Characterization of bead-based reactions and mechanical supernatant dilution in digital microfluidic devices

Discrete flow microfluidic devices have been identified as a technology that can be used to efficiently deliver health care services by reducing the cycle times and reagent consumption of biological protocols and medical diagnostic procedures. These devices also have the potential to reduce overhead costs by performing these applications at the point of care. Digital microfluidic devices are one promising discrete flow microfluidic platform that can individually create, manipulate, and mix droplets through the application of asymmetric electric fields. The work presented here suggests that (1) monitoring electrical properties of droplets during specific chemical reactions and (2) supernatant dilution via mechanical filtration can be integrated into digital microfluidic immunoassay devices. Measurement of electrical properties during the bead based chemical reaction between p-nitrophenyl phosphate and particles with bound antibodies conjugated to alkaline phosphatase resulted in measureable difference in capacitance and resistance when compared to the control particles. A single filtration cycle using the mechanical supernatant dilution method demonstrated here reduced the fluorescence intensity in particle laden droplet by approximately 80%.