(Invited) On-Chip Characterization of Microcapsules Using a Capacitive Sensor for Microencapsulation and Single-Cell Analysis Applications

Introduction Droplet microfluidics has emerged as a versatile tool for a wide range of biomedical applications. Recently, various types of microfluidic droplet-generation platforms such as T-junction, flow-focusing, and co-flow, have been used for high throughput generation of microcapsules containing cells, drugs and biomolecules. microfluidic microencapsulation is a fast and well-controlled method for the generation of uniform microcapsules with the capability of tuning the size and physicochemical properties of microcapsules during the encapsulation process [1,2]. In a microfluidic droplet generation system, droplet formation can be widely classified into three regimes (squeezing, dripping, and jetting). The quality of the generated droplets in terms of stability and uniformity can be highly affected by the type of flow regimes. Since the flow regime and size of the droplets can be influenced by a small change in the system variables (such as the flow rate ratio of the dispersed and continuous phase), real-time monitoring of the droplet generation is vital especially for biomedical applications [3,4]. To address the above challenges, in this work we developed microfluidic droplet generation devices (T-junction and flow-focusing) for a well-controlled encapsulation of probiotic bacteria. In order to characterize microcapsules, a capacitive sensor was designed and integrated into the chip. Finally, the performance of the fabricated microfluidic device for on-chip monitoring of the encapsulating process was evaluated. Materials and Methods The device is made out of gold microelectrodes integrated into a polydimethylsiloxane (PDMS) chip. The microfluidic chip was fabricated in a cleanroom facility using a glass substrate with electrodes patterned by photolithography and wet etching process. A microfluidic channel was then fabricated with inlets and outlets by pouring PDMS over a mold followed by bonding the PDMS channel to the glass slide via plasma treatment machine. The dispersion phase (DP) containing alginate and Escherichia coli DH5-alpha (E. coli DH5a), as a bacterial model, was injected through a central channel. The continuous phase (CP) was the mixture solution of mineral oil and span 80 that injected through the other channel. To characterize the generated microcapsules, the change in capacitance between the electrodes was recorded using a potentiostat as probiotic bacteria were encapsulated on the chip. Results and Conclusions E.coli cells were e