- Email: [email protected]
CdS and ZnS quantum dots embedded in hyaluronic acid films
Journal of Alloys and Compounds 481 (2009) 402–406
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
CdS and ZnS quantum dots embedded in hyaluronic acid films G. Khachatryan a , K. Khachatryan a , L. Stobinski b,c,∗ , P. Tomasik a , M. Fiedorowicz a , H.M. Lin d a
Department of Chemistry, Agricultural University, Balicka 122, 30-149 Krakow, Poland Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 48/52, 01-224 Warsaw, Poland c Faculty of Materials Science and Engineering, Warsaw University of Technology, Woloska 141, 02-507 Warszawa, Poland d Department of Materials Engineering, Tatung University, Taipei 104, Taiwan, ROC b
a r t i c l e
i n f o
Article history: Received 2 November 2008 Received in revised form 28 February 2009 Accepted 2 March 2009 Available online 14 March 2009 Keywords: Quantum dots (QDs) Biocomposites Light-emitting foils Nanocrystals Semiconductors
a b s t r a c t An in situ synthesis of ZnS and CdS quantum dots (QDs) in an aqueous solution of sodium hyaluronate (Hyal) produced foils emitting light on excitation with a UV light. The wavelength of emission was only slightly QDs size and more QDs concentration dependent and reached up to ∼320 nm in the case of ZnS and ∼400–450 nm in the case of CdS. Nanoparticles remained as non-agglomerated 10–20 nm nanoclusters. CdS/Hyal and ZnS/Hyal—QDs biocomposites were characterized using photoluminescence (PL), IR spectrometric techniques, and Transmission Electron Microscopy (TEM). The absolute molecular weights, radii of gyration, Rg , and thermodynamic properties of the obtained foils are given. Electric resistivity studies performed for the hyaluronic foil in the 100–1000 V range have revealed that the hyaluronate foil has very weak conducting properties and QDs only insignificantly affect those properties as QDs practically did not interact with the foil. Size exclusion chromatography showed a decrease in the molecular weight of the hyaluronate after generation of QDs in its solution, particularly in the lower molecular fraction of the hyaluronate. The generation of CdS QDs was more destructive for the polysaccharide matrix. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Single-component quantum dots (QDs) could be identified as nanoparticles of sulfides and selenides of metals, most typically of zinc and cadmium. They develop emission when excited with a UV light. The wavelength of emission depends on the size of the nanoparticles [1,2]. Their semiconducting properties originate from their excitons confined in all three spatial dimensions [3]. QDs enjoy a wide range of applications as transistors, components of solar cells, light-emitting devices and diode lasers but also as agents for medical imaging [4–7], fluorescent labels [8–10], fluorescent probes [11–15], and immunosensors [16,17]. Nanoparticles of some materials show a strong tendency towards agglomeration on their isolation from suspensions. Agglomerated particles lose advantages resulting from their nanodimensions. Therefore, they are usually applied in form of suspensions to glasses, cosmetics, sterile curtains and so on. Willingly they are synthesized in combinations with various inorganic materials among them carbon nanotubes [18,19] and fullerenes [20]. Some organic materials also appeared to be suitable partners
∗ Corresponding author at: Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 48/52, 01-224 Warsaw, Poland. Tel.: +48 22 3433431; fax: +48 22 3433333. E-mail address: [email protected] (L. Stobinski). 0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2009.03.011
for quantum dots stabilizing them, for instance, thioglycerol [21] and dithiolane [22], and providing series of novel composites of interesting optical, that is luminescent, and non-linear electroluminescent properties [23,24]. Sometimes, QDs are synthesized in the presence of organic molecules which prevent them from agglomeration and form a coating of the QDs [25]. Success in the application of QDs in biological studies have frequently been associated with their conjugation with proteins [26–30], peptides [31] and amino acids [32]. Therefore, studies on polysaccharides as components of composites with QDs have focused on aminopolysaccharides such as chitosan [3,33–38], cellulose [39], and other saccharides [40–45]. There are several methods of preparation of QDs, among them colloidal synthesis [2,46–49] seems to be cheapest and least hazardous. In such processes precursors of quantum dots blended under controlled concentration with an organic surfactant and a solvent are heated to split into monomeric molecules then allowed to crystallize under specially adjusted regimes. The size of quantum dots can be controlled with pH and even selected pH modifier [50]. The size of QDs can be controlled with pH and even selection of the pH modifier [50]. In some cases in situ synthesis can be competitive [18]. Other methods are based, for instance, on electrochemical assembly [51,52], radio-frequency sputtering [53], metal-organic chemical vapor deposition [54], formation of nanocrystals in self-assembling fatty acid layers (socalled Langmuir–Blodgett technique) [55]. Recently synthesis of sulfide QDs from metal salts in dimethylsulfoxide has been reported
G. Khachatryan et al. / Journal of Alloys and Compounds 481 (2009) 402–406
[56]. The latter served as the solvent and source of sulfur. Also solid state, one pot reaction of Zn and either sulfur or selenium attracts attention [57]. In this paper authors present an original, simple, cheap and nondestructive for the matrix, in situ synthesis of ZnS and CdS QDs in aqueous solution of sodium hyaluronate (Hyal), which is an anionic polysaccharide. Several properties of Hyal suggest it as a potential biodegradable matrix for synthesis non-agglomerated nanocrystals. It has well defined polymer chains [58] providing anticipated effects by involvement of its –OH, –NHCOCH3 and –COO− coordination centers in preventing aggregation and controlling growth for ZnS and CdS nanocrystals. Foils could readily be drawn of the Hyal/QDs composites. Potentially, such foils could be used as fluorescent labels and probes. CdS/Hyal and ZnS/Hyal—QDs biocomposites were characterized with UV–vis, photoluminescence (PL), and IR spectrometric techniques, and Transmission Electron Microscopy (TEM). The absolute molecular weights, radii of gyration, Rg , and thermodynamic properties of obtained foils are also given. 2. Experimental 2.1. Generation of quantum dots Hyal/ZnS and Hyal/CdS nanocomposites were prepared from hyaluronic acid Na salt (Mw ≤ 3.48 × 105 ) and either (CH3 COO)2 Zn (Aldrich, 99.99%) or CdSO4 (Aldrich, 99.99+% trace metals basis) and Na2 S (Aldrich, Na2 S·9H2 O ≥99.99%). Na hyaluronate (CPN Ltd, The Czech Republic) (1 g) dissolved in deionized then distilled water (19 ml) [5% (v/v)] was treated with the salt to prepare either a 10−2 or 10−3 M solution, then a stoichiometric amount of Na2 S in an aqueous solution was added. The resulting suspension was centrifuged and dried. 2.2. Preparation of film The centrifuged deposits were applied to a clean, smooth either Teflon or glass surface and left to evaporate in the air. The dry foil was collected and stored in closed vessels. 