DNA Nanobots and Origami

What can I say? I'm super stoked for our first science topic. My scientific passion is for molecular biology- enzymes, mitochondria, and DNA are enticingly baffling. Don't worry: I haven't forgotten about the remainder of my San Francisco trip. I haven't forgotten about other fashion requests. But this, when I saw it, was too good to pass up. You all need to know about it, and if you talk about this at your next dinner party, believe me, your guests will be amazed.

First, we need to start with a basic biology refresher. DNA, the information molecule in all cells, is comprised of 4 basic building blocks, or nucleotides. Generally they are abbreviated as G, A, T, & C. The nucleotides are strung together in an order or sequence that the cell translates as some sort of useful information. If even from high school biology or sci-fi entertainment, we are probably all familiar in some way or another with the double-helix spiral shape of DNA. A DNA molecule is most stable when the strand pairs with a complimentary strand. G's bind to C's, and A's bind to T's. This is how you get that characteristic spiral ladder formation.


Naturally, DNA is used to store all the information an organism needs to survive. More recently however, researchers have created exciting applications for DNA in nanotechnology. Just a few months ago, researchers reported the invention of nanobot "spiders"! The spiders are exponentially smaller than the period at the end of this sentence. What is even more exciting is that these nanobots are powered by the same DNA interactions discussed above, not battery or solar powered. "How?" you ask. So glad you did! I'll tell you!

The nanobots are comprised mostly of DNA, not for information but for movement, stability, and carrying cargo. The basic spider shape has 2-3 DNA legs with feet made of only one strand of DNA. DNA arms may also exist to carry certain types of predetermined cargo composed of a small particle.

DNA Nanobot Spider
(deceivingly simple looking, no?)
F's = single stranded DNA feet
H's = singled stranded DNA hands
Green = double helix DNA body
(Image from Gu et al., 2010)

In order to really understand how these actually move, we need to talk about DNA origami. Seriously, this is a real term apparently. You'll quickly see why. DNA origami was developed by Paul Rothemund at Caltech in 2006. DNA origami is simply sheets of DNA double-helices folded into shapes! The sequence of the DNA in the origami can be controlled by the origami creator. Rothemund has created simple shapes like rectangles to more complicated shapes like stars, triangles, and even smiley faces!


So! Just like Rothemund, researchers created a sheet of DNA origami with a "track" for the spider to follow. The track is made of sequences specific to the DNA sequence on the spider feet. Put the DNA bot on the track, and the feet will "stick" to the sequence specific track. This still doesn't explain movement. The feet also come furnished with a DNA cutter, or enzyme! So, the bot places its foot on a track step and binds to the DNA. The track has a signal to initiate the DNA cutter, causing the DNA interactions between feet and track to be separated. The cutting action releases the foot and allows it to bind to the next step on the track. Thus, spiders are powered to move along a predetermined path. Currently, spiders can take approximately 50 steps before falling off the origami sheet. Amazingly, inventors also have created a stop signal in the track, forcing the DNA bot to "stop dead in its tracks". Ha! :)

Left side: DNA foot + cutter enzyme attached to origami, then releasing
Right side: "spider" following track
(Image from Lund et al., 2010)

Just the fact that we can do this is amazing! Nanotechnology has advanced light years in the past decade. But the dreams envisioned by researchers for these elegant little bots are enormous. According to an interview conducted by ScienceNews, the dream is to use the nanobots as a disease therapy. Hopefully, they will crawl along your cell membranes, identify cancerous cells, and help your body destroy them. We are more lightyears from this reality, but this is where science is heading.

Please ask if you have any questions! And if there are any other science topics you'd like me cover, let me know!



References:

DNA on the Move. Gwyneth Dickey. September 11, 2010. http://www.sciencenews.org

Hongzhou Gu, Jie Chao, Shou-Jun Xiao & Nadrian C. Seeman. 2010. A proximity-based programmable DNA nanoscale assembly line. Nature. May 13, 2010. http://www.nature.com

Kyle Lund, Anthony J. Manzo, Nadine Dabby, Nicole Michelotti, Alexander Johnson-Buck, Jeanette Nangreave, Steven Taylor, Renjun Pei, Milan N. Stojanovic, Nils G. Walter, Erik Winfree & Hao Yan. Molecular robots guided by prescriptive landscapes. Nature. May 13, 2010. http://www.nature.com