- Email: [email protected]
Fabrication and characterization and biosensor application of gold nanoparticles on the carbon nanotubes
Accepted Manuscript Title: Fabrication and Characterization and Biosensor Application of Gold Nanoparticles on the Carbon Nanotubes Author: T. Ghodselahi N. Aghababaie H. Mobasheri K.Z. Salimi M.P. Akbarzadeh M.A. Vesaghi PII: DOI: Reference:
S0169-4332(15)01659-1 http://dx.doi.org/doi:10.1016/j.apsusc.2015.07.092 APSUSC 30819
To appear in:
APSUSC
Received date: Revised date: Accepted date:
15-4-2015 12-7-2015 14-7-2015
Please cite this article as: T. Ghodselahi, N. Aghababaie, H. Mobasheri, K.Z. Salimi, M.P. Akbarzadeh, M.A. Vesaghi, Fabrication and Characterization and Biosensor Application of Gold Nanoparticles on the Carbon Nanotubes, Applied Surface Science (2015), http://dx.doi.org/10.1016/j.apsusc.2015.07.092 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.
Fabrication and Characterization and Biosensor Application of Gold Nanoparticles on the Carbon Nanotubes
ip t
T. Ghodselahia,b*, N. Aghababaieb , H. Mobasheric,d, K. Z. Salimic, M. P. Akbarzadehe and M. A. Vesaghie a
Nano Mabna Iranian Inc., PO Box 1676664116, Tehran, Iran School of Physics, Institute for research in fundamental sciences, PO Box 19395-5531, Tehran, c Laboratory of Membrane Biophysics, Institute of Biochemistry and Biophysics, University of Tehran, PO Box 13145-1384, Tehran, Iran d Iran Biomaterials Research Institute (BRC), University of Tehran, Tehran, Iran e Department of Physics, Sharif University of Technology, PO Box 11365-9161,Tehran, Iran
us
cr
b
an
[email protected] Fax:98-21-22280415 phone: 98-21-22280692 Abstract: Gold nanoparticles (Au NPs) were synthesized by co-deposition of RF-Sputtering and
M
RF-PECVD from acetylene gas and Au target on the Carbon nanotubes (CNTs). The CNTs were prepared by Thermal Chemical Vapor Deposition (TCVD) and Pd nanoparticles catalyst. TEM
d
image shows that high-density and uniform distribution of Au NPs were grown on the CNTs.
te
XRD analysis indicates that Au NPs have fcc crystal structure and CNTs have a good graphite
Ac ce p
structure. Raman spectroscopy results suggest that our sample includes double-walled CNTs. It is resulted that intensity of D-band reduces and G- band intensity raises and Radial breathing mode (RBM) is changed by immobilizing of Au NPs on the CNTs. Raman results that the free electrons on the CNTs increase by immobilizing of Au NPs. Also Localized Surface Plasmon Resonance (LSPR) peak of Au NPs has red-shift and broadens when it is immobilized on the CNTs. The change in LSPR peak rises from decreasing of local electrons density on the Au NPs surface. Raman and LSPR spectroscopy suggest that there are charge transferring and chemical bonds between Au NPs and CNTs. We applied the prepared sensor chips of Au NPs @ CNTs to detect DNA primer at femtomolar concentration based on the LSPR technique. Keywords: gold nanoparticles; carbon nanotubes; Localized Surface Plasmon Resonance (LSPR) 1 Page 1 of 16
1. Introduction Novel nanomaterials are expected to further impact biomedicine as advanced biosensors, diagnostics, and drug delivery systems [1]. Composites containing both noble metal
ip t
nanoparticles and CNTs, in which nanoparticles are attached on the surface of the CNTs, have potential application in sensors, optical electronics, and heterogeneous catalysis due to their high
cr
specific area and electrical conductivity and peculiar structural characteristics [2, 3]. Gold and
us
silver coated CNT also improved broad-band optical limiter [4]. It was suggested that the Au NPs @CNT system is a potential candidate for a nanostructure-based DNA sensor [5] and for
an
fabricating amperometric acetylcholinesterase biosensor [6]. Au NPs @CNTs were formed in aqueous solution using 1-pyrenemethylamine as the inter linker. [7]. Synthesis and
M
characterization of carbon nanotube/metal nanoparticle composites in organic media have been
d
reported [8]. Decoration of carbon nanotubes with silver nanoparticles was used for advanced
te
CNT/polymer nanocomposites [9]. Au NPs can be loaded on CNTs by regenerative ion exchange too [10]. The functionalized multiwalled carbon nanotubes are used for such Au NPs @CNT
Ac ce p
nanocomposites [11, 12]. Patterning of Ag NPs on CNT using the electrochemical deposition method has been reported [13]. All of these studies indicate that high-density and uniform assembly of Au NPs on CNTs has a high potential application in different fields. In this paper, we introduce a simple method for the direct assembly of high density of Au NPs on CNTs to reach a LSPR biosensor chip. The manufacturing method is co-deposition of RFsputtering and RF-PECVD in a vacuum deposition system from acetylene gas and Au target. There are several advantages for this synthesis method. The synthesis of Au NPs on CNTs takes place at room temperature without requirement of any harmful chemical reaction. In this simple method, we have a homogeneous Au NPs immobilizing on CNTs without functionalizing of
2 Page 2 of 16
CNTs too. Moreover, acetylene gas plays an important role in the formation of Au NPs in plasma and assists to immobilize them on the CNTs. The inter-particle distance of Au NPs and LSPR absorption peak can be controlled by acetylene gas pressure in this method. The CNTs were
ip t
prepared by Thermal Chemical Vapor Deposition (TCVD) and Pd nanoparticles catalyst. Raman and LSPR spectroscopy were employed to investigate change in free electrons on the CNTs and
cr
local electron density on the surface of Au NPs when Au NPs were immobilized on the CNTs.
us
The prepared Au NPs @CNT LSPR chip sensors were applied to detect DNA primer at fM concentration by real time recording of LSPR peak without probe employing and label free. The
an
main results of the present research are synthesis of Au NPs @
CNTs sensor chips without functionalizing, study of charge transferring in interface of Au NPs
te
2. Experimental
d
M
and CNTs, and investigation of LSPR bio-sensor application of Au NPs @ CNTs chip.