2.3. FTIR-ATR spectrophotometry The FTIR-ATR spectrum of the film was recorded in the range of 4000–500 cm−1 at resolution of 4 cm−1 using a MATTSON 3000 FT-IR (Madison, Wisconsin, USA) spectrophotometer. That instrument was equipped with a 30SPEC 30◦ reflectance adapter fitted with the MIRacle ATR accessory from PIKE Technologies Inc., Madison, Wisconsin, USA. 2.4. Photoluminescence spectrophotometry Photoluminescence (PL) measurements for Hyal/CdS and ZnS QDs films were performed at room temperature using a PerkinElmer Life Sciences LS50B spectrofluorometer (Norwalk, CT) at excitation wavelength of 290 nm and emission wavelength of 300–600 nm. 2.5. Transmission Electron Microscopy The surface morphology of the thin films was observed with a Hitachi 800 TEM/STEM. 2.6. High performance size exclusion chromatography (HPSEC-MALLS-RI) Foil samples (100 mg) were suspended in water (100 ml). The mixtures were gently agitated at room temperature for 24 h. The resulting clear solutions were filtered through 5 m cellulose acetate filters (Whatman, England) prior to injection. The high performance size exclusion chromatography (HPSEC) system for determination of average molecular weight and radii of gyration consisted of a pump (Shimadzu 10AC, Tokyo, Japan), an injection valve (model 7021, Rheodyne, Palo Alto, CA, USA), a TSK PWH guard column (Tosoh Corporation, Tokyo, Japan), and two connected size exclusion columns TSKgel GMPWXL (300 × 7.8 mm, Tosoh Corporation, Tokyo, Japan) and TSKgel 2500 PWXL (300 × 7.8 mm, Tosoh Corporation, Tokyo, Japan). A multiangle laser light scattering detector (MALLS) operating in chromatographic mode using a He–Ne laser light source (630.0 nm) (Dawn-DSP-F, Wyatt Technology, Santa Barbara, CA, USA) and a differential refractive index detector (L7490, Merck, Darmstadt, Germany) were connected to the columns. The columns were maintained at 30 ◦ C. The mobile phase (0.15 M NaNO3 with 0.02% sodium azide) was filtered through 0.2 and 0.1 m cellulose acetate filters (Whatman, England). The flow rate of the mobile phase and the sample injection volume were 0.4 ml/min and
403
500 l, respectively. The output voltage of refractive index (RI) and light scattering (LS) at 18 angles was used for calculation of the weight-average molecular weight (Mw ) and radius of gyration (Rg ) using Astra 4.73.04 software (Wyatt Technology, Santa Barbara, CA, USA). In calculations of Mw and RG dn/dc value 0.167 (ml/g) for Hyal [59] was applied. The Berry plot with third order polynomial fit was applied in the calculation of Mw and Rg values. Separations were run in duplicates. 2.7. Differential scanning calorimetry Thermal gravimetry analysis coupled with mass spectrometry analysis (MSTG/DTG/SDTA) experiments were performed in Mettler-Toledo 851e apparatus in 150 l corundum crucibles, closed by a lid with a hole, under flow of argon (80 ml/min), within temperature range 30–800 ◦ C with heating rate of 10 ◦ C/min. The simultaneous evolved gas analysis (EGA) was performed during the experiments with a joined on-line quadruple mass spectrometer (QMS) (Thermostar Balzers). The differential scanning calorimetry (DSC) experiments were performed in Mettler-Toledo 821e calorimeter equipped with an intracooler Haake in 40 l aluminum crucibles under constant flow of argon (80 ml/min) within temperature range 25–400 ◦ C. 2.8. Electric resistivity Measurements were performed with 0.2 mm thick 3.0 cm × 0.5 cm foil leaflets involving the two-point method. Connections were made with silver plated copper wires (0.2 mm diameter and 5 cm long) bound around the leaflet foil. Points of contacts were additionally covered with a graphite paste then dried. The measuring system was equipped with a stabilized high voltage supplier (ZWM-42, Polon, Warsaw, Poland) and picoamperometer (Unitra-OBREP, Warsaw, Poland). The system was shielded from outer electric field with a thin metallic cage.
3. Results and discussion Hyal can successfully play the role of a matrix for ZnS and CdS QDs. Both kind QDs have been generated either from zinc acetate or cadmium sulfate, with sodium sulfide added. Hyal foils containing nanoclusters of ZnS and CdS, which could readily be developed easily, emitted light when illuminated with 253 nm light. The wavelength of emission depends on the type of QDs, and the intensity of their emission depends on their concentration. The fluorescence spectra of the Hyal/ZnS and Hyal/CdS nanocomposites are presented in Fig. 1. The emission bands with maxima at ∼410 and ∼475 nm for samples containing ZnS and CdS containing samples, respectively, exhibit some shoulders and inflections, and in the spectrum of the foil containing CdS there are even two well formed bands of lower intensity. They could be considered as the result of the non-uniform size of the included QDs. The sizes and morphologies of the as-prepared nanoparticles were studied by means of the TEM microscopy. Fig. 2 shows a TEM image of as-prepared CdS QDs. It is typical also for ZnS QDs. Spherical CdS QDs are well separated and particle size distribution ranges between 10 and 20 nm and such were also ZnS QDs. The FTIR-ATR spectra in the spectral range 750–4000 cm−1 for Hyal, and CdS and ZnS QDs/Hyal films are presented in Fig. 3. There is very limited number of changes in the spectrum of Hyal after QDs generation. Thus, in the CdS/Hyal composite foil the double peak with more intensive component at 1597 cm−1 (amide II band) and lower component at 1556 cm−1 (carboxylate asymmetric valence band) turned into a single peak centered at 1556 cm−1 with long wavelength shoulders above 1600 cm−1 (likely the amide I band) and 1597 cm−1 . In the spectrum of original Hyal, this double peak was more intensive than the adjoining shorter wavelength triple peak at 1405 cm−1 (carboxylate symmetric valence band), 1373 and 1321 cm−1 (primary and secondary alcoholic deformation bands). In the spectrum of the CdS/Hyal foil the intensity of the latter group of bands decreased. In the spectrum of the ZnS/Hyal foil the intensity ratio of these groups of bands practically did not change but, in turn, the intensity of the band located at 1141 cm−1 (skeletal acetal valence band) increased over that for the group of bands located above 1500 cm−1 . In the whole range of the spectrum
404
G. Khachatryan et al. / Journal of Alloys and Compounds 481 (2009) 402–406
Fig. 3. FTIR-ATR spectra of hyaluronic acid and its composites with ZnS and CdS QDs.
Fig. 1. Emission spectra of the ZnS/Hyal (A) and CdS/Hayl (B) preparations.
no significant band shifts could be noted. Insignificant band shifts could result from changes in the molecular weight of the samples. Such molecular weight-dependent band shifts in the IR spectra of Hyal have been recently observed [59]. Under such circumstances strong interactions of QDs with the Hyal matrix may be ruled out. TGA thermograms of the pure Hyal foil and the nanocomposites are shown in Fig. 4. The presence of CdS QDs had no influence on the thermal decomposition of Hyal. The foil held slightly less water and
Fig. 2. TEM image of CdS quantum dots (dark spots, diameter 10–20 nm) in sodium hyaluronate. Visible rings as artifacts emerged have been arrived during the development of the TEM negative film.
