FlowProtocol

Recently, microdroplets is becoming a newly rapidly developed research technology. In order to provide stable driving forces for the microdroplets system, we demonstrated a high precision and high stability constant pressure air pump, which can generate two independent stable pressures for giving forces to drive reagents. The construct of the air pump was the combination of hardware and software, via the idea of embedded system and modularization, and the PID algorithm. This integrated constant pressure air pump is called Pneumatic Supply System, and the system is a wireless, high stability (±1 mBar) and short response time (less than 1.0s) constant pressure air pump operated with a customized smartphone application or computer program. This system showed great performance in steady state and response time, and it can be used to generate all kinds of uniform-sized droplets and applied in the field of microdroplets exactly.

Pneumatic Supply System has better stability compared with the injection pump (TS-2A, Longer pump). The flow waveform of Pneumatic Supply System is shown in Figure 1A, and the other one of injection pump is shown in Figure1B. Both the overshoot flow are around 100 μL/min, but the Pneumatic Supply System has less fluctuation. The response time of the system shows in the Figure1C, the time consumption was less than 1.0 s when the pressure changed to the target value or reduced to zero (atmospheric pressure). Figure 4B shows the accuracy of the system; a smooth and steady of pressure waveform with a precision of 1 mbar when the target pressure is 1000 mbar.

The platform was constructed with user device, Pneumatic Supply System, a microfluidics chip (Dolomite, United Kingdom), fluorinated ethylene-propylene (FEP) pipes, and flow resistance (FR), as shown in Figure 3A. The microfluidics chip is a Droplet Junction Chip of Dolomite, and its part number is 3000158, please visit the website (http://www.dolomite-microfluidics.com) for the specific parameters of the chip. Figure 3B, C shows the detail of the chip. The usage of flow resistance was aimed at reducing the flow rate of the two phases.

Pictures of changes of visible neck at the crossing when droplets were generated with different ratio of Poil and Pwater (Poil is the pressure of oil, Pwater is the pressure of water). The Poil/Pwater of A – H were 1, 0.33, 0.25, 0.125, 2, 3, 18, 28, respectively. And the diameter of the droplets is relative to the ratio of Poil and Pwater.

Pictures of droplets with different diameters. The histogram is the size distribution of the droplets.

We adopt two methods to complete the sorting, one is based on piezoelectric ceramics (Figure Ⅰ), and the other is based on the dielectric electrophoresis (Figure Ⅱ). Figure ⅢA shows that the droplet had not been affected yet, and then the droplet had a displacement perpendicular to the direction of movement under the force of piezoelectric ceramics in the Figure ⅢB, and Figure ⅢC, D show that the droplet was sorted successfully. Figure ⅣA -D shows the whole process that droplet had been sorted by the dielectric electrophoresis. The amplitude of the applied voltage is 800 V and the frequency is 1000 Hz.

In summary, we demonstrated a stable, reliable, convenient and practical system, with a wide range and rapid response. The system drives reagents stably, so that it can generates uniform droplets fast. When the pressure of water (disperse phase) increased, changes of the particle size in one micrometer might be achieved, using the Pneumatic Supply System with high accuracy and good stability, without considering the artificial error during analyzing the distribution of the particle size. In addition, the waste of reagents can be reduced and the experiment time can be shortened, as the system has a rapid response capability. In addition, the system can be used to complete the sorting of particles.