Au NPs were prepared by a capacitance coupled RF-PECVD system with 13.56 MHz power
Ac ce p
supply. The reactor consists of two electrodes with different sizes. The smaller electrode was gold and was set as powered electrode. The other electrode was grounded through the body of the stainless steel chamber. The deposition was performed at room temperature on the CNTs and also on the quartz substrate over this electrode. The chamber was evacuated to a base pressure of 10−5 mbar prior to deposition and then pressure was increased to the desired pressure with acetylene gas. The deposition was carried out in a constant RF power of 160 W and initial pressure of 0.04 mbar. The details of Au NPs growth is similar deposition of Cu NPs which was reported in our previous paper [14-16]. The Au NPs content of samples increases with reduction of initial pressure of the chamber in constant power regime, by utilizing this property, carbon
3 Page 3 of 16
composite films are grown with different percentage of Au NPs and different grain size of Au NPs nanoparticle. When the initial pressure is less than 0.03 mbar, Au thin film will grow on CNTs and if the initial pressure is greater than 0.05 mbar Au NPs will not growth on CNTs,
ip t
therefore the pressure and RF power of the process was adjusted to give a proper LSPR absorption of samples. The CNTs were prepared by TCVD and Pd nanoparticles catalyst. The
cr
TCVD system consist a furnace, a quartz tube of 60 cm length and 40 mm inner diameter, a
us
temperature controller and a thermocouple. A flow of 80 sccm LPG is introduced to the reactor at 825º C for CNTs synthesis. The composition of LPG was C3 (54%), C4 (45%) and C5 (1%)
an
analyzed by a gas chromatograph (Hewlett Packard, Palo Alto, CA, USA). It also contains 10 ppm sulfur. After 15 min of CNTs growth, the reactor was allowed to cool down below 300 ºC
M
under a flow of Ar before exposure to air. Details of CNTs growth is given in our previous
d
reports [17-19]. In this work we used quartz substrate and spin coating technique for deposition
te
of Pd NPs catalyst on the substrate [20]. The spin speed and spin time were optimized as 4000 RPM and 20 s in order to obtain a uniform distribution and small size of Pd NPs on the quartz
Ac ce p
substrate. The samples dried at room temperature and these processes were repeated for 20 times. The substrate was quartz since its transparency property is suitable for biosensor application of LSPR of Au NPs. TEM image shows growth of Au NPs on the CNTs. The CNTs without and with Au NPs were characterized by Raman spectroscopy. The LSPR absorption spectra were recorded using UV-visible spectrometer in wavelength range of 400 - 850 nm. X-ray diffraction data of the samples were recorded in a powder diffractometer. The X-ray source was a Co Kα radiation. Using these LSPR sensor chips, fM concentration of single stranded DNA primers a decamer (ten-deoxycytosine) in T.E. buffer was detected. LSPR absorption spectra was recorded using UV-visible spectrometer Stellar.net (Florida, USA) which employs an optical fiber to
4 Page 4 of 16
transfer a non-polarized light beam (400 nm - 850 nm) through sensor chip of Au NPs @ CNTs on the quartz substrate to a CCD detector. The LSPR spectra of biosensor chip upon exposure to fM concentration of DNA primers was recorded inside a quartz cell and LSPR absorption peak
ip t
was recorded sequentially at intervals of 30 min for 3 hours. Recently we have reported synthesis and biosensor properties of Au NPs and Ag@Au bimetallic nanoparticles on the carbon thin
us
cr
films based on LSPR technique [21, 22].
3. Results and Discussion
an
The CNTs were prepared by TCVD on the quartz substrate. Then Au NPs were prepared by a capacitance coupled RF-PECVD system on the CNTs. For TEM sample preparation, an
M
extremely small amount of Au NPs @ CNTs was extracted from quartz substrate and was
d
suspended in ethanol solvent. The samples were dispersed on the carbon film coating TEM grids.
te
TEM micrograph of Au NPs @CNTs is shown in Fig 1. This image reveals the formation Au NPs with a narrow size distribution on the CNTs. This figure indicates that Au NPs with average
Ac ce p
particle size of 7 nm were immobilized almost homogeneously on the CNT with a diameter of less than 5 nm. In Fig.1, Point A shows cross section whereas a white point is observed in the center and Au NPs are environment.
5 Page 5 of 16
an
us
cr
ip t
A
M
Fig. 1. TEM micrograph of Au NPs@CNTs. Raman spectroscopy was used to characterize overall information of the structure and
d
crystallinity of the synthesized CNTs before and after Au NPs immobilizing. Raman spectrum of
te
the prepared CNTs and Au NPs @CNTs are shown in Fig 2a and b respectively. There are two
Ac ce p
main peaks in Fig 2a, G-band at 1581cm-1 which indicates the formation of graphitized CNTs and the D-band at 1330 cm-1 which indicates the existence of the disorder carbon such as defective graphite structure for CNTs (Solid line). After Au NPs immobilization on CNTs G band is shifted to lower frequency (1559 cm-1) and D-band frequency has not shift whereas its intensity reduces (Dashed line). The peak intensity ratio of G and D band (IG/ID) is obtained 0.99 for bare CNT and 1.15 for Au NPs @CNT. Unlike graphite, two most intense peaks of G band can be recognized which basically originate from the symmetry breaking of the tangential vibration when the graphene sheet is rolled to make a cylindrically shaped tube [22]. These peaks are labeled G+ for atomic displacements along the tube axis, and G− for modes with atomic displacement along the circumferential direction [23]. These two peaks can be observed in 6 Page 6 of 16
Raman spectra of single and double-walled CNTs [24]. In Fig 2a, G− becomes sharp and is appeared as a shoulder of G+ after immobilizing of Au NPs on the CNTs (Dashed line). The difference between the G band line shape for semiconducting and metallic CNTs is evident in the
ip t
line shape of the G− feature, which is broaden for metallic SWNTs in comparison with the semiconducting tubes, and this broadening is related to the presence of free electrons in
cr
nanotubes with metallic character [25, 26]. The observation of a metallic-like G band when a
us
semiconducting line shape should be observed indicates the presence of charged impurities [27].
(b)
CNT CNT+Au
ZONE 001 ZONE 001
RBM
1000
1500
2000
te
d
M
Intensity (a.u.)
Intensity (a.u.)
+
D G G
ZONE 001 Map 2
an
(a) CNT CNT+Au
2500
3000
100
Ac ce p
Raman shift (cm-1)
200
300
400
500
Raman shift (cm-1)
Fig. 2. Raman spectrum of the synthesized CNT and Au NPs @CNT ,G and D modes (a) and RBM modes (b).
