Droplet microfluidics combined with optical detection has emerged as a transformative avenue for high-throughput single-cell assays. However, these platforms often suffer from limited sensitivity and signal heterogeneity due to intrinsic optical and geometric constraints. We investigate how key operating parameters influence the performance of a droplet-based optomicrofluidic system. Our experiments probe optical interactions between guided light and aqueous droplets encapsulating fluorescent particles flowing in an oil medium. Geometric optics simulations model light-droplet interaction, while florescence simulations quantify signal variation due to particle size and position. Experimentally, we observe two refracted optical signals: a droplet-refracted signal that scales with droplet diameter, and a particle-refracted signal arising from light interaction with encapsulated particles. Both experiments and simulations reveal that the particle-refracted signal is prominent when the particle-to-droplet size ratio $D_{\mathrm{p}}^{\ast }$ is between 0.23 and 0.33, enabling label-free detection. Experiments also show that particles located near the droplet center ($r_{\mathrm{p}}^{\ast }<0.4$) exhibit a reduced angular dependence, producing more uniform fluorescence signals. Simulations indicate that the fluorescence intensity increases with $D_{\mathrm{p}}^{\ast }$, with a strong rise from 0.33 to 0.5 and a more gradual increase up to 0.66. Further, simulations show that reducing the thickness of the oil layer consistently increases fluorescence by minimizing optical losses at the droplet/channel interface. Our results demonstrate that controlling $D_{\mathrm{p}}^{\ast }$, particle position, and oil-layer thickness significantly increases fluorescence intensity and uniformity. These findings establish a quantitative and experimentally validated framework for optimizing droplet-based fluorescence detection, with potential applications in microflow cytometry and single-cell assays.

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• Medical physics & public health
• Metrology
• Particle-laden flows
• Refraction
• Cells
• Drops & bubbles
• Microfluidic devices
• Optical techniques