A. Wang, D. Koh, K.W. Oh
SMALL (Sensors and MicroActuators Learning Lab), Department of Electrical Engineering, The State University of New York at Buffalo,
Keywords: microfluidics, vacuum-driven microfluidics, centrifugal microfluidics
Summary:Abstract In this paper, a combination of vacuum and centrifugal forces was studied for recirculate samples inside the chambers. Hybridization of DNA is one of widely used approaches to compare and analyze identical or related sequences DNA molecules. However, accelerating of hybridization rate is a problem. Jose et al  has reported liquid recirculation using the interplay of capillary and centrifugal forces, which requires hydrophilic surface. In other words, additional coatings are needed to make channel surface being hydrophilic including PDMS, one of common materials used for microfluidic. In this study, vacuum-driven microfluidic was used with the centrifugal force to achieve recirculating samples inside chamber. Vacuum-driven microfluidics can drive the samples despite the surface condition [2, 3]. Details The test device schematic and its measured vacuum-driven flow rates are shown in Fig. 1. Microfluidic chips were degassed inside the vacuum chamber at - 27 in.Hg overnight. After the device was taken out from the vacuum chamber, the flow rate was measured over the time, where exposed time = 0 min stands for the moment that the device was taken out from a vacuum chamber. Three devices with a same design was tested for measuring flow rate. As reported in , the flow rate is time-variant since the stored air concentration inside PDMS decreases as the device started to be exposed to air. In this experiment, the device was used at least after the degassed device was exposed to air for 10 min to avoid abrupt flow rate change during the operation. Next, the centrifugal-driven pressure as shown in Fig. 2 was calculated using  P_c=ρω^2 r∆r , where ρ is density of the liquid, ω is angular acceleration and r is the distance between the center of liquid mass from the center of rotation. The water was used for this experiment (ρ=〖10〗^3 kgm^(-3)). The test device to study recirculating sample inside chamber was shown in Fig. 2 (a). The sequence images of tested sample flow inside chamber using vacuum-driven force and centrifugal-driven force are shown in Fig. 3. The device has vents, which vacuum driven flow and centrifugal driven flow can be switched by sealing/ unsealing vents. After sample was loaded into a degassed device, vacuum-driven force and centrifugal force was applied reciprocally to pull and push sample inside the chamber. First, sample was loaded into the inlet. Next, the vents were sealed to allow the sample flow inside the channel using the vacuum force. Next, the vents were unsealed and the device was placed on a spin coater to apply 1200 revolutions per minute (RPM). Samples were pushed back to the left side of the chamber, which is the far side from the center of rotation. Thus, samples would be push and pull inside the chamber (one loop). By continuing the same process, the device can be used for further recirculation. The device has a potential to be used for multiple applications such as hybridization of DNA.