Biomedical Engineering Reference
In-Depth Information
5.2 CELLULAR-BASED BIOSENSORS FOR NANOTOXICITY
Whole-cell EIS-based sensors, pioneered by Giaever and Keese, were the first demonstration of a
system capable of monitoring the proliferation and motion of a population of anchorage-dependent
cell cultures
in vitro
(Giaever and Keese 1984). Giaever and Keese cultured human lung fibro-
blast cells on modified cell culture dishes consisting of a large reference electrode (2 cm
2
) and four
smaller electrodes (3 × 10
−4
cm
2
). They applied an alternating current (AC) voltage, through a resis-
tor, to a single small electrode in the dish, resulting in a constant current source, which enabled the
impedance to be determined by the measurement of the resulting voltage. They were able to observe
the effects of cell proliferation (impedance increase) as well as the micromotion of the cells (fluctua-
tions in observed impedance).
Giaever and Keese then used their biosensor to examine the effects of different proteins on cell
adhesion, spreading, and motility (Giaever and Keese 1986), to create a mathematical model of
cell motion (Giaever and Keese 1989), and the use of this impedance method in cell-based sensor
applications (Giaever and Keese 1991, 1992, 1993). Connelly et al. modified Giaever and Keese's
biosensor design by adding a glass ring around the electrode area, to contain the cell culture media,
and inserting a permeable, cellulose nitrate membrane to separate the culture dish into two sides,
each with two measurement electrodes, creating a control and a test electrode (Connolly et al. 1990).
EIS technology is shown to be sensitive enough to measure the micromotion of a cell and, there-
fore, be able to monitor the progression of cytotoxicity with rapid, real-time, and multisample analy-
sis, creating a versatile, noninvasive tool that is able to provide quantitative information with respect
to alterations in cellular function under various nanomaterial exposures. Thus, EIS biosensors are
ideal for detecting toxic nanomaterials in industrial products, chemical substances, environmental
samples (e.g., air, soil, and water), or biological systems (e.g., bacteria, viruses, or tissue compo-
nents), as they are able to monitor the progression of the cytotoxicity in real time, demonstrating the
kinetic effects of the nanomaterials toward whole cells.
Chip-based biosensors show a promising future for monitoring cellular nanotoxicity as they
allow rapid, real-time, and multisample analysis creating a versatile, noninvasive tool that is able to
provide quantitative information with respect to alterations in cellular function under various nano-
material exposures. A different chip-based approach to evaluate nanotoxicity was experimented by
Kim et al. (2011). They fabricated a chip using a lithography technique where gold was the sens-
ing electrode and was modified with RGD-MAP-C to enhance cell (SH-SY5Y) adhesion on the
chip. Silica nanoparticles of various sizes and surface chemistries were examined to understand the
effects of induced nanotoxicity on SH-SY5Y cells by studying the cell viability at different concen-
trations of nanoparticles ranging from 50 to 400 μg/mL and at various time points. Electrochemical
measurements of nanotoxicity were recorded using differential pulse voltametry and were com-
pared to absorption- and fluorescence-based techniques to evaluate the benefits of electrochemical
measurements in assessing nanotoxicity.
5.3 TECHNIQUES AND DEVICES FOR NANOTOXICITY TESTING
Nanoparticles with many novel properties are used in various applications and come in contact with
complex and dynamic biological systems. It is challenging to characterize nanoparticles throughout
their biological interaction and to quantify the uptake rate and localization inside cells. Cells under
nanotoxicity may undergo necrosis or repairable, oxidative DNA damage, recovering from it even-
tually or resulting in apoptosis. Nanotoxicity may alter cell differentiation, proliferation, morphol-
ogy, or cell-cell communication. Traditional methods for evaluating nanotoxicity consist of bulk
analysis, where the resultant is assumed to be the average of the whole cell population. Cell hetero-
geneity has been recently studied by researchers, suggesting that the cells in a subpopulation may
exhibit different behavior from the general population (Irish et al. 2006; Graf and Stadtfeld 2008).
This means that the cell population study in aggregation may hinder some very important cell
