- Email: [email protected]
Preparation and characterization of fluorescent silica coated magnetic hybrid nanoparticles
Colloids and Surfaces A: Physicochem. Eng. Aspects 386 (2011) 11–15
Contents lists available at ScienceDirect
Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa
Preparation and characterization of fluorescent silica coated magnetic hybrid nanoparticles Kaliyaperumal Viswanathan ∗ National Chinan University, Department of applied chemistry, No. 1, University Road, Puli, Nantou County, 54561, Taiwan, ROC
a r t i c l e
i n f o
Article history: Received 25 February 2011 Received in revised form 10 June 2011 Accepted 16 June 2011 Available online 23 June 2011 Keywords: Nanoparticles Magnetic material
a b s t r a c t In this report we describe the synthesis, characterization of fluorescent silica coated magnetic hybrid nanoparticles. These nanoparticles have been synthesized by combining the co-precipitation, polymerization and sol–gel technology with fluorescent dye. And their size can range from about 80 to 90 nm in diameter. The nanoparticles were characterized by atomic force microscopy (AFM), fourier transform infrared (FTIR) spectroscopy, spectrofluorometer, X-ray diffraction patterns (XRD) and an energy-dispersive X-ray spectroscopy (EDS). Concluding, this report has provided simple and efficient method for the design of new water-soluble fluorescent silica coated magnetic hybrid nanoparticles for biomedical, analytical and catalytic applications. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
1. Introduction In recent years, different kinds of studies in biology and biomedicine includes nanoparticles as a tool, and the surface modification of nanoparticles adds to their usefulness and alters their intrinsic characteristics [1,2]. Fluorescent magnetic nanoparticles are very attractive for cell-line studies. The magnetic properties of the nanoparticles are useful in preconcentrating the specific target molecules or cells by using an external magnetic field [3,4]. At the same time, the fluorescent code helps the researcher understand the specific target site of the cells. Magnetic nanoparticles with a core–shell structure offered more features in biological science. The nanoparticles shells are mainly composed of organic or inorganic materials [5,6], and helps to create effective surface modification with biomolecules [7,8]. In this work, initially we developed magnetic hybrid nanoparticles, we used polyvinyl pyrrolidone (PVP) and tetraethyl orthosilicate as a template to form a hybrid network, and the binding was accelerated by using heat. The heating process promoted the hydrogen bond formation between the polyvinyl pyrrolidone carbonyl groups and hydroxyl groups of the tetraethyl orthosilicate, and then, the iron oxide (Fe3 O4 ) nanoparticles efficiently anchored themselves onto the pyrrolidine ring of the PVPs. This reaction was accelerated by using ammonium hydroxide as a catalyst. To improve their versatility, the magnetic hybrid nanoparticles were coated with organic fluorescent silica layer. The coating of silica layer helps to avoid the photo bleaching effect from the
∗ Corresponding author. Tel.: +886 0931040470; fax: +886 49 2917 956. E-mail address: [email protected]
surrounding environment and it also offered the way for surface functional modification of biomolecules for biochemical applications. The method reported here is very simple, fast and it needs low sample handling compared with micro emulsion method. 2. Materials and methods 2.1. Synthesis of oleic acid-coated magnetic nanoparticles Oleic acid-coated magnetic nanoparticles were prepared by slightly modified steps of our previously published method [9]. Briefly, the ferrous chloride and ferric chloride were mixed in a molar ratio of 1:2 in milli-Q-water at a concentration of 0.15 M iron ions. And then, 10 mL of ammonium hydroxide, 1 mL of oleic acid were added. The sample was heated up to 80 ◦ C for 30 min and stirred. After that, we separated oleic acid-coated magnetic nanoparticles under the magnet, and the particles were collected and washed with distilled water. Finally it was dried in a vacuum oven at 50 ◦ C for 2 h. 2.2. Preparation of magnetic hybrid nanoparticles Initially 2 wt.% poly vinyl pyrrolidone (m.wt.40,000) solution was prepared using milli-Q-water. For magnetic hybrid nanoparticles synthesis, we took 20 mL of ethanol, 10 mL of 2% PVP solution and 1 mL of tetraethyl orthosilicate (TEOS) in a 50 mL conical flask. And this solution was heated at 80 ◦ C for 60 min with stirring. After that, the flask was allowed to cool. And then 3 mL of iron oxide (Fe3 O4 ) nanoparticles, 1 mL of ammonia hydroxide solution were added and the solution was stirred for 3 h at room temperature.
