Hydrodynamic focusing and interdistance control of particle-laden flow for microflow cytometry
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Single-file focusing and minimum interdistance of micron-size objects in a sample is a prerequisite for accurate flow cytometry measurements. Here, we report analytical models for predicting the focused width of a sample stream b as a function of channel aspect ratio α, sheath-to-sample flow rate ratio f and viscosity ratio λ in both 2D and 3D focusing. We present another analytical model to predict spacing between an adjacent pair of objects in a focused sample stream as a function of sample concentration C, mobility ϕ of the objects in the prefocused and postfocused regions and flow rate ratio f in both 2D and 3D flow focusing. Numerical simulations are performed using Ansys Fluent VOF model to predict the width of sample stream in 2D and 3D hydrodynamic focusing for different sample-to-sheath viscosity ratios, aspect ratios and flow rate ratios. Experiments are performed on both planar and three-dimensional devices fabricated in PDMS to demonstrate focusing of sample stream and spacing of polystyrene beads in the unfocused and focused stream at different sample concentrations C. The predictions of the analytical model and simulations are compared with experimental data, and a good match is found (within 12 %). Further, mobility of objects is experimentally studied in 2D and 3D focusing, and the spread of the mobility data is used as tool for the demonstration of particle focusing in flow cytometer applications.
KeywordsViscosity Ratio Flow Rate Ratio Optical Window Sample Stream Focus Sample
The authors would like to thank DST and DBT India and IIT Madras for providing the financial support for the project. We thank Chemical Engineering Department IIT Madras, for providing an additional syringe pump which was required for the experiments. We acknowledge MEMS Lab, Department of EE, IIT Madras, for supporting with the photolithography work. The authors also acknowledge P. G. Senapathy Computer Center, IIT Madras, for providing Virgo cluster facility for the simulations. Our special thanks to Interdisciplinary Program, IIT Madras, which enabled this work.
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