Feature Of The Week 10/16/2016: Real-time Functional Analysis of Inertial Microfluidic Devices via Spectral Domain Optical Coherence Tomography
Inertial microfluidic devices have recently attracted considerable interest due to their unique capability of high-throughput filtration, separation, and sorting of particles and live cells in a continuous flow manner. However, the underlying mechanism is not fully understood yet, which is due to limited options for real-time three-dimensional (3D) tracking and analysis of particles and live cells in microfluidic channels. Although micro-particle image velocimetry using optical confocal microscopy can be used to resolve the position of microparticles in 3D, it often requires exogenous labels to provide fluorescence contrast which is not always favorable for live cell analysis. To better understand the sorting process and track particles and live cells in unperturbed states, an imaging technology capable of functional analysis, such as particle size measurements and spectroscopic characterization, is highly desired.
In addressing this need, we recently demonstrate the capability of spectral-domain optical coherence tomography technology (SD-OCT) for visualizing and further enabling functional analysis of sorting microspheres and cells using an inertial microfluidic device. By employing high-speed (a frame rate of 350 Hz), high-resolution (a lateral resolution of 3 µm and an axial resolution of 1 µm) acquisition of cross-sectional images of a spiral microchannel, the microfluidic focusing of microspheres along both the horizontal and vertical directions can be recorded simultaneously. Using microspheres with known diameters, we validated the sub-micrometer precision of the particle size analysis based on a scattering model of spherical microparticles. This further allows us to determine the position and diameter of microspheres in a spiral microfluidic channel under various flow rates. Moreover, live HT-29 cells from the human colon adenocarcinoma cell line were used as the model system to further demonstrate the feasibility of SD-OCT imaging technology for monitoring the sorting process of live cells. Interestingly, the pressure-induced deformation of the microfluidic channels can also be measured simultaneously from the acquired SD-OCT images. This high-resolution 3D volumetric imaging method can be used not only for real-time monitoring of microfluidic-based sorting, but also for advancing our general understanding of microfluidic systems and providing guides for the design of novel inertial microfluidic particle sorting devices.
For more information see recent Article. Courtesy Cheng Sun and Hao Zhang from Northwestern University.