Real-time impedimetric microfluidic droplet measurement: IDM

Abstract

Droplet-based micro uidic systems require a precise control on droplet physical properties, hence measuring the morphological properties of droplets is critical to obtain high sensitivity analysis. The ability to perform such measurements in real-time is another demand which has not been addressed yet. In this study, coplanar electrodes were used, and con gured in di erential measurement mode for impedimetric measurement of size and velocity. To obtain the size of the droplets, detailed 3D nite element simulations of the system were performed. The interaction of the non-uniform electric eld and the droplet was investigated. The electrode geometry optimization steps were described and design guideline rules were laid out. Size of the electrodes was optimized based on the simulations for droplet lengths ranging from 300 to 1500 μm. A user-friendly software was developed for real-time observation of droplet length and velocity together with in-situ statistical analysis results. A detailed comparison between impedimetric and optical measurement tools is given. Finally, to illustrate the bene t of having real-time analysis, iDM was used for experimental studies. First study case is the response time of the syringe pump and pressure pump driven droplet generation devices. This analysis allows one to evaluate the `warm-up' time for a droplet generator system after which droplets reach the desired stead-state size required by the assay of interest. Second, an evaluation chip was designed to investigate e ective factors and their interplay with droplet length variation. A comprehensive design of experiment (DoE) method is utilized. Analyzing the obtained results revealed e ect of each factor and their interactions. Exploiting results of this study contributes to monodisperse micro uidic droplet generation. Monodisperse polymeric particles of polyethylene glycol were synthesized to demonstrate the potentials of monodisperse droplet generation in biochemical synthesis/analysis.