A Novel Pressure Indicator for Continuous Flow PCR Chip Using Micro Molded PDMS Pillar Arrays
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A Novel Pressure Indicator for Continuous Flow PCR Chip Using Micro Molded PDMS Pillar Arrays Yi Zhao and Xin Zhang Laboratory of Microsystems Technology, Department of Manufacturing Engineering, Boston University, 15 Saint Mary’s Street, Boston, MA 02215, USA ABSTRACT DNA amplification is one of the most routine experiments carried out in biological laboratories. Continuous flow PCR chip releases biologists from their laborious exercises. The use of such chip is, however, hindered by costly expense of the syringe pump, which is used to maintain a constant flow rate. In this paper, we demonstrate a novel pressure indicator which makes up an in-line flow sensor in a continuous flow PCR chip. The pressure of PCR channel is achieved from pattern change in fabricated microstructures, and converted to volume flow rate. A polymeric PCR chip with such pressure indicators is presented. With a much less expense as compared to its conventional peers, this indicator has a wide potential for the use in the laboratories which runs daily activities like sequencing or mutagenesis. INTRODUCTION Continuous flow PCR (polymerase chain reaction) chip, first reported by Kopp [1], has received considerable attention in recent years. This chip has three well-defined zones kept at 95°, 77°, and 60°C using thermostated copper blocks with PID temperature control. The PCR sample and buffer solution are hydrostatically pumped through a single channel etched into the glass chip using two precision syringe pumps. The channel passing through the three temperature zones defines the thermal cycling process. The thermal cycles are realized by keeping temperatures constant over time at different locations in the system and moving the sample through the individual temperature zones. Given that the time delay for the sample to reach a new temperature solely depends on the time needed to transport the sample into the appropriate temperature zone by heating the fluid element in the channel, the volume flow rate is crucial for the time-space conversion. It is to ensure the sample can perform cycles of denaturation, annealing and extension successively. A precision syringe pump is currently in use for most cases in the above system. However, its costly expense, usually over one thousand dollars, keeps it from the use by a wide public in their daily PCR experiments. The syringe pump also raises a problem in system integration because it needs to be close to the PCR chip, or the long flexible transfer tube will somehow compromise accuracy of volume flow rate. Moreover, the syringe pump lacks capability for responding to possible variation in micro channels. Thus, an economic in-line flow meter is urgently required. Many engineered flow sensors for microfluidic systems arise right at the moment to provide feedback based on a number of sensing principles, including differential pressure [2], dispersion of a thermal pulse [3], injection and subsequent detection of a charge pulse carried along in the fluid as ionic species [4], and many etc. Despite si
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