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We have performed restriction mapping of DNA molecules using restriction endonucleases in nanochannels with diameters of 100-200 nm. The location of the restriction reaction within the device is controlled by electrophoresis and diffusion of [Mg.sup.2+] and EDTA. We have successfully used the restriction enzymes Sinai, Sacl, and Pacl, and have been able to measure the positions of restriction sites with a precision of [approximately equal to] 1.5 kbp in 1 min using single DNA molecules.

We show that genomic-length DNA molecules imaged in nano-channels have an extension along the channel that scales linearly with the contour length of the polymer, in agreement with the scaling arguments developed by de Gennes for self-avoiding confined polymers. This fundamental relationship allows us to measure directly the contour length of single DNA molecules confined in the channels, and the statistical analysis of the dynamics of the polymer in the nanochannel allows us to compute the SD of the mean of the extension. This statistical analysis allows us to measure the extension of [lambda]. DNA multimers with a 130-nm SD in 1 min.

The basic principles of how forces are generated through the magnetic susceptibility of an object and how microfluidics can be combined with micron-scale magnetic field gradients to greatly enhance in principle the fractionating power of magnetic fields are discussed. The cell-specific magnetic beads to extract certain cell types can be used to advantage to build practical microfluidic devices for the magnetic separation of blood cells.

We describe a method for wetting micro- and nanofluidic devices with water or any other pure liquid. The process is performed by enclosing the fluidic device in a liquid-filled cell, heating the cell to a temperature above the critical point of the liquid, and subsequent cooling of the cell to room temperature. Because the process liquid is essentially a gas during wetting, arbitrary shapes can be wetted. We demonstrate wetting of micro- and nanostructures in a fused-silica device with only a single inlet. The process is low-cost, fast, safe, and very reliable.