Au
NP,
respectively.
n z / 2 J n1/ 2 ( z) Yn1/ 2 ( z) with 1/ 2
ro of
where m and is the relative complex refractive index and relative permeability
n z / 2 J n1/ 2 ( z ) 1/ 2
J n 1/ 2 and Yn1/ 2
,
Bessel functions,
-p
x 2 an f / and m nnano / n f , where nnano and n f are respectively the refractive
re
index of Au NP and solvent.
The absorption cross section is the difference value of the extinction and
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absorption cross section Cabs Cext Csca . The energy absorbed by a NP is
Q Cabs F , where F is flux of light energy. The energy fluence that absorbed by Au
na
NPs in unit time is expressed as S abs =C abs I , where I is incident laser power density. According to the formulas listed above, the absorption cross section and energy that
ur
absorbed by Au NPs can be obtained. Accordingly, relations between absorption efficiency and NP size as well as the light wavelength can be theoretically simulated.
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2.2 Temperature raising and thermal diffusion of Au NP The distance among Au NPs is much larger than the NP diameter for the solution
is dilute, it is reasonable to assume that the there is no interaction among NPs and only a single Au NP is needed to be analyzed. The light that irradiates into solution is absorbed by Au NPs, which is changed into thermal energy that heats NP to a high temperature, and the heated NP transfers thermal energy to water around the NP subsequently. Because the mass transfer in nanoscale is neglectable[17], so the transfer 4
of thermal energy can be described by heat conduction equations listed as follows
mcm
Tm K mTm Sabs / V t
for r a
( 6)
W cW
TW KW TW 0 t
for r a
(7)
and
where m and cm is the density and specific heat of Au NP, respectively. Tm is the temperature and K m is the thermal conductivity of Au NP. W and cW is the
ro of
density and specific heat of water, respectively. TW is the temperature and KW is the thermal conductivity of water. The equation (5) and (6) are applicative when the intensity is low and does not lead to vaporization of water.
2.3 The derivation of photothermal conversion efficiency of Au NP
-p
Figure 1 shows the schematic diagram of experimental setup that used to measure the transfer efficiency of Au NPs from light to thermal energy. A laser beam
re
at wavelength of 532 nm irradiates vertically from top to bottom of Au NPs solution, a probe-typed thermocouple is used to measure the time-varying temperature of the
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solution. Based on this experimental setup, a model is established to deduce the photo-thermal transfer efficiency of Au NPs. Two hypotheses should be proposed
na
before establishment of the model. The first one is that the time of photo-thermal transfer of Au NP is rather short and can be neglected, and thermal radiation can also be neglected. The second one is that the temperature of solution is nearly uniformly
ur
distributed. In fact, the photo-thermal transfer of Au NP accomplishes within several hundreds of picoseconds[15], and negligible thermal radiation in Au NPs solution can
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be confirmed in the experimental section, so the first hypothesis is true. For the second one, because there is a few solution in test tube, a nearly uniform distribution of temperature is easily accomplished, so the second hypothesis is also true.
5
Figure 1. The schematic diagram of experimental setup
Based on the experimental setup and the hypotheses, a steady state heat conduction model is established to describe the photothermal conversion of Au NPs
C
dT Qi Qc Qr dt
(8)
where
re
-p
C mAu C pAu mwC pw Qi I
ro of
solution[15,16]. The temperature of Au NPs solution can be expressed as
(10) (11)
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Qc B T Tamb
(9)
Where C is the equivalent heat capacity of solution, mAu and mw is the mass of Au
na
NPs and water, C pAu and C pw is specific heat of Au NPs and water, respectively. Qi is thermal energy that converts from the laser energy that absorbed by Au NPs,
ur
which is expressed as Qi Sabs , where is pulse duration of laser. I is laser power,
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is photo-thermal transfer efficiency of Au NP. T is temperature of solution, Tamb is environment temperature. Qc and Qr is the energy that transfers from solution to external environment through heat conduction and thermal radiation, respectively. B is thermal conductivity coefficient from solution to external environment. Assuming that the thermal radiation of Au NPs during laser irradiation can be ignored, then by using equations (8) to (11), the time-varying temperature of solution can be expressed as 6
T Tamb
Bt I be C B
(12)
where b is a coefficient that can be obtained by analyzing the experimental results. If the pulse duration is long enough, then there is e
Bt C
0 , and the temperature of
solution reaches to a stabilized value T0 Tamb
I B
(13)
If the coefficient B can be obtained, the photo-thermal transfer efficiency can be
ro of
obtained accordingly by using equation (13). When the temperature of solution rises to a certain value and then ceases the laser irradiation, the temperature of solution declines as follows
k
(14)
-p
T Tamb e
Bt C
The coefficient B can be obtained by fitting the temperature of cooling process with
can be obtained.
