Microfluidic separation of viruses from blood cells based on intrinsic transport processes
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Schematic illustration of the device structure with labeled dimensions (a) and a photograph showing the device in action (b). The device contains two layers of microchannels: the biological sample is injected into the top layer and a carrier buffer is injected into the bottom to allow the separation of the cells versus viral particles by their intrinsic movements. In the photograph, the dark dash line outlines the bottom layer channel and the light dash line outlines the top layer channel.
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Numerical analysis of the concentration change for different sized particles in a two layer structure. (a) Vertical distance traveled by bioparticles of various sizes in water due to intrinsic movements. The travel distances were calculated using the sedimentation or diffusion equations presented in the text. (b) COMSOL simulation showing the concentration evolution for a two layer structure where a suspension containing a diffusive solute was layered on a carrier fluid. The solute diffusion coefficient was set to be 4.39 × 10−12 m2/s, corresponding to that of the 100 nm particles in water. The density and viscosity of the medium was set to be 1 g/cm3 and 0.001 Pa · s. The convection velocity in the y direction was set to be 46 μm/s so the concentration profiles after different contact time could be plotted. The color indicates the relative concentration and the slices correspond to various time points post initiation of diffusion. The diffusion times were labeled next to the slices. (c) The concentration profile along the z direction dissected from (b) with the diffusion time labeled on the right. It takes over 3400 s for 100 nm particles to reach the concentration equilibrium in the simulated geometry. (d) COMSOL simulation showing expected particle concentration remaining in the top layer at different time points. A ratio of 0.5 (dashed line) indicates no preferential particle residence. The numerical analysis suggests that bioparticles with diameters of 5–10 μm sediment to the bottom layer in ∼200 s while over 50% of the nanoparticles remain in the top layer. The relative nanoparticle concentration remaining in the top layer depends on its size or diffusion coefficient.
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Representative UV-Vis absorption spectra of (a) nanoparticle and (b) microparticle suspensions retrieved from the microchip at a flow rate of 3 μl/min. The 100 nm polystyrene nanoparticles were labeled with Firefli™ Fluorescent Red (Ex 542/Em 612 nm) and 5 μm polystyrene microparticles were labeled by Firefli™ Fluorescent Green (Ex 468/Em 508 nm). Suspensions containing a single type of synthetic particles were injected into the top inlet of at 3 μl/min. The outflow from the top and bottom outlets were analyzed by UV-Vis spectroscopy and repetitive spectra are presented. The absorbance at 545 nm for nanoparticles and 470 nm for microparticles were used to quantify their concentrations since they correlated linearly with the particle concentration. Similar spectra were acquired for other flow conditions. (c) Experimental data (solid dots and solid squares) showing the ratio of particles retrieved from the top outlet at different residence time points. PBS/SDS solutions containing either 5 μm or 100 nm polystyrene particles were injected into the top inlet and particle free PBS/SDS solution was injected into the bottom inlet. The two layers had identical flow rates of 20, 15, 10, 6, and 3 μl/min, and the particle residence time in the devices were calculated for the plot. Each data point was repeated in at least 3 devices, and error bars represent standard deviations from these repeats. The experimental measurements closely matched results from COMSOL simulation (blue and red lines).
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Relative ratios of blood cells and HIV viral particles retrieved from the top outlet. The biological samples were injected into the top inlet and PBS (for experiments containing blood) or PBS/1% BSA (for blood free experiments) was injected into the bottom. Both layers had identical flow rates of either 6 μl/min (a) or 3 μl/min (b). (a) At a flow rate of 6 μl/min, 87.3 ± 6.3% of HIV viral particles were retrieved from the top outlet in the absence of blood cells. When HIV particles were spiked in blood diluted ten times by PBS, 68.2 ± 3.3% of viruses and 12.8 ± 4.4% of blood cells were retrieved from the top outlet. In whole blood, 44.4 ± 8.7% of viruses and 19.2 ± 8.2% of blood cells were retrieved from the top outlet. (b) When the flow rate was 3 μl/min for both layers, 84.2 ± 5.8% of HIV viral particles were retrieved from the top outlet in the absence of blood cells. When HIV particles were spiked in blood diluted ten times by PBS, 64.5 ± 6.0% of viruses and 11.6 ± 6.3% of blood cells were retrieved from the top outlet. In whole blood, 46.5 ± 4.7% of viruses and 35.7 ± 4.5% of blood cells were retrieved from the top outlet.
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Calculated Péclet numbers for typical biological particles of different sizes under intrinsic movements of sedimentation and diffusion. The terminal velocity and diffusion coefficient were calculated using Eqs. (1) and (2) in the text. The parameters used for the calculations are as follows: characteristic length = 100 μm (thickness of the biological sample layer tested in the experiments below), solution density = 1 g/cm3, bioparticle density = 1.05 g/cm3 (lower limit for cells and viruses), solution viscosity = 0.001 Pa · s, and temperature = 296 K.
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