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

Zhang, Chunsun; Xing, Da

An important drawback of the PCR chip microsystems is the generation of air bubbles. which not only cause large temperature difference in the sample but also expel the sample from the PCR chamber. The formation of air bubbles has two prerequisites: the liquid must be superheated and there must be nucleation site(s). Several methods have been used to avoid the prerequisites and inhibit the bubble generation: (i) The structural design of PCR chamber. A diamond-shaped or rhomboidal chamber is superior to a circular chamber in preventing bubble formation (10, 51) . Recently, Gong et al. reported that the deeper the PCR chamber, the more difficult it is for the PCR solution to flow into the chamber without trapping bubbles. However, the size of the chamber or the shape and size of the inlet and outlet have little or no influence on the bubble formation (28) . (ii) The surface treatment of the PCR chamber. In general, the wetting properties of the PCR chamber and its inlet/outlet have an obvious effect on the bubble formation. When the chamber surface is highly hydrophilic, the PCR sample can flow into the chamber smoothly and rapidly without bubble formation (28, 31, 35, 51) . (iii) The sealing pressurization of the PCR chamber. Under pressurization and high-temperature, the gas solubility will increase and the dissolved gases and microbubbles in the PCR sample cannot grow up in volume, thus preventing the air bubble formation (37, 50, 57, 62, 63) . (iv) Degasification of the PCR sample. This process can eliminate non-condensable gases in the PCR sample before loading and consequently decrease the risk of bubble formation (56) . (v) The addition of high boiling-point biocompatible reagents to the PCR sample. When a solvent with a boiling point above 1008C (e.g. glycol, glycerol or poly(ethylene glycol)) is included in the PCR sample, the boiling point of the resulting sample is increased, and thus preventing bubble formation at high temperatures (56).