Method for Characterization of Passive Mechanical Filtration of Particles in Digital Microfluidic Devices

Abstract

The ability to remove unbound biological material from a reaction site has applications in many biological protocols, such as those used to detect pathogens and biomarkers. One specific application where washing is critical is the Enzyme-Linked ImmunoSorbent Assay (ELISA). This protocol requires multiple washing steps to remove multiple reagents from a reaction site. Previous work has suggested that a passive mechanical comb filter can be used to wash particles in digital microfluidic devices. A method for the characterization of passive mechanical filtration of particles in Digital MicroFluidic (DMF) devices is presented in this work. In recent years there has been increased development of Lab-On-A-Chip (LOAC) devices for the automation and miniaturization of biological protocols. One platform for further research is in digital microfluidics. A digital microfluidic device can control the movement of pico-to nanoliter droplets of fluid using electrical signals without the use of pumps, valves, and channels. As such, fluidic pathways are not hardwired and the path of each droplet can be easily reconfigured. This is advantageous in biological protocols requiring the use of multiple reagents. Fabrication of these devices is relatively straight forward, since fluid manipulation is possible without the use of complex components. This work presents a method to characterize the performance of a digital microfluidic device using passive mechanical supernatant dilution via image analysis using a low cost vision system. The primary metric for performance of the device is particle retention after multiple passes through the filter. Repeatability of the process will be examined by characterizing performance of multiple devices using the same filter geometry. Qualitative data on repeatability and effectiveness of the dilution technique will also be attained by observing the ease with which the droplet disengages from the filter and by measuring the quantity of fluid trapped on the filter after each filtration step.