0927-7757/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2011.06.017
12
K. Viswanathan / Colloids and Surfaces A: Physicochem. Eng. Aspects 386 (2011) 11–15
Thereafter the PVP/SiO2 /Fe3 O4 nanoparticles were magnetically separated, which was followed by washing with mill-Q-water and finally dried in a vacuum oven at 37 ◦ C for 2 h. 2.3. Preparation of fluorescent silica coated magnetic hybrid nanoparticles Fluorescent silica coated magnetic hybrid nanoparticles were prepared using a modified procedure reported previously [10], briefly, 10 mL of ethanol, 0.5 mL of tetraethylorthosilicate, 5 mL of 6 × 10−3 mol of Tris (2,2 -bipyridyl) dichlororuthenium (II) hexa hydrate fluorescent dye and 1 mL of ammonium hydroxide solution was taken in a conical flask. And this solution was mixed for 2 h at room temperature to which 3 mL of previously prepared magnetic hybrid nanoparticles were added. The resulting solution was then stirred for 3 h at room temperature. There after the nanoparticles were magnetically separated, and washed with distilled water. Finally it was dried in a vacuum oven at 37 ◦ C for 2 h. 3. Results and discussion The sizes of the synthesized nanoparticles were confirmed by using atomic force microscopy (AFM), it was shown in Fig. 1. It indicated that, the nanoparticles exhibited the size around 80–90 nm. To examine the fluorescence property of these particles, the fluorescent silica coated magnetic hybrid nanoparticles solution was excited at 455 nm and emission of fluorescence was observed at 600 nm (Fig. 1a). The magnetic sensitivity of the prepared nanoparticles was measured using the hysteresis loop. We performed field-dependent magnetization of the nanoparticles at 5 K as shown in Fig. 2 and compared magnetization of the iron oxide nanoparticles before and after the application of the shell coating. The saturation magnetization (Ms ) and remanent magnetization (MR) clearly showed that the magnetization value of the iron oxide nanoparticles decreased after the application of the shell coating while the coercivity (Hc) remained nearly constant. Prior to coating, the magnetic hybrid nanoparti-
cles showed 22.189 emu/g of magnetization, while after coating, it decreased to 10.69 emu/g. The fluorescent silica coated magnetic hybrid nanoparticles magnetization results showed that the magnetization value of iron oxide nanoparticles divided by a substantial mass of silica materials. From the magnetization curve, we calculated the reduced remanence value (MR/Ms ) of magnetic hybrid nanoparticles, which was (0.64), while for the fluorescent silica-coated hybrid magnetic nanoparticles, the value was (0.67). The magnetization values were comparable with other previously published methods, such as polymer shell coated magnetic mesoporous silica nanoparticles (3.0 emu/g) [11], polymer microcapsules embedded magnetic nanoparticles (0.2 emu/g) [12], glycidyl methacrylate coated magnetic nanoparticles (1.74 emu/g) [13] copolymer coated magnetic nanoparticles (8 emu/g)[14], magnetic poly(MMA-DVB-GMA) nanospheres (5 emu/g) [15], magnetic poly(MMA-DVB) nanospheres (4 emu/g) [16]. X-ray diffraction patterns (XRD) of the nanoparticles were showed in Fig. 2a. The diffraction peaks and their relative intensities indicated that, the magnetic hybrid nanoparticles successfully coated with fluorescent silica layer. Loaded dye concentration is a major criterion for determining emission intensity of nanoparticles. The dye quantity incorporated in the nanoparticles surface was quantified using 1 mg/mL of nanoparticles. Initially we plotted the standard calibration curve by using serially diluted Tris (2,2 -bipyridyl) dichlororuthenium (II) hexa hydrate fluorescent dye in phosphate buffered saline solution. After that 1 mg/mL of the sample was taken to conduct a test. It was stirred in and dissolved in phosphate buffered saline solution under mild stirring. The emission intensity of the solution was recorded after that. We estimated 1 mg/mL of nanoparticles surface contained 5 × 10−7 (M) of Tris (2,2 -bipyridyl) dichlororuthenium (II) hexa hydrate fluorescent dye. The photo stability of the nanoparticles were shown in Fig. 3. The intensities of fluorescent silica coated magnetic hybrid nanoparticles with concentration of 4 mg/mL stored in a dark container at 4 ◦ C can be maintained about 95% of the original intensity even after 4 weeks, respectively. These results show that fluorescent nanoparticles are relatively stable against photo bleaching. Silica coated
Fig. 1. Particle size measurement of synthesized nanoparticles: the particle size measurement was carried out using atomic force microscopy (AFM). (a) Emission spectra were recorded using spectrofluorometer (excitation wave length (): 455 nm).
