Preparation of thermosensitive gold nanoparticles by plasma pretreatment and UV grafted polymerization

Preparation of thermosensitive gold nanoparticles by plasma pretreatment and UV grafted polymerization

Thin Solid Films 518 (2010) 7557–7562 Contents lists available at ScienceDirect Thin Solid Films j o u r n a l h o m e p a g e : w w w. e l s ev i e...

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Thin Solid Films 518 (2010) 7557–7562

Contents lists available at ScienceDirect

Thin Solid Films j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / t s f

Preparation of thermosensitive gold nanoparticles by plasma pretreatment and UV grafted polymerization Ko-Shao Chen a,⁎, Tsui-Shan Hung a, Hsin-Ming Wu a, Jen-Yuan Wu a, Ming-Tse Lin b, Chi-Kuang Feng c a b c

Department of Materials Engineering, Tatung University, Taipei, Taiwan Department of Bioengineering, Tatung University, Taipei, Taiwan Department of Medical Research and Education, Taipei Veterans General Hospital, Taiwan

a r t i c l e

i n f o

Available online 21 May 2010 Keywords: Plasma Graft Gold nanoparticle Surface modification

a b s t r a c t This work is to develop an easy method of plasma treatment and graft polymerization to prepare thermosensitive gold nanoparticles. Gold nanoparticles (Nano-Au) were reduced by trisodium citrate combined with hydrogen tetrachloroaurate(III) tetrahydrate (chloroauric acid) and modified with 11mercaptoundecanoic acid (MUA) by the self-assembly monolayers (SAM). The surface graft polymerization of N-isopropylacrylamide (NIPAAm) was carried out by two steps, using O2 plasma pretreatment of the surface on MUA SAM modified Nano-Au to form the peroxide groups on Nano-Au(MUA), and then subsequently using UV light to induce grafting with thermosensitive polymer. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to direct investigation of the particle size and morphology in situ. The diameters of the gold nanoparticles measured from the TEM images are in good agreement with data measured at room temperature which is about 15 nm. The thermosensitive gold nanoparticles were characterized by chemical structure of surface (ESCA) and Fourier-transform infrared spectroscopy (FTIR). ESCA result suggests that plasma treatments can be employed to generate peroxides on the Nano-Au(MUA) for the subsequent UV graft polymerization of PNIPAAm. © 2010 Elsevier B.V. All rights reserved.

1. Introduction Metallic nanoparticles became a subject which has been paid much attention during the past decade due to their unique physical and chemical properties and corresponding broad applications in catalysis, photonics, electronics, optics, sensors, drug delivery and so on [1]. Nano-Au exhibit surface plasmon absorption in the visible region [2]. Based on the optical properties, chromatic sensors actuators, antibacterial/antimicrobial materials, and drug delivery vehicles using Nano-Au have been widely investigated [3–5]. Potential applications such as sensors, make polymer–metal nanostructure composite an important class of materials. Among the polymers investigated for composite formation with gold nanostructures, those based on N-isopropylacrylamide are the most widely studied. The thermoresponsive polymer is water-soluble below their phase-transition temperatures and insoluble above them [6,7]. A reversible phase transition of thermoresponsive polymers is achieved by controlling the solution temperature [8]. But the surface active of gold is weak, therefore the use of self-assembled monolayers to connect with polymer and metal nanostructure have been studied extensively. Self-Assembled Monolayers (SAM), most commonly of

⁎ Corresponding author. 40 Zhongshan North Road, 3rd Section, Taipei 104, Taiwan. E-mail address: [email protected] (K.-S. Chen). 0040-6090/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2010.05.043

thiols on gold has been an active research area for nearly two decades. For most of these applications, the self-assembled monolayers need to be further functionalized so that it can be connected to polymer. So far there is much more versatile in applications to introduce the desired functionality onto a SAM after its formulation. In general, polymerization of thermosensitive polymer PNIPAAm on Nano-Au was carried out by two steps. Polymerization of thermosensitive polymer was done and then thiol was grafted on it, finally using SAM with nano-Au particles [9–13]. But the reaction steps were too unstable and took a long time. In this study, the method is modified Nano-Au with MUA by the SAM and O2 plasma pretreatment of the surface on modified Nano-Au (MUA). In order to enhance the other applications of Nano-Au(MUA) and without there being any deterioration in the nano properties, surface modification plays a very important role involving the various fields. There are several methods that have been considered and developed for altering the interactions of materials with their environments such as adsorption, oxidation by strong acids, ozone treatment, plasma (glow discharge), corona discharge, photo activation (UV), ion, electron beam and so on. Among these methods, plasma surface modification processes account for most of the commercial use of plasma technology because they are fast. A major advantage of plasma surface modification in comparison with most of other treatments is that it is free of harmful sub-products from the operation process and would not destroy the bulk structure of materials. After O2

