DNA electrophoresis in microlithographic arrays

WE have used optical microlithography to fabricate capped quasi-two-dimensional obstacle courses in SiO₂. We report here observations using epifluorescence microscopy of the electrophoresis and length fractionation of large DNA molecules confined in arrays. Simple reptation theory, based on the work of deGennes¹, predicts that at low electric fields the electrophoretic mobility of a polymer of length L much greater than the persistence length p scales inversely with L (ref. 2). But elongation of the coil in the matrix at sufficiently strong electric fields³ results in a length-independent electrophoretic mobility^4,5. The application of suitably timed pulsed electric fields restores the fractionating power of gels for long molecules⁶ but the protocols of pulsed-field electrophoresis are semi-empirical because the complex and ill-understood gel matrix plays a critical role in fractionation. Microlithographically constructed obstacle arrays, with their low dimensionality, small volume and extremely reproducible topography, will make it possible to understand the motion and fractionation of large polymer molecules in complex but well characterized topologies.