the rate as well as degree of decomposition remained unchanged but the foil with ZnS which also carried slightly less water than foil from Hyal started to decompose at slightly lower temperature and the rate of decomposition was slightly slower. Such result also points to either none or negligible interactions between QDs and the matrix. The pattern of DSC thermograms of Hyal foil (Fig. 5), practically unchanged by the presence of QDs, also supported the above opinion. An immediate optical feature of quantum dots is their coloration. The coloration is directly related to the energy levels of QD. Larger QDs have more closely packed energy levels in which the electron–hole pair can be trapped. Therefore, electron–hole pairs in larger QDs show a longer lifetime. Because there are no essential interactions between QDs and their matrix, the general dependence of the emission wavelength and size of QDs [60–62] should be valid also for QDs in Hyal matrix. Recent articles suggest [63,64] that the shape of QD can also be a factor in the coloration, but as yet not enough information has become available. Furthermore, the lifetime of fluorescence is determined by the size of QDs [1]. As can be seen from Fig. 2, QDs are mainly ball shaped. Size exclusion chromatography showed (Table 1) a decrease in the molecular weight of Hyal after generation of QDs in its solution. Higher molecular fraction of Hyal suffered smaller damage than the lower molecular fraction. Generation of CdS QDs was more destructive. However, in every case the decrease in radius of gyration, Rg ,
Fig. 4. Thermogravimetric curves of sodium hyaluronate (solid line). ZnS, dash–dot line; CdS, dotted line.
G. Khachatryan et al. / Journal of Alloys and Compounds 481 (2009) 402–406
405
Table 2 Parameters of the y = ax + b linear relationship for the voltage–current intensity correlations for the foils made of plain hyaluronate (Hyal) and quantum dots containing hyaluronate foils. Foil
a
b
Hyal Hyal/ZnSa Hyal/ZnSb Hyal/CdSa Hyal/CdSb
3E−09 4E−09 3E−09 3E−09 4E−09
−2E−08 −4E−08 9E−22 −1E-08 −3E−09
a b
Quantum dots generated from the 10−3 M solutions. Quantum dots generated from the 10−2 M solutions.
4. Conclusions
Fig. 5. DSC thermograms of sodium hyaluronate (solid line), Hyal-CdS (dotted line) and Hyal-ZnS (dashed line).
Table 1 Absolute molecular weight of the original hyaluronate (Hyal) fractions and their changes after generation of QDs inside hyaluronatea (Rg , radius of gyration). Sample
Mw × 10 Fraction I
Mw × 10 Fraction II
Rg Fraction I (nm)
Rg Fraction II (nm)
Hyal Hyal/ZnS Hyal/CdS
3.48 2.70 (22.4) 2.60 (25.3)
1.81 1.32 (28.7) 1.17 (35.4)
79.4 61.9 (22.0) 62.7(21.0)
61.7 48.5 (21.4) 48.5(21.4)
a
5
5
The percentage of decrease in the original values is given in parentheses.
was practically identical. The observed degradation of Hyal could result from its contact with the alkaline reagent. Hydrolysis of Na2 S increased the pH of the reaction mixture above 7. Under such conditions, the acetamido groups could split apart from the degradation typical for polysaccharides [65] in alkaline media. Electric resistivity studies performed for the Hyal foil in the range of 100–1000 V revealed a perfect linearity of the current–voltage (I–V) characteristic (see Fig. 6). This function and its parameters (Table 2) suggest that the foil has very weak conducting properties. QDs of both types in the foil did not deteriorate this linearity and only insignificantly decreased the slope of the correlation. The parameters of the linear relationship are given in Table 2. The opposite effects of the concentration upon a and b parameters in the case of ZnS and CdS QDs could not be discussed as neither the thickness and area of the investigated foils nor the dimension of QDs could be standardized.
Fig. 6. The current–voltage (I–V) characteristic for the hyaluronic acid foil.
Nanometer-sized semiconductor ZnS and CdS particles have been successfully prepared within hyaluronic acid film matrix. Because of involvement of hyaluronic acid coordination centers, this polysaccharide was proven to be efficient in preventing aggregation and controlling growth for ZnS and CdS nanocrystals. Acknowledgements This work was supported by the Polish Council for Science through the Development Grant for the years 2008-2011 and the BIONAN 2008 Scientific Net. References [1] A.F. van Driel, G. Allan, C. Delerue, P. Lodahl, W.L. Vos, D. Vanmaekelbergh, Phys. Rev. Lett. 95 (2005) 236804. [2] L.L. Yang, J.H. Yang, X.Y. Liu, Y.J. Zhang, Y.X. Wang, H.G. Fan, D.D. Wang, J.H. Lang, J. Alloys Compd. 463 (2008) 92–95. [3] C.B. Murray, C.R. Kagan, M.G. Bawendi, Annu. Rev. Mater. Sci. 30 (2000) 545–610. [4] J. Itoh, R.Y. Osamura, Meth. Mol. Biol. 374 (2007) 29–42. [5] X. Gao, L.W. Chung, S. Nie, Meth. Mol. Biol. 374 (2007) 135–145. [6] J.V. Frangioni, S.-W. Kim, S. Ohnishi, S. Kim, M.G. Bawendi, Meth. Mol. Biol. 374 (2007) 147–159. [7] K. Manzoor, S. Johny, D. Thomas, S. Setua, D. Menon, S. Nair, Nanotechnology 20 (2009) 065102. [8] R.L. Ornberg, H. Liu, Meth. Mol. Biol. 374 (2007) 3–10. [9] D.S. Lidke, P. Nagy, T.M. Jovin, D.J. Arndt-Jovin, Meth. Mol. Biol. 374 (2007) 69–79. [10] J.K. Jaiswal, S.M. Simon, Meth. Mol. Biol. 374 (2007) 93–104. [11] T.J. Deerinck, B.N. Giepmans, B.L. Smarr, M.E. Martone, M.E. Ellisman, Meth. Mol. Biol. 374 (2007) 43–53. [12] C. Bozuyigues, S. Levi, A. Triller, M. Dahan, Meth. Mol. Biol. 374 (2007) 81–91. [13] W. Gu, T. Pellegrino, W.J. Park, R. Boudreau, M.A. Gros, A.P. Aliviasatos, C.A. Larabell, Meth. Mol. Biol. 374 (2007) 125–131. [14] D.H. Geho, J.K. Killian, A. Nandi, J. Pastor, P. Gurnani, K.P. Rosenblatt, Meth. Mol. Biol. 374 (2007) 229–237. [15] R. Freeman, I. Willner, Nanoletters 9 (2009) 322–326. [16] E.R. Goldman, H.T. Uyeda, A. Hayhurst, H. Mattoussi, Meth. Mol. Biol. 374 (2007) 207–227. [17] B.B. Zhang, X.F. Liang, L.J. Hao, J. Cheng, X.Q. Gong, X.H. Liu, G.P. Ma, J. Chang, J. Photochem. Photobiol. B 94 (2009) 45–50. [18] L. Stobinski, J. Peszke, P. Tomasik, H.-M. Lin, J. Alloys Compd. 455 (2008) 137–141. [19] W. Wang, G.K. Liu, H.S. Cho, Y. Guo, D. Shi, J. Lian, R.C. Ewing, Chem. Phys. Lett. 469 (2009) 149–152. [20] H. Song, Y.Y. Zhai, Z.K. Zhou, Z.H. Hao, L. Zhou, Modern Phys. Lett. B 22 (2008) 3207–3213. [21] C. Unni, D. Philip, K.G. Gopchandran, Spectrochim. Acta A 71 (2008) 1402–1407. [22] I. Yildiz, S. Ray, T. Benelli, F.M. Raymo, J. Mater. Chem. 18 (2008) 3940–3947. [23] T. Stoferle, U. Scherf, R.F. Mahrt, Nanoletters 9 (2009) 453–456. [24] Z.A. Tan, B. Hedrick, F. Zhang, T. Zhu, J. Xu, R.H. Henderson, J. Ruzyllo, A.Y. Wang, IEEE Photonics Technol. Lett. 20 (2008) 1998–2000. [25] M.L. Hassan, A.F. Ali, J. Cryst. Growth 310 (2008) 5252–5258. [26] T.Q. Vu, R. Maddipati, T.A. Blute, B.J. Nehilla, L. Nusblat, T.A. Desai, Nanoletters 5 (2005) 603–607. [27] R.L. Ornberg, T.F. Harper, H. Liu, Nat. Methods 2 (2005) 79–81. [28] A. Sarkar, R.B. Robertson, J.M. Fernandez, Proc. Natl. Acad. Sci. U.S.A. 101 (2004) 12882–12886. [29] F. Pinaud, D. King, H.P. Moore, S. Weiss, J. Am. Chem. Soc. 126 (2004) 6115–6123. [30] A. Gokarna, S.K. Lee, J.S. Hwang, Y.H. Cho, Y.T. Lim, B.H. Chung, M. Lee, J. Korean Phys. Soc. 3 (2008) 3047–3050. [31] D. Bardelang, M.B. Zaman, I.L. Moudrakovski, S. Pawsey, J.C. Margeson, D.S. Wang, X.H. Wu, J.A. Ripmeester, C.I. Ratcliffe, K. Yu, Adv. Mater. 20 (2008) 4517–4520.
