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Dispersion of single-walled carbon nanotubes modified with poly-l-tyrosine in water.

Kojima M, Chiba T, Niishima J, Higashi T, Fukuda T, Nakajima Y, Kurosu S, Hanajiri T, Ishii K, Maekawa T, Inoue A - Nanoscale Res Lett (2011)

Bottom Line: In this study, complexes composed of poly-l-tyrosine (pLT) and single-walled carbon nanotubes (SWCNTs) were produced and the dispersibility of the pLT/SWCNT complexes in water by measuring the ζ potential of the complexes and the turbidity of the solution were investigated.It is found that the absolute value of the ζ potential of the pLT/SWCNT complexes is as high as that of SWCNTs modified with double-stranded DNA (dsDNA) and that the complexes remain stably dispersed in the water at least for two weeks.Thermogravimetry analysis (TGA) and visualization of the surface structures of pLT/SWCNT complexes using an atomic force microscope (AFM) were also carried out.

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Affiliation: Bio-Nano Electronics Research Centre, Toyo University 2100, Kujirai, Kawagoe, Saitama 350-8585, Japan. maekawa@toyo.jp.

ABSTRACT
In this study, complexes composed of poly-l-tyrosine (pLT) and single-walled carbon nanotubes (SWCNTs) were produced and the dispersibility of the pLT/SWCNT complexes in water by measuring the ζ potential of the complexes and the turbidity of the solution were investigated. It is found that the absolute value of the ζ potential of the pLT/SWCNT complexes is as high as that of SWCNTs modified with double-stranded DNA (dsDNA) and that the complexes remain stably dispersed in the water at least for two weeks. Thermogravimetry analysis (TGA) and visualization of the surface structures of pLT/SWCNT complexes using an atomic force microscope (AFM) were also carried out.

No MeSH data available.


AFM images of pLT and pLT/SWCNT complexes. (a) AFM image of pLT and the height distribution along line A-B. PLT folded to form sphere-like structures on the surface of an Si substrate. (b) AFM image of pLT/SWCNT complexes and the height distribution along line C-D. (c) AFM image of a pLT/SWCNT complex and the height distribution along line E-F. The thicknesses of pLT adsorbed onto the SWCNT varied cyclically in the axial direction of the SWCNT.
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Figure 4: AFM images of pLT and pLT/SWCNT complexes. (a) AFM image of pLT and the height distribution along line A-B. PLT folded to form sphere-like structures on the surface of an Si substrate. (b) AFM image of pLT/SWCNT complexes and the height distribution along line C-D. (c) AFM image of a pLT/SWCNT complex and the height distribution along line E-F. The thicknesses of pLT adsorbed onto the SWCNT varied cyclically in the axial direction of the SWCNT.

