Design and Fabrication of Microfluidic PCR Chips
Authors
Szegletes, Zita ; Ballay, Boldizsár
Term
4. semester
Education
Publication year
2025
Submitted on
2025-10-13
Pages
46
Abstract
Polymerase chain reaction (PCR) is a method to copy DNA by cycling through three temperatures: denaturation (separating strands), annealing (primers bind), and extension (new DNA is built). Continuous-flow PCR speeds this up by keeping fixed temperature zones and moving the sample through them, which lowers the thermal mass (less material must be heated) and uses fewer reagents. In very small channels, however, PCR components can stick to the walls (adsorption) because of the high surface-to-volume ratio, which can inhibit the reaction. Droplet-based PCR avoids this by packaging the sample into tiny droplets that do not touch the channel surfaces. We designed and built a chip that combines continuous-flow with droplet-based PCR in a fixed-loop path capable of 25 cycles. The chip has microfluidic channels etched into silicon with an integrated T-junction to form droplets, and the channels are sealed with a PDMS (silicone) cover plate. We first simulated how heat would distribute across the device. In practice, we created stable temperature regions using one resistive heater and one thermoelectric (Peltier) heater on two edges of the chip. Copper blocks helped shape these zones: two heating elements defined the denaturation and annealing regions, and the extension region arose from the heat gradient between them. The device reliably produced stable, uniform droplets. The PCR product obtained on the chip was shorter than expected.
Polymerasekædereaktion (PCR) er en metode til at kopiere DNA ved at skifte mellem tre temperaturer: denaturering (DNA-strenge adskilles), annealing/hybridisering (primere binder), og forlængelse (nyt DNA bygges). Kontinuerligt-flow PCR gør dette hurtigere ved at holde faste temperaturzoner og lade prøven passere igennem dem, hvilket sænker den termiske masse (mindre materiale skal opvarmes) og sparer reagenser. I meget små kanaler kan PCR-komponenter dog hænge fast på væggene (adsorption) på grund af et højt overflade-til-volumen-forhold, hvilket kan hæmme reaktionen. Dråbebaseret PCR modvirker dette ved at indkapsle prøven i små dråber, som ikke rører kanalvæggene. Vi har designet og fremstillet en chip, der kombinerer kontinuerligt-flow med dråbebaseret PCR i en fast sløjfe, der kan køre 25 cykler. Chippen har mikrofluidiske kanaler ætset i silicium med et indbygget T‑kryds til at danne dråber, og kanalerne er forseglet med en PDMS (silikone) dæksplade. Vi simulerede først varmefordelingen i enheden. I praksis skabte vi stabile temperaturzoner ved hjælp af én resistiv varmer og ét termoelektrisk (Peltier) element på to af chippens kanter. Kobberblokke hjalp med at forme zonerne: to varmeelementer definerede denaturerings- og annealingszonerne, og forlængelseszonen opstod fra varmegradienten mellem dem. Enheden producerede pålideligt stabile og ensartede dråber. PCR‑produktet på chippen var kortere end forventet.
[This apstract has been rewritten with the help of AI based on the project's original abstract]
Keywords