Best Practices for Droplet Dispensing and Sizing in Single-Microdroplet Experiments

Controlled droplet dispensing and accurate droplet sizing are key technical requirements for most experimental approaches to studying individual microdroplets, yet both present significant practical challenges. This tutorial presents best-practice approaches for droplet generation and sizing in single-microdroplet studies, with a particular focus on droplet-on-demand dispensing technologies and in situ optical sizing methods. Under constant conditions, droplet-on-demand dispensers offer controlled, highly reproducible droplet generation across a range of sizes (typically ∼20–80 μm diameter, with <1% variation). We discuss the principles governing dispenser performance and examine the influence of operating parameters, fluid properties, dispenser loading, and jet breakup dynamics on droplet size reproducibility. Particular attention is given to the stochastic nature of droplet formation and the role of satellite droplets, which can introduce substantial uncertainties and complicate precise size control. Complementary droplet sizing methodologies are reviewed, including imaging, phase function-based light-scattering measurements, and cavity-enhanced spectroscopic techniques, highlighting their respective strengths, limitations, and achievable precision. By integrating practical guidance on dispenser operation with a critical assessment of available sizing approaches, this tutorial provides researchers with a framework for improving experimental reproducibility, minimizing artifacts, and achieving accurate droplet size determination in microdroplet investigations.