Mentions: Figure 1a shows the sedimentation of SWCNTs in DW and the dispersion of pLT/SWCNT complexes in DW. Note that the mass concentrations of SWCNTs were 0.1 mg ml-1 in both cases. The pLT/SWCNT complexes remained stably dispersed in DW for at least 14 days at 25°C, whereas the SWCNTs without any surface modification gradually coagulated to each other, and finally, were completely sedimented in DW (see also Figure 1c). Figure 1b shows the ζ potential of each material: i.e. (a) SWCNTs in DW, (b) SWCNTs in TritonX-100 solution, (c) dsDNA/SWCNT complexes in DW, and (d) pLT/SWCNT complexes in DW. Note that the data shown in Figure 1b were taken 14 days after each material had been dispersed in DW. The absolute value of the ζ potential of pLT/SWCNT complexes in DW was higher than that of SWCNTs in TritonX-100 solution and was slightly lower than that of dsDNA/SWCNT complexes in DW. It is known that the particles disperse stably in water when the absolute value of the ζ potential of each particle is greater than 20 mV [30,31], with which the present results coincide: that is, for the pLT/SWCNT and dsDNA/SWCNT complexes, the absolute values of the ζ potentials were, respectively, 42.3 and 46.2 mV, and the complexes remained stably dispersed in DW for al least 14 days: however, SWCNTs in DW, the absolute value of the ζ potentials of which was 13.0 mV, finally got sedimented (see also Figure 1a). SWCNTs in TritonX-100 solution, the absolute value of the ζ potential of which was 30.0 mV, also got dispersed stably. The time variation of the turbidity of each solution is shown in Figure 1c. The turbidity of the pLT/SWCNT in DW, which was slightly lower than that of the dsDNA/SWCNT in DW, but higher than that of the SWCNTs in TritonX-100 solution, was almost constant for 14 days, whereas the turbidity of the SWCNTs in DW immediately decreased due to quick coagulations and sedimentations of SWCNTs in DW. There is a clear correlation between the turbidity of each solution and the ζ potential of each material in the solution: that is, the higher the absolute value of the ζ potential of a material is, the higher the turbidity of the solution becomes (see Figure 1b, c). The TGA data obtained for pLT, SWCNTs, and pLT/SWCNTs complexes are shown in Figure 2. Both pLT and pLT/SWCNT complexes started decomposing at 300°C, whereas SWCNTs did not decompose at least up to 800°C. Note that the decomposition temperature of pLT obtained by the present TGA analysis, that is, 300°C, coincides with that measured previously [32]. pLT was definitely adsorbed onto SWCNTs judging by the TGA data of pLT/SWCNT complexes. The quantum calculations of the interactions between a single tyrosine molecule and a [6,6] SWCNT were carried out by the PM3 method (Gaussian03, Gaussian Co., Pittsburgh, PA, USA). As shown in Figure 3, a tyrosine molecule was adsorbed onto a SWCNT via the interactions between the six-membered rings as in the case of Fmoc/Tyr/SWCNT complexes [29]. The gap between the six-membered rings was approximately 0.45 nm, which is quite similar to that between graphitic layers [33]. It is supposed that the decomposition temperature of the pLT adsorbed onto SWCNTs was almost the same as that of pLT, that is, 300°C (see Figure 2), since the interactions between the rings are not very strong [29]. Judging by the weight loss obtained by the TGA analysis (Figure 2), 0.2 μg of pLT was adsorbed onto 1 μg of SWCNTs on average. AFM images of pLT and pLT/SWCNT complexes are shown in Figure 4. pLT without any immobilizations onto SWCNTs folded by itself to form sphere-like structures (see Figure 4a). The whole surfaces of the SWCNTs were covered with pLT, and the thickness of the pLT layers adsorbed onto SWCNTs varied from 1 to 4 nm (Figure 4b, c). It is supposed that pLT was adsorbed onto SWCNTs via the interactions between six-membered rings as mentioned above, and pLT folded to form sphere-like structures on the surfaces of SWCNTs, the thickness of which varied cyclically in the axial direction of the SWCNTs (Figure 4c). A TEM image of a pLT/SWCNT complex is also shown in the Additional file 1, where the mass concentration of pLT in DW was set at 0.2 mg ml-1 to obtain a clearer image. The pLT/SWCNT complexes dispersed stably in water thanks to the polar -OH group in tyrosine. In the case of tryptophan/SWCNT complexes, on the other hand, they did not disperse in water due to the hydrophobic group in tryptophan although it was adsorbed onto SWCNTs via the interactions among six-membered rings. Biomolecules such as enzymes can be attached to pLT, and therefore enzyme/pLT/SWCNT complexes can be produced so that new biosensors and devices may be developed in combination with SWCNT electronics [34]. The authors will be carrying out spectroscopic analyses such as Raman and Infrared spectroscopies of pLT/SWCNT complexes so that the structures of and conformational changes in pLT immobilised on SWCNTs may be clearly understood. The authors will also be investigating the adsorption of various biomolecules, viruses, and bacteria onto pLT/SWCNT complexes so that the complexes may be used as adsorbers, filters, or screening devices for organic molecules, viruses, and bacteria. The authors will also be measuring the electric and electronic properties of the complexes so that the above mentioned biosensors may be developed.


