Biomedical Engineering Reference
In-Depth Information
mechanisms, understating that is only visible at single-cell level. Single-cell nanotoxicity studies
are believed to provide more realistic cell behavior under nanoparticle interactions.
5.3.1 c
arBoN
f
IBer
M
Icroelectrode
Carbon fiber microelectrodes have been widely used for single-cell analysis due to their ability to
detect diffusion-limited current at very high scan rates, allowing quick measurements of fast tempo-
ral events of the cells (Bard 2001). Carbon fiber microelectrodes have high sensitivities due to their
very small tip (5-10 μm) and low noise for very sensitive detections of changes in cell behavior. The
carbon fiber microelectrode amperometry technique has the potential to reveal the biophysics of
exocytosis and, thus, can be an important tool in understanding cellular communication under the
influence of nanoparticles.
Marquis et al. (2008) conducted carbon fiber microelectrode amperometry to characterize sero-
tonin exocytosis from murine peritoneal mast cells cocultured with fibroblasts in the presence of
Au nanoparticles. The interaction between various concentrations of serum-coated Au nanoparticles
sized between 12 and 46 nm after coculturing with mast cells for 48 h, suggested an altered exocytosis
mechanism. The study reported decreases in granule transport and fusion events, and increased intra-
cellular matrix expansions and a higher number of serotonin exocytosis per granule. A further expan-
sion of these studies showed the effects on cell viability when the nanoparticle exposure was extended
for 48 and 72 h (Marquis et al. 2009). Love and Haynes (2010) carried out a study to evaluate the
effect of citrate-reduced noble nanoparticles, Au (28 nm), and Ag (61 nm), on neuroendocrine cells.
An inductively coupled plasma-atomic emission spectroscopy (ICP-AES) measurement was carried
out for the uptake quantification; cells were lysed and the total metal content was a measure of the
nanoparticle uptake. The rate of uptake for 1 nM of Ag and Au nanoparticles was found to be differ-
ent for each type after 24 h of exposure, 3.4 × 10
4
versus 7.5 × 10
5
nanoparticles per cell, respectively,
suggesting a higher internalization of the Au nanoparticles. The differences in the rates of nanoparticle
internalization were assumed to be affected by several factors such as size, surface charge, and func-
tionalization. Transmission electron microscopy (TEM) was used for the localization of nanoparticle
assessment and to verify the internalization of nanoparticles in cellular granules and not only on the
cell membrane. Carbon fiber microelectrode amperometry revealed the changing exocytosis behav-
ior of chromaffin cells in this study. Metal oxides are commonly used in consumer products. The
carbon fiber microelectrode amperometry technique has been used to understand the nanotoxicity of
metal oxide (nonporous SiO
2
, porous SiO
2
, and nonporous TiO
2
) nanoparticles on immune cells by
Maurer-Jones et al. (2010). The results revealed functional changes in chemical messenger secretions
from mast cell granules. Nanoparticle surface properties are known to play a major role in deciding
their interactions with biological systems. Marques et al. (2011) executed a study on noble nanopar-
ticles, Au (~26.5 nm), and Ag (~33.3 nm), with different zeta potentials (surface charge), by modifying
the nanoparticle surface using cationic or anionic thiols. It was noted that positive surface-charged
nanoparticles (Au+ and Ag+) were more susceptible to internalization by the mast cells compared
to their negatively charged counterparts (Au- and Ag-). Carbon fiber microelectrode amperometry
was further utilized by Love et al. (2012) to evaluate the changes in cellular communication in neu-
roendocrine cells after size-dependent Ag nanoparticle- and surface-functionalized Au nanoparticle
exposure for 24 h. The study revealed that even if the Ag nanoparticles (15−60 nm) did not alter
cell viability, they showed size-dependent cellular uptake and an increase in the speed of exocytosis-
release kinetics. On the other hand, polyethylene glycol (PEG)-functionalized Au nanoparticles did
not change cell viability. However, they decreased the number of molecules released from each vesicle.
5.3.2 a
toMIc
f
orce
M
Icroscopy
Atomic force microscopy is a powerful, force-sensitive technique and has been successfully
applied in single-cell studies to gather the information on cell structure, topography, membrane
