Nano-to submicron particle analysis in microfluidics: Unveiling the potential of light extinction spectroscopy in flow

The light extinction spectroscopy (LES) technique is emerging as a versatile analytical tool for multiphasic systems comprising nano-to submicron particles suspensions. Coupling LES at the microfluidic scale offers new avenues for characterization of particle suspensions in this range, enabling precise control of fluid dynamics and reduced sample volumes. This study explores the applicability of LES at the microfluidic scale, focusing on its use for characterizing dielectric and metallic nano-to submicron particles of various sizes and morphologies. Different modelling methodologies employed to calculate particles extinction cross-sections are discussed, emphasizing the impact of their nature and morphology on optical resonances. For metallic nanoparticles, the study highlights the significant role of plasmonic resonances in extinction spectra and evaluates the impact of size distribution and shape anisotropy. Comparative experiments performed in two different microfluidic configurations (continuous flow, and segmented - i.e., droplets - flow) validated the modelling approaches for both latex and silica submicron particles. Experimental data on gold and silver nanoparticles exhibited excellent agreement with theoretical models, even on synthesis, demonstrating the capability of LES for accurately determining particle size and morphology distributions. These results are moreover consistent with TEM analysis.