Measuring flow dynamics in a microfluidic chip using optical coherence tomography with 1 µm axial resolution

• Paper presents a 1 µm axial resolution spectral-domain optical coherence tomography system. The broad band light including the visible wavelength range is used to maximize the resolution.
• Flow velocity characterization down to 1 µm from a wall to detect boundary layer dynamics.
• Measurements were conducted in a commercial microchannel with extremely small dimensions.

An experimental verification of simulated flow dynamics in a novel design of microfluidic device can be difficult, especially, in devices such as mixers or deterministic lateral displacement (DLD) arrays. Doppler optical coherence tomography (DOCT) is one of the visualization modalities used to measure flow velocity profiles in microfluidic channels, capillaries and microvascular networks. Previously conducted flow measurements with high speed spectral-domain optical coherence tomography (SD-OCT) devices have had typical axial resolution in the range few microns which can be insufficient for accurate mapping of flow dynamics in microchannels. This paper introduces a high-speed SD-OCT system with an axial resolution of 1.2 µm in air (below 1 µm in water) to evaluate flow in a microfluidic chip. The A-line acquisition rate of the device is 123 kHz. Flow velocities from 1% Intralipid suspension are obtained across the microfluidic channel with the specified height of 20 µm and the width of 50 µm. The results show that the utilized SD-OCT device can visualize flows as close as 1 µm from the channel wall. The flow rate of 0.63 µl/min, determined from the cross-sectional velocity map, agreed well with the value of 0.67 µl/min set to the syringe pump.