Mixtures of SWNTs suspended in aqueous glycodendron solutions resulted in
complete solubilization through specific adsorption of the glycosylated pyrene
motif onto the nanotubes, regardless of the nature of the sugars. The suspensions
of functionalized SWNTs exhibited remarkable stability in water for several
months. Furthermore, unlike thick and heterogeneous coatings generated with the
previous use of glycopolymers [75], the well-defined glycodendrons uniformly
wrapped the nanostructure to form small bundles, as revealed by scanning electron
microscopy (SEM) and transmission electron microscopy (TEM).
The capability of the assemblies to bind to specific proteins was probed with
different labeled lectins using fluorescein isothiocyanante (FITC)-conjugated
Canavalia ensiformis (Con A), Arachis hypogaea (PNA) and Psophocarpus
tetragonolobus (PTA) agglutinins, which recognize α-mannose, lactose, and βgalactose, respectively. As expected, specific recognition-induced fluorescence
was generated and measured by fluorescence microscopy when mannosylated 25SWNT was treated with Con A, whereas no substantial signal was detected from
unrelated PTA and PNA lectins. Similarly, galactosylated 26-SWNT and
lactosylated 27-SWNT bound to FITC-PTA and both labeled PNA and PTA,
respectively. Additional experiments were conducted with mixed glycosylated
structures around the SWNT to more accurately model the sugar diversity present
on cell surfaces. Hence, SWNTs functionalized with a mixture of mannosylated and
lactosylated G(2)-dendrons at various ratios, were incubated with a 1:1 mixture of
Texas Red-conjugated PNA and FITC-labeled Con A. Importantly, fluorescence
intensities associated with specific recognition events simultaneously increased
with the percentage of complementary ligands presented in the initial mixtures.
These results strongly suggest that multiple epitopes displayed on SWNTs could
bind simultaneously to discrete proteins. The authors took advantage of the
functionalized SWNT-associated specific fluorescence to investigate and observe
the strong interaction of the labeled nanosystems with Chinese hamster ovary
(CHO) cell surfaces. In fact, the remaining binding sites of tetravalent Con A,
which partly bound to mannosylated SWNT structures, offered additional
opportunities for subsequent complexation with Man residues present on cellsurface glycans. Finally, G(2) and G(3) glycodendrimer-coated SWNTs induced
no cytotoxicity in the presence of HEK293 cells whereas unfunctionalized
nanotubes hampered their growth.
CNTs also represent attractive candidates for multifunctional carrier systems by
virtue of their inherent dual role both as hosts for active payload that can be located
in the internal spaces and as active frameworks for subsequent covalent chemical
surface modifications. An eye-catching example demonstrating that filled and
carbohydrate-functionalized SWNTs could be used as efficient radioprobes with
specific ability to target organs in vivo has been published [76]. The authors first
filled SWNTs with metal halide such as CuBr and the more relevant Na
125 I, carried
out at high temperature. The subsequent cooling process was responsible for
closing of the ends of the SWNTs, resulting in the desired encapsulation of highdensity radio-emitting nanocrystals by using molten phase capillary wetting.
312
N. Kottari et al.
complete solubilization through specific adsorption of the glycosylated pyrene
motif onto the nanotubes, regardless of the nature of the sugars. The suspensions
of functionalized SWNTs exhibited remarkable stability in water for several
months. Furthermore, unlike thick and heterogeneous coatings generated with the
previous use of glycopolymers [75], the well-defined glycodendrons uniformly
wrapped the nanostructure to form small bundles, as revealed by scanning electron
microscopy (SEM) and transmission electron microscopy (TEM).
The capability of the assemblies to bind to specific proteins was probed with
different labeled lectins using fluorescein isothiocyanante (FITC)-conjugated
Canavalia ensiformis (Con A), Arachis hypogaea (PNA) and Psophocarpus
tetragonolobus (PTA) agglutinins, which recognize α-mannose, lactose, and βgalactose, respectively. As expected, specific recognition-induced fluorescence
was generated and measured by fluorescence microscopy when mannosylated 25SWNT was treated with Con A, whereas no substantial signal was detected from
unrelated PTA and PNA lectins. Similarly, galactosylated 26-SWNT and
lactosylated 27-SWNT bound to FITC-PTA and both labeled PNA and PTA,
respectively. Additional experiments were conducted with mixed glycosylated
structures around the SWNT to more accurately model the sugar diversity present
on cell surfaces. Hence, SWNTs functionalized with a mixture of mannosylated and
lactosylated G(2)-dendrons at various ratios, were incubated with a 1:1 mixture of
Texas Red-conjugated PNA and FITC-labeled Con A. Importantly, fluorescence
intensities associated with specific recognition events simultaneously increased
with the percentage of complementary ligands presented in the initial mixtures.
These results strongly suggest that multiple epitopes displayed on SWNTs could
bind simultaneously to discrete proteins. The authors took advantage of the
functionalized SWNT-associated specific fluorescence to investigate and observe
the strong interaction of the labeled nanosystems with Chinese hamster ovary
(CHO) cell surfaces. In fact, the remaining binding sites of tetravalent Con A,
which partly bound to mannosylated SWNT structures, offered additional
opportunities for subsequent complexation with Man residues present on cellsurface glycans. Finally, G(2) and G(3) glycodendrimer-coated SWNTs induced
no cytotoxicity in the presence of HEK293 cells whereas unfunctionalized
nanotubes hampered their growth.
CNTs also represent attractive candidates for multifunctional carrier systems by
virtue of their inherent dual role both as hosts for active payload that can be located
in the internal spaces and as active frameworks for subsequent covalent chemical
surface modifications. An eye-catching example demonstrating that filled and
carbohydrate-functionalized SWNTs could be used as efficient radioprobes with
specific ability to target organs in vivo has been published [76]. The authors first
filled SWNTs with metal halide such as CuBr and the more relevant Na
125 I, carried
out at high temperature. The subsequent cooling process was responsible for
closing of the ends of the SWNTs, resulting in the desired encapsulation of highdensity radio-emitting nanocrystals by using molten phase capillary wetting.
312
N. Kottari et al.