A compact and facile microfluidic droplet creation device using a piezoelectric diaphragm micropump for droplet digital PCR platforms

Abstract

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.

Vacuum‐driven fluid manipulation by a piezoelectric diaphragm micropump for microfluidic droplet generation with a rapid system response time

“…In our previous study, the present system featured a rapid system response time, i.e., the time required for droplet formation to stabilize . Specifically, droplet formation started almost immediately after the PZT actuator was turned on.…”

“…Although PZT diaphragm pumps are self‐priming and capable of pumping both liquid and gas , they are normally used to deliver liquids through a pump chamber. However, in our previous study, we used a PZT diaphragm micropump to evacuate air from the sealed outlet reservoir of a PDMS microfluidic chip, thus reducing the pressure inside . This decreased pressure enabled oil and aqueous solution, preloaded in two separate inlet reservoirs, to be pulled into microchannels and merged at a T‐junction.…”

“…In our previous work, we used a commercially available PZT diaphragm micropump with a model specific controller . The controller generated a standard wave (modified sine wave) voltage suitable for actuating the PZT pump element.…”

“…In the present study, we investigate the influence of the operational wave voltage parameters for the PZT pump element (i.e., V p‐p and wave frequency) on droplet creation characteristics using the same microfluidic droplet preparation setup as that in our previous study (refer to Fig. and Supporting Information Section 1.1) .…”

“…In summary, building on the work of our recent publication , in the present study we investigated the influence of the voltage parameters applied to a PZT pump, such as V p‐p and wave frequency, on droplet formation characteristics. Stepwise changes to V p‐p altered the droplet generation rate based on the specific V p‐p value, which changed rapidly after changes to the input voltage (<0.5 s) while the droplet size remained constant.…”