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3. Results and discussions
re
equation (14). According to the above analyses, the photo-thermal transfer efficiency
3.1 The optical absorption of Au NPs
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Figure 2 (a) shows the linear absorption spectra of Au NP in water based on Mie theory. It can be seen that with increase of diameter of Au NP, the peak wavelength of
ur
the SPR increases. With increase of diameter of Au NP, the absorption of Au NP increases firstly and decreases subsequently, the Au NP with diameter of 70 nm
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possesses the largest absorbance. Figure 2 (b) show the absorption cross section versus the diameter of Au NP. It can be seen that when the diameter of Au NP increases from 10 to 30 nm, the absorption cross section increases a little. However, when the diameter of Au NP increase from 50 to 200 nm, the absorption cross section increases remarkably, where there is a inflection point at 70 nm. The reason is that the absorption cross section is the product of absorbance and cross section, i.e.
Cabs Qabs a2 , although Au NP with diameter of 70 nm possesses the largest 7
absorbance, the cross section of NP increases quadratically with the diameter, so the
3.0 2.5 2.0 1.5 1.0 0.5 450
500
550
600
650
700
40 35
(b)
30 25 20 15 10
0.0 400
14
150nm 100nm 90nm 80nm 70nm 60nm 50nm 40nm 30nm 20nm
2
(a)
3.5
Absorbace of Au NP (a.u.)
4.0
Absorption cross section (m x10 )
absorption cross section increases monotonically and exhibits an inflection point.
750
5 0 -5 0
50
100
150
200
Diameter of Au NP (nm)
ro of
Wavelength (nm)
Figure 2 (a) The linear absorption of Au NPs with different diameters. (b) The absorption cross section of Au NP versus diameter of Au NP.
3.2 The change of temperature of Au NP and surrounding water
-p
Figure 3 (a) shows time-varying temperature of Au NP and the surrounding water, the NP diameter is 20 nm and the laser intensity is 5.0×109 W/m2. It can be seen that
re
from 0 to 4 ns, the temperature of Au NP increases rapidly, and then, from 6 to 10 ns, the temperature of Au NP increases slowly. The reveals that the laser energy absorbed
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by Au NP is converted into thermal energy that heats NP, subsequently, the heated NP starts to transfer thermal energy to surrounding water. When the laser irradiation
na
persists 10 ns, the temperature of Au NP rises from 20 ℃ (indoor temperature) to 40.5 ℃. When the irradiation of laser persists 20 ns, the temperature of Au NP rises to 41.7 ℃. And when the irradiation of laser persists 100 ns, the temperature of Au NP
ur
rises to 43.4 ℃. These reveal that, with the persistence of laser irradiation at low intensity, the temperature of Au NP increases slowly and reaches to a saturated value.
