RESUMEN
Polymerase chain reaction (PCR) is the most common method used for nucleic acid (DNA) amplification. The development of PCR-performing microfluidic reactors (µPCRs) has been of major importance, due to their crucial role in pathogen detection applications in medical diagnostics. Closed loop (CL) is an advantageous type of µPCR, which uses a circular microchannel, thus allowing the DNA sample to pass consecutively through the different temperature zones, in order to accomplish a PCR cycle. CL µPCR offers the main advantages of the traditional continuous-flow µPCR, eliminating at the same time most of the disadvantages associated with the long serpentine microchannel. In this work, the performance of three different CL µPCRs designed for fabrication on a printed circuit board (PCB) was evaluated by a computational study in terms of the residence time in each thermal zone. A 3D heat transfer model was used to calculate the temperature distribution in the microreactor, and the residence times were extracted by this distribution. The results of the computational study suggest that for the best-performing microreactor design, a PCR of 30 cycles can be achieved in less than 3 min. Subsequently, a PCB chip was fabricated based on the design that performed best in the computational study. PCB constitutes a great substrate as it allows for integrated microheaters inside the chip, permitting at the same time low-cost, reliable, reproducible, and mass-amenable fabrication. The fabricated chip, which, at the time of this writing, is the first CL µPCR chip fabricated on a PCB, was tested by measuring the temperatures on its surface with a thermal camera. These results were then compared with the ones of the computational study, in order to evaluate the reliability of the latter. The comparison of the calculated temperatures with the measured values verifies the accuracy of the developed model of the microreactor. As a result of that, a total power consumption of 1.521 W was experimentally measured, only ~7.3% larger than the one calculated (1.417 W). Full validation of the realized CL µPCR chip will be demonstrated in future work.
RESUMEN
The novel COVID-19 global pandemic has raised, among many others, major concerns regarding the impact of infection during pregnancy. Current evidence suggests that vertical transmission from mother to baby, antenatally or intrapartum, does occur, but is uncommon. According to the published reports of infants born to COVID-19-affected mothers, as well as the anecdotal experience of current practices worldwide, it appears that investigations regarding the potential of SARS-COV-2 vertical transmission in pregnancy have so far been based, to a large extent, on PCR testing of neonatal pharyngeal swab samples. Given that the transplacental route of intrauterine transmission for SARS-COV-2 is less likely to immediately involve the upper respiratory tract of the newborn, contrary to what happens after birth, it would be advisable to include appropriate biological samples, such as cord blood, placenta, amniotic fluid and neonatal blood, along with the pharyngeal samples, in order to contribute significantly to such investigations. It is important to point out that negative PCR tests of neonatal pharyngeal samples do not exclude the possibility of intrauterine viral transmission, while positive pharyngeal swabs are more likely to reflect intrapartum or postpartum contaminants, rather than antenatal intrauterine transmission, in the absence of other criteria. Revision and enhancement of the so far prevailing practices appear important, in order to facilitate the development of good clinical practice for managing neonates and ensuring safety of families and healthcare providers.
