Cells are the basic element in humans, animals and plants. As they are so tiny, the manipulation of these small matters is impossible with humans’ hands and we cannot even see them with bare eyes. In this video, I am going to bring you into a microfluidic device; the place where cells and particles can be manipulated by conducting PDMS.
This is a simple PDMS-based microfluidic device with two inlets and two outlets. But what make it interesting is conducting PDMS electrodes embedded along the sidewall. These conducting PDMS electrodes generate nonuniform electric fields along the width and height of the channel that ultimately induce a dielectrophoretic or DEP force on cells.
Cells from branch A are focused by the flow from upper branch B and transport near the electrodes where electric fields are markedly strong. Cells that are more polarized than the suspending medium experience an attractive force and transport towards lower branch C whereas those that are less polarized than the suspending medium experience a repulsive force and move towards upper branch D.
The first experiment demonstrates that 5 micron latex particles can be pushed away from electrodes for all AC electric field frequencies, implying that these particles are less polarized than the suspending medium. When the particle size is scaled down like 0.5 micron, the particles are found to be attracted to the electrodes at 1 MHz. After 3 minutes, a tremendous number of particles are collected incredibly. Interestingly, the particles instantly experience a repulsive DEP force at 80 MHz.
These are yeast cells in a NaCl solution. At 10 kHz, cells are repelled from the electrodes, resembling the case of 5 micron latex particles. The cells also formed a chain with neighboring cells along the electric field lines as a result of the dipole-dipole interactions. At 10 MHz, cells are quickly collected at the electrodes. The formation of cells allows the chains to experience a larger DEP force, thus causing the chains to move even faster.
In this experiment, we use our device to separate 5 micron from 0.5 micron particles. Initially, both particles transport near electrodes and completely go to the lower branch. By applying 1 MHz AC frequency, 0.5 micron smaller particles are attracted near electrodes while 5 micron larger particles are repelled from electrodes, causing them to separate continuously. Within seconds, clear separation is manifest.
The final demonstration is the separation of yeast cells and 5 micron latex particles. Yeast cells in black color experiencing an attractive force preferentially move towards the lower branch while the particles spend their time approximately 5 seconds to be separated by a repulsive force into the other branch.
With the help of microfluidics, scientists can now manipulate cells, not visible to human eyes. As demonstrated by the experiments, the use of conducting PDMS electrodes has made cell manipulation simpler and more effective.
« Hide
