Researchers from the Chinese Academy of Sciences’ Shanghai Institute of Microsystem and Information Technology published a new high-pressure liquid seal method in Microsystems & Nanoengineering on September 27th, 2024. The method successfully prevents bubble formation in PDMS-based PCR chips.
The impact of water vapor on bubble formation during PCR (temperature: 25–95 °C, pressure: 101.325 kPa). a Saturation vapor pressure of water. b Thermal expansion only causes a slight increase in gas volume (black line), while the equilibrium effect of water vapor leads to a larger volume of isothermal expansion (red line). The synergistic effect of thermal expansion and isothermal expansion of water vapor results in the maximum increase in bubble volume (blue line). c Calculated bubble volume generated from degassed porous PDMS during PCR. The inset shows the total pressure of air and water vapor if the volume is constant. d The volume of saturated water vapor formed by the air dissolved from the water. Rapid cooling reduced the volume from 8% to 1.2%, indicating that the main component of these bubbles at 95 °C is water vapor. e Possible mechanisms for bubble formation involving the equilibrium of water vapor and the overflow of air in the PDMS and PCR solutions. Image Credit: Microsystems & Nanoengineering
The new finding has fundamentally changed the understanding of PCR chip technology: bubble formation in polydimethylsiloxane (PDMS)-based chips is mostly caused by water vapor rather than air expansion. A high-pressure liquid seal method that successfully removes bubbles and stops water loss during the polymerase chain reaction (PCR) process has been developed as a result of this discovery.
The innovation opens the door for more effective applications in vital domains, including virus detection and cancer screening, by streamlining chip design, improving operational stability, and increasing PDMS PCR chip reliability.
Polymerase chain reaction (PCR) technology is a key component of contemporary diagnostics. It allows for accurate nucleic acid measurement in a variety of applications, from prenatal testing to disease detection. Microfluidic chips, particularly those composed of PDMS, have become popular because of their small size, quick reaction times, and capacity to manage several reactions at once.
However, a recurrent issue has hampered their wider adoption: the development of bubbles and sample moisture loss while thermal cycling. These difficulties affect sample quantities and raise the possibility of cross-contamination and ion concentration variations, limiting PCR accuracy. Addressing these technical barriers has become a top research focus in the search for more dependable PCR chip technology.
Their findings showed that water vapor diffusion, rather than air expansion, is the fundamental mechanism behind bubble formation. By generating a high-pressure liquid environment, the researchers eliminated vapor-induced bubbles, considerably enhancing PCR chip performance and reliability.
The researchers discovered that water vapor saturation pressure increases dramatically at high temperatures, resulting in bubble formation within PDMS chips. Unlike previous notions that bubbles were caused by trapped air expansion, tests demonstrated that water vapor may enter PDMS and form bubbles even without significant thermal expansion. To counteract this, the scientists created a high-pressure liquid seal technology that keeps the internal pressure above 109 kPa.
This method avoids bubble formation and reduces water loss, removing the need for complex structural changes or additional sealing material. Furthermore, the liquid seal is a protective barrier, separating the chip from external air and reducing the “respiratory” effect, which increases evaporation. The approach was successfully validated in digital PCR (dPCR) chips, proving its ability to keep samples intact and reduce cross-contamination.
This study marks a significant leap forward in PCR chip technology by resolving the long-standing issue of bubble formation. The high-pressure liquid seal technique simplifies chip design while significantly enhancing PCR reliability and efficiency, making it more accessible for a wide range of diagnostic applications.
Dr. Tiegang Xu, Study Lead Researcher, Chinese Academy of Sciences
This breakthrough has far-reaching ramifications outside the laboratory. The high-pressure liquid seal technology, which ensures precise and consistent PCR results, can revolutionize medical diagnostics, particularly cancer screening, infectious disease detection, and prenatal testing. The ability to avoid bubble formation and water loss improves chip durability, lowering the risk of error and contamination.
Furthermore, this innovation might spur the creation of affordable, disposable PCR chips, increasing access to state-of-the-art diagnostic instruments in areas with limited resources. Considering its ease of use and efficiency, the method has the potential to hasten the adoption of microfluidic PCR technology in research and clinical settings, opening up new avenues for precision medicine.
The National Natural Science Foundation of Guangdong Province (2021A1515010266), the 2021 Foshan Science and Technology Innovation Team for Young-Top Talents (2120001010795), the Guangdong Provincial Key Laboratory of Sensor Technology and Biomedical Instrument (2020B1212060077), the Shenzhen Science and Technology Program (20202206193000001, 20220816161126002), and the National Natural Science Foundation of China (82372088) all provided support for this study.
Journal Reference:
Gao, S., et al. (2025) Overcoming bubble formation in polydimethylsiloxane-made PCR chips: mechanism and elimination with a high-pressure liquid seal. Microsystems & Nanoengineering. doi.org/10.1038/s41378-024-00725-1