Autonomous polymer loading and sample injection for microchip electrophoresis.

We have developed an extremely simple method for microchip electrophoresis. Loading of a sieving polymer solution and injection of a sample solution are autonomously executed by a microchip fabricated in poly(dimethylsiloxane) (PDMS). In advance, the energy for the fluid pumping is stored in bulk PDMS by evacuating air dissolved in PDMS, and the information for the sample plug regulation is coded into the microchannel design. Besides the simplicity, our method brings about an advantageous effect: sample compaction due to the discontinuous electrophoretic mobility at the sample/polymer interface. The sample compaction effect was moderate in ordinary size-dependent separation for double-stranded DNA and was extreme in affinity electrophoresis for single-stranded DNA (ssDNA). In the latter separation mode, ssDNA components were sequence-specifically separated by difference in affinity to a probe oligonucleotide immobilized to the sieving polymer matrix. We separated up to 60-mer ssDNA mixtures based on single-base substitutions. The separation processes included typically 100-fold sample compaction and were completed within 15-30 s. This technology provides easy, simple, and sensitive method for detection of gene point mutations and typing of single-nucleotide polymorphisms.