K. Viswanathan / Colloids and Surfaces A: Physicochem. Eng. Aspects 386 (2011) 11–15
13
Fig. 2. Field-dependent magnetization at 5K for (A) polymer–silica–superparamagnetic magmite hybrid nanoparticles (B) fluorescent silica coated magnetic hybrid nanoparticles. (a) XRD patterns of (i) polymer–silica–superparamagnetic magmite hybrid nanoparticles (ii) fluorescent silica coated magnetic hybrid nanoparticles.
nanoparticles surface contained regularly spaced pattern of oxygen atoms, so we tested the effect of different pH on standard fluorescence of nanoparticles. The results were shown in Fig. 4. Based on this (i) the fluorescent silica coated magnetic hybrid nanoparticles showed 20% of fluorescent intensity quenching at pH-4 compared with physiological pH 7.4 (ii) the emission spectra showed there is no significant changes in line width (1/2 ) up to pH 4, these results indicated that, (i) there is a possi-
Fig. 3. Photostability studies of synthesized nanoparticles.
Fig. 4. Different pH effects on standard fluorescence of synthesized nanoparticles (a). Different solvent effects on standard fluorescence of synthesized nanoparticles. (b) Ultra violet absorption based polyvinylpyrrolidone and tetraethyl orthosilicate binding confirmation.
bility of weak hydrogen bonding between the silanol groups of silica network and the acid-sensitive moieties of the dye complexes, (ii) the deprotonated silanol groups exist on silica surfaces electrostatically interact with the positively charged ruthenium (II) complexes, as well as with the negatively charged states of the peripheral acidic groups it makes fluorescence changes. We tested the effect of different solvents on standard fluorescence of nanoparticles, and this was shown in Fig. 4a. Based on that, the fluorescent intensity slightly increased in -mercaptoethanol compared with control phosphate buffer saline but in methanol the fluorescent intensity decreased slightly. The confirmation of hybrid network between the polyvinylpyrrolidone and tetraethyl orthosilicate were observed by using ultraviolet absorption spectra, it was shown Fig. 4b. Based on that, the spectral changes were recorded
14
K. Viswanathan / Colloids and Surfaces A: Physicochem. Eng. Aspects 386 (2011) 11–15
Fig. 5. FTIR spectra confirmation of nanoparticles (a). The elemental analyses of synthesized nanoparticles: the analysis was carried out using energy-dispersive X-ray spectroscopy (EDS). (b) Photograph under a magnetic field of fluorescent silica coated magnetic hybrid nanoparticles.
K. Viswanathan / Colloids and Surfaces A: Physicochem. Eng. Aspects 386 (2011) 11–15
at 240 nm. The fourier transform infrared (FTIR) spectroscopy analysis was carried out using a potassium bromide (KBr) background. It was shown in Fig. 5. The nanoparticles exhibited distinguishable bands measuring around 3432.54 cm−1 (OH), 1644.81 cm−1 (PVP), 1294.37 cm−1 (ruthenium (II) dye), 1088.88 cm−1 (Si–O–Si), 586.75 cm−1 (Fe–O). The elemental analysis was performed using energy-dispersive X-ray spectroscopy (EDS), and the results were shown in Fig. 5a. Based on that, the synthesized nanoparticles contained O (50.8%), Cu (10.7%), Fe (10.6%), Si (24.7%), Ru (3.2%). The EDX results confirmed that, the synthesized nanoparticles were made of silica, polymer, fluorescent dye and iron oxide. The magnetic field separations of the nanoparticles were shown in Fig. 5b. In the absence of an external magnet, the dispersion was homogeneous and bright orange. Once the magnet was placed beside the vial, the nanoparticles were quickly moved and accumulate near magnetic field. 4. Conclusion In conclusion, this report demonstrated that fluorescent silica coated magnetic hybrid nanoparticles were successfully synthesized. The methods offered several advantages such as, the PVP acts as an effective surface protecting agents as well as surface stabilizer and intermediate, so the large sized aggregates are completely avoided. In addition, the polymer–silica hybrid architecture allowed anchoring of magnetic nanoparticles, and the versatility of nanoparticles were improved by coating of fluorescent dyes and silica shell. Furthermore, the dye-coated nanoparticles own superior advantages of strong fluorescent intensity and excellent photo stability. This may lead to many promising applications in cell labeling, intracellular imaging, enzyme immobilization, cancer therapies, cell separation and MRI contrast agents. Acknowledgement This work was supported by the National Science Council of Taiwan.