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Figure 3 (b) shows time-varying temperature of water around an Au NP with diameter of 20 nm. Because the temperature of NP does not exceed the temperature of phase transition of water (100 ℃), so the temperature at interface of NP and water is continuously distributed. The temperature at 10 nm is the temperature at the surface of Au NP, or the temperature of Au NP itself. It can be seen that, after irradiation of 100 ns, at 3 nm away from Au NP (i.e. r=13 nm), the temperature rises to 37.2 ℃; at 8 nm 8
away from Au NP (i.e. r=18 nm), the temperature rises to 32.4 ℃; at 15 nm away from Au NP (i.e. r=25 nm), the temperature rises to 28.8 ℃; at 80 nm away from Au NP (i.e. r=90 nm), the temperature rises to 22.6 ℃. At the position 100 nm away from the surface of NP, the temperature of water is nearly the same as the indoor temperature (20 ℃). These indicate that the photothermal effects of Au NP is limited
2
8
32
128
0ns 1ns 2ns 3ns 4ns 5ns 6ns 7ns 8ns 9ns 10ns 12ns 15ns 20ns 30ns 40ns 60ns 80ns 100ns
10nm 13nm 18nm 25nm 34nm 47nm 65nm 90nm 126nm 174nm
40 35 30 25 20
512
Radius from the center of Au NP (nm)
(b)
Radius from the center of Au NP (nm)
45
0
20
40
ro of
(a)
o
44 42 40 38 36 34 32 30 28 26 24 22 20 0.5
Temperature of surrounding water( C)
o
Temperature of Au NP and water ( C)
to a range of dozens of nanometers.
60
80
100
120
Persist time of laser irradiation (ns)
-p
Figure 3 Under laser irradiation intensity of 5.0×109 W/m2, (a) the time-varying temperature of Au NP with diameter of 20 nm and the surrounding water, (b) the time-varying temperature of water
re
around an Au NP with diameter of 20 nm, where r=10 nm is the surface of Au NP.
Figure 4 (a) shows the saturated temperature of Au NP with diameter of 20 nm
lP
under irradiation of different laser intensity. The saturated temperature is shown to increase with increase of intensity (the maximum temperature is below 100 ℃).
na
Figure 4 (b) shows that, under irradiation of different laser intensity, the temperature of Au NP is saturated when irradiation time persists 20 ns, this is the theoretical foundation for the application of photothermal therapy based on Au NP. Specifically
ur
speaking, under irradiation of 1.0×1010 W/m2, when the irradiation time persists 100 ns, the temperature of Au NP rises to 65.7 ℃, under this circumstances the water
Jo
around Au NP is still liquid state, which can kill the cell that contacts Au NP and does not affect the cell dozens of nanometers away from Au NP.
9
Increasing of temperature( C)
o
(a)
(b)
o
Increasing temperature ( C)
50 40 30 20 10 0 6
4
2
0
9
8
2
10
(b)
50 45 40 35 30 25 20 15 10 5 0
9
2
10x10 W/m 2 9 9x10 W/m 2 9 8x10 W/m 2 9 7x10 W/m 2 9 6x10 W/m 2 9 5x10 W/m 2 9 4x10 W/m 2 9 3x10 W/m 2 9 2x10 W/m 2 9 1x10 W/m
0
20
Optical intensity (10 W/m )
40
60
80
100 120 140
Irradiation time (ns)
Figure 4 (a) The saturated temperature of Au NP with diameter of 20 nm under irradiation of
ro of
different laser intensity. (b) The saturation of temperature of Au NP under irradiation of different laser intensity.
Figure 5 (a) shows time-varying temperature of Au NPs with different diameter
under irradiation of 5.0×109 W/m2. It can be seen that, with increase of diameter, the
-p
time that reaches the saturated temperature of Au NP increases. Figure 5 (b) shows the temperature of Au NPs with different diameter under the irradiation of intensity of
re
5.0×109 W/m2, the irradiation time is 100 ns. It can be seen that with the diameter increases from 10 to 60 nm, the saturated temperature of Au NP rises remarkably. And
lP
with the diameter of NP increases from 80 to 200 nm the saturated temperature of Au NP decreases. The NP with diameter of 80 nm possesses the highest saturated temperature. These indicate that there is Au NP with the optimum diameter (≈80 nm),
na 9
2
200nm 150nm 100nm 90nm 80nm 70nm 60nm 50nm 40nm 30nm 20nm 10nm
ur 0
20
40
60
250
(a)
I0=5X10 W/m
80
Increasing temperature(K)
275 250 225 200 175 150 125 100 75 50 25 0
Jo
o
Temperature of Au NP ( C)
which possesses the highest photothermal conversion efficiency.