406
G. Khachatryan et al. / Journal of Alloys and Compounds 481 (2009) 402–406
[32] J.N. Rebilly, P.W. Gardner, G.R. Darling, J. Bacsa, M.J. Rosseinsky, Inorg. Chem. 47 (2008) 9390–9399. [33] A.J. Sutherland, Curr. Opin. Solid State Mater. Sci. 6 (2002) 365–370. [34] Z. Li, Y. Du, Z. Zhang, D. Pang, React. Funct. Polym. 55 (2003) 35–43. [35] I. Sondi, O. Siiman, E. Matijevic, J. Colloid Interface Sci. 275 (2004) 503–507. [36] W.B. Tan, Y. Zhang, J. Biomed. Mater. Res. A 75 (2005) 56–62. [37] X.H. Wang, Y.M. Du, S. Ding, L.H. Fan, X.W. Shi, Q.Q. Wang, G.G. Xiong, Physica E (Amsterdam) 30 (2005) 96–100. [38] Q. Nie, W.B. Tan, Y. Zhang, Nanotechnology 17 (2006) 140–144. [39] Q. Xu, M.P. Tucker, P. Arenkiel, X. Ai, G. Rumbles, J. Sugiyama, M.E. Himmel, S.Y. Ding, Cellulose 16 (2009) 19–26. [40] X.L. Sun, W. Cui, C. Haller, E.L. Chaikof, Chembiochem 5 (2004) 1593–1596. [41] F. Osaki, T. Kanamori, S. Sando, T. Sera, Y. Aoyama, J. Am. Chem. Soc. 126 (2004) 6520–6521. [42] H.M.E. Dirar, Chin. Phys. Lett. 25 (2008) 4480–4481. [43] Z.Y. Cheng, S.H. Liu, P.W. Beines, N. Ding, P. Jakubowicz, W. Knoll, Chem. Mater. 20 (2008) 7215–7219. [44] C.H. Wang, Y.S. Hsu, C.A. Peng, Biosens. Bioelectron. 24 (2008) 1012–1019. [45] H.B. Li, C.P. Han, Chem. Mater. 20 (2008) 6053–6059. [46] C.B. Murray, S. Sun, W. Gaschler, H. Doyle, T.A. Betley, C.R. Kogan, IBM J. Res. Dev. 45 (2001) 47–56. [47] M. Inoguchi, K. Suzuki, K. Kageyama, H. Takagi, Y. Sakabe, J. Am. Ceram. Soc. 91 (2008) 3850–3855. [48] X.Y. Ye, W.D. Zhuang, Y. Fang, Y.S. Hu, K. Zhao, X.W. Huang, Mater. Chem. Phys. 112 (2008) 730–733. [49] B.S. Amma, K. Manzoor, K. Ramakrishna, M. Pattabi, Mater. Chem. Phys. 112 (2008) 789–792. [50] X.X. Ren, G.L. Zhao, H. Li, W. Wu, G.R. Han, J. Alloys Compd. 465 (2008) 534–539.
[51] S. Bandyophadhyay, A.E. Miller, H.C. Chang, G. Banerjee, D.F. Yue, R.E. Richer, S. Jones, J.A. Eastman, M. Chandrasekhar, Nanotechnology 7 (1996) 360– 371. [52] R. Freeman, R. Gill, M. Beissenhirtz, J. Wilner, Photochem. Photobiol. Sci. 6 (2007) 416–422. [53] G. Mayer, M. Fonin, U. Rudiger, R. Schneider, D. Gerthsen, N. Janssen, R. Bratschitsch, Nanotechnology 20 (2009) 075601. [54] S.M. Lan, W.Y. Uen, C.E. Chan, K.J. Chang, S.C. Hung, Z.Y. Li, T.N. Yang, C.C. Chiang, P.J. Huang, M.D. Yang, G.C. Chi, C.Y. Chang, J. Mater. Sci. Mater. Electron. 20 (2009) 441–445. [55] P. Mandal, S.S. Talwar, R.S. Srinivasa, S.S. Major, Appl. Phys. A 94 (2009) 577–584. [56] Y.B. Li, L. Ma, X. Zhang, A.G. Joly, Z.L. Liu, W. Chen, J. Nanosci. Nanotechnol. 8 (2008) 5646–5651. [57] S.V. Pol, V.G. Pol, J.M. Calderon-Moreno, S. Cheylan, A. Gedanken, Langmuir 24 (2008) 10462–10466. [58] E.D. Atkins, J.K. Sheehan, Biochem. J. 125 (1971) 92P. [59] S. Hokputsa, J. Kornelia, C. Alexander, S. Harding, Eur. Biophys. J. 32 (2003) 450–496. [60] T. Fujisawa, T.H. Oosterkamp, W.G. van der Wiel, B.W. Broer, R. Aguado, S. Tarucha, L.P. Kouwenhoven, Science 282 (1998) 932–935. [61] N.Y. Hwang, S.R.E. Yang, Solid State Commun. 143 (2007) 176–178. [62] K. Baert, B. Kolaric, W. Libaers, R.A.L. Vallee, M. Di Vece, P. Lievens, K. Clays, Res. Lett. Nanotechnol. (2008), ID 974072. [63] S.J. Prado, C. Trallero-Giner, V. López-Richard, A.M. Alcalde, G.E. Marques, Phys. Rev. B 69 (2004) R201311. [64] D.R. Santos, Q. Fanyao, A.M. Alcalde, P.C. Morais, Phys. E 26 (2005) 331–336. [65] J.A. Alkrad, Y. Mrestani, D. Stroehl, S. Wartewig, R. Neubert, J. Pharm. Biomed. Anal. 31 (2003) 545–550.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
CdS and ZnS quantum dots embedded in hyaluronic acid films G. Khachatryan a , K. Khachatryan a , L. Stobinski b,c,∗ , P. Tomasik a , M. Fiedorowicz a , H.M. Lin d a
Department of Chemistry, Agricultural University, Balicka 122, 30-149 Krakow, Poland Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 48/52, 01-224 Warsaw, Poland c Faculty of Materials Science and Engineering, Warsaw University of Technology, Woloska 141, 02-507 Warszawa, Poland d Department of Materials Engineering, Tatung University, Taipei 104, Taiwan, ROC b
a r t i c l e
i n f o
Article history: Received 2 November 2008 Received in revised form 28 February 2009 Accepted 2 March 2009 Available online 14 March 2009 Keywords: Quantum dots (QDs) Biocomposites Light-emitting foils Nanocrystals Semiconductors
a b s t r a c t An in situ synthesis of ZnS and CdS quantum dots (QDs) in an aqueous solution of sodium hyaluronate (Hyal) produced foils emitting light on excitation with a UV light. The wavelength of emission was only slightly QDs size and more QDs concentration dependent and reached up to ∼320 nm in the case of ZnS and ∼400–450 nm in the case of CdS. Nanoparticles remained as non-agglomerated 10–20 nm nanoclusters. CdS/Hyal and ZnS/Hyal—QDs biocomposites were characterized using photoluminescence (PL), IR spectrometric techniques, and Transmission Electron Microscopy (TEM). The absolute molecular weights, radii of gyration, Rg , and thermodynamic properties of the obtained foils are given. Electric resistivity studies performed for the hyaluronic foil in the 100–1000 V range have revealed that the hyaluronate foil has very weak conducting properties and QDs only insignificantly affect those properties as QDs practically did not interact with the foil. Size exclusion chromatography showed a decrease in the molecular weight of the hyaluronate after generation of QDs in its solution, particularly in the lower molecular fraction of the hyaluronate. The generation of CdS QDs was more destructive for the polysaccharide matrix. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Single-component quantum dots (QDs) could be identified as nanoparticles of sulfides and selenides of metals, most typically of zinc and cadmium. They develop emission when excited with a UV light. The wavelength of emission depends on the size of the nanoparticles [1,2]. Their semiconducting properties originate from their excitons confined in all three spatial dimensions [3]. QDs enjoy a wide range of applications as transistors, components of solar cells, light-emitting devices and diode lasers but also as agents for medical imaging [4–7], fluorescent labels [8–10], fluorescent probes [11–15], and immunosensors [16,17]. Nanoparticles of some materials show a strong tendency towards agglomeration on their isolation from suspensions. Agglomerated particles lose advantages resulting from their nanodimensions. Therefore, they are usually applied in form of suspensions to glasses, cosmetics, sterile curtains and so on. Willingly they are synthesized in combinations with various inorganic materials among them carbon nanotubes [18,19] and fullerenes [20]. Some organic materials also appeared to be suitable partners
