Modular on-chip sensor for flow and monodispersity analysis in droplet-based microfluidics

Droplet-based microfluidics has emerged as a core technology in developing Lab-On-A-Chip systems thanks to miniaturization, rapid analytical response, and low cross-contamination risk. As a result, detecting and characterizing dispersed phases is crucial across several applications, including biological research, drug development, clinical diagnostics, and the synthesis of micro/nanoparticles. Despite efforts to achieve high sensitivity, specificity, speed, and robustness, current fabrication technologies remain challenging, costly, and complex, which limits broader adoption. Thus, this work presents the design and fabrication of a modular droplet-based sensor system integrating off-the-shelf electronic components and PMMA-based flow-focusing microfluidic chips. The system employs an optical light source and light detector for detection, counting, and characterizing water-in-oil systems, enabling on-chip measurement of droplet length, volume, and monodispersity. Experimental validation demonstrated high accuracy, with a 2.06% error rate and a coefficient of variation of 2.35%, confirming stable and monodisperse droplet generation across multiple channel widths. Furthermore, the proposed sensor system offers an affordable, user-friendly, and easy-to-fabricate modular design, with an easily interchangeable microfluidic module. These findings support the development of an ASSURED (Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment-free, and Deliverable to end-users) Lab-on-PCB system.