Radial breathing modes (RBM) of CNTs without and with Au NPs immobilizing in low frequency region is shown in Fig 2b. The CNTs diameter can be estimated from RBM mode since its frequency has an inverse relation with CNT diameter [26]. For large diameter tube, the intensity of the RBM feature is weak and is hardly observable [23]. The RBM mode of the present sample is sharp and is observed in high frequency (around 300 cm-1) that suggests low diameter of CNTs. This mode is changed after Au NPs immobilizing as shown in Fig 2b. The 7 Page 7 of 16
RBM band also allows distinguishing between single, double and multi-walled CNTs [24]. The double-walled CNTs spectrum presents a double RBM due to the diameters of the inner and outer tubes [24]. There are two RBM bands in Fig 2b. The band of higher Raman shift
ip t
corresponds to the inner diameter and other with lower Raman shift corresponds to the outer diameter. After Au NPs deposition, the energies of the bands will not change, the intensity of
cr
photons that reach to inner CNTs will reduces hence the intensity of Raman shift of inner
us
diameter reduces as it can be seen in Fig. 2 b. The Raman spectroscopy results suggest that the present sample contains double walled CNTs. The appearance of G− after Au NPs immobilizing
an
on the CNTs indicates the presence of free electrons on carbon nanotubes with metallic character. Similar changes are observed by change in chirality of CNT. Since immobilizing Au
M
NPS on the CNTs does not affect the chirality, the reason of change in free electrons on the
d
CNTs is attributed to Au NPs and also chemical bonding and charge transferring between Au
Au (311)
Au (220)
10
C (102)
15
Au (200)
20
Au (111)
Intensity (a.u.)
25
C (004)
30
C (002)
Ac ce p
te
NPs and CNTs.
5
20
40
60
80
100
2 Theta (degree)
Fig. 3. XRD profile of Au NPs@ CNTs. 8 Page 8 of 16
X-ray diffraction profile of the Au NPs@ CNTs sample is shown in Fig 3. The diffraction peaks at 44.6º, 52º, 76.5º, 93.3º are assigned to (111), (200), (220), (311) plane of fcc Au crystal respectively [28]. The sharp diffraction peaks at 31ºand 64.5º are assigned to (002) and (004)
ip t
corresponding to inter-planar spacing of 3.41 A ˚of graphite structure. The small peak at 57º
(100) corresponds to a crystal spacing of 2.12 A˚ of ideal 2H graphite structure [29]. It was
cr
reported that the intensity of the (002) peak increases for lower alignment of the CNTs [30]. In
us
our sample, CNTs are not aligned and lie horizontally on the quartz substrate, but has a good graphite structure hence a sharp peak can be observed for inter-planar spacing. UV-vis
Ac ce p
te
d
M
an
absorption spectra of Au NPs (a), Au NPs @CNTs (b) and CNTs (c) are shown in Fig. 4.
Fig. 4. UV-vis absorption spectrum of Au NPs (a), Au NPs @CNT (b), CNT alone(C) and obtained data from subtract CNTs spectrum from Au NPs @CNT spectrum (d).
A peak at 556 nm is observed (spectrum a) for the sample of Au NPs on the quartz substrate that corresponds to the LSPR of Au NPs. When Au NPs were deposited on CNTs, LSPR peak lies on 9 Page 9 of 16
the absorption spectrum of CNTs and is shifted to 550 nm as one can see in Fig. 4 (spectrum b). The Au NPs were deposited on the quartz and also on the CNTs substrate in the same run of deposition. The LSPR peak of Au NPs is widen and is shifted to lower wavelengths when it is
ip t
immobilized on the CNTs. We extracted CNTs absorption spectrum from Au NPs @CNTs spectrum to eliminate the effect of slope which is present in spectrum of CNTs.
cr
The result of this subtracting process is shown with Dash-dotted line in Fig 4 (spectrum d). By
us
comparison of the obtained data and spectrum of Au NPs on the quartz substrate, (a, d lines), it is resulted that when Au NPs were immobilized on the CNTs, LSPR peak of Au NPs is shifted
an
from 556 to 589 nm and it broadens. This red-shift and broadening can be assigned to charge transferring between Au NPs and CNTs and reduction of local electron density on the surface of
M
Au NPs. This suggests an increase in the free electrons on the CNTs. The LSPR result is
Ac ce p
te
d
consistent with Raman results that were discussed in previous section.
Fig. 5. Real time LSPR absorption peak of Au NPs @CNTs in presence of the fM concentration of DNA primer up to 3h. Inset of figure reveals real time evolution of LSPR wavelength shift. 10 Page 10 of 16
The biosensor response of the prepared Au NPs@CNTs was investigated too. AuNPs@CNTs was utilized to detect DNA primer without probe immobilization and lable free. Real time LSPR spectra of Au NPs@CNTs in presence of DNA at fM concentrations are shown
ip t
in Fig 5. Also the corresponding real time LSPR wavelength shift is shown in the inset of Fig 5. A blue-shift was observed for the LSPR of Au NPs during 3 hours exposure to DNA. When the
cr
sample is exposed to DNA, the environment of Au NPs is changed immediately and inter-
us
particle distance increases, resulting in a blue-shift in LSPR peak. Then DNA is absorbed on the Au NPs and the inter-particles coupling reduces due to presence of DNA between NPs up to 3
an
hour. The observed blue-shift in real-time LSPR recording after DNA exposure can be attributed to breaking of inter-particles coupling due to change in environment dielectric constant without
d
M
any change in inter-particles distance. The wavelength shifts in inset of Fig. 5 follow from Eq. 1.
(1)
te
S (1 exp(t / ))
Ac ce p
where Sλ is wavelength shift sensitivity and τ is response time of LSPR sensor chip. The wavelength shift sensitivity and response time of LSPR sensor chips were estimated from fitting of data of inset of Fig 5 with Eq. 1 in presence of DNA primer at fM concentration. The wavelength shift sensitivity and response time of LSPR sensor chip of Au NPs@CNTs were extracted from the fitting were around 8.5 nm and 30 min, respectively.
4. Conclusions The LSPR chip sensor of Au NPs @CNTs was synthesized by co-deposition of RF-Sputtering and RF-PECVD from acetylene gas and Au target on the CNTs. The CNTs were prepared by TCVD and Pd nanoparticles catalyst. We obtained a high-density and uniform assembly of Au 11 Page 11 of 16
NPs on the CNTs without functionalizing of CNTs or Au NPs. The Raman results indicate that our sample includes double-walled CNTs and free electrons on them increases after immobilizing of Au NPs on the CNTs. Also change in position and width of LSPR peak of Au
ip t
NPs indicated that local electron density on the Au NPs surface reduces which is in agreement with Raman spectra results. The synthesis of high-density and uniform distribution of the Au
cr
NPs on the CNTs and the study of charge transferring in interface of Au NPs and CNTs are
us
important for LSPR sensor applications of Au NPs@CNTs. The LSPR sensor chips were utilized to detect DNA primer at fM level without probe in a label free manner. Our chip sensor shows a
an
good response to low concentration of DNA. A short response time and a high sensitivity were obtained for our LSPR sensor chip of Au NPs@CNTs.
d
data and Mrs. Amini for TEM image.
