Today and tomorrow, we're reporting on presentations at an important conference on Productive Nanosystems: Launching the Technology Roadmap. Chris Phoenix is providing live blog coverage for us...
Fourth talk: Keith Firman, University of Portsmouth, UK. Title: Biological Molecular Motors for Nanodevices.
The interesting thing about biology is that it crosses both the micro and the nanoscale. He'll talk about chemical motors, overview types of biological molecular motors, give examples of nanodevices incorporating molecular motors, talk about single-molecule measurements, toxicity testing biosensor, and a proposed biosensor/nanoactuator.
(As a side