A fully autonomous method of creating highly monodispersed emulsion droplets with a low sample dead volume was realized using a degassed poly(dimethylsiloxane) (PDMS) microfluidic chip possessing a simple T-junction channel geometry with two inlet reservoirs for oil and water to be loaded and one outlet reservoir for the collection of generated droplets. Autonomous transport of oil and water phases in the channel was executed by permeation of air confined inside the outlet reservoir into the degassed PDMS. The only operation required for droplet creation was simple pipetting of oil and aqueous solutions into the inlet reservoirs. Long-lasting fluid transport in the current system enabled us to create ca. 51,000 monodispersed droplets (with a coefficient of variation of <3% for the droplet diameter) in 80 min with a maximum droplet generation rate of ca. 12 Hz using a PDMS chip that had been degassed overnight. With multiple time-course measurements, the reproducibility in the current method of droplet preparation was confirmed, with tunable droplet sizes achieved simply by changing the cross-sectional dimensions of the microchannel. Furthermore, it was verified that the resultant droplets could serve as microreactors for digital polymerase chain reactions. This hands-free technique for preparing monodispersed droplets in a very facile and inexpensive fashion is intended for, but not limited to, bioanalytical applications and is also applicable to material syntheses.

A PDMS microfluidic chip with T-junction channel geometry, two inlet reservoirs, and one outlet reservoir was reversibly adhered on a glass plate through the viscoelastic properties of PDMS. This formed a detachable microfluidic device for creation of water-in-oil emulsion droplets that were used as discrete reaction compartments for the droplet digital PCR. The PDMS/glass device could continuously produce monodisperse droplets without leakage of fluids using a vacuum-driven autonomous micropumping method. This droplet preparation technique only required evacuation of air dissolved in the PDMS before loading of oil and aqueous phases into separate inlet reservoirs. Degassing of the PDMS chip at approximately 300 Pa for 1.5 h in a vacuum desiccator gave 40 000 droplets in 80 min, which corresponded to a generation frequency of up to nine droplets per second. Over multiple runs the droplet creation was very reproducible, and the size reproducibility of generated droplets (polydispersity of up to 4.1%) was comparable to that acquired using other microfluidic droplet preparation techniques. Because the PDMS chip can be peeled off the glass plate, blocked channels can easily be fixed when they arise, and this extends the lifetime of the chip. Single DNA molecules partitioned into the droplets were successfully amplified by PCR. In addition, the droplet digital PCR platform allowed absolute quantification of low copy numbers of target DNA, and was robust against instrumental variance.

We have exploited a compact and facile microfluidic droplet creation device consisting of a poly(dimethylsiloxane) microfluidic chip possessing T-junction channel geometry, two inlet reservoirs, and one outlet reservoir, and a piezoelectric (PZT) diaphragm micropump with controller. Air was evacuated from the outlet reservoir using the PZT pump, reducing the pressure inside. The reduced pressure within the outlet reservoir pulled oil and aqueous solution preloaded in the inlet reservoirs into the microchannels, which then merged at the T-junction, successfully forming water-in-oil emulsion droplets at a rate of ∼1000 per second with minimal sample loss. We confirmed that the onset of droplet formation occurred immediately after turning on the pump (<1 s). Over repeated runs, droplet formation was highly reproducible, with droplet size purity (polydispersity, <4%) comparable to that achieved using other microfluidic droplet preparation techniques. We also demonstrated single-molecule PCR amplification in the created droplets, suggesting that the device could be used for effective droplet digital PCR platforms in most laboratories without requiring great expense, space, or time for acquiring technical skills.

We previously developed a technique that enabled automatic creation of monodisperse water-in-oil droplets with the use of an air-evacuated PDMS microfluidic device. Although the device generated droplets over a long-time period, the production rate was slow (∼10 droplets per second). In the current study, we aimed to improve this rate, using the same fluid pumping principle described in our previous work, by remodeling our device configuration. To achieve this aim, we developed a new device with a much larger PDMS surface area-to-volume ratio within the air-trapping void space (178 cm ), than that of our earlier device (5.0 cm ). This design approach was based on the idea that a larger PDMS surface area-to-volume ratio was likely to create a higher vacuum inside the void space, thereby contributing to faster liquid flow and an increased droplet generation rate. The new device consisting of five layers featuring a degassed PDMS slab as a detachable liquid-suction actuator, which was stacked on a lower microfluidic layer. In this device, the rate of droplet production increased during the time-course droplet formation and reached ca. 470 droplets per second immediately before completely consuming the loaded aqueous solution (20 μL).

Electrophoresis 2017, 38, 296–304. DOI: The cover picture shows some major steps in the workflow of our droplet digital PCR platform. A poly(dimethylsiloxane) (PDMS) microfluidic chip with T‐junction channel geometry was reversibly adhered on a glass plate through the viscoelastic properties of PDMS. This formed a detachable microfluidic device for creation of water‐in‐oil droplets that were used as discrete reaction partitions for the droplet digital PCR. Our droplet preparation technique only required evacuation of air dissolved in the PDMS before loading oil and aqueous phase into separate inlet reservoirs. Because the PDMS chip can be peeled off the glass plate, blocked channels can easily be fixed when they arise. The fluorescence analysis of thermally cycled droplet samples showed that the proportions of positive partitions (i.e., fluorescent droplets) followed the Poisson distribution.