Micro-velocity fiber probe based on Fe₃O₄-PDMS filled microcavity for on-chip microfluidic

Real-time measurement of microflow velocities is essential for on-chip microfluidic systems and human vessels, particularly when flow velocities serve as regulators of biochemical processes and indicators of reaction outcomes. In this study, a hot-wire fiber probe for the microflow sensing was designed and fabricated by incorporating Fe₃O₄-polydimethylsiloxane (Fe₃O₄-PDMS) into the microcavity. A Fabry–Pérot (F-P) sensing cavity was formed between the single mode fiber (SMF) and Fe₃O₄-PDMS. The Fe₃O₄ enables strong absorption of 980 nm laser and generates heat as reliable heat sources. Under the influence of heat convection, the fluid removes heat to establish specific equilibrium temperatures. With the fluctuation of equilibrium temperature, Fe₃O₄-PDMS expands or contracts regularly, resulting in corresponding changes in lengths of F-P sensing cavities, and interference spectra also shift with changes of flow rates. In the range of 0.278 μL/s to 3.058 μL/s, the probe exhibits high sensitivities and robustness, which provides potential value detection of microfluidic chips and humans.