15
References [1] I. Safarik, M. Safarikova, Magnetic techniques for the isolation and purification of proteins and peptides, Biomagnetic Res. Technol. 22 (2004) 1–17. [2] S.K. Sahoo, S. Parveen, J.J. Panda, The present and future of nanotechnology in human health care, Nanomedicine 3 (2007) 20–31. [3] J. Kim, Y. Piao, T. Hyeon, Multifunctional nanostructured materials for multimodal imaging, and simultaneous imaging and therapy, Chem. Soc. Rev. 38 (2009) 372–390. [4] A. Burns, H. Ow, U. Wiesner, Fluorescent core–shell silica nanoparticles: towards “Lab on a Particle” architectures for nanobiotechnology, Chem. Soc. Rev. 35 (2006) 1028–1042. [5] Y. Ge, Y. Zhang, S. He, F. Nie, G. Teng, N. Gu, Fluorescence modified chitosancoated magnetic nanoparticles for high-efficient cellular imaging, Nanoscale Res. Lett. 4 (2009) 287–295. [6] P. Tartaj, T.G. Carreno, C.J. Serna, Single-step nanoengineering of silica coated maghemite hollow spheres with tunable magnetic properties, Adv. Mater. 13 (2001) 1620–1624. [7] D. Knopp, D. Tang, R. Niessner, Bioanalytical applications of biomoleculefunctionalized nanometer-sized doped silica particles, Anal. Chim. Acta 647 (2009) 14–30. [8] O. Veiseh, J.W. Gunn, M. Zhang, Design and fabrication of magnetic nanoparticles for targeted drug delivery and imaging, Adv. Drug Deliv. Rev. 62 (2010) 284–304. [9] H.Y. Tsai, C.F. Hsu, I.W. Chiu, C. Bor Fuh, Detection of C-reactive protein based on immunoassay using antibody-conjugated magnetic nanoparticles, Anal. Chem. 79 (2007) 8416–8419. [10] Y. Lu, Y. Yin, B.T. Mayers, Y. Xia, Modifying the surface properties of superparamagnetic iron oxide nanoparticles through a sol–gel approach, Nano Lett. 2 (2002) 183–186. [11] B. Chang, X. Sha, J. Guo, Y. Jiao, C. Wang, W. Yang. Thermo and pH dual responsive, polymer shell coated, magnetic mesoporous silica nanoparticles for controlled drug release. J. Mater. Chem., in press. [12] H.Y. Koo, S.T. Chang, W.S. Choi, J.H. Park, D.Y. Kim, O.D. Velev, Emulsion-based synthesis of reversibly swellable, magnetic nanoparticle-embedded polymer microcapsules, Chem. Mater. 18 (2006) 3308–3313. [13] W. Wang, Y. Xu, D.I.C. Wang, Z. Li, Recyclable nanobiocatalyst for enantioselective sulfoxidation: facile fabrication and high performance of chloroperoxidase-coated magnetic nanoparticles with iron oxide core and polymer shell, J. Am. Chem. Soc. 131 (2009) 12892– 12893. [14] N.A.D. Burke, H.D.H. Stover, F.P. Dawson, Magnetic nanocomposites: preparation and characterization of polymer-coated iron nanoparticles, Chem. Mater. 14 (2002) 4752–4761. [15] H. Liu, J. Guo, L. Jin, W. Yang, C. Wang, Fabrication and functionalization of dendritic poly(amidoamine)-immobilized magnetic polymer composite microspheres, J. Phys. Chem. B 112 (2008) 3315–3321. [16] X. Liu, Y. Guan, Z. Ma, H. Liu, Surface modification and characterization of magnetic polymer nanospheres prepared by miniemulsion polymerization, Langmuir 20 (2004) 10278–10282.