M
Acknowledgement: The authors would like to thank Dr. Malekfar for discussion about Raman
te
References
[1] R. Singh, D. Pantarotto, D. McCarthy, O. Chaloin, J. Hoebeke, C. D. Partidos, J. P. Briand,
Ac ce p
M. Prato, A. Bianco, K. Kostarelos, J. Am. Chem. Soc. 127 (2005) 4388. [2] Y. Shi, R. Yang, P. K. Yuet, Carbon 47 (2009) 1146. [3] X. Li, Y. Liu, L. Fu, L. Cao, D. Wei, G. Yu, D. Zhu, Carbon 44 (2006) 3113. [4] K. C. Chin, A. Gohel, W. Z. Chen, H. I. Elim, W. Ji, G. L. Chong, C. H. Sow, A. T. S. Wee, Chem. Phys. Lett. 409 (2005)85.
[5] P. Pannopard, P. Khongpracha, M. Probst, J. Limtrakul, J. Mol. Graph. Model. 26 (2008) 1066. [6] D. Du, M. Wang, J. Cai, Y. Qin, A. Zhang, Sens. Actu. B 143 (2010) 524. [7] Y. Y. Ou, M. H. Huang, J. Phys. Chem. B 110 (2006) 2031.
12 Page 12 of 16
[8] V. Tzitzios, V. Georgakilas, E. Oikonomou, M. Karakassides, D. Petridis, Carbon 44 (2006) 848. [9] F. Xin, L. Li, Composites 42 (2011) 961.
[11] X. Hou, L. Wang, F. Zhou, F. Wang, Carbon 47 (2009) 1209.
cr
[12] G. Wei, C. Pan, J. Reichert, K. D. Jandt, Carbon 48 (2010) 645.
ip t
[10] Y. Gu, X. Hou, H. Hu, B. F. Yu, L.Wang, F. Zhou, Mater. Chem. Phys. 116 (2009) 284.
us
[13] M. P. N. Bui, X. H. Pham, K. N. Han, C. A. Li, Y. S. Kim, G. H. Seong, Sens. Actu. B 150 (2010) 436.
an
[14] T. Ghodselahi, M. A. Vesaghi, A. Shafiekhani, A. Baradaran, A. Karimi, Z. Mobini, Surf. Coat. Technol. 202 (2008) 2731.
M
[15] T. Ghodselahi, M. A. Vesaghi, A. Gelali, H. Zahrabi, S. Solaymani, Appl. Surf. Sci. 258
d
(2011) 727.
te
[16] T. Ghodselahi, M. A. Vesaghi, A.Shafiekhani, J. Phys. D: Appl. Phys. 42 (2008) 015308.
1511.
Ac ce p
[17] M. P. Akbarzadeh, M. Ranjbar, M. A. Vesaghi, A. Shafiekhani, Appl. Surf. Sci. 257 (2010)
[18] M. P. Akbarzadeh, A. Shafiekhani, M. A. Vesaghi, Appl. Surf. Sci. 256 (2009) 1365. [19] M. P. Akbarzadeh, R. Poursalehi, M. A.Vesaghi, A. Shafiekhani, physica B 405 (2010) 3468.
[20] D. Bornside, C. Macosko, L. Scriven, J. Appl. Phys. 66 (1989) 5185. [21] T. Ghodselahi, S. Arsalani, T. Neishaboorynejad, Appl. Surf. Sci. 301 (2014) 230. [22] T. Ghodselahi, S. Hoornama, M.A. Vesaghi, B. Ranjbar, A. Azizi, H. Mobasheri Appl. Surf. Sci. 314 (2014)138. [23] A. Jorio, M. A. Pimenta, A. G. S. Filho, R. Saito, G. Dresselhaus, M. S. Dresselhaus, New J.
13 Page 13 of 16
Phys. 5 (2003) 139.1. [24] S. Costa, E. B. Palen, M. Kruszynska, A. Bachmatiuk, R. J. Kalenczuk, Materials SciencePoland 26 (2008) 433.
ip t
[25] M. A. Pimenta, A. Marucci, S. Empedocles, M. Bawendi, E. B. Hanlon, A. M. Rao, P. C. Eklund, R. E. Smalley, G. Dresselhaus, M. S. Dresselhaus, Phys. Rev.B, 58 (1998) 16016.
cr
[26] S. D. M. Brown, A. Jorio, P. Corio, M. S. Dresselhaus, G. Dresselhaus, R. Saito, K. Kneipp,
us
Phys. Rev. B 63 (2001) 155414.
[27] A. M. Rao, P. C. Eklund, S. Bandow, A. Thess, R. E. Smalley, Nature 388 (1997) 257.
an
[28] JC-PDS database, Internatinal Center for Diffraction Data (1999). [29] J. Hahn, S. B. Heo, J. S. Suh, Carbon 43 (2005) 2618.
Ac ce p
te
d
M
[30] A. Cao, C. Xu, L. Ji, D. Wu, B. Wei, Chem. Phys. Lett. 344 (2011) 13.
14 Page 14 of 16
ip t cr us
Fig. 1. TEM micrograph of Au NPs@CNTs.
an
Fig. 2. Raman spectrum of the synthesized CNT and Au NPs @CNT ,G and D modes (a) and
Fig. 3. XRD profile of Au NPs@ CNTs.
M
RBM modes (b).
Fig. 4. UV-vis absorption spectrum of Au NPs (a), Au NPs @CNT (b), CNT alone(C) and
te
d
obtained data from subtract CNTs spectrum from Au NPs @CNT spectrum (d). Fig. 5. Real time LSPR absorption peak of Au NPs @CNTs in presence of the fM concentration
Ac ce p
of DNA primer up to 3h. Inset of figure reveals real time evolution of LSPR wavelength shift.
Introducing a simple method for the direct assembly of Au NPs on CNTs to reach a Localized Surface Plasmon Resonance (LSPR) biosensor chip.
The prepared biosensor chip was characterized by TEM, XRD, Raman spectroscopy and LSPR spectroscopy.
Raman and LSPR spectroscopy were employed to investigate charge transferring in interface of Au NPs and CNTs.
