High-throughput on-line multi-detection for refractive index, velocity, size, and concentration measurements of micro-two-phase flow using optical microfibers

We demonstrate that high-throughput on-line multi-detection (refractive index, segment velocity, size, and concentration) with high resolution can be achieved simultaneously for micro-two-phase flow by microfibers in the microfluidic chip. The microfibers were immersed in the fluid channel in perpendicular to the flow direction with direct contact of test samples to increase the space resolution and detection sensitivity. A novel “soft sealing” method has been developed for microfiber installing in microfluidic chip, where the continuous phase fluid is applied to surround the microfiber and protect it from vibrations and chip-wall contact, to stabilize the microfiber signal. The time-domain microfiber signal is directly applied to quantify the refractive index of test samples, and different operation modes of this measuring technique have been systematically analyzed. With only tiny sample volume (∼100 nanoliters), the measurement resolution for refractive index and concentration can reach 2×10−4 and 2×10−3, respectively. For both velocity and size measurements, the maximum deviation between this measuring technique and image analysis method is less than 3%, while the overall measurement uncertainty is no more than 3.4%.