100
(b)
200 150 100
120
50 0 0
Irradiation time (ns)
25
50
75 100 125 150 175 200
Diamter of Au NP (nm)
Figure 5 (a) Time-varying temperature of Au NPs with different diameter under irradiation of 5.0×109 W/m2. (b) The saturated temperature of Au NPs with different diameter under irradiation of 5.0×109 W/m2, the irradiation time is 100 ns. 10
3.3 The measurement of photothermal conversion efficiency of Au NP Figure 6 (a) shows the Au NP solution fabricated through the reduction of Au3+ of HAuCl4 by sodium citrate. Figure 6 (b) shows the transmission electron microscope image of the Au NPs, it can be seen that the average diameter of these NPs is 20 nm. Figure 6 (c) shows optical extinction spectrum of the Au NPs solution, the SPR peak locates at 532 nm, where there are strong absorption and scattering of light when the wavelength of incident light is close to this peak. (b)
4.0
(c)
Optical extinction (a.u)
(a)
3.5 2.5 2.0 1.5 1.0 0.5 0.0 300
ro of
Au NP with diameter of 20 nm
3.0
400
500
600
700
800
900
Wavelength (nm)
-p
Figure 6 (a) Au NP solution. (b) Transmission electron microscope image of Au NPs. (c) The optical extinction spectrum of Au NP solution, the average diameter of Au NPs is 20 nm.
re
To verify the hypothesis that the thermal radiation of Au NPs can be neglected in the first hypothesis, the Au NP solution is divided into two parts, one part of Au NPs
lP
solution is filled in a test tube where there is silver plating on the wall, and the other part of Au NPs solution is filled in a test tube where there is no silver plating on the
na
wall, both the test tubes are wrapped with degreasing cotton to prevent heat conduction from the tubes to external environment. Figure 7 (a) and (b) shows the test tube with and without silver plating on the wall, which is wrapped with degreasing
ur
cotton, respectively. A continuous wave laser with wavelength of 532 nm and power of 200 mW is used to irradiate vertically from top to bottom of Au NPs solution, the
Jo
volume of the solution is 5 mL (the diameter of the test tube is 20 mm). The time-varying temperature of Au NPs solution is measured by a probe-typed thermocouple. Figure 7 (c) shows the heating curve of the temperature of Au NPs solution filled in the test tube with and without silver plating on the wall, respectively. It can be seen that the heating curves of Au NPs solution with and without silver plating on the wall are almost the same, which reveals that the thermal radiation from Au NPs solution to external environment is insignificant. 11
Temperature of Au NP solution (℃)
14
(a)
(b)
(c)
12 10 8 6 4 2
With silver plating on tube wall Without silver plating on tube wall
0 0
1000
2000
3000
4000
Irradiation time (s)
Figure 7 (a) Test tube with silver plating on the wall, (b) test tube without silver plating on the wall, both tubes are wrapped with degreasing cotton. (c) Heating curves of the temperature of Au NPs solution filled in the test tube with and without silver plating on the wall.
ro of
To investigate the effect of Au NP concentration to photothermal conversion efficiency, the as-produced Au NPs solution is diluted to a half and a quarter of the
original concentration, respectively. Each solution is irradiated by laser at 532 nm
-p
with power of 200 mw, when the temperature of solution is saturated, the laser
irradiation is stopped and the cooling process starts. The time-varying temperature of
re
heating and cooling process of the solution with original concentration, a half and a
(a)
Temperature variation of solution (K)
h=0.6290
B=0.0196 W/K
h=0.6546
lP
B=0.0241 W/K
5
6
(b)
5
4
4
3
3
2
na
2
1
1
Experimental result Theoretical fitting of heat up Theoretical fitting of heat release
0 0
Jo
6
B=0.0222 W/K
Experimental result Theoretical fitting of heat up Theoretical fitting of heat release
0
1000 2000 3000 4000 5000 6000 Heating and cooling time (s)
Temperature variation of solution (K)
6
ur
Temperature variation of solution (K)
quarter of the original concentration is shown in figure 8 (a), (b), and (c), respectively.
