An optical-coding method to measure particle distribution in microfluidic devices

Abstract

We demonstrated an optical coding method to measure the position of each particle in a microfluidic channel. The technique utilizes a specially designed pattern as a spatial mask to encode the forward scattering signal of each particle. From the waveform of the forward scattering signal, one can obtain the information about the particle position and velocity. The technique enables us to experimentally investigate the complex relations between particle positions within the microfluidic channel and flow conditions and particle sizes. The method also produces insight for important phenomenon in microfluidic and lab-on-a-chip devices such as inertial focusing, Dean flow, flow confinement, etc.

Figure 1

(a) Schematic of our optical-coding microfluidic device setup. (b) An illustration of spatial pattern for optical coding. Three representative forward-scattering signals are shown for particles travelling through different positions of the microfluidic channel. Each trapezoidal slit has its base lengths of 100 μm and 50 μm. The width of each peak, W1 through W4, in the signal is used to acquire the position of particles along the x-direction. The method to find the position along the y-direction will be discussed later.

Figure 2

Scatter plots of particle position along x-axis versus forward scattering intensity, (a) and (c), and particle velocity versus intensity, (b) and (d), at flow rates of 25 μL/min and 50 μL/min, respectively. Red circle: 15 μm beads, Green circle: 10 μm beads, Blue circle: 5 μm beads.

Figure 3

Simulated flow velocity profile on the x-y plane at a flow rate of (a) 25μL/min and (b) 50 μL/min.

Figure 4

Spatial distribution of particles within microfluidic channels. (a) and (b) are results for 5 and 10 μm beads at a flow rate of 25 μL/min. (c) and (d) are results for 5 and 10 μm beads at a flow rate of 50 μL/min. The color bar shows the frequency of microbeads population.

Figure 5

(a) Scatter plot of fibroblast position along x-axis versus forward scattering intensity and (b) Spatial distribution of fibroblast within the microfluidic channel at a flow rate of 30 μL/min.