We present an integrated circuit/microfluidic chip that traps and moves individual
living biological cells and chemical droplets along programmable paths using dielectrophoresis
(DEP). Our chip combines the biocompatibility of microfluidics with the programmability and
complexity of integrated circuits (ICs). The chip is capable of simultaneously and independently
controlling the location of thousands of dielectric objects, such as cells and chemical droplets.
The chip consists of an array of 128 � 256 pixels, 11 � 11 �m in size, controlled by built-in
SRAM memory, also similar in architecture to a computer display or a CCD; each pixel can be energized by a radio frequency (RF) voltage of up to 5 Vpp. The IC was
built in a commercial foundry and the microfluidic chamber was fabricated on its top surface at
Harvard. Using this hybrid chip, we have moved yeast and mammalian cells through a microfluidic
chamber at speeds up to 30 �m sec-1. Thousands of cells can be individually trapped and
simultaneously positioned in controlled patterns. The chip can trap and move pL droplets of
water in oil, split one droplet into two, and mix two droplets into one. Our IC/microfluidic
chip provides a versatile platform to trap and move large numbers of cells and fluid droplets
individually for lab-on-a-chip applications.
The DEP chip is a small integrated circuit approximately 2x3mm in size. Its surface contains
a display of 128 x 256 pixels. Each pixel is 11 x 11 �m in area an can be set to either
0V or 5V.
Dielectrophoresis (DEP)
Dielectrophoresis is the motion of a dielectric object in a nonuniform electric field.
A non-uniform electric field induces dipoles. If the dipole induced on the object is
stronger than that induced on the surrounding fluid (ie. the object is more polarizable than
the fluid), it will feel a force. By applying an appropriate local electric field pattern,
any particle with a dielectric constant different to that of the surrounding medium can be
manipulated with DEP. Nowadays, dielectrophoresis are widely used to manipulate, transport,
separate and sort different types of particles.
Two dielectric objects are floating in a non-uniform electric field. The top object is more
polarizable than the surrounding fluid and hence feels a force pushing it towards the electric
field maxima. The bottom object is less polarizable than the fluid and is hence
attracted to the electric field minima. These are respectively called positive and negative
DEP (+FDEP and -FDEP).
Manipulating Droplets
Splitting, moving and combining water drops in oil with DEP. This time sequence shows a droplet
of dyed water between a layer of fluorocarbon oil below and hydrocarbon oil above. The pixels
energized with Vpix in each frame are highlighted in white.
Manipulating Cells
The hybrid integrated circuit / microfluidic chip traps and moves individual cells.
A fluid, containing cells, is placed on the chip�s surface and cells are attracted to active
pixels.
Large numbers of cells can be positioned into patterns by activating precisely-defined
combinations of pixels. This can be done by sending a bitmap image file to the chip.
One such example is the picture below where �Lab on a Chip� was written using yeast cells.
The chip can also move cells in real-time. This video shows two cells dancing in coordination
to music. The cells move by following the electric fields which are being transferred between
neighboring pixels.
Thousands of cells can also be moved simultaneously. Below we show a video of a dancer being
played using thousands of yeast cells. The video is sent to the chip in .gif format through a
USB port.
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Westervelt Group 2016 | webmaster: Sagar Bhandari