0
h=0.6911
1000 2000 3000 4000 5000 6000 Heating and cooling time (s)
(c)
5 4 3 2 1
Experimental result Theoretical fitting of heat up Theoretical fitting of heat release
0 0
1000 2000 3000 4000 5000 6000 Heating and cooling time (s)
Figure 8 Time-varying temperature of heating and cooling process of solution with (a) original concentration, (b) a half of original concentration, and (c) a quarter of original concentration. 12
The heating and cooling curve can be well fitted with formula (12) and (14), respectively. All these indicate that the proposed model in this work is reasonable. The coefficient B and photo-thermal transfer efficiency can be obtained accordingly. Specifically speaking, for the solution with original concentration, a half and a quarter of original concentration, is 0.629, 0.655, an 0.691, respectively. Theoretically, from formula (12), it can be seen that the saturated temperature T0 directly relates to the photo-thermal transfer efficiency through the relation =B （T0 -Tamb ) / I . However,
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in a specific experiment, the measured temperature may not be the theoretically defined saturated temperature. A reason is that the intensity of a laser beam attenuates
according to the Lambert law, and the other is that the Gaussian laser intensity is
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non-uniformly distributed, which lead to temperature gradient in the solution, so the temperature measured by thermocouple is lower than the saturated temperature that
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locates at the center of the laser beam. Accordingly, there are deviations between the experimental results and theoretical curves, therefore it is understandable that there
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are deviations in the obtained .
3.3 The thermal effect of Au NPs to saccharomycetes cell
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To investigate the thermal effect of Au NPs to biological cell, saccharomycetes cells are attached with Au NPs in water, which are irradiated with laser at 532 nm. Figure 9 shows the time-varying temperature of heating and cooling curves of
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saccharomycetes cells with and without Au NPs, where the intensity of laser is 340 mW/cm2, the horizontal line denotes that the saccharomycetes cells cannot survive
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when the temperature exceeds 55 ℃. It can be seen that when the irradiance of laser persists 10 minutes, the temperature of saccharomycetes cells attached with Au NPs exceeds 72 ℃, whereas the temperature of saccharomycetes cells without Au NPs is 49 ℃.
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℃
Time-varying temperature( )
80 70 60
55 centigrade
50 40 30 Saccharomycetes cells with Au NPs Saccharomycetes cells without Au NPs Inactive temperature of cells, 55
20
℃
0
5
10
15
20
Heating an cooling time (min)
Figure 9 Time-varying temperature of heating and cooling curves of the saccharomycetes cells with and without Au NPs, the intensity is 340 mW/cm2, the horizontal line denotes that the
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saccharomycetes cells cannot survive when the temperature exceeds 55 ℃.
The dead saccharomycetes cell can be dyed with trypan blue whereas the survived saccharomycetes cell cannot be dyed with trypan blue. All the irradiated
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saccharomycetes cells are dyed with trypan blue, which are then examined by using a microscope to stat the survival rate of the cells, the images are shown in figure 10,
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where the dyed calls are black and the un-dyed cells are transparent. Figure 10 (a) shows the image of saccharomycetes cells attached with Au NPs, it can be seen that
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the survival rate of these cells exceeds 96%, which indicates that Au NPs cannot kill saccharomycetes cells. Figure 10 (b) shows the image of the irradiated saccharomycetes cells without Au NPs, the irradiance time is 10 minutes. It can be
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seen that the survival rate of these cells exceeds 92%, which indicates that the photothermal effect of saccharomycetes cells is not enough to kill the cells. Figure 10
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(c) shows the image of the irradiated saccharomycetes cells that attached with Au NPs (the volume ratio of cell solution versus NPs solution is 1:1), the irradiance time is 10
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minutes. It can be seen that the survival rate of these cells is less than 33%, which indicates that the photothermal effect of Au NPs kills the cells effectively. Figure 10 (d) shows the image of the irradiated saccharomycetes cells that attached with Au NPs (the volume ratio of cell solution versus NPs solution is 1:2), the irradiance time is 10 minutes. It can be seen that the survival rate of these cells is less than 30%, which also indicates that the photothermal effect of Au NPs kills the cells effectively. The experimental resuls in figure 10 (c) and (d) reveal that the volume ratio of cell 14
solution versus NPs solution is not the dominant factor that kills the cells, in fact, the dominant factor is that the photo-thermal effect of the attached Au NPs on the cells. Figure 10 (e) shows the image of the irradiated saccharomycetes cells that attached with Au NPs (the volume ratio of cell solution versus NPs solution is 1:1), the irradiance time is 10 minutes and the intensity of laser is decreased to 170 mW/cm2. It can be seen that the survival rate of these cells is about 100%, which indicates that the photothermal effect of Au NPs is not enough to kill the cells.