Contents lists available at ScienceDirect
Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa
Preparation and characterization of fluorescent silica coated magnetic hybrid nanoparticles Kaliyaperumal Viswanathan ∗ National Chinan University, Department of applied chemistry, No. 1, University Road, Puli, Nantou County, 54561, Taiwan, ROC
a r t i c l e
i n f o
Article history: Received 25 February 2011 Received in revised form 10 June 2011 Accepted 16 June 2011 Available online 23 June 2011 Keywords: Nanoparticles Magnetic material
a b s t r a c t In this report we describe the synthesis, characterization of fluorescent silica coated magnetic hybrid nanoparticles. These nanoparticles have been synthesized by combining the co-precipitation, polymerization and sol–gel technology with fluorescent dye. And their size can range from about 80 to 90 nm in diameter. The nanoparticles were characterized by atomic force microscopy (AFM), fourier transform infrared (FTIR) spectroscopy, spectrofluorometer, X-ray diffraction patterns (XRD) and an energy-dispersive X-ray spectroscopy (EDS). Concluding, this report has provided simple and efficient method for the design of new water-soluble fluorescent silica coated magnetic hybrid nanoparticles for biomedical, analytical and catalytic applications. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
1. Introduction In recent years, different kinds of studies in biology and biomedicine includes nanoparticles as a tool, and the surface modification of nanoparticles adds to their usefulness and alters their intrinsic characteristics [1,2]. Fluorescent magnetic nanoparticles are very attractive for cell-line studies. The magnetic properties of the nanoparticles are useful in preconcentrating the specific target molecules or cells by using an external magnetic field [3,4]. At the same time, the fluorescent code helps the researcher understand the specific target site of the cells. Magnetic nanoparticles with a core–shell structure offered more features in biological science. The nanoparticles shells are mainly composed of organic or inorganic materials [5,6], and helps to create effective surface modification with biomolecules [7,8]. In this work, initially we developed magnetic hybrid nanoparticles, we used polyvinyl pyrrolidone (PVP) and tetraethyl orthosilicate as a template to form a hybrid network, and the binding was accelerated by using heat. The heating process promoted the hydrogen bond formation between the polyvinyl pyrrolidone carbonyl groups and hydroxyl groups of the tetraethyl orthosilicate, and then, the iron oxide (Fe3 O4 ) nanoparticles efficiently anchored themselves onto the pyrrolidine ring of the PVPs. This reaction was accelerated by using ammonium hydroxide as a catalyst. To improve their versatility, the magnetic hybrid nanoparticles were coated with organic fluorescent silica layer. The coating of silica layer helps to avoid the photo bleaching effect from the
∗ Corresponding author. Tel.: +886 0931040470; fax: +886 49 2917 956. E-mail address: [email protected]
surrounding environment and it also offered the way for surface functional modification of biomolecules for biochemical applications. The method reported here is very simple, fast and it needs low sample handling compared with micro emulsion method. 2. Materials and methods 2.1. Synthesis of oleic acid-coated magnetic nanoparticles Oleic acid-coated magnetic nanoparticles were prepared by slightly modified steps of our previously published method [9]. Briefly, the ferrous chloride and ferric chloride were mixed in a molar ratio of 1:2 in milli-Q-water at a concentration of 0.15 M iron ions. And then, 10 mL of ammonium hydroxide, 1 mL of oleic acid were added. The sample was heated up to 80 ◦ C for 30 min and stirred. After that, we separated oleic acid-coated magnetic nanoparticles under the magnet, and the particles were collected and washed with distilled water. Finally it was dried in a vacuum oven at 50 ◦ C for 2 h. 2.2. Preparation of magnetic hybrid nanoparticles Initially 2 wt.% poly vinyl pyrrolidone (m.wt.40,000) solution was prepared using milli-Q-water. For magnetic hybrid nanoparticles synthesis, we took 20 mL of ethanol, 10 mL of 2% PVP solution and 1 mL of tetraethyl orthosilicate (TEOS) in a 50 mL conical flask. And this solution was heated at 80 ◦ C for 60 min with stirring. After that, the flask was allowed to cool. And then 3 mL of iron oxide (Fe3 O4 ) nanoparticles, 1 mL of ammonia hydroxide solution were added and the solution was stirred for 3 h at room temperature.
