A poly(dimethylsiloxane) microfluidic sheet reversibly adhered on a glass plate for creation of emulsion droplets for droplet digital PCR

Abstract

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.

Rapid automatic creation of monodisperse emulsion droplets by microfluidic device with degassed PDMS slab as a detachable suction actuator

“…Furthermore, the overall CV for the diameters of all droplets measured at fixed intervals throughout all repeated runs was 4.9% ( n = 1 100; i.e., 220 droplets/run × 5 runs). This result was close to that obtained with our former device format (4.1%) . Details of the conditions used for the droplet data collection are given in the legend of Table .…”

“…There are two reasons for this decrease in production rate, as explained in our recent publication . Briefly, the liquid flow into the outlet chamber reduces the air capacity of the chamber (i.e., the void volume), which in turn increases the pressure in the chamber.…”

“…Although the maximum droplet generation rate was increased without any coalescence issues, the rate sharply decreased upon reaching the maximum value and eventually declined to only a few droplets per second. There are two reasons for this decrease in production rate, as explained in our recent publication [32]. Briefly, the liquid flow into the outlet chamber reduces the air capacity of the chamber (i.e., the void volume), which in turn increases the pressure in the chamber.…”

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

“…Microfluidics technology has commonly been used for droplet preparation in ddPCR studies because it allows for rapid droplet generation (rates up to a few kHz) with limited polydispersity (droplet diameter CV typically within a few percent) . With a few exceptions , many reported microfluidic droplet generation setups have used syringe infusion pumps, which are often large and expensive, to supply liquid to a microfluidic chip . Moreover, the numerous tubes, connectors, and fittings used to connect syringes to the microfluidic chip are cumbersome, increase dead volumes, and risk cross‐contamination.…”

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

“…Some research groups have developed compact, low‐cost, and simple fluid pumping systems for microfluidic droplet generation and there have been a few implementations of such devices. These include piezoelectric (PZT) actuator‐based pumps , responsive hydrogel‐based pumps , degassed poly(dimethylsiloxane) (PDMS)‐powered pumps , and finger squeeze‐driven pumps .…”