Miniaturized PCR chips for nucleic acid amplification and analysis: latest advances and future trends

Zhang, Chunsun; Xing, Da

Since the PCR is temperature sensitive, it is essential to choose a proper temperature measurement technique to determine or at least to estimate the temperature within the PCR chip. In general, the measurement techniques can be classified into three categories based on the nature of the contact mode between the temperature measuring element and the PCR chip (solid) or PCR solution (liquid): (i) Invasive. The measuring element is in direct contact with the PCR chip or solution. (ii) Semi-invasive. The PCR solution is treated in some manner to enable remote observation, e.g. inclusion of dye whose color changes with temperature. (iii) Noninvasive. The PCR solution is observed remotely, e.g. IR thermography. Due to their low cost and convenience, invasive temperature measurements are still most widely used (4). However, there are several obvious challenges associated with these measuring techniques: First, regardless of the nature of the temperature sensing element, it will add some thermal mass to the PCR chip, ultimately decreasing the chamber PCR thermal cycling rates. Second, they can obtain temperature data only at a few discrete points or lines and thus do not reflect the overall temperature field of the PCR chip or solution. Third, the temperature sensor within the PCR solution will inhibit the PCR and increase the risk of sample cross contamination. Fourth, the use of invasive temperature measurement involves a disturbance, which manifests itself as a difference between the temperature being measured and that which would exist in the absence of the temperature-measuring element.