0927-7757/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2011.06.017
12
K. Viswanathan / Colloids and Surfaces A: Physicochem. Eng. Aspects 386 (2011) 11–15
Thereafter the PVP/SiO2 /Fe3 O4 nanoparticles were magnetically separated, which was followed by washing with mill-Q-water and finally dried in a vacuum oven at 37 ◦ C for 2 h. 2.3. Preparation of fluorescent silica coated magnetic hybrid nanoparticles Fluorescent silica coated magnetic hybrid nanoparticles were prepared using a modified procedure reported previously [10], briefly, 10 mL of ethanol, 0.5 mL of tetraethylorthosilicate, 5 mL of 6 × 10−3 mol of Tris (2,2 -bipyridyl) dichlororuthenium (II) hexa hydrate fluorescent dye and 1 mL of ammonium hydroxide solution was taken in a conical flask. And this solution was mixed for 2 h at room temperature to which 3 mL of previously prepared magnetic hybrid nanoparticles were added. The resulting solution was then stirred for 3 h at room temperature. There after the nanoparticles were magnetically separated, and washed with distilled water. Finally it was dried in a vacuum oven at 37 ◦ C for 2 h. 3. Results and discussion The sizes of the synthesized nanoparticles were confirmed by using atomic force microscopy (AFM), it was shown in Fig. 1. It indicated that, the nanoparticles exhibited the size around 80–90 nm. To examine the fluorescence property of these particles, the fluorescent silica coated magnetic hybrid nanoparticles solution was excited at 455 nm and emission of fluorescence was observed at 600 nm (Fig. 1a). The magnetic sensitivity of the prepared nanoparticles was measured using the hysteresis loop. We performed field-dependent magnetization of the nanoparticles at 5 K as shown in Fig. 2 and compared magnetization of the iron oxide nanoparticles before and after the application of the shell coating. The saturation magnetization (Ms ) and remanent magnetization (MR) clearly showed that the magnetization value of the iron oxide nanoparticles decreased after the application of the shell coating while the coercivity (Hc) remained nearly constant. Prior to coating, the magnetic hybrid nanoparti-
cles showed 22.189 emu/g of magnetization, while after coating, it decreased to 10.69 emu/g. The fluorescent silica coated magnetic hybrid nanoparticles magnetization results showed that the magnetization value of iron oxide nanoparticles divided by a substantial mass of silica materials. From the magnetization curve, we calculated the reduced remanence value (MR/Ms ) of magnetic hybrid nanoparticles, which was (0.64), while for the fluorescent silica-coated hybrid magnetic nanoparticles, the value was (0.67). The magnetization values were comparable with other previously published methods, such as polymer shell coated magnetic mesoporous silica nanoparticles (3.0 emu/g) [11], polymer microcapsules embedded magnetic nanoparticles (0.2 emu/g) [12], glycidyl methacrylate coated magnetic nanoparticles (1.74 emu/g) [13] copolymer coated magnetic nanoparticles (8 emu/g)[14], magnetic poly(MMA-DVB-GMA) nanospheres (5 emu/g) [15], magnetic poly(MMA-DVB) nanospheres (4 emu/g) [16]. X-ray diffraction patterns (XRD) of the nanoparticles were showed in Fig. 2a. The diffraction peaks and their relative intensities indicated that, the magnetic hybrid nanoparticles successfully coated with fluorescent silica layer. Loaded dye concentration is a major criterion for determining emission intensity of nanoparticles. The dye quantity incorporated in the nanoparticles surface was quantified using 1 mg/mL of nanoparticles. Initially we plotted the standard calibration curve by using serially diluted Tris (2,2 -bipyridyl) dichlororuthenium (II) hexa hydrate fluorescent dye in phosphate buffered saline solution. After that 1 mg/mL of the sample was taken to conduct a test. It was stirred in and dissolved in phosphate buffered saline solution under mild stirring. The emission intensity of the solution was recorded after that. We estimated 1 mg/mL of nanoparticles surface contained 5 × 10−7 (M) of Tris (2,2 -bipyridyl) dichlororuthenium (II) hexa hydrate fluorescent dye. The photo stability of the nanoparticles were shown in Fig. 3. The intensities of fluorescent silica coated magnetic hybrid nanoparticles with concentration of 4 mg/mL stored in a dark container at 4 ◦ C can be maintained about 95% of the original intensity even after 4 weeks, respectively. These results show that fluorescent nanoparticles are relatively stable against photo bleaching. Silica coated
Fig. 1. Particle size measurement of synthesized nanoparticles: the particle size measurement was carried out using atomic force microscopy (AFM). (a) Emission spectra were recorded using spectrofluorometer (excitation wave length (): 455 nm).
