800 Seconds Until the Flow Slows: Researchers in Perm Develop Mathematical Model for PCR Tests
Portable PCR systems face a physical constraint: as DNA copies accumulate, they begin to slow the fluid flow that carries them through the reaction chamber. Researchers in Perm have developed a model that can predict this hidden limit before a device is built.
Polymerase chain reaction (PCR) is no longer confined to research laboratories. The technique is now used to detect infectious agents, establish paternity and conduct forensic testing. Conventional PCR, however, requires a thermal cycler, a relatively large instrument that repeatedly heats and cools a sample tube. As a result, testing is typically performed in an equipped laboratory rather than at a patient's side or at a crime scene.
Convection PCR works differently. Inside a small chamber, differences in temperature cause the liquid to circulate on its own, carrying the sample through regions with different temperatures. But this convenient design has a limitation. As DNA molecules accumulate in the solution, its physical properties change, potentially slowing the fluid flow. Researchers at Perm National Research Polytechnic University (PNRPU) have developed a mathematical model that describes this process. It can help engineers determine in advance where the chamber's performance limit lies.
Identifying the Hidden Limit
The researchers tested the model using software that simulates fluid flow and heat transfer inside a PCR chamber. They tracked the reaction for approximately 1,000 seconds, a period long enough for DNA molecules to accumulate to levels that can be detected. The simulations showed that after about 800 seconds, the molecules build up to a point where they begin to slow the fluid circulating through the chamber.
The finding has implications beyond the scientific model itself. The technology it underpins could help engineers select the optimal chamber geometry, temperature profile and solution properties during the design stage, reducing the number of physical experiments needed.
Another advantage is its potential to expand access to molecular diagnostics beyond major medical centers. Compact systems could be used in district hospitals, outpatient clinics, mobile testing units and field laboratories – including settings without fully equipped laboratories or where access to reliable electricity is limited.
A Laboratory in a Suitcase
In recent years, infectious disease diagnostics has advanced rapidly, with new milestones in testing speed, portability and accuracy emerging year after year.
In 2022, Russia's Federal Medical-Biological Agency (FMBA) registered the portable Izaskrin-8 device, which can detect the genetic material of pathogens, including SARS-CoV-2, in less than 30 minutes. In 2023, the Troitsk Engineering Center unveiled the ROST-5 mobile DNA analyzer. It uses a microfluidic cartridge with six wells and can test for up to 12 pathogens in a single run. In 2026, Perm Polytechnic published the first version of a convection PCR model that accounts for thermophoresis. That same year, another important development followed: the FMBA of Russia patented a device and method for convection PCR amplification using a disposable chip cartridge and real-time optical detection.
Planning Ahead
It is important to understand that the PNRPU development is a mathematical model. It does not manufacture electronic components, reagents or optical systems. However, the model could be incorporated into engineering software to reduce the need for trial-and-error experimentation when developing domestically designed PCR analyzers. It could also give Russia's diagnostics sector a reliable tool for designing devices that are compact, cost-effective and accurate.
