In situ thermal diagnostics of the micro-PCR system using liquid crystals

A simple, reliable liquid crystal (LC) thermometry of a polymerase chain reaction (PCR) chip that has a microchamber inside the chip and a film heater and a film sensor patterned on the surface is firstly introduced. The silicon-based PCR chip is made by MEMS technology. A non-linear feedback proportional-integral control scheme adjusts the power input of the Pt heater to control the surface temperature of the micro-PCR chip measured by the Pt sensor with an accuracy of less than +/- 0.1 degrees C at steady state. We use the LC thermometry to analyze the temperature distribution in the microchamber of the micro-PCR chip. The reflected colors of LC's inside the microchamber are captured through a charge-coupled device (CCD) camera, subsequently analyzed using a hue-based color analysis system. Two LC's of which individual working range is near the typical PCR temperature of 55 degrees C and 72 degrees C are calibrated in a constant temperature bath with a resolution of less than +/- 0.3 degrees C. While the average microchamber temperature near the annealing temperature is similar to the surface temperature, it is lower than the surface temperature by ca. 1 degrees C in the range of the extension temperature. Also, the temperature variations along the center of the microchamber, are less than 1.5 +/- 0.5 degrees C and 3 +/- 0.3 degrees C in the range of the annealing and the extension temperature, respectively. (C) 2005 Elsevier B.V. All rights reserved.