Au NPs @CNT LSPR chip sensors were applied to detect DNA primer at fM concentration by recording of LSPR peak without probe employing and label free. 15 Page 15 of 16
16
Page 16 of 16
d
te
Ac ce p us
an
M
cr
ip t
S0169-4332(15)01659-1 http://dx.doi.org/doi:10.1016/j.apsusc.2015.07.092 APSUSC 30819
To appear in:
APSUSC
Received date: Revised date: Accepted date:
15-4-2015 12-7-2015 14-7-2015
Please cite this article as: T. Ghodselahi, N. Aghababaie, H. Mobasheri, K.Z. Salimi, M.P. Akbarzadeh, M.A. Vesaghi, Fabrication and Characterization and Biosensor Application of Gold Nanoparticles on the Carbon Nanotubes, Applied Surface Science (2015), http://dx.doi.org/10.1016/j.apsusc.2015.07.092 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.
Fabrication and Characterization and Biosensor Application of Gold Nanoparticles on the Carbon Nanotubes
ip t
T. Ghodselahia,b*, N. Aghababaieb , H. Mobasheric,d, K. Z. Salimic, M. P. Akbarzadehe and M. A. Vesaghie a
Nano Mabna Iranian Inc., PO Box 1676664116, Tehran, Iran School of Physics, Institute for research in fundamental sciences, PO Box 19395-5531, Tehran, c Laboratory of Membrane Biophysics, Institute of Biochemistry and Biophysics, University of Tehran, PO Box 13145-1384, Tehran, Iran d Iran Biomaterials Research Institute (BRC), University of Tehran, Tehran, Iran e Department of Physics, Sharif University of Technology, PO Box 11365-9161,Tehran, Iran
us
cr
b
an
[email protected] Fax:98-21-22280415 phone: 98-21-22280692 Abstract: Gold nanoparticles (Au NPs) were synthesized by co-deposition of RF-Sputtering and
M
RF-PECVD from acetylene gas and Au target on the Carbon nanotubes (CNTs). The CNTs were prepared by Thermal Chemical Vapor Deposition (TCVD) and Pd nanoparticles catalyst. TEM
d
image shows that high-density and uniform distribution of Au NPs were grown on the CNTs.
te
XRD analysis indicates that Au NPs have fcc crystal structure and CNTs have a good graphite
Ac ce p
structure. Raman spectroscopy results suggest that our sample includes double-walled CNTs. It is resulted that intensity of D-band reduces and G- band intensity raises and Radial breathing mode (RBM) is changed by immobilizing of Au NPs on the CNTs. Raman results that the free electrons on the CNTs increase by immobilizing of Au NPs. Also Localized Surface Plasmon Resonance (LSPR) peak of Au NPs has red-shift and broadens when it is immobilized on the CNTs. The change in LSPR peak rises from decreasing of local electrons density on the Au NPs surface. Raman and LSPR spectroscopy suggest that there are charge transferring and chemical bonds between Au NPs and CNTs. We applied the prepared sensor chips of Au NPs @ CNTs to detect DNA primer at femtomolar concentration based on the LSPR technique. Keywords: gold nanoparticles; carbon nanotubes; Localized Surface Plasmon Resonance (LSPR) 1 Page 1 of 16
1. Introduction Novel nanomaterials are expected to further impact biomedicine as advanced biosensors, diagnostics, and drug delivery systems [1]. Composites containing both noble metal
ip t
nanoparticles and CNTs, in which nanoparticles are attached on the surface of the CNTs, have potential application in sensors, optical electronics, and heterogeneous catalysis due to their high
cr
specific area and electrical conductivity and peculiar structural characteristics [2, 3]. Gold and
us
silver coated CNT also improved broad-band optical limiter [4]. It was suggested that the Au NPs @CNT system is a potential candidate for a nanostructure-based DNA sensor [5] and for
an
fabricating amperometric acetylcholinesterase biosensor [6]. Au NPs @CNTs were formed in aqueous solution using 1-pyrenemethylamine as the inter linker. [7]. Synthesis and
M
characterization of carbon nanotube/metal nanoparticle composites in organic media have been
d
reported [8]. Decoration of carbon nanotubes with silver nanoparticles was used for advanced
te
CNT/polymer nanocomposites [9]. Au NPs can be loaded on CNTs by regenerative ion exchange too [10]. The functionalized multiwalled carbon nanotubes are used for such Au NPs @CNT
Ac ce p
nanocomposites [11, 12]. Patterning of Ag NPs on CNT using the electrochemical deposition method has been reported [13]. All of these studies indicate that high-density and uniform assembly of Au NPs on CNTs has a high potential application in different fields. In this paper, we introduce a simple method for the direct assembly of high density of Au NPs on CNTs to reach a LSPR biosensor chip. The manufacturing method is co-deposition of RFsputtering and RF-PECVD in a vacuum deposition system from acetylene gas and Au target. There are several advantages for this synthesis method. The synthesis of Au NPs on CNTs takes place at room temperature without requirement of any harmful chemical reaction. In this simple method, we have a homogeneous Au NPs immobilizing on CNTs without functionalizing of
2 Page 2 of 16
CNTs too. Moreover, acetylene gas plays an important role in the formation of Au NPs in plasma and assists to immobilize them on the CNTs. The inter-particle distance of Au NPs and LSPR absorption peak can be controlled by acetylene gas pressure in this method. The CNTs were
ip t
prepared by Thermal Chemical Vapor Deposition (TCVD) and Pd nanoparticles catalyst. Raman and LSPR spectroscopy were employed to investigate change in free electrons on the CNTs and
cr
local electron density on the surface of Au NPs when Au NPs were immobilized on the CNTs.
us
The prepared Au NPs @CNT LSPR chip sensors were applied to detect DNA primer at fM concentration by real time recording of LSPR peak without probe employing and label free. The
an
main results of the present research are synthesis of Au NPs @
CNTs sensor chips without functionalizing, study of charge transferring in interface of Au NPs
te
2. Experimental
d
M
and CNTs, and investigation of LSPR bio-sensor application of Au NPs @ CNTs chip.
