Biomedical Engineering Reference
In-Depth Information
In addition, strategic manipulations of RNA have shown the ability to avoid
recognition by the mammalian immune system.
64
Moreover, unlike DNA
(which needs to be transcribed), RNA is directly functional in cells and, once
released from a carrier (e.g., CNTs), it may be translated to yield a protein or
act as antisense RNA to suppress protein synthesis, or act as interfering RNA
(RNAi) to silence a target gene.
With the purpose of using RNA for advanced biomedical applications, Rao
et al.
proposed single-molecule luorescence microscopy as a useful method
to investigate nucleic acids because the method is non-invasive and rapid
in image acquisition.
65
The group also exploited resonance Raman analysis
to study CNTs, since the nanotubes, especially SWCNTs, show characteristic
peaks. Therefore, they suggested the combination of these two techniques
as an ideal tool for evaluating the non-speciic binding of RNA polymer
(poly(rU)), consisting of 500-2,600 nucleotides labelled with OliGreen
luorescent dye corresponding to Uracil (U) residues and isolated CNTs
on a silicon substrate. Fluorescence images indicated poly(rU) molecules
as individual small blobs, most probably because of the tertiary structure
of poly(rU) into loops. Moreover, since poly(rU) molecules appeared to be
distributed along the contour of SWCNTs, the results suggested that the
π
-
stacking and hydrophobic interactions between the poly(rU) molecules and
the tubes was likely to be stronger than the van der Waals and hydrophobic
interactions between the bases and the silicon substrate. Micro-Raman
spectra showed the characteristic radial breathing mode (RBM) within 190-
290 cm
−1
and the
G
band centered at 1,593 cm
−1
. No remarkable shifts in the
peak positions were seen in the poly(rU)-bound SWCNT spectra, because of
the non-speciic binding of RNA to the tubes, which should not provide any
signiicant charge transfer. Conversely, the SWCNT-poly(rU) hybrids exhibited
a marked decrease in the intensity of the RBM band and a small enhancement
in the
D
band intensity compared with SWCNTs alone, thus conirming an
effective binding of poly(rU) onto SWCNTs.
In comparison with the previously reported covalent binding scheme
by Kam
et al.
60
and Pantarotto
et al.
,
61
the non-speciic binding between
SWCNTs and poly(rU) offers more lexibility for the tracking and release of
the load carried by SWCNTs upon delivery. In order to study the translocation
of SWCNTs inside the cells, Lu
et al.
performed a radioisotope labelling
assay on the tubes with thymidine (methyl-[
3
H]), while concentrations of
SWCNTs were kept lower than 0.4 mg/mL.
66
The uptake of SWCNT-poly(rU)
complexes was suggested to be a result of the amphipathic character of
both cell membrane and SWCNT-poly(rU) hybrids. Once internalised inside
MCF7 cells, endosomes in the cytoplasm could have stored SWCNTs after
poly(rU) translocation inside the nucleus (as indicated by their presence
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