(a)
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(b)
(d)
(e)
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(c)
Figure 9 The images of saccharomycetes cells. (a) Cells attached with Au NPs. (b) Cells without
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Au NPs. (c) Irradiated cells attached with Au NPs. (d) Irradiated cells attached with Au NPs, the
volume ratio of cell solution versus NPs solution is 1:2. (e) Irradiated cells attached with Au NPs, the volume ratio of cell solution versus NPs solution is 1:1.
Conclusion Au NPs are important nanomaterials for their application in the photo-thermal therapy. In this work, the linear optical properties of Au NPs are investigated through theoretical simulations according to Mie theory. It is found that the absorption peak 15
wavelength increases with increase of the diameter of Au NP. The NP with diameter of 70 nm exhibits the strongest absorption. The time-varying temperatures of a single Au NP and the surrounding water are simulated based on the classics heat conduction model. It is found that, at the initial stage of the laser irradiation, the increase of temperature of Au NP is fast, and then with persistence of the laser irradiation, the increase of temperature of Au NP slows down, ultimately, the temperature tends to be a saturate value. The time-varying temperature of water is similar to that of Au NP, the range of the temperature changing is limited to be dozens of nanometers from the
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surface of Au NP. Because it is difficult to investigate the transfer efficiency from photo energy to thermal energy of a single Au NP, so in this paper the steady state
heat conduction model is established and the corresponding experiment is formulated. In the corresponding experiments, the time-varying temperature of Au NPs solution is
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measured, by fitting the time-varying temperature of heating curves and cooling curves, the transfer efficiency is deduced to be about 0.7. The photo-thermal effect of
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Au NPs to saccharomycetes cells are investigated, it is found that saccharomycetes cells can be killed only if Au NPs are attached to the cells. This is a reference for the
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Acknowledgements
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photothermal therapy of Au NPs.
This work is financially supported by the National Science Foundation of China
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(NSFC Grant No. 11574064); the National Key R&D Program of China (Grant No. 2017YFE0121000 and 2018YFC0114800); the key research and development project
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of Shandong Province (Grant No. 2017CXGC1002), Shandong Provincial Natural Science Foundation,
(Grant
No.
ZR2017MF041
and
ZR2018MF026),
and
HITWH-Weihai City Co-construction Project (Grant No. ITGAZMZ001702 and ITGAZMZ001803).
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References
[1] Khlebtsov N G, Dykman L A. Optical properties and biomedical applications of plasmonic nanoparticles[J]. Journal of Quantitative Spectroscopy and Radiative Transfer, 2010, 111(1): 1-35. [2] Peng Huang, Jing Lin, Wanwan Li, Pengfei Rong, Zhe Wang, Shouju Wang, Xiaoping Wang, Xiaolian Sun, Maria Aronova, Gang Niu, Richard D. Leapman, Zhihong Nie, and Xiaoyuan
ro of
Chen, Biodegradable gold nanovesicles with an ultrastrong plasmonic coupling effect for photoacoustic imaging and photothermal therapy[J], Angew. Chem. Int. Ed. 2013, 52: 13958-13964.