Dispersion of single-walled carbon nanotubes modified with poly-l-tyrosine in water.

Kojima M, Chiba T, Niishima J, Higashi T, Fukuda T, Nakajima Y, Kurosu S, Hanajiri T, Ishii K, Maekawa T, Inoue A - Nanoscale Res Lett (2011)

AFM images of pLT and pLT/SWCNT complexes. (a) AFM image of pLT and the height distribution along line A-B. PLT folded to form sphere-like structures on the surface of an Si substrate. (b) AFM image of pLT/SWCNT complexes and the height distribution along line C-D. (c) AFM image of a pLT/SWCNT complex and the height distribution along line E-F. The thicknesses of pLT adsorbed onto the SWCNT varied cyclically in the axial direction of the SWCNT.
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Figure 4: AFM images of pLT and pLT/SWCNT complexes. (a) AFM image of pLT and the height distribution along line A-B. PLT folded to form sphere-like structures on the surface of an Si substrate. (b) AFM image of pLT/SWCNT complexes and the height distribution along line C-D. (c) AFM image of a pLT/SWCNT complex and the height distribution along line E-F. The thicknesses of pLT adsorbed onto the SWCNT varied cyclically in the axial direction of the SWCNT.
Mentions: Figure 1a shows the sedimentation of SWCNTs in DW and the dispersion of pLT/SWCNT complexes in DW. Note that the mass concentrations of SWCNTs were 0.1 mg ml-1 in both cases. The pLT/SWCNT complexes remained stably dispersed in DW for at least 14 days at 25°C, whereas the SWCNTs without any surface modification gradually coagulated to each other, and finally, were completely sedimented in DW (see also Figure 1c). Figure 1b shows the ζ potential of each material: i.e. (a) SWCNTs in DW, (b) SWCNTs in TritonX-100 solution, (c) dsDNA/SWCNT complexes in DW, and (d) pLT/SWCNT complexes in DW. Note that the data shown in Figure 1b were taken 14 days after each material had been dispersed in DW. The absolute value of the ζ potential of pLT/SWCNT complexes in DW was higher than that of SWCNTs in TritonX-100 solution and was slightly lower than that of dsDNA/SWCNT complexes in DW. It is known that the particles disperse stably in water when the absolute value of the ζ potential of each particle is greater than 20 mV [30,31], with which the present results coincide: that is, for the pLT/SWCNT and dsDNA/SWCNT complexes, the absolute values of the ζ potentials were, respectively, 42.3 and 46.2 mV, and the complexes remained stably dispersed in DW for al least 14 days: however, SWCNTs in DW, the absolute value of the ζ potentials of which was 13.0 mV, finally got sedimented (see also Figure 1a). SWCNTs in TritonX-100 solution, the absolute value of the ζ potential of which was 30.0 mV, also got dispersed stably. The time variation of the turbidity of each solution is shown in Figure 1c. The turbidity of the pLT/SWCNT in DW, which was slightly lower than that of the dsDNA/SWCNT in DW, but higher than that of the SWCNTs in TritonX-100 solution, was almost constant for 14 days, whereas the turbidity of the SWCNTs in DW immediately decreased due to quick coagulations and sedimentations of SWCNTs in DW. There is a clear correlation between the turbidity of each solution and the ζ potential of each material in the solution: that is, the higher the absolute value of the ζ potential of a material is, the higher the turbidity of the solution becomes (see Figure 1b, c). The TGA data obtained for pLT, SWCNTs, and pLT/SWCNTs complexes are shown in Figure 2. Both pLT and pLT/SWCNT complexes started decomposing at 300°C, whereas SWCNTs did not decompose at least up to 800°C. Note that the decomposition temperature of pLT obtained by the present TGA analysis, that is, 300°C, coincides with that measured previously [32]. pLT was definitely adsorbed onto SWCNTs judging by the TGA data of pLT/SWCNT complexes. The quantum calculations of the interactions between a single tyrosine molecule and a [6,6] SWCNT were carried out by the PM3 method (Gaussian03, Gaussian Co., Pittsburgh, PA, USA). As shown in Figure 3, a tyrosine molecule was adsorbed onto a SWCNT via the interactions between the six-membered rings as in the case of Fmoc/Tyr/SWCNT complexes [29]. The gap between the six-membered rings was approximately 0.45 nm, which is quite similar to that between graphitic layers [33]. It is supposed that the decomposition temperature of the pLT adsorbed onto SWCNTs was almost the same as that of pLT, that is, 300°C (see Figure 2), since the interactions between the rings are not very strong [29]. Judging by the weight loss obtained by the TGA analysis (Figure 2), 0.2 μg of pLT was adsorbed onto 1 μg of SWCNTs on average. AFM images of pLT and pLT/SWCNT complexes are shown in Figure 4. pLT without any immobilizations onto SWCNTs folded by itself to form sphere-like structures (see Figure 4a). The whole surfaces of the SWCNTs were covered with pLT, and the thickness of the pLT layers adsorbed onto SWCNTs varied from 1 to 4 nm (Figure 4b, c). It is supposed that pLT was adsorbed onto SWCNTs via the interactions between six-membered rings as mentioned above, and pLT folded to form sphere-like structures on the surfaces of SWCNTs, the thickness of which varied cyclically in the axial direction of the SWCNTs (Figure 4c). A TEM image of a pLT/SWCNT complex is also shown in the Additional file 1, where the mass concentration of pLT in DW was set at 0.2 mg ml-1 to obtain a clearer image. The pLT/SWCNT complexes dispersed stably in water thanks to the polar -OH group in tyrosine. In the case of tryptophan/SWCNT complexes, on the other hand, they did not disperse in water due to the hydrophobic group in tryptophan although it was adsorbed onto SWCNTs via the interactions among six-membered rings. Biomolecules such as enzymes can be attached to pLT, and therefore enzyme/pLT/SWCNT complexes can be produced so that new biosensors and devices may be developed in combination with SWCNT electronics [34]. The authors will be carrying out spectroscopic analyses such as Raman and Infrared spectroscopies of pLT/SWCNT complexes so that the structures of and conformational changes in pLT immobilised on SWCNTs may be clearly understood. The authors will also be investigating the adsorption of various biomolecules, viruses, and bacteria onto pLT/SWCNT complexes so that the complexes may be used as adsorbers, filters, or screening devices for organic molecules, viruses, and bacteria. The authors will also be measuring the electric and electronic properties of the complexes so that the above mentioned biosensors may be developed.