∗ Corresponding author at: Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 48/52, 01-224 Warsaw, Poland. Tel.: +48 22 3433431; fax: +48 22 3433333. E-mail address: [email protected] (L. Stobinski). 0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2009.03.011
for quantum dots stabilizing them, for instance, thioglycerol [21] and dithiolane [22], and providing series of novel composites of interesting optical, that is luminescent, and non-linear electroluminescent properties [23,24]. Sometimes, QDs are synthesized in the presence of organic molecules which prevent them from agglomeration and form a coating of the QDs [25]. Success in the application of QDs in biological studies have frequently been associated with their conjugation with proteins [26–30], peptides [31] and amino acids [32]. Therefore, studies on polysaccharides as components of composites with QDs have focused on aminopolysaccharides such as chitosan [3,33–38], cellulose [39], and other saccharides [40–45]. There are several methods of preparation of QDs, among them colloidal synthesis [2,46–49] seems to be cheapest and least hazardous. In such processes precursors of quantum dots blended under controlled concentration with an organic surfactant and a solvent are heated to split into monomeric molecules then allowed to crystallize under specially adjusted regimes. The size of quantum dots can be controlled with pH and even selected pH modifier [50]. The size of QDs can be controlled with pH and even selection of the pH modifier [50]. In some cases in situ synthesis can be competitive [18]. Other methods are based, for instance, on electrochemical assembly [51,52], radio-frequency sputtering [53], metal-organic chemical vapor deposition [54], formation of nanocrystals in self-assembling fatty acid layers (socalled Langmuir–Blodgett technique) [55]. Recently synthesis of sulfide QDs from metal salts in dimethylsulfoxide has been reported
G. Khachatryan et al. / Journal of Alloys and Compounds 481 (2009) 402–406
[56]. The latter served as the solvent and source of sulfur. Also solid state, one pot reaction of Zn and either sulfur or selenium attracts attention [57]. In this paper authors present an original, simple, cheap and nondestructive for the matrix, in situ synthesis of ZnS and CdS QDs in aqueous solution of sodium hyaluronate (Hyal), which is an anionic polysaccharide. Several properties of Hyal suggest it as a potential biodegradable matrix for synthesis non-agglomerated nanocrystals. It has well defined polymer chains [58] providing anticipated effects by involvement of its –OH, –NHCOCH3 and –COO− coordination centers in preventing aggregation and controlling growth for ZnS and CdS nanocrystals. Foils could readily be drawn of the Hyal/QDs composites. Potentially, such foils could be used as fluorescent labels and probes. CdS/Hyal and ZnS/Hyal—QDs biocomposites were characterized with UV–vis, photoluminescence (PL), and IR spectrometric techniques, and Transmission Electron Microscopy (TEM). The absolute molecular weights, radii of gyration, Rg , and thermodynamic properties of obtained foils are also given. 2. Experimental 2.1. Generation of quantum dots Hyal/ZnS and Hyal/CdS nanocomposites were prepared from hyaluronic acid Na salt (Mw ≤ 3.48 × 105 ) and either (CH3 COO)2 Zn (Aldrich, 99.99%) or CdSO4 (Aldrich, 99.99+% trace metals basis) and Na2 S (Aldrich, Na2 S·9H2 O ≥99.99%). Na hyaluronate (CPN Ltd, The Czech Republic) (1 g) dissolved in deionized then distilled water (19 ml) [5% (v/v)] was treated with the salt to prepare either a 10−2 or 10−3 M solution, then a stoichiometric amount of Na2 S in an aqueous solution was added. The resulting suspension was centrifuged and dried. 2.2. Preparation of film The centrifuged deposits were applied to a clean, smooth either Teflon or glass surface and left to evaporate in the air. The dry foil was collected and stored in closed vessels. 2.3. FTIR-ATR spectrophotometry The FTIR-ATR spectrum of the film was recorded in the range of 4000–500 cm−1 at resolution of 4 cm−1 using a MATTSON 3000 FT-IR (Madison, Wisconsin, USA) spectrophotometer. That instrument was equipped with a 30SPEC 30◦ reflectance adapter fitted with the MIRacle ATR accessory from PIKE Technologies Inc., Madison, Wisconsin, USA. 2.4. Photoluminescence spectrophotometry Photoluminescence (PL) measurements for Hyal/CdS and ZnS QDs films were performed at room temperature using a PerkinElmer Life Sciences LS50B spectrofluorometer (Norwalk, CT) at excitation wavelength of 290 nm and emission wavelength of 300–600 nm. 2.5. Transmission Electron Microscopy The surface morphology of the thin films was observed with a Hitachi 800 TEM/STEM. 2.6. High performance size exclusion chromatography (HPSEC-MALLS-RI) Foil samples (100 mg) were suspended in water (100 ml). The mixtures were gently agitated at room temperature for 24 h. The resulting clear solutions were filtered through 5 m cellulose acetate filters (Whatman, England) prior to injection. The high performance size exclusion chromatography (HPSEC) system for determination of average molecular weight and radii of gyration consisted of a pump (Shimadzu 10AC, Tokyo, Japan), an injection valve (model 7021, Rheodyne, Palo Alto, CA, USA), a TSK PWH guard column (Tosoh Corporation, Tokyo, Japan), and two connected size exclusion columns TSKgel GMPWXL (300 × 7.8 mm, Tosoh Corporation, Tokyo, Japan) and TSKgel 2500 PWXL (300 × 7.8 mm, Tosoh Corporation, Tokyo, Japan). A multiangle laser light scattering detector (MALLS) operating in chromatographic mode using a He–Ne laser light source (630.0 nm) (Dawn-DSP-F, Wyatt Technology, Santa Barbara, CA, USA) and a differential refractive index detector (L7490, Merck, Darmstadt, Germany) were connected to the columns. The columns were maintained at 30 ◦ C. The mobile phase (0.15 M NaNO3 with 0.02% sodium azide) was filtered through 0.2 and 0.1 m cellulose acetate filters (Whatman, England). The flow rate of the mobile phase and the sample injection volume were 0.4 ml/min and
403
