In this work, we report the fabrication of carbon-microelectromechanical system (C-MEMS) based contactless dielectrophoresis chip for the separation of Red Blood Cell (RBC) and plasma from whole blood. Blood is the most important functional body fluid and it is necessary to separate plasma and RBC for common disease diagnosis. Use of centrifugal force and microfilters are the conventional methods for this separation. To make a portable and cost effective device, researchers found a method of geometry driven separation by means of changing the blood flow channel shapes. This method was not popular because of the pressure driven flow of blood in the channel and the need of the apparatus including syringe pump, tubing, etc. Dielectrophoresis is one of the best methods for this application. But the contact dielectrophoresis (sample is in contact with the electrodes) damages the RBC because of the use of high voltage (more than 100V). It may also cause electrochemical effect, bubble formation and joule heating in the sample.

In our development, one Indium Tin Oxide (ITO) coated glass was used as the bottom substrate. ITO coated side was used as the bottom electrode and microchannel was made in SU-8 by UV photolithography on the other side of the substrate. In a separate process, SU-8 derived carbon electrode was fabricated on Si/SiO₂ substrate using the conventional C-MEMS process and transferred to 200µm thick PDMS layer. This polydimethylsiloxane (PDMS) layer was used to cover the microchannel in such a way that the carbon electrode was on the upper side of the device, aligned with the microchannel. These two electrodes (ITO and carbon) were capacitively coupled with the microchannel. The eletrostatic force is induced in the blood cells flow in the channel upon applying high frequency (1MHz) electric field to the electrodes. When blood flows in the channel, the electrostatic force combines with the capillary force and produces velocity difference between RBC and plasma resulting in their separation. In the preliminary experiment, we observed the separation of RBC and plasma at less than 1V_p-p with 1MHz frequency.