Label-Free In-Situ Estimation of Microparticle Concentration in Micro-Optofluidic Device

In-situ detection and quantification of microparticles remain challenging in embedded lab-on-chip platforms, where limited optical accessibility makes conventional microscope-based analysis impractical. To address this limitation, in this study, a micro-optofluidic platform was developed integrating light delivery and detection directly within the device, thereby enabling label-free concentration estimation without external imaging or sample extraction. The sensing principle exploits concentration-dependent changes in transmitted light caused by microparticle scattering within the microchannel. The platform was evaluated using HL60 cells and PMMA microparticles (CA6) at five concentration levels, ranging from the particle-free condition to 107MPsmL−1, under coherent laser and LED illumination. Ray-tracing simulations reproduced light propagation and particle–light interactions within the device, predicting particle-dependent differences in the optical flux collected by the detection fiber that were consistent with the experimental response. The measurements revealed a progressive reduction in the transmitted signal with increasing microparticle concentration, with laser illumination providing greater sensitivity and clearer discrimination between the two microparticle types than LED illumination. Three-way ANOVA confirmed that microparticle type, concentration, and illumination source, as well as their interactions, significantly affected the detected optical signal (p-value < 0.001). These findings demonstrate that the integrated optical architecture can distinguish concentration-dependent responses across biological and synthetic microparticle suspensions. The proposed platform represents a compact and fully label-free solution for in-situ microparticle monitoring, supporting the future development of self-contained microfluidic sensing platforms.