[3] Xiaohua Huang, Prashant K. Jain, Ivan H. El-Sayed, Mostafa A. El-Sayed, Plasmonic
-p
photothermal therapy (PPTT) using gold nanoparticles[J], Lasers Med Sci., 2008, 23: 217-228.
re
[4] Jibin Song, Zheng Fang, Chenxu Wang, Jiajing Zhou, Bo Duan, Lu Pu and Hongwei Duan, Photolabile plasmonic vesicles assembled from amphiphilic gold nanoparticles for
lP
remote-controlled traceable drug delivery[J], Nanoscale, 2013, 5: 5816-5824. [5] Haichuan Jin, Guiping Lin, Lizhan Bai, Aimen Zeiny, Dongsheng Wen,
Steam generation
in a nanoparticle-based solar receiver[J], Nano Energy, 2016, 28: 397-406.
na
[6] Alexander O. Govorov and Hugh H. Richardson, Generating heat with metal nanoparticles[J], Nanotoday, 2007, 2(1): 30-38.
ur
[7] Jing-Liang Li and Min Gu, Gold-Nanoparticle-Enhanced Cancer Photothermal Therapy[J], IEEE Journal of Selected Topics in Quantum Electronics, 2010, 16(4): 989-996.
Jo
[8] Yeonee Seol, Amanda E. Carpenter, Thomas T. Perkins, Gold nanoparticles: enhanced optical trapping and sensitivity coupled with significant heating[J], 2006, 31(16): 2429-2431.
[9] Vincenzo Amendola, Roberto Pilot, Marco Frasconi, Onofrio M Maragò, Maria Antonia Iatì, Surface plasmon resonance in gold nanoparticles: a review[J], Journal of Physics: Condens. Matter, 2017, 29: 203002-1-48. [10] Xiong Liu, Mark Atwater, Jinhai Wang, Qun Huo ， Extinction coefficient of gold nanoparticles with different sizes and different capping ligands[J], Colloids and Surfaces B: 17
Biointerfaces, 2007, 58: 3-7. [11] Min Hu and Gregory V. Hartland, Heat Dissipation for Au Particles in Aqueous Solution: Relaxation Time versus Size[J], J. Phys. Chem. B 2002, 106: 7029-7033. [12] Voisin C, Christofilos D, Loukakos P A, et al. Ultrafast electron-electron scattering and energy exchanges in noble-metal nanoparticles[J]. Physical Review B, 2004, 69(19): 195416. [13] Comaschi T, Balerna A, Mobilio S. Temperature dependence of the structural parameters of gold nanoparticles investigated with EXAFS[J]. Physical Review B, 2008, 77(7): 075432-1-10.
ro of
[14] Poul M. Bendix, S. Nader S. Reihani, and Lene B. Oddershede, Direct Measurements of Heating by Electromagnetically Trapped Gold Nanoparticles on Supported Lipid Bilayers[J], ACS Nano, 2010, 4(4): 2256-2262.
[15] D. Keith Roper, W. Ahn, and M. Hoepfner, Microscale heat transfer transduced by surface
-p
plasmon resonant gold nanoparticles[J]. The Journal of Physical Chemistry. C, Nanomaterials and Interfaces, 2007, 111(9): 3636-3641.
re
[16] Ke Jiang, David A. Smith, and Anatoliy Pinchuk, Size-Dependent Photothermal Conversion
27073-27080.
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Efficiencies of Plasmonically Heated Gold Nanoparticles[J], J. Phys. Chem. C, 2013, 117:
[17] E Sassaroli, K C P Li and B E O’Neill, Numerical investigation of heating of a gold
na
nanoparticle and the surrounding microenvironment by nanosecond laser pulses for nanomedicine applications[J], Phys. Med. Biol. 2009, 54: 5541–5560. [18] Thomas Grosges, and Dominique Barchiesi, Gold Nanoparticles as a Photothermal Agent in
ur
Cancer Therapy: The Thermal Ablation Characteristic Length[J], Molecules, 2018, 23: 1316-1-13.
Jo
[19] G. Mie, Beiträge zur Optik trüber Medien, speziell kolloidaler Metallösungen[J], Annals of Physics, 1908, 25: 377-445.
[20] Lentz W J. Generating Bessel functions in Mie scattering calculations using continued fractions[J], Applied Optics, 1976, 15(3): 668-671.
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