It is difficult to introduce long genomic DNA molecules into nanometer scale fluidic channels directly from the macroscale world because of the steep entropic barrier caused by necessary stretching of the polymer. We present a very simple technique using optical lithography to fabricate continuous spatial gradient structures which smoothly narrow the cross section of a volume from the micron to the nanometer length scale, greatly reducing the local entropic barrier to nanochannel entry. This technique, diffraction gradient lithography, can be very valuable for the fabrication of micro/nano total analysis systems.

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