Low Detection Limit Microflow Measurement Using Single-Fiber Optical Tweezers

With the rapid advancement of microfluidic technology, the precise measurement of microflows is critical in biomedical engineering, chemical analysis, and environmental monitoring. Current measurement methods often suffer from limited scalability and potential interference with fluid dynamics. This study introduces a low detection limit (DL) flow measurement method that uses single-fiber optical tweezers to capture individual silica microspheres outside a microcapillary as flow indicators. Under fluid flow, the microspheres exhibit microscale positional shifts within the optical trap. By analyzing these signal changes in real time, accurate flow measurements are achieved. Our experimental results demonstrate significant advantages in detecting low flow rates using this method. For sample solutions with a concentration of 0.05 wt.%, the method achieves a minimum flow DL of 6 nL/min, a linearity of 0.993, a sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 14.36 \; \mu $ </tex-math></inline-formula>s/(nL/min), and a maximum standard deviation of approximately 0.092%. The piconewton-level optical force allows this sensor structure to detect extremely low flow rates. Additionally, the microcapillary provides a controlled and stable microflow environment, ensuring that the measurement process does not interfere with fluid flow, thereby reducing deviations.