Bottom Line: In this study, complexes composed of poly-l-tyrosine (pLT) and single-walled carbon nanotubes (SWCNTs) were produced and the dispersibility of the pLT/SWCNT complexes in water by measuring the ζ potential of the complexes and the turbidity of the solution were investigated.It is found that the absolute value of the ζ potential of the pLT/SWCNT complexes is as high as that of SWCNTs modified with double-stranded DNA (dsDNA) and that the complexes remain stably dispersed in the water at least for two weeks.Thermogravimetry analysis (TGA) and visualization of the surface structures of pLT/SWCNT complexes using an atomic force microscope (AFM) were also carried out.

View Article: PubMed Central - HTML - PubMed

Affiliation: Bio-Nano Electronics Research Centre, Toyo University 2100, Kujirai, Kawagoe, Saitama 350-8585, Japan. maekawa@toyo.jp.

ABSTRACT
In this study, complexes composed of poly-l-tyrosine (pLT) and single-walled carbon nanotubes (SWCNTs) were produced and the dispersibility of the pLT/SWCNT complexes in water by measuring the ζ potential of the complexes and the turbidity of the solution were investigated. It is found that the absolute value of the ζ potential of the pLT/SWCNT complexes is as high as that of SWCNTs modified with double-stranded DNA (dsDNA) and that the complexes remain stably dispersed in the water at least for two weeks. Thermogravimetry analysis (TGA) and visualization of the surface structures of pLT/SWCNT complexes using an atomic force microscope (AFM) were also carried out.

No MeSH data available.