High-fidelity fractionation of ssDNA fragments differing in size by one-base on a spiral-channel electrophoretic chip.

For the fractionation of fragments of interest from selective PCR products generated by high coverage gene expression profiling (HiCEP) analysis, high-resolution with the ability to discriminate and fractionate fragments differing by one base (base pair) in size is highly required. We report here on a new 4-inch diameter spiral-channel chip device for automatic high-fidelity fractionation. Overlapping DNA fragments of 180, 181 and 182 bases, with only one-base difference in size, were successfully fractionated. The collected fragments were PCR amplified, and then evaluated by size checking analysis, DNA sequencing, and homolog search. The high-resolution fractionation has been achieved because of the combined contributions of (i) the high-resolution separation using a 30 cm long spiral channel, (ii) a blocking technique to avoid contamination from unselected fragments during CE, and (iii) precise micro-scale target extraction. Contaminations due to unselected fractions have been greatly decreased to a negligible level by optimization of the extraction position and extraction time corresponding to the targeted segment only. This technique can be adapted to a wide range of applications, such as protein or cell collections where requirements for the high purity are more important than the amount of recovered fractionated material.