BIOMEDICAL APPLICATIONS IV: CARBON NANOTUBE-NUCLEIC ACID COMPLEXES FOR BIOSENSORS, GENE DELIVERY AND SELECTIVE CANCER THERAPY - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 130

were combined with plasmid DNA electrostatically. Their diversiied nature
in terms of surface functionalisation and charges allowed for discriminating
the inluencing factors in gene transfection: in fact SWCNT-NH 3 + and SWCNT-
Lys-NH 3 + shared the same dimensions and exposed surface, while SWCNT-
Lys-NH 3 + had a similar surface charge load as MWCNT- NH 3 + .
Scanning electron microscopy (SEM) proved very useful in studying the
supramolecular lattice formed when functionalised CNTs were exposed to
different ratios of plasmid. Images at the microscope showed that parallel
bundles of nanotubes formed a framework to which condensed packets of
DNA adhered. Interestingly, the DNA conjugated to MWCNTs (Fig. 5.26a-c)
appeared more stretched than in SWCNTs, where smaller aggregate particles
were formed (Fig. 5.26d-f ). However, the risk is that if DNA is too tightly
complexed, it may be unable to detach from the nanotube, thereby leading
to compromised gene expression. As a proof of that, SWCNT-NH 3 + appeared
more eficient at gene transfer when complexed to DNA at an 8:1 charge
Figure 5.26. SEM images of CNT-DNA complexes formed at a 6:1 charge ratio: (a-
c) MWNT-NH 3 + :DNA; (d-f ) SWNT-NH 3 + :DNA. Reproduced from Singh et al. 87 with
permission.