Au NPs were prepared by a capacitance coupled RF-PECVD system with 13.56 MHz power
Ac ce p
supply. The reactor consists of two electrodes with different sizes. The smaller electrode was gold and was set as powered electrode. The other electrode was grounded through the body of the stainless steel chamber. The deposition was performed at room temperature on the CNTs and also on the quartz substrate over this electrode. The chamber was evacuated to a base pressure of 10−5 mbar prior to deposition and then pressure was increased to the desired pressure with acetylene gas. The deposition was carried out in a constant RF power of 160 W and initial pressure of 0.04 mbar. The details of Au NPs growth is similar deposition of Cu NPs which was reported in our previous paper [14-16]. The Au NPs content of samples increases with reduction of initial pressure of the chamber in constant power regime, by utilizing this property, carbon
3 Page 3 of 16
composite films are grown with different percentage of Au NPs and different grain size of Au NPs nanoparticle. When the initial pressure is less than 0.03 mbar, Au thin film will grow on CNTs and if the initial pressure is greater than 0.05 mbar Au NPs will not growth on CNTs,
ip t
therefore the pressure and RF power of the process was adjusted to give a proper LSPR absorption of samples. The CNTs were prepared by TCVD and Pd nanoparticles catalyst. The
cr
TCVD system consist a furnace, a quartz tube of 60 cm length and 40 mm inner diameter, a
us
temperature controller and a thermocouple. A flow of 80 sccm LPG is introduced to the reactor at 825º C for CNTs synthesis. The composition of LPG was C3 (54%), C4 (45%) and C5 (1%)
an
analyzed by a gas chromatograph (Hewlett Packard, Palo Alto, CA, USA). It also contains 10 ppm sulfur. After 15 min of CNTs growth, the reactor was allowed to cool down below 300 ºC
M
under a flow of Ar before exposure to air. Details of CNTs growth is given in our previous
d
reports [17-19]. In this work we used quartz substrate and spin coating technique for deposition
te
of Pd NPs catalyst on the substrate [20]. The spin speed and spin time were optimized as 4000 RPM and 20 s in order to obtain a uniform distribution and small size of Pd NPs on the quartz
Ac ce p
substrate. The samples dried at room temperature and these processes were repeated for 20 times. The substrate was quartz since its transparency property is suitable for biosensor application of LSPR of Au NPs. TEM image shows growth of Au NPs on the CNTs. The CNTs without and with Au NPs were characterized by Raman spectroscopy. The LSPR absorption spectra were recorded using UV-visible spectrometer in wavelength range of 400 - 850 nm. X-ray diffraction data of the samples were recorded in a powder diffractometer. The X-ray source was a Co Kα radiation. Using these LSPR sensor chips, fM concentration of single stranded DNA primers a decamer (ten-deoxycytosine) in T.E. buffer was detected. LSPR absorption spectra was recorded using UV-visible spectrometer Stellar.net (Florida, USA) which employs an optical fiber to
4 Page 4 of 16
transfer a non-polarized light beam (400 nm - 850 nm) through sensor chip of Au NPs @ CNTs on the quartz substrate to a CCD detector. The LSPR spectra of biosensor chip upon exposure to fM concentration of DNA primers was recorded inside a quartz cell and LSPR absorption peak
ip t
was recorded sequentially at intervals of 30 min for 3 hours. Recently we have reported synthesis and biosensor properties of Au NPs and Ag@Au bimetallic nanoparticles on the carbon thin
us
cr
films based on LSPR technique [21, 22].
3. Results and Discussion
an
The CNTs were prepared by TCVD on the quartz substrate. Then Au NPs were prepared by a capacitance coupled RF-PECVD system on the CNTs. For TEM sample preparation, an
M
extremely small amount of Au NPs @ CNTs was extracted from quartz substrate and was
d
suspended in ethanol solvent. The samples were dispersed on the carbon film coating TEM grids.
te
TEM micrograph of Au NPs @CNTs is shown in Fig 1. This image reveals the formation Au NPs with a narrow size distribution on the CNTs. This figure indicates that Au NPs with average
Ac ce p
particle size of 7 nm were immobilized almost homogeneously on the CNT with a diameter of less than 5 nm. In Fig.1, Point A shows cross section whereas a white point is observed in the center and Au NPs are environment.
5 Page 5 of 16
an
us
cr
ip t
A
M
Fig. 1. TEM micrograph of Au NPs@CNTs. Raman spectroscopy was used to characterize overall information of the structure and
d
crystallinity of the synthesized CNTs before and after Au NPs immobilizing. Raman spectrum of
te
the prepared CNTs and Au NPs @CNTs are shown in Fig 2a and b respectively. There are two
Ac ce p
main peaks in Fig 2a, G-band at 1581cm-1 which indicates the formation of graphitized CNTs and the D-band at 1330 cm-1 which indicates the existence of the disorder carbon such as defective graphite structure for CNTs (Solid line). After Au NPs immobilization on CNTs G band is shifted to lower frequency (1559 cm-1) and D-band frequency has not shift whereas its intensity reduces (Dashed line). The peak intensity ratio of G and D band (IG/ID) is obtained 0.99 for bare CNT and 1.15 for Au NPs @CNT. Unlike graphite, two most intense peaks of G band can be recognized which basically originate from the symmetry breaking of the tangential vibration when the graphene sheet is rolled to make a cylindrically shaped tube [22]. These peaks are labeled G+ for atomic displacements along the tube axis, and G− for modes with atomic displacement along the circumferential direction [23]. These two peaks can be observed in 6 Page 6 of 16
Raman spectra of single and double-walled CNTs [24]. In Fig 2a, G− becomes sharp and is appeared as a shoulder of G+ after immobilizing of Au NPs on the CNTs (Dashed line). The difference between the G band line shape for semiconducting and metallic CNTs is evident in the
ip t
line shape of the G− feature, which is broaden for metallic SWNTs in comparison with the semiconducting tubes, and this broadening is related to the presence of free electrons in
cr
nanotubes with metallic character [25, 26]. The observation of a metallic-like G band when a
us
semiconducting line shape should be observed indicates the presence of charged impurities [27].
(b)
CNT CNT+Au
ZONE 001 ZONE 001
RBM
1000
1500
2000
te
d
M
Intensity (a.u.)
Intensity (a.u.)
+
D G G
ZONE 001 Map 2
an
(a) CNT CNT+Au
2500
3000
100
Ac ce p
Raman shift (cm-1)
200
300
400
500
Raman shift (cm-1)
Fig. 2. Raman spectrum of the synthesized CNT and Au NPs @CNT ,G and D modes (a) and RBM modes (b).
