An Integrated Microfluidic Fiber-optic Flowmeter based on Flexible Fabry-Perot Cavity

Microfluidics plays a significant role in various fields, including material synthesis, drug delivery, and disease diagnosis, and the flow velocity has a critical effect on the products. However, there is a lack of approaches for monitoring the flow velocity in the microchannel. To address this, we propose a novel fiber-optic flowmeter based on a flexible Fabry-Perot (F-P) cavity for online and non-invasive monitoring of products from the microfluidic devices. The flexible F-P cavity is constructed with a fiber-optic probe and gold-coated polydimethylsiloxane (PDMS) film, which can be easily integrated with versatile microfluidic devices through oxygen plasma bonding. Depending on the numerical investigation of film deformation under various film and fluid parameters, we experimentally characterize the sensitivity, reversibility, stability, and repeatability of this flowmeter. Then, the adaptability of the flowmeter is demonstrated by monitoring the flow velocity of seawater and sucrose solution. Moreover, we integrate this flowmeter with multiple microfluidic devices to verify the integration performance. Finally, we successfully achieve online and non-invasive monitoring of mixing efficiency, droplet diameter, and microalgae separation efficiency in the integrated microfluidic devices. This flowmeter can monitor the products from the microfluidic devices for disease diagnosis and drug delivery, with the advantages of good adaptability and easy integration.