An open-source, modular optoelectrical sensor for on-chip flow characterization in droplet-based microfluidics.

Droplet-based microfluidics has become a leading technology for Lab-on-Chip applications, from single-cell analysis and nanoparticle synthesis to clinical diagnostics. In these applications, accurate measurement of droplet length, volume, velocity, and monodispersity is critical for reliable operation. Despite recent advances, the routine characterization of these parameters still relies on high-speed cameras, microscopes, and off-chip post-processing, limiting portability, autonomy, and field deployment. To address these limitations, this work presents an open-source, cost-effective, embedded optoelectrical sensor platform built from off-the-shelf components. The platform performs multiparameter droplet characterization on-chip in two sequential firmware stages, with all signal conditioning and analysis executed on an Arduino-Zero microcontroller. The system integrates two custom PCB sensing modules: a light-dependent-resistor (LDR) array for droplet velocity, and a TSL2561 photodiode for length, volume, and monodispersity. Both are illuminated by a dedicated light-source PCB and housed in a 3D-printed alignment enclosure that hosts a replaceable PMMA flow-focusing chip. We provide complete documentation, including build instructions, embedded firmware, and example applications. The resulting modular, equipment-free architecture supports the development of Lab-on-PCB systems for rapid prototyping of autonomous, droplet-based microfluidic devices.