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Fig. 1. Reaction steps for the preparation of thermosensitive Nano-Au particle.

plasma pretreatment, there are carboxyl group and peroxides on the Nano-Au (MUA), it could be used in photo-induced grafting with thermosensitive polymer [14–17]. The abstraction of peroxides on

Nano-Au (MUA) from the surface results in the formation of free radicals on the Nano-Au(MUA) after O2 plasma pretreated. Subsequently the activated surface exposure to air causes oxygen to be

Fig. 2. TEM micrographs of (a)Nano-Au particles, (b) Nano-Au(MUA), (c) Nano-Au(MUA)–PNIPAAm. Scale bars correspond to 40 nm.

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Fig. 3. FE-SEM (a) gold nano particles, (b) Nano-Au(MUA), (c) Nano-Au(MUA)–PNIPAAm and dry in T b 40 °C and (d) Nano-Au(MUA)–PNIPAAm and dry in T N 40 °C.

Fig. 4. Nano-Au(MUA)–PNIPAAm (a) at room temperature, (b) after heating followed by cooling the solutions.

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Fig. 5. Nano-Au(MUA)–PNIPAAm continue heat to increase temperature to 40 °C for 15 min and cooling to room temperature. (a) Down layer and (b) clean solution on up layer.

incorporated on to the Nano-Au(MUA) surfaces, leading to surface oxidation and the formation of peroxides and hydroperoxides species. The peroxides species formed will subsequently initiate the surface free radical coupling reaction with thermosensitive polymer grafted by UV light [18–20]. 2. Experimental 2.1. Preparation of thermosensitive gold nanoparticles Reaction steps of the gold nanoparticles with PNIPAAm are shown in Fig. 1. By the chemical reduction method, the gold nanoparticle was synthesized by 38.8 mM trisodium citrate (Wako) combined with 1 mM hydrogen tetrachloroaurate(III) tetrahydrate (chloroauric acid) (HAuCl4 4H2O) (Wako) in boiling bath, then 0.15 mM 11-mercaptoundecanoic acid (MUA) (Aldrich) including thiol group was used to modify the surface of gold nanoparticle. This MUA modified Au nanoparticles were initiated by O2 plasma pretreatment (40 mTorr, 100 W). Subsequently use UV grafting polymerization of NIPAAm solution (10 mmol) (Eastman Kodak) and ammonium peroxodisulfate (APS, 0.1 mmol) (Wako) on the Au nano-particles to formed the thermoseneitive gold nano particles. Irradiation with a high-pressure mercury lamp (1000 W) was carried out at room temperature.

Fig. 7. FTIR spectra of (a) Nano-Au(MUA), (b) PNIPAAm, (c) Nano-Au(MUA)–PNIPAAm, and (d) Nano-Au(MUA)–g-PNIPAAm.

3. Result and discussion 3.1. Transmission electron microscopy (TEM) TEM was used to direct investigation of the particle size and morphology in situ. Fig. 2 shows the TEM image of the gold nano particles. As shown in Fig. 2(a), the diameters of the gold nanoparticles measured from the TEM images are in good agreement with data measured at room temperature which is about 15 nm. As shown in Fig. 2(b), after the gold nanoparticle modified with MUA by SAM, the

Fig. 6. Schematic representation of the structure of Nano-Au(MUA)–PNIPAAm and its thermosensitive response.

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3.4. FTIR spectra

Fig. 8. ESCA wide-scan spectra of: (a) PNIPAAm, (b) Nano-Au(MUA) and (c) Nano-Au (MUA)–PNIPAAm.

