Using catalysts to stamp nanopatterns w...(now working as a postdoctoral researcher...)

A 100 nanometer limit of resolution is about 1,000 times tinier than a human hairs width. While that seems very precise, the Duke team now reports it can boost accuracy limits to less than 2 nanometers by entirely eliminating inking.

Clark and graduate student Matthew Johannes crafted a microstamp out of a gel-like material called polyacrylamide, which compresses more uniformly than the silicone material known as PDMS which is normally used in microstamping.

In lieu of ink, Snyder, Toone and graduate student Briana Vogen suspended a biological catalyst on the stamp with a molecular tether of amino acids. For this proof-of-principle demonstration, Toones team chose as a catalyst the biological enzyme exonuclease I, derived from the bacterium E. coli.

In one set of experiments, the polyacrylamide stamp pattern bearing the tethered enzymes was then pressed on a surface of gold that had been covered with a uniform coating of single-stranded DNA molecules. The DNA molecules had also been linked to fluorescent dye molecules to make the coating visible under a microscope.

Wherever the enzyme met the DNA, the end of the DNA chain and its attached dye were broken off and removed. That created a dye-less pattern of dots on the DNA coating, each dot measuring about 10 millionths of a meter diameter each.

The microdots are very precise because the catalyst that created them could not shift its position more than the length of its chemical tether -- less than 1 nanometer, the Duke team reported. "Whether the stamp was left on for a short period of time, or for days, the pattern did not change, Clark said.

The inkless microstamp could also re-use the same suspended catalyst molecule repeatedly. Enzymes can deteriorate with extended use, Clark acknowledged. But because of our tether attachment chemistry, we can easily wash the old enzyme off, put on a new
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