500 l, respectively. The output voltage of refractive index (RI) and light scattering (LS) at 18 angles was used for calculation of the weight-average molecular weight (Mw ) and radius of gyration (Rg ) using Astra 4.73.04 software (Wyatt Technology, Santa Barbara, CA, USA). In calculations of Mw and RG dn/dc value 0.167 (ml/g) for Hyal [59] was applied. The Berry plot with third order polynomial fit was applied in the calculation of Mw and Rg values. Separations were run in duplicates. 2.7. Differential scanning calorimetry Thermal gravimetry analysis coupled with mass spectrometry analysis (MSTG/DTG/SDTA) experiments were performed in Mettler-Toledo 851e apparatus in 150 l corundum crucibles, closed by a lid with a hole, under flow of argon (80 ml/min), within temperature range 30–800 ◦ C with heating rate of 10 ◦ C/min. The simultaneous evolved gas analysis (EGA) was performed during the experiments with a joined on-line quadruple mass spectrometer (QMS) (Thermostar Balzers). The differential scanning calorimetry (DSC) experiments were performed in Mettler-Toledo 821e calorimeter equipped with an intracooler Haake in 40 l aluminum crucibles under constant flow of argon (80 ml/min) within temperature range 25–400 ◦ C. 2.8. Electric resistivity Measurements were performed with 0.2 mm thick 3.0 cm × 0.5 cm foil leaflets involving the two-point method. Connections were made with silver plated copper wires (0.2 mm diameter and 5 cm long) bound around the leaflet foil. Points of contacts were additionally covered with a graphite paste then dried. The measuring system was equipped with a stabilized high voltage supplier (ZWM-42, Polon, Warsaw, Poland) and picoamperometer (Unitra-OBREP, Warsaw, Poland). The system was shielded from outer electric field with a thin metallic cage.
3. Results and discussion Hyal can successfully play the role of a matrix for ZnS and CdS QDs. Both kind QDs have been generated either from zinc acetate or cadmium sulfate, with sodium sulfide added. Hyal foils containing nanoclusters of ZnS and CdS, which could readily be developed easily, emitted light when illuminated with 253 nm light. The wavelength of emission depends on the type of QDs, and the intensity of their emission depends on their concentration. The fluorescence spectra of the Hyal/ZnS and Hyal/CdS nanocomposites are presented in Fig. 1. The emission bands with maxima at ∼410 and ∼475 nm for samples containing ZnS and CdS containing samples, respectively, exhibit some shoulders and inflections, and in the spectrum of the foil containing CdS there are even two well formed bands of lower intensity. They could be considered as the result of the non-uniform size of the included QDs. The sizes and morphologies of the as-prepared nanoparticles were studied by means of the TEM microscopy. Fig. 2 shows a TEM image of as-prepared CdS QDs. It is typical also for ZnS QDs. Spherical CdS QDs are well separated and particle size distribution ranges between 10 and 20 nm and such were also ZnS QDs. The FTIR-ATR spectra in the spectral range 750–4000 cm−1 for Hyal, and CdS and ZnS QDs/Hyal films are presented in Fig. 3. There is very limited number of changes in the spectrum of Hyal after QDs generation. Thus, in the CdS/Hyal composite foil the double peak with more intensive component at 1597 cm−1 (amide II band) and lower component at 1556 cm−1 (carboxylate asymmetric valence band) turned into a single peak centered at 1556 cm−1 with long wavelength shoulders above 1600 cm−1 (likely the amide I band) and 1597 cm−1 . In the spectrum of original Hyal, this double peak was more intensive than the adjoining shorter wavelength triple peak at 1405 cm−1 (carboxylate symmetric valence band), 1373 and 1321 cm−1 (primary and secondary alcoholic deformation bands). In the spectrum of the CdS/Hyal foil the intensity of the latter group of bands decreased. In the spectrum of the ZnS/Hyal foil the intensity ratio of these groups of bands practically did not change but, in turn, the intensity of the band located at 1141 cm−1 (skeletal acetal valence band) increased over that for the group of bands located above 1500 cm−1 . In the whole range of the spectrum
404
G. Khachatryan et al. / Journal of Alloys and Compounds 481 (2009) 402–406
Fig. 3. FTIR-ATR spectra of hyaluronic acid and its composites with ZnS and CdS QDs.
Fig. 1. Emission spectra of the ZnS/Hyal (A) and CdS/Hayl (B) preparations.
no significant band shifts could be noted. Insignificant band shifts could result from changes in the molecular weight of the samples. Such molecular weight-dependent band shifts in the IR spectra of Hyal have been recently observed [59]. Under such circumstances strong interactions of QDs with the Hyal matrix may be ruled out. TGA thermograms of the pure Hyal foil and the nanocomposites are shown in Fig. 4. The presence of CdS QDs had no influence on the thermal decomposition of Hyal. The foil held slightly less water and
Fig. 2. TEM image of CdS quantum dots (dark spots, diameter 10–20 nm) in sodium hyaluronate. Visible rings as artifacts emerged have been arrived during the development of the TEM negative film.
the rate as well as degree of decomposition remained unchanged but the foil with ZnS which also carried slightly less water than foil from Hyal started to decompose at slightly lower temperature and the rate of decomposition was slightly slower. Such result also points to either none or negligible interactions between QDs and the matrix. The pattern of DSC thermograms of Hyal foil (Fig. 5), practically unchanged by the presence of QDs, also supported the above opinion. An immediate optical feature of quantum dots is their coloration. The coloration is directly related to the energy levels of QD. Larger QDs have more closely packed energy levels in which the electron–hole pair can be trapped. Therefore, electron–hole pairs in larger QDs show a longer lifetime. Because there are no essential interactions between QDs and their matrix, the general dependence of the emission wavelength and size of QDs [60–62] should be valid also for QDs in Hyal matrix. Recent articles suggest [63,64] that the shape of QD can also be a factor in the coloration, but as yet not enough information has become available. Furthermore, the lifetime of fluorescence is determined by the size of QDs [1]. As can be seen from Fig. 2, QDs are mainly ball shaped. Size exclusion chromatography showed (Table 1) a decrease in the molecular weight of Hyal after generation of QDs in its solution. Higher molecular fraction of Hyal suffered smaller damage than the lower molecular fraction. Generation of CdS QDs was more destructive. However, in every case the decrease in radius of gyration, Rg ,
Fig. 4. Thermogravimetric curves of sodium hyaluronate (solid line). ZnS, dash–dot line; CdS, dotted line.