Fourier-transform infrared (FTIR) spectroscopy is a valuable technique to confirm polymerization of PNIPAAm based polymer and evaluate the influence of polymer–metal nanostructure composites. Fig. 7 shows the FTIR spectra of the modified Nano-Au: (a) Nano-Au (MUA), there are thiol group and carboxyl in MUA, the S–H stretching (2500–2550 cm− 1), COOH stretching (3500 cm− 1); (b) PNIPAAm, the N–H stretching (3295 cm− 1), second amide N–H stretching (1548 cm− 1), and deformation of two methyl groups (1387 and 1368 cm− 1) in the spectra of the PNIPAAm; (c) and (d) are Nano-Au (MUA)–PNIPAAm under different conditions, (c) is in room temperature. Comparing (c) with (a), COOH is weak because it provides peroxide to graft thermosensitive polymer. Fig. 7(d) is to increase temperature higher than LCST of thermosensitive polymer and the Nano-Au(MUA)–PNIPAAm will drop down, the characteristic group is similar with (b) PNIPAAm. 3.5. Chemical structure of surface (ESCA)

Nano-Au(MUA) particle showed well-separated. In Fig. 2(c) the thermosensitive polymer can be clearly seen in this image, which shows a shadow around the spherical gold core. The Nano-Au(MUA)– PNIPAAm has a reasonably narrow size distributions and the shadow shows PNIPAAm cross-linking polymer on Nano-Au. 3.2. FE-SEM The FE-SEM images of the gold nanoparticle, Nano-Au(MUA) and Nano-Au(MUA)–PNIPAAm are shown in Fig. 3. The images show that while the gold nanoparticle and Nano-Au(MUA) are highly spherical, the PNIPAAm polymer grafted on nanoparticles are substantially more irregular in appearance. PNIPAAm is one of the most widely studied polymers due to its ability to show dramatic volume change when the volume transition temperature is exceeded. Below lower critical solution temperature (LCST), polymer is in hydrophilic condition. However, as the temperature increases and exceeds LCST, the hydrogel becomes hydrophobic. A reversible phase transition of thermoresponsive polymers is achieved by controlling the solution temperature. In Fig. 3(c) and (d) it shows that Nano-Au(MUA)–PNIPAAm dried in room temperature and dried in the temperature N 40 °C. Nano-Au(MUA)– PNIPAAm dried in the temperature N 40 °C, the gold nano particles were wrapped in PNIPAAm polymer and centralized. 3.3. UV–Vis Nano-Au(MUA)–PNIPAAm was still dissolved in water, and the colour of the solution is pink, as shown in Fig. 4(a). Fig. 4(b) shows photo of the pink solutions after the solution has been heated and cooled. The structure of gold nanoparticles composites was studied by UV–vis spectroscopy. The absorbance peak around 520 nm was the surface plasma absorption of Au nanocomposites. Fig. 5 shows the absorption of the Nano-Au(MUA)–PNIPAAm after changing from room temperature to 40 °C. When the temperature is greater than the LCST of PNIPAAm, Nano-Au(MUA)–PNIPAAm will subside. The absorption of Nano-Au (MUA)–PNIPAAm was about 520 nm. The clear solution on uplayer didn't have the notable absorption pick. Considering the thermo sensitivity of Nano-Au(MUA)–PNIPAAm, the enhancement of temperature would lead to the hydrophobicity of PNIPAM, finally resulting in the aggregation of adjacent particles to larger ones thus the aggrandizement of mean size of nanocomposites and precipitation. The schematic representation of the structure of Nano-Au(MUA)–PNIPAAm and its thermosensitive response is shown in Fig. 5. In Fig. 6, it shows that at low temperatures (T b 32 °C) the network is swollen in water and is hydrophilic. Above the volume transition (T N 32 °C), the network becomes hydrophobic and can thus accumulate hydrophobic phase and aggregation.

