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Unzipping DNA
Stellacci, who studied materials science in Italy at the Politecnico di Milano, came to MIT in 2002 with the idea of replicating the printing process that naturally occurs in cells. When a cell divides, it first needs to replicate its DNA. With its double-helix design, DNA is like a long, twisted zipper. During replication, an enzyme unzips the DNA, separating it into two strands. Next, free-floating nucleotides – the DNA letters A, C, T, and G – match up with their complements in the separated strands, yielding two identical copies of the original double helix. The cell then divides into two “daughter” cells, and each gets its own copy of the DNA.

What Stellacci and his MIT team – including doctoral candidate Arum Amy Yu, Professor Henry Smith, and electrical-engineering graduate student Tim Savas – have done is harness this replication process as a manufacturing technique. Working out of two labs run by Stellacci in Building 13 on the third floor, the researchers started with master microarrays spotted with single strands of DNA and a solution containing those strands’ complements. The arrays were provided by chemical-engineering professor Anthony Guiseppi-Elie and doctoral candidate G. Scott Taylor, both from Virginia Commonwealth University in Richmond, VA. On each array were 16 dots, each containing a larger number of single-stranded DNA molecules aligned in upright positions, standing in rows like soldiers. The complementary DNA in the solution had been chemically modified so that one end of each strand contained an extra chemical group that likes to stick to surfaces such as gold or silicon.

In the first of three steps, Yu, who hopes to graduate in 2006 with a PhD in materials science, immersed a master microarray in the solution. The complementary strands automatically attached to the strands in the master, forming complete double-stranded DNA, with the sticky ends facing up. Next, Yu gently laid a piece of gold on top of the rows of upright molecules, so that the sticky ends bound to it. Last, she heated the genetic sandwich to 80 degreesC, which caused the DNA to unzip. When Yu pulled away the piece of gold, she had a surface spotted with single strands of DNA that were the mirror images of those on the master. She repeated the three steps using the mirror image and was able to produce a mirror image of it as well – that is, a rough copy of the master.

“The idea of rapid replication is very attractive. It lowers your cost. If you could reproduce a master with very little work, that’s ideal,” says Byron Gates, an expert in surface chemistry and an assistant professor at Simon Fraser University in Burnaby, British Columbia.

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