Civil Engineering Reference
In-Depth Information
uptake and cytotoxicity. h e surface charge of CNCs could be adjusted for penetra-
tion inside the cell without causing any cellular damage. Due to favorable electrostatic
interaction, the HEK 293 and S
f
9 cells uptook the l uorescent CNCs (CNCs-RBITC)
without af ecting the integrity of the cell membrane and with no noticeable cytotox-
icity, whereas CNCs-FITC did not show signii cant internalization (only aggregation
around the cells) at physiological pH. Along with other features, their noncytotoxicity
and membrane permeability make them perfect candidates for optical bioimaging and
drug delivery systems [238]. Overall, all the l uorescently labeled CNCs could not pen-
etrate the cells, but i ne tuning of the l uorescent functionality of CNCs can be used for
signii cant cellular uptake.
15.9.5
pH-Sensing Materials
A range of nanomaterials has already been modii ed to have sensing capabilities but
little attention has been given to CNCs [240]. CNCs have high surface area and reac-
tive functional (-OH) groups, which make these nanocrystals potential candidates
for converting into sensing nanomaterials by surface functionalization for applications
in diverse i elds [241, 242]. Nielsen
et al.
developed ratiometric pH-sensing nanopar-
ticles by two simple and versatile synthetic pathways for dual l uorescent labeling of
CNCs. h ey also demonstrated the usefulness of these synthetic pathways, which can
be applied for the preparation of a range of sensing nanoparticles using analyte respon-
sive dyes having a suitable functional group turning CNCs into sensing nanomaterials.
Moreover, the click-reaction of thiolene can be used to modify the surface of CNCs,
expecting that the reaction can be expanded to include virtually any thiol. h e aver-
age amount of FITC attached to the CNCs was estimated by UV/Vis spectra in 0.1 M
NaOH, ensuring dianionic form of FITC was present with a peak maximum at 490
nm. So a direct correlation between FITC content and absorption intensity could be
obtained. Fluorescence spectrometry was used to estimate the RBITC content because
the absorbance of RBITC was too low to show a distinct peak in the UV/Vis spectra of
the CNCs. h e amount of FITC and RBITC attached to CNCs was estimated to be 2.8
μmol g
-1
cellulose and 2.1 μmol g
-1
cellulose, respectively, and the reaction resulted in
no distinguishable changes in crystallinity or morphology as determined by XRD and
AFM, respectively. h e responsiveness towards pH of the CNCs was determined by
suspending them in a series of McIlvaine buf ers 14 ranging from pH 3.5 to pH 8.0 and
measuring the l uorescence emission intensities at ?
ex
= 490 nm, ?
em
= 520 nm and ?
ex
=
540 nm, ?
em
= 570 nm [243]. h e morphology (AFM images), suspensions and emission
spectra of pH responsive CNCs, at dif erent pH values, and intensity ratios vs pH values
are shown in Figure 15.18.
15.10
Conclusion
h e research on extraction of CNCs from dif erent sources and uniform dispersion in
polymer matrices has always been an important issue in the i eld of bionanocompos-
ites. h e nanoscale dimensions of cellulosic i bers along with their biodegradability and