Radial breathing modes (RBM) of CNTs without and with Au NPs immobilizing in low frequency region is shown in Fig 2b. The CNTs diameter can be estimated from RBM mode since its frequency has an inverse relation with CNT diameter [26]. For large diameter tube, the intensity of the RBM feature is weak and is hardly observable [23]. The RBM mode of the present sample is sharp and is observed in high frequency (around 300 cm-1) that suggests low diameter of CNTs. This mode is changed after Au NPs immobilizing as shown in Fig 2b. The 7 Page 7 of 16
RBM band also allows distinguishing between single, double and multi-walled CNTs [24]. The double-walled CNTs spectrum presents a double RBM due to the diameters of the inner and outer tubes [24]. There are two RBM bands in Fig 2b. The band of higher Raman shift
ip t
corresponds to the inner diameter and other with lower Raman shift corresponds to the outer diameter. After Au NPs deposition, the energies of the bands will not change, the intensity of
cr
photons that reach to inner CNTs will reduces hence the intensity of Raman shift of inner
us
diameter reduces as it can be seen in Fig. 2 b. The Raman spectroscopy results suggest that the present sample contains double walled CNTs. The appearance of G− after Au NPs immobilizing
an
on the CNTs indicates the presence of free electrons on carbon nanotubes with metallic character. Similar changes are observed by change in chirality of CNT. Since immobilizing Au
M
NPS on the CNTs does not affect the chirality, the reason of change in free electrons on the
d
CNTs is attributed to Au NPs and also chemical bonding and charge transferring between Au
Au (311)
Au (220)
10
C (102)
15
Au (200)
20
Au (111)
Intensity (a.u.)
25
C (004)
30
C (002)
Ac ce p
te
NPs and CNTs.
5
20
40
60
80
100
2 Theta (degree)
Fig. 3. XRD profile of Au NPs@ CNTs. 8 Page 8 of 16
X-ray diffraction profile of the Au NPs@ CNTs sample is shown in Fig 3. The diffraction peaks at 44.6º, 52º, 76.5º, 93.3º are assigned to (111), (200), (220), (311) plane of fcc Au crystal respectively [28]. The sharp diffraction peaks at 31ºand 64.5º are assigned to (002) and (004)
ip t
corresponding to inter-planar spacing of 3.41 A ˚of graphite structure. The small peak at 57º
(100) corresponds to a crystal spacing of 2.12 A˚ of ideal 2H graphite structure [29]. It was
cr
reported that the intensity of the (002) peak increases for lower alignment of the CNTs [30]. In
us
our sample, CNTs are not aligned and lie horizontally on the quartz substrate, but has a good graphite structure hence a sharp peak can be observed for inter-planar spacing. UV-vis
Ac ce p
te
d
M
an
absorption spectra of Au NPs (a), Au NPs @CNTs (b) and CNTs (c) are shown in Fig. 4.
Fig. 4. UV-vis absorption spectrum of Au NPs (a), Au NPs @CNT (b), CNT alone(C) and obtained data from subtract CNTs spectrum from Au NPs @CNT spectrum (d).
A peak at 556 nm is observed (spectrum a) for the sample of Au NPs on the quartz substrate that corresponds to the LSPR of Au NPs. When Au NPs were deposited on CNTs, LSPR peak lies on 9 Page 9 of 16
the absorption spectrum of CNTs and is shifted to 550 nm as one can see in Fig. 4 (spectrum b). The Au NPs were deposited on the quartz and also on the CNTs substrate in the same run of deposition. The LSPR peak of Au NPs is widen and is shifted to lower wavelengths when it is
ip t
immobilized on the CNTs. We extracted CNTs absorption spectrum from Au NPs @CNTs spectrum to eliminate the effect of slope which is present in spectrum of CNTs.
cr
The result of this subtracting process is shown with Dash-dotted line in Fig 4 (spectrum d). By
us
comparison of the obtained data and spectrum of Au NPs on the quartz substrate, (a, d lines), it is resulted that when Au NPs were immobilized on the CNTs, LSPR peak of Au NPs is shifted
an
from 556 to 589 nm and it broadens. This red-shift and broadening can be assigned to charge transferring between Au NPs and CNTs and reduction of local electron density on the surface of
M
Au NPs. This suggests an increase in the free electrons on the CNTs. The LSPR result is
Ac ce p
te
d
consistent with Raman results that were discussed in previous section.
Fig. 5. Real time LSPR absorption peak of Au NPs @CNTs in presence of the fM concentration of DNA primer up to 3h. Inset of figure reveals real time evolution of LSPR wavelength shift. 10 Page 10 of 16
The biosensor response of the prepared Au NPs@CNTs was investigated too. AuNPs@CNTs was utilized to detect DNA primer without probe immobilization and lable free. Real time LSPR spectra of Au NPs@CNTs in presence of DNA at fM concentrations are shown
ip t
in Fig 5. Also the corresponding real time LSPR wavelength shift is shown in the inset of Fig 5. A blue-shift was observed for the LSPR of Au NPs during 3 hours exposure to DNA. When the
cr
sample is exposed to DNA, the environment of Au NPs is changed immediately and inter-
us
particle distance increases, resulting in a blue-shift in LSPR peak. Then DNA is absorbed on the Au NPs and the inter-particles coupling reduces due to presence of DNA between NPs up to 3
an
hour. The observed blue-shift in real-time LSPR recording after DNA exposure can be attributed to breaking of inter-particles coupling due to change in environment dielectric constant without
d
M
any change in inter-particles distance. The wavelength shifts in inset of Fig. 5 follow from Eq. 1.
(1)
te
S (1 exp(t / ))
Ac ce p
where Sλ is wavelength shift sensitivity and τ is response time of LSPR sensor chip. The wavelength shift sensitivity and response time of LSPR sensor chips were estimated from fitting of data of inset of Fig 5 with Eq. 1 in presence of DNA primer at fM concentration. The wavelength shift sensitivity and response time of LSPR sensor chip of Au NPs@CNTs were extracted from the fitting were around 8.5 nm and 30 min, respectively.
4. Conclusions The LSPR chip sensor of Au NPs @CNTs was synthesized by co-deposition of RF-Sputtering and RF-PECVD from acetylene gas and Au target on the CNTs. The CNTs were prepared by TCVD and Pd nanoparticles catalyst. We obtained a high-density and uniform assembly of Au 11 Page 11 of 16
NPs on the CNTs without functionalizing of CNTs or Au NPs. The Raman results indicate that our sample includes double-walled CNTs and free electrons on them increases after immobilizing of Au NPs on the CNTs. Also change in position and width of LSPR peak of Au
ip t
NPs indicated that local electron density on the Au NPs surface reduces which is in agreement with Raman spectra results. The synthesis of high-density and uniform distribution of the Au
cr
NPs on the CNTs and the study of charge transferring in interface of Au NPs and CNTs are
us
important for LSPR sensor applications of Au NPs@CNTs. The LSPR sensor chips were utilized to detect DNA primer at fM level without probe in a label free manner. Our chip sensor shows a
an
good response to low concentration of DNA. A short response time and a high sensitivity were obtained for our LSPR sensor chip of Au NPs@CNTs.
d
data and Mrs. Amini for TEM image.