K. Viswanathan / Colloids and Surfaces A: Physicochem. Eng. Aspects 386 (2011) 11–15
13
Fig. 2. Field-dependent magnetization at 5K for (A) polymer–silica–superparamagnetic magmite hybrid nanoparticles (B) fluorescent silica coated magnetic hybrid nanoparticles. (a) XRD patterns of (i) polymer–silica–superparamagnetic magmite hybrid nanoparticles (ii) fluorescent silica coated magnetic hybrid nanoparticles.
nanoparticles surface contained regularly spaced pattern of oxygen atoms, so we tested the effect of different pH on standard fluorescence of nanoparticles. The results were shown in Fig. 4. Based on this (i) the fluorescent silica coated magnetic hybrid nanoparticles showed 20% of fluorescent intensity quenching at pH-4 compared with physiological pH 7.4 (ii) the emission spectra showed there is no significant changes in line width (1/2 ) up to pH 4, these results indicated that, (i) there is a possi-
Fig. 3. Photostability studies of synthesized nanoparticles.
Fig. 4. Different pH effects on standard fluorescence of synthesized nanoparticles (a). Different solvent effects on standard fluorescence of synthesized nanoparticles. (b) Ultra violet absorption based polyvinylpyrrolidone and tetraethyl orthosilicate binding confirmation.
bility of weak hydrogen bonding between the silanol groups of silica network and the acid-sensitive moieties of the dye complexes, (ii) the deprotonated silanol groups exist on silica surfaces electrostatically interact with the positively charged ruthenium (II) complexes, as well as with the negatively charged states of the peripheral acidic groups it makes fluorescence changes. We tested the effect of different solvents on standard fluorescence of nanoparticles, and this was shown in Fig. 4a. Based on that, the fluorescent intensity slightly increased in -mercaptoethanol compared with control phosphate buffer saline but in methanol the fluorescent intensity decreased slightly. The confirmation of hybrid network between the polyvinylpyrrolidone and tetraethyl orthosilicate were observed by using ultraviolet absorption spectra, it was shown Fig. 4b. Based on that, the spectral changes were recorded
14
K. Viswanathan / Colloids and Surfaces A: Physicochem. Eng. Aspects 386 (2011) 11–15
Fig. 5. FTIR spectra confirmation of nanoparticles (a). The elemental analyses of synthesized nanoparticles: the analysis was carried out using energy-dispersive X-ray spectroscopy (EDS). (b) Photograph under a magnetic field of fluorescent silica coated magnetic hybrid nanoparticles.
K. Viswanathan / Colloids and Surfaces A: Physicochem. Eng. Aspects 386 (2011) 11–15
at 240 nm. The fourier transform infrared (FTIR) spectroscopy analysis was carried out using a potassium bromide (KBr) background. It was shown in Fig. 5. The nanoparticles exhibited distinguishable bands measuring around 3432.54 cm−1 (OH), 1644.81 cm−1 (PVP), 1294.37 cm−1 (ruthenium (II) dye), 1088.88 cm−1 (Si–O–Si), 586.75 cm−1 (Fe–O). The elemental analysis was performed using energy-dispersive X-ray spectroscopy (EDS), and the results were shown in Fig. 5a. Based on that, the synthesized nanoparticles contained O (50.8%), Cu (10.7%), Fe (10.6%), Si (24.7%), Ru (3.2%). The EDX results confirmed that, the synthesized nanoparticles were made of silica, polymer, fluorescent dye and iron oxide. The magnetic field separations of the nanoparticles were shown in Fig. 5b. In the absence of an external magnet, the dispersion was homogeneous and bright orange. Once the magnet was placed beside the vial, the nanoparticles were quickly moved and accumulate near magnetic field. 4. Conclusion In conclusion, this report demonstrated that fluorescent silica coated magnetic hybrid nanoparticles were successfully synthesized. The methods offered several advantages such as, the PVP acts as an effective surface protecting agents as well as surface stabilizer and intermediate, so the large sized aggregates are completely avoided. In addition, the polymer–silica hybrid architecture allowed anchoring of magnetic nanoparticles, and the versatility of nanoparticles were improved by coating of fluorescent dyes and silica shell. Furthermore, the dye-coated nanoparticles own superior advantages of strong fluorescent intensity and excellent photo stability. This may lead to many promising applications in cell labeling, intracellular imaging, enzyme immobilization, cancer therapies, cell separation and MRI contrast agents. Acknowledgement This work was supported by the National Science Council of Taiwan.
