Impedimetric measurement methods are a novel approach to the characterization of fluid in biological applications. Lab on a chip (LOAC) technologies could be combined with impedimetrics to benefit these applications. LOAC devices are currently being developed to pursue the miniaturization of larger scale processes. Current research shows great flexibility in using LOAC devices to reproduce biological processes such as those used in medical diagnostic applications. With a smaller form factor, testing that generally requires off-site lab usage can be deployed at the point-of-care. LOAC devices also have the potential to lower operating costs by reducing reagent volumes, labor costs, and cycle times.
Digital microfluidic devices (DMF) are one promising LOAC platform. These devices manipulate discrete droplets of fluid using electric fields. As such, DMF devices can create, move, merge, and mix droplets while eliminating mechanical components like channels, pumps, and valves. Manipulation of discrete volumes over a planar array of electrodes allows for the possibility of highly flexible, reconfigurable devices.
Addressable positions on a DMF device have conductive planes above and below the droplets which form a parallel plate capacitor. Using this principle, the electrical properties of the system can be measured in the same circuit that is used for droplet manipulation, removing the need for additional sensing components. This research tests the hypothesis that the impedance of a particle laden droplet in a DMF device can be modelled using an equivalent circuit model for particles that span more than half the gap height. The fundamental understanding gained increases sensitivity in impedimetric measurements, and can also be used for DMF applications in medical diagnostics, cell manipulation and observation, and condition based maintenance. This research presents an analytical model based on an equivalent circuit of a particle laden droplet. The proposed model predicts that droplet impedance is a function of device geometry, particle size, particle concentration, and the electrical properties of the particles and the surrounding medium.