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

Zhang, Chunsun; Xing, Da

One of the motivations for the development of on-chip PCR is to process a sample of small volume. Based on the reaction volumes of the conventional PCR, we define small volume as 3 ml. Within the last two years many small-volume PCRs have been performed (see Table 1 Landers's group developed a glass/PDMS hybrid PCR-CE chip with on-chip pressure injection using elastomeric valves and the product of 278 bp could be amplified within a PCR chamber of 280 nl (26) . Recently, this group also reported a solid-phase extraction (SPE)-PCR-CE integrated glass/PDMS hybrid chip with a 550-nl reaction chamber (27) . However, large-volume (43 ml) on-chip PCRs are still in use (see Table 1 ). For example, Lee's group developed several PCR chip devices with different functions and volumes of 10 ml or more (38, 40, 45, 47, 48, 89) . A PCR chip device proposed by Shen et al. had a reaction volume of 25 ml (70). When working with samples containing a very low concentration of the target (e.g. in diagnostics), the large-volume PCR has several obvious advantages over small-volume PCR: (i) Evaporative loss of sample during thermal cycling on PCR amplification may be negligible. (ii) The largevolume PCR allows the routine detection techniques such as gel electrophoresis to be used for the analysis of PCR products. (iii) The large-volume PCR sampling is accomplished using a conventional manual sampling gun, making large-volume sample handling during reaction set up relatively easy. However, the large PCR reaction volume can be disadvantageous for low-molecule PCR amplification, especially for single-molecule or single-cell analysis. On the contrary, the submicroliter, nanoliter or picoliter PCR systems are robust in performing analysis with single molecule or cell sensitivity (17, 31, 35, 43, 49, 78, 92, 93) . However, as the sample volume is decreased, evaporation of sample solution and introduction of a small amount of solution into the reaction chamber/channel can be the major drawbacks for PCR analysis. In addition, as PCR volumes are decreased, amplification is increasingly prone to biochemical surface absorption problems at the chamber/channel walls due to the increasing surface-to-volume ratio.