An Electrical Detection System for In Situ Characterization of Microbubbles in Flow Focusing Microfluidic Devices

Flow focusing microfluidic devices (FFMDs) have been investigated for the production of monodisperse populations of microbubbles for biomedical engineering applications. High-speed optical microscopy is commonly used to monitor FFMD microbubble production parameters, such as diameter and production rate, but this limits the scalability and portability of the approach. In this thesis, a novel FFMD design featuring integrated electronics for measuring microbubble diameters and production rates is presented. A micro Coulter Particle Counter (µCPC), using electrodes integrated within the expanding nozzle of an FFMD (FFMD-µCPC), was designed, fabricated and tested. Finite element analysis (FEA) of optimal electrode geometry was performed and validated with experimental data. Electrical data was collected for 8-20 µm diameter microbubbles at production rates up to 325,000 MB / s and compared to both high-speed microscopy data and FEA simulations. Within a valid operating regime, Coulter counts of microbubble production rates matched optical reference values. The Coulter method agreed with the optical reference method in evaluating the microbubble diameter to a coefficient of determination of 0.91.