A flow-focusing microfluidic device was fabricated for thermal lens nanoparticle detection. In this device, sample flow was first sandwiched by lateral z-axis sheath flows, and then by horizontal xy-plane sheath flows. The three-dimensional flow focus was visualized using an aqueous dye solution. Subsequently, 500-nm-sized red polystyrene particles were individually detected by the thermal lens detection method. When 1 μL of sample solution containing 300 particles/μL was passed through the thermal lens detection point, 255 ± 20 peaks corresponding to particles were observed.
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