Fig. 8 shows the ESCA wide-scan spectra for (a) UV grafted PNIPAAm, (b) Nano-Au after MUA treatment and (c) Nano-Au(MUA) after O2 plasma treatment and subsequent grafting PNIPAAm respectively. The spectrum showed in Fig. 7(a) exhibits three main peak components, which are associated with carbon, oxygen and nitrogen species. These three peaks are the main elements of PNIPAAm. The spectrum showed in Fig. 8(a) shows the Nano-Au (MUA). After O2 plasma treatment and subsequent grafting with thermosensitive polymer (Fig. 8(b)), besides the occurrence of nitrogen component, the intensities of the oxygen and carbon increase significantly. The result is consistent with expectation of the photo graft PNIPAAm polymer. The O2 plasma causes produce the free radical existing at the MUA-treated surface. 4. Conclusion In this paper, a method for forming Nano-Au(MUA)-PNIPAAm was investigated. This method could polymerize the thermosensitive polymer on nanoparticles stable and fast. Characterization of the optical properties and structural morphologies of the composite particles by UV–vis spectroscopy, FE-SEM and TEM support the formation of discrete PNIPAAm hydrogel grafted on gold nanoparticle. This method is expected to be useful as a stimuli-responsive optical device, such as surface plasmon resonance-based sensing materials, because of the combination of optical properties of gold nano particles and control over the inter-particle distance using thermoresponsiveness of PNIPAAm. Acknowledgement This study is financially supported by NSC 97-2221-E-036-006MY3. References [1] D. Zhao, X. Chen, Y. Liu, C. Wu, R. Ma, Y. An, L. Shi, J. Colloid Interface Sci. 331 (2009) 104. [2] A. Ghosh, C.R. Patra, P. Mukherjee, M. Sastry, Rajiv Kumar, Microporous Mesoporous Mater. 58 (2003) 201. [3] J.H. Youk, Polymer 44 (2003) 5053. [4] J.H. Kim, T.R. Lee, Polym. Mater. Sci. Eng. 90 (2004) 637. [5] D. Suzuki, H. Kawaguchi, Langmuir 21 (2005) 8175. [6] J. Shan, J. Chen, M. Nuopponen, H. Tenhu, Langmuir 20 (2004) 4671. [7] M.Q. Zhu, L.Q. Wang, G.J. Exarhos, A.D.Q. Li, J. Am. Chem. Soc. 126 (2004) 2656. [8] E.A. Kazimierska, M. Ciszkowska, Electroanalysis 17 (2005) 1384. [9] D.J. Kim, S.M. Kang, B. Kong, W.J. Kim, H.J. Paik, H. Choi, I.S. Choi, Macromol. Chem. Phys. 206 (2005) 1941. [10] A. Aqil, H. Qiu, J.F. Greisch, R. Je´roˆmea, E.D. Pauw, C. Je´roˆme, Polymer 49 (2008) 1145e1153.

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[11] J.I. Edahiro, K. Sumaru, T. Takagi, T. Shinbo, T. Kanamori, M. Sudoh, Eur. Polym. J. 44 (2008) 300. [12] M. Nuopponen, H. Tenhu, Langmuir 23 (2007) 5352. [13] M. Karg, I. Pastoriza-Santos, J. Perez-Juste, T. Hellweg, L.M. Liz-Marzan, Polym. Microgels Nanorod Coat. 3 (2007) 1222. [14] K.S. Chen, S.C. Chen, H.R. Lin, T.R. Yan, C.C. Tseng, Mater. Sci. Eng. C 27 (2007) 716. [15] K.S. Chen, S.C. Chen, Y.C. Yeh, W.C. Lien, H.R. Lin, J.M. Yang, Adv. Mater. Res. 15–17 (2007) 187.

[16] K.S. Chen, M.S. Li, H.M. Wu, M.R. Yang, J.Y. Tian, F.Y. Huang, H. Yuan, Surf. Coat. Technol 200 (2006) 3270. [17] K.S. Chen, Y.A. Ku, C.H. Lee, H.R. Lin, T.R. Yan, D.C. Sheu, T.M. Chen, Mater. Sci. Eng. C 25 (2005) 472. [18] J. Zhang, C.Q. Cui, T.B. Lim, E.T. Kang, Macromol. Chem. Phys. 201 (2000) 1653. [19] K.S. Chen, C.W. Chou, S.H. Hsu, H.R. Li, Mater. Sci. Forum 426–432 (2003) 3267. [20] K.S. Chen, M.R. Yang, Y.A. Ku, T.M. Chen, F.H. Lin, Mater. Sci. Forum 426–432 (2003) 2101.