M
Acknowledgement: The authors would like to thank Dr. Malekfar for discussion about Raman
te
References
[1] R. Singh, D. Pantarotto, D. McCarthy, O. Chaloin, J. Hoebeke, C. D. Partidos, J. P. Briand,
Ac ce p
M. Prato, A. Bianco, K. Kostarelos, J. Am. Chem. Soc. 127 (2005) 4388. [2] Y. Shi, R. Yang, P. K. Yuet, Carbon 47 (2009) 1146. [3] X. Li, Y. Liu, L. Fu, L. Cao, D. Wei, G. Yu, D. Zhu, Carbon 44 (2006) 3113. [4] K. C. Chin, A. Gohel, W. Z. Chen, H. I. Elim, W. Ji, G. L. Chong, C. H. Sow, A. T. S. Wee, Chem. Phys. Lett. 409 (2005)85.
[5] P. Pannopard, P. Khongpracha, M. Probst, J. Limtrakul, J. Mol. Graph. Model. 26 (2008) 1066. [6] D. Du, M. Wang, J. Cai, Y. Qin, A. Zhang, Sens. Actu. B 143 (2010) 524. [7] Y. Y. Ou, M. H. Huang, J. Phys. Chem. B 110 (2006) 2031.
12 Page 12 of 16
[8] V. Tzitzios, V. Georgakilas, E. Oikonomou, M. Karakassides, D. Petridis, Carbon 44 (2006) 848. [9] F. Xin, L. Li, Composites 42 (2011) 961.
[11] X. Hou, L. Wang, F. Zhou, F. Wang, Carbon 47 (2009) 1209.
cr
[12] G. Wei, C. Pan, J. Reichert, K. D. Jandt, Carbon 48 (2010) 645.
ip t
[10] Y. Gu, X. Hou, H. Hu, B. F. Yu, L.Wang, F. Zhou, Mater. Chem. Phys. 116 (2009) 284.
us
[13] M. P. N. Bui, X. H. Pham, K. N. Han, C. A. Li, Y. S. Kim, G. H. Seong, Sens. Actu. B 150 (2010) 436.
an
[14] T. Ghodselahi, M. A. Vesaghi, A. Shafiekhani, A. Baradaran, A. Karimi, Z. Mobini, Surf. Coat. Technol. 202 (2008) 2731.
M
[15] T. Ghodselahi, M. A. Vesaghi, A. Gelali, H. Zahrabi, S. Solaymani, Appl. Surf. Sci. 258
d
(2011) 727.
te
[16] T. Ghodselahi, M. A. Vesaghi, A.Shafiekhani, J. Phys. D: Appl. Phys. 42 (2008) 015308.
1511.
Ac ce p
[17] M. P. Akbarzadeh, M. Ranjbar, M. A. Vesaghi, A. Shafiekhani, Appl. Surf. Sci. 257 (2010)
[18] M. P. Akbarzadeh, A. Shafiekhani, M. A. Vesaghi, Appl. Surf. Sci. 256 (2009) 1365. [19] M. P. Akbarzadeh, R. Poursalehi, M. A.Vesaghi, A. Shafiekhani, physica B 405 (2010) 3468.
[20] D. Bornside, C. Macosko, L. Scriven, J. Appl. Phys. 66 (1989) 5185. [21] T. Ghodselahi, S. Arsalani, T. Neishaboorynejad, Appl. Surf. Sci. 301 (2014) 230. [22] T. Ghodselahi, S. Hoornama, M.A. Vesaghi, B. Ranjbar, A. Azizi, H. Mobasheri Appl. Surf. Sci. 314 (2014)138. [23] A. Jorio, M. A. Pimenta, A. G. S. Filho, R. Saito, G. Dresselhaus, M. S. Dresselhaus, New J.
13 Page 13 of 16
Phys. 5 (2003) 139.1. [24] S. Costa, E. B. Palen, M. Kruszynska, A. Bachmatiuk, R. J. Kalenczuk, Materials SciencePoland 26 (2008) 433.
ip t
[25] M. A. Pimenta, A. Marucci, S. Empedocles, M. Bawendi, E. B. Hanlon, A. M. Rao, P. C. Eklund, R. E. Smalley, G. Dresselhaus, M. S. Dresselhaus, Phys. Rev.B, 58 (1998) 16016.
cr
[26] S. D. M. Brown, A. Jorio, P. Corio, M. S. Dresselhaus, G. Dresselhaus, R. Saito, K. Kneipp,
us
Phys. Rev. B 63 (2001) 155414.
[27] A. M. Rao, P. C. Eklund, S. Bandow, A. Thess, R. E. Smalley, Nature 388 (1997) 257.
an
[28] JC-PDS database, Internatinal Center for Diffraction Data (1999). [29] J. Hahn, S. B. Heo, J. S. Suh, Carbon 43 (2005) 2618.
Ac ce p
te
d
M
[30] A. Cao, C. Xu, L. Ji, D. Wu, B. Wei, Chem. Phys. Lett. 344 (2011) 13.
14 Page 14 of 16
ip t cr us
Fig. 1. TEM micrograph of Au NPs@CNTs.
an
Fig. 2. Raman spectrum of the synthesized CNT and Au NPs @CNT ,G and D modes (a) and
Fig. 3. XRD profile of Au NPs@ CNTs.
M
RBM modes (b).
Fig. 4. UV-vis absorption spectrum of Au NPs (a), Au NPs @CNT (b), CNT alone(C) and
te
d
obtained data from subtract CNTs spectrum from Au NPs @CNT spectrum (d). Fig. 5. Real time LSPR absorption peak of Au NPs @CNTs in presence of the fM concentration
Ac ce p
of DNA primer up to 3h. Inset of figure reveals real time evolution of LSPR wavelength shift.
Introducing a simple method for the direct assembly of Au NPs on CNTs to reach a Localized Surface Plasmon Resonance (LSPR) biosensor chip.
The prepared biosensor chip was characterized by TEM, XRD, Raman spectroscopy and LSPR spectroscopy.
Raman and LSPR spectroscopy were employed to investigate charge transferring in interface of Au NPs and CNTs.
Au NPs @CNT LSPR chip sensors were applied to detect DNA primer at fM concentration by recording of LSPR peak without probe employing and label free. 15 Page 15 of 16
16
Page 16 of 16
d
te
Ac ce p us
an
M
cr
ip t