15
References [1] I. Safarik, M. Safarikova, Magnetic techniques for the isolation and purification of proteins and peptides, Biomagnetic Res. Technol. 22 (2004) 1–17. [2] S.K. Sahoo, S. Parveen, J.J. Panda, The present and future of nanotechnology in human health care, Nanomedicine 3 (2007) 20–31. [3] J. Kim, Y. Piao, T. Hyeon, Multifunctional nanostructured materials for multimodal imaging, and simultaneous imaging and therapy, Chem. Soc. Rev. 38 (2009) 372–390. [4] A. Burns, H. Ow, U. Wiesner, Fluorescent core–shell silica nanoparticles: towards “Lab on a Particle” architectures for nanobiotechnology, Chem. Soc. Rev. 35 (2006) 1028–1042. [5] Y. Ge, Y. Zhang, S. He, F. Nie, G. Teng, N. Gu, Fluorescence modified chitosancoated magnetic nanoparticles for high-efficient cellular imaging, Nanoscale Res. Lett. 4 (2009) 287–295. [6] P. Tartaj, T.G. Carreno, C.J. Serna, Single-step nanoengineering of silica coated maghemite hollow spheres with tunable magnetic properties, Adv. Mater. 13 (2001) 1620–1624. [7] D. Knopp, D. Tang, R. Niessner, Bioanalytical applications of biomoleculefunctionalized nanometer-sized doped silica particles, Anal. Chim. Acta 647 (2009) 14–30. [8] O. Veiseh, J.W. Gunn, M. Zhang, Design and fabrication of magnetic nanoparticles for targeted drug delivery and imaging, Adv. Drug Deliv. Rev. 62 (2010) 284–304. [9] H.Y. Tsai, C.F. Hsu, I.W. Chiu, C. Bor Fuh, Detection of C-reactive protein based on immunoassay using antibody-conjugated magnetic nanoparticles, Anal. Chem. 79 (2007) 8416–8419. [10] Y. Lu, Y. Yin, B.T. Mayers, Y. Xia, Modifying the surface properties of superparamagnetic iron oxide nanoparticles through a sol–gel approach, Nano Lett. 2 (2002) 183–186. [11] B. Chang, X. Sha, J. Guo, Y. Jiao, C. Wang, W. Yang. Thermo and pH dual responsive, polymer shell coated, magnetic mesoporous silica nanoparticles for controlled drug release. J. Mater. Chem., in press. [12] H.Y. Koo, S.T. Chang, W.S. Choi, J.H. Park, D.Y. Kim, O.D. Velev, Emulsion-based synthesis of reversibly swellable, magnetic nanoparticle-embedded polymer microcapsules, Chem. Mater. 18 (2006) 3308–3313. [13] W. Wang, Y. Xu, D.I.C. Wang, Z. Li, Recyclable nanobiocatalyst for enantioselective sulfoxidation: facile fabrication and high performance of chloroperoxidase-coated magnetic nanoparticles with iron oxide core and polymer shell, J. Am. Chem. Soc. 131 (2009) 12892– 12893. [14] N.A.D. Burke, H.D.H. Stover, F.P. Dawson, Magnetic nanocomposites: preparation and characterization of polymer-coated iron nanoparticles, Chem. Mater. 14 (2002) 4752–4761. [15] H. Liu, J. Guo, L. Jin, W. Yang, C. Wang, Fabrication and functionalization of dendritic poly(amidoamine)-immobilized magnetic polymer composite microspheres, J. Phys. Chem. B 112 (2008) 3315–3321. [16] X. Liu, Y. Guan, Z. Ma, H. Liu, Surface modification and characterization of magnetic polymer nanospheres prepared by miniemulsion polymerization, Langmuir 20 (2004) 10278–10282.