G. Khachatryan et al. / Journal of Alloys and Compounds 481 (2009) 402–406
405
Table 2 Parameters of the y = ax + b linear relationship for the voltage–current intensity correlations for the foils made of plain hyaluronate (Hyal) and quantum dots containing hyaluronate foils. Foil
a
b
Hyal Hyal/ZnSa Hyal/ZnSb Hyal/CdSa Hyal/CdSb
3E−09 4E−09 3E−09 3E−09 4E−09
−2E−08 −4E−08 9E−22 −1E-08 −3E−09
a b
Quantum dots generated from the 10−3 M solutions. Quantum dots generated from the 10−2 M solutions.
4. Conclusions
Fig. 5. DSC thermograms of sodium hyaluronate (solid line), Hyal-CdS (dotted line) and Hyal-ZnS (dashed line).
Table 1 Absolute molecular weight of the original hyaluronate (Hyal) fractions and their changes after generation of QDs inside hyaluronatea (Rg , radius of gyration). Sample
Mw × 10 Fraction I
Mw × 10 Fraction II
Rg Fraction I (nm)
Rg Fraction II (nm)
Hyal Hyal/ZnS Hyal/CdS
3.48 2.70 (22.4) 2.60 (25.3)
1.81 1.32 (28.7) 1.17 (35.4)
79.4 61.9 (22.0) 62.7(21.0)
61.7 48.5 (21.4) 48.5(21.4)
a
5
5
The percentage of decrease in the original values is given in parentheses.
was practically identical. The observed degradation of Hyal could result from its contact with the alkaline reagent. Hydrolysis of Na2 S increased the pH of the reaction mixture above 7. Under such conditions, the acetamido groups could split apart from the degradation typical for polysaccharides [65] in alkaline media. Electric resistivity studies performed for the Hyal foil in the range of 100–1000 V revealed a perfect linearity of the current–voltage (I–V) characteristic (see Fig. 6). This function and its parameters (Table 2) suggest that the foil has very weak conducting properties. QDs of both types in the foil did not deteriorate this linearity and only insignificantly decreased the slope of the correlation. The parameters of the linear relationship are given in Table 2. The opposite effects of the concentration upon a and b parameters in the case of ZnS and CdS QDs could not be discussed as neither the thickness and area of the investigated foils nor the dimension of QDs could be standardized.
Fig. 6. The current–voltage (I–V) characteristic for the hyaluronic acid foil.
Nanometer-sized semiconductor ZnS and CdS particles have been successfully prepared within hyaluronic acid film matrix. Because of involvement of hyaluronic acid coordination centers, this polysaccharide was proven to be efficient in preventing aggregation and controlling growth for ZnS and CdS nanocrystals. Acknowledgements This work was supported by the Polish Council for Science through the Development Grant for the years 2008-2011 and the BIONAN 2008 Scientific Net. References [1] A.F. van Driel, G. Allan, C. Delerue, P. Lodahl, W.L. Vos, D. Vanmaekelbergh, Phys. Rev. Lett. 95 (2005) 236804. [2] L.L. Yang, J.H. Yang, X.Y. Liu, Y.J. Zhang, Y.X. Wang, H.G. Fan, D.D. Wang, J.H. Lang, J. Alloys Compd. 463 (2008) 92–95. [3] C.B. Murray, C.R. Kagan, M.G. Bawendi, Annu. Rev. Mater. Sci. 30 (2000) 545–610. [4] J. Itoh, R.Y. Osamura, Meth. Mol. Biol. 374 (2007) 29–42. [5] X. Gao, L.W. Chung, S. Nie, Meth. Mol. Biol. 374 (2007) 135–145. [6] J.V. Frangioni, S.-W. Kim, S. Ohnishi, S. Kim, M.G. Bawendi, Meth. Mol. Biol. 374 (2007) 147–159. [7] K. Manzoor, S. Johny, D. Thomas, S. Setua, D. Menon, S. Nair, Nanotechnology 20 (2009) 065102. [8] R.L. Ornberg, H. Liu, Meth. Mol. Biol. 374 (2007) 3–10. [9] D.S. Lidke, P. Nagy, T.M. Jovin, D.J. Arndt-Jovin, Meth. Mol. Biol. 374 (2007) 69–79. [10] J.K. Jaiswal, S.M. Simon, Meth. Mol. Biol. 374 (2007) 93–104. [11] T.J. Deerinck, B.N. Giepmans, B.L. Smarr, M.E. Martone, M.E. Ellisman, Meth. Mol. Biol. 374 (2007) 43–53. [12] C. Bozuyigues, S. Levi, A. Triller, M. Dahan, Meth. Mol. Biol. 374 (2007) 81–91. [13] W. Gu, T. Pellegrino, W.J. Park, R. Boudreau, M.A. Gros, A.P. Aliviasatos, C.A. Larabell, Meth. Mol. Biol. 374 (2007) 125–131. [14] D.H. Geho, J.K. Killian, A. Nandi, J. Pastor, P. Gurnani, K.P. Rosenblatt, Meth. Mol. Biol. 374 (2007) 229–237. [15] R. Freeman, I. Willner, Nanoletters 9 (2009) 322–326. [16] E.R. Goldman, H.T. Uyeda, A. Hayhurst, H. Mattoussi, Meth. Mol. Biol. 374 (2007) 207–227. [17] B.B. Zhang, X.F. Liang, L.J. Hao, J. Cheng, X.Q. Gong, X.H. Liu, G.P. Ma, J. Chang, J. Photochem. Photobiol. B 94 (2009) 45–50. [18] L. Stobinski, J. Peszke, P. Tomasik, H.-M. Lin, J. Alloys Compd. 455 (2008) 137–141. [19] W. Wang, G.K. Liu, H.S. Cho, Y. Guo, D. Shi, J. Lian, R.C. Ewing, Chem. Phys. Lett. 469 (2009) 149–152. [20] H. Song, Y.Y. Zhai, Z.K. Zhou, Z.H. Hao, L. Zhou, Modern Phys. Lett. B 22 (2008) 3207–3213. [21] C. Unni, D. Philip, K.G. Gopchandran, Spectrochim. Acta A 71 (2008) 1402–1407. [22] I. Yildiz, S. Ray, T. Benelli, F.M. Raymo, J. Mater. Chem. 18 (2008) 3940–3947. [23] T. Stoferle, U. Scherf, R.F. Mahrt, Nanoletters 9 (2009) 453–456. [24] Z.A. Tan, B. Hedrick, F. Zhang, T. Zhu, J. Xu, R.H. Henderson, J. Ruzyllo, A.Y. Wang, IEEE Photonics Technol. Lett. 20 (2008) 1998–2000. [25] M.L. Hassan, A.F. Ali, J. Cryst. Growth 310 (2008) 5252–5258. [26] T.Q. Vu, R. Maddipati, T.A. Blute, B.J. Nehilla, L. Nusblat, T.A. Desai, Nanoletters 5 (2005) 603–607. [27] R.L. Ornberg, T.F. Harper, H. Liu, Nat. Methods 2 (2005) 79–81. [28] A. Sarkar, R.B. Robertson, J.M. Fernandez, Proc. Natl. Acad. Sci. U.S.A. 101 (2004) 12882–12886. [29] F. Pinaud, D. King, H.P. Moore, S. Weiss, J. Am. Chem. Soc. 126 (2004) 6115–6123. [30] A. Gokarna, S.K. Lee, J.S. Hwang, Y.H. Cho, Y.T. Lim, B.H. Chung, M. Lee, J. Korean Phys. Soc. 3 (2008) 3047–3050. [31] D. Bardelang, M.B. Zaman, I.L. Moudrakovski, S. Pawsey, J.C. Margeson, D.S. Wang, X.H. Wu, J.A. Ripmeester, C.I. Ratcliffe, K. Yu, Adv. Mater. 20 (2008) 4517–4520.
406
G. Khachatryan et al. / Journal of Alloys and Compounds 481 (2009) 402–406
[32] J.N. Rebilly, P.W. Gardner, G.R. Darling, J. Bacsa, M.J. Rosseinsky, Inorg. Chem. 47 (2008) 9390–9399. [33] A.J. Sutherland, Curr. Opin. Solid State Mater. Sci. 6 (2002) 365–370. [34] Z. Li, Y. Du, Z. Zhang, D. Pang, React. Funct. Polym. 55 (2003) 35–43. [35] I. Sondi, O. Siiman, E. Matijevic, J. Colloid Interface Sci. 275 (2004) 503–507. [36] W.B. Tan, Y. Zhang, J. Biomed. Mater. Res. A 75 (2005) 56–62. [37] X.H. Wang, Y.M. Du, S. Ding, L.H. Fan, X.W. Shi, Q.Q. Wang, G.G. Xiong, Physica E (Amsterdam) 30 (2005) 96–100. [38] Q. Nie, W.B. Tan, Y. Zhang, Nanotechnology 17 (2006) 140–144. [39] Q. Xu, M.P. Tucker, P. Arenkiel, X. Ai, G. Rumbles, J. Sugiyama, M.E. Himmel, S.Y. Ding, Cellulose 16 (2009) 19–26. [40] X.L. Sun, W. Cui, C. Haller, E.L. Chaikof, Chembiochem 5 (2004) 1593–1596. [41] F. Osaki, T. Kanamori, S. Sando, T. Sera, Y. Aoyama, J. Am. Chem. Soc. 126 (2004) 6520–6521. [42] H.M.E. Dirar, Chin. Phys. Lett. 25 (2008) 4480–4481. [43] Z.Y. Cheng, S.H. Liu, P.W. Beines, N. Ding, P. Jakubowicz, W. Knoll, Chem. Mater. 20 (2008) 7215–7219. [44] C.H. Wang, Y.S. Hsu, C.A. Peng, Biosens. Bioelectron. 24 (2008) 1012–1019. [45] H.B. Li, C.P. Han, Chem. Mater. 20 (2008) 6053–6059. [46] C.B. Murray, S. Sun, W. Gaschler, H. Doyle, T.A. Betley, C.R. Kogan, IBM J. Res. Dev. 45 (2001) 47–56. [47] M. Inoguchi, K. Suzuki, K. Kageyama, H. Takagi, Y. Sakabe, J. Am. Ceram. Soc. 91 (2008) 3850–3855. [48] X.Y. Ye, W.D. Zhuang, Y. Fang, Y.S. Hu, K. Zhao, X.W. Huang, Mater. Chem. Phys. 112 (2008) 730–733. [49] B.S. Amma, K. Manzoor, K. Ramakrishna, M. Pattabi, Mater. Chem. Phys. 112 (2008) 789–792. [50] X.X. Ren, G.L. Zhao, H. Li, W. Wu, G.R. Han, J. Alloys Compd. 465 (2008) 534–539.
[51] S. Bandyophadhyay, A.E. Miller, H.C. Chang, G. Banerjee, D.F. Yue, R.E. Richer, S. Jones, J.A. Eastman, M. Chandrasekhar, Nanotechnology 7 (1996) 360– 371. [52] R. Freeman, R. Gill, M. Beissenhirtz, J. Wilner, Photochem. Photobiol. Sci. 6 (2007) 416–422. [53] G. Mayer, M. Fonin, U. Rudiger, R. Schneider, D. Gerthsen, N. Janssen, R. Bratschitsch, Nanotechnology 20 (2009) 075601. [54] S.M. Lan, W.Y. Uen, C.E. Chan, K.J. Chang, S.C. Hung, Z.Y. Li, T.N. Yang, C.C. Chiang, P.J. Huang, M.D. Yang, G.C. Chi, C.Y. Chang, J. Mater. Sci. Mater. Electron. 20 (2009) 441–445. [55] P. Mandal, S.S. Talwar, R.S. Srinivasa, S.S. Major, Appl. Phys. A 94 (2009) 577–584. [56] Y.B. Li, L. Ma, X. Zhang, A.G. Joly, Z.L. Liu, W. Chen, J. Nanosci. Nanotechnol. 8 (2008) 5646–5651. [57] S.V. Pol, V.G. Pol, J.M. Calderon-Moreno, S. Cheylan, A. Gedanken, Langmuir 24 (2008) 10462–10466. [58] E.D. Atkins, J.K. Sheehan, Biochem. J. 125 (1971) 92P. [59] S. Hokputsa, J. Kornelia, C. Alexander, S. Harding, Eur. Biophys. J. 32 (2003) 450–496. [60] T. Fujisawa, T.H. Oosterkamp, W.G. van der Wiel, B.W. Broer, R. Aguado, S. Tarucha, L.P. Kouwenhoven, Science 282 (1998) 932–935. [61] N.Y. Hwang, S.R.E. Yang, Solid State Commun. 143 (2007) 176–178. [62] K. Baert, B. Kolaric, W. Libaers, R.A.L. Vallee, M. Di Vece, P. Lievens, K. Clays, Res. Lett. Nanotechnol. (2008), ID 974072. [63] S.J. Prado, C. Trallero-Giner, V. López-Richard, A.M. Alcalde, G.E. Marques, Phys. Rev. B 69 (2004) R201311. [64] D.R. Santos, Q. Fanyao, A.M. Alcalde, P.C. Morais, Phys. E 26 (2005) 331–336. [65] J.A. Alkrad, Y. Mrestani, D. Stroehl, S. Wartewig, R. Neubert, J. Pharm. Biomed. Anal. 31 (2003) 545–550.