(113c) 3D Electrodes Integrated in Microfluidic Channels for Automated Single Cell Electrorotation Spectra Acquisition

Samuel C.
Kilchenmann, Iness R. Benmessaoud, Pietro Maoddi, Marta A. Comino, Carlotta
Guiducci

Electrorotation
is a known technique to extract electrical parameters of cells. As the
rotational torque is highly dependent on the electric field strength, previous
works focused on optimizing the shape of planar electrodes, to achieve uniform
field strengths. Mostly, the optimization was performed only in 2D space and
electrode distances above 100 μm were considered. While this strategy might
lead to valid results in the electrode center, it is not suitable in cases of
small electrodes, where the inter-electrode distance is in the range of the
channel height, as the electrical fields will have a strong curvature and
dependence on height. For this reason, in our lab, we focus on the application
of 3D electrodes for electrorotation experiments. Such electrodes allow to
achieve electric fields that have no dependence on the z-position and thus the
rotation torque is constant over the full channel height. A direct consequence
is that the signal amplitudes can be lowered, as for a given signal amplitude,
3D electrodes lead to a higher torque moment inside the microfluidic chamber,
compared to a similar planar design. Ultimately 3D electrodes reduce the risk
of cell and electrode damage, as they lead to lower electric field peaks and to
lower thermal heating effects.

Furthermore, 3D
electrodes were shown to lead to more stable particle trapping in microfluidic
channels [1]. This can be used to achieve simultaneous trapping and rotation of
particles inside microfluidic channels by applying simultaneous DEP and ROT
signals [2]. For this reason, we developed a fabrication process to achieve 3D
electrodes integrated in microfluidic channels [3] and we currently employ
electrorotation experiments to extract complete electrorotation spectra of one
single cells. The cells are injected into the system by microfluidic sample
handling with a pressure driven system that allows for high control on flow and
instantaneous flow stop. The latter in combination with the DEP trapping,
allows for high precision in cell positioning. The good control over the
electric field and the precise positioning of single cells by means of DEP lead
to high control of experimental conditions and side effects such as clustering
and particle-particle interactions can be reduced. For this reason, this system
allows to extract a single cell electrorotation spectrum and to compare it to
the rest of the population.

[1]          J.
Voldman, M. Toner, M. L. Gray, and M. A. Schmidt,
“Design and analysis of extruded quadrupolar dielectrophoretic traps,” J. Electrostat.,
vol. 57, no. 1, pp. 69–90, 2003.

[2]          A. Rohani,
W. Varhue, Y.-H. Su, and N. S. Swami, “Electrical
tweezer for highly parallelized electrorotation measurements over a wide
frequency bandwidth.,” Electrophoresis, vol. 35, no. 12–13, pp. 1795–802, Jul.
2014.

[3]          S. C. Kilchenmann, E. Rollo,
P. Maoddi, and C. Guiducci, “Metal-Coated SU-8 Structures for High-Density 3-D
Microelectrode Arrays,” J. Microelectromechanical Syst., pp. 1–7, 2016.