Continuous Flow Thermal Cycler Microchip for DNA Cycle Sequencing

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Abstract
We report here on the use of a polymer-based continuous flow thermal cycler (CFTC) microchip for Sanger cycle sequencing using dye terminator chemistry. The CFTC chip consisted of a 20-loop spiral microfluidic channel hot-embossed into polycarbonate (PC) that had three well-defined temperature zones poised at 95, 55, and 60 °C for denaturation, renaturation, and DNA extension, respectively. The sequencing cocktail was hydrodynamically pumped through the microreactor channel at different linear velocities ranging from 1 to 12 mm/s. At a linear velocity of 4 mm/s resulting in a 36-s extension time, a read length of >600 bp could be obtained in a total reaction time of 14.6 min. Further increases in the flow rate resulted in a reduction in the total reaction time but also produced a decrease in the sequencing read length. The CFTC chip could be reused for subsequent sequencing runs (>30) with negligible amounts of carryover contamination or degradation in the sequencing read length. The CFTC microchip was subsequently coupled to a solid-phase reversible immobilization (SPRI) microchip made from PC for purification of the DNA sequencing ladders (i.e., removal of excess dye-labeled dideoxynucleotides, DNA template, and salts) prior to gel electrophoresis. Coupling of the CFTC chip to the SPRI microchip showed read lengths similar to that obtained from benchtop instruments but did not require manual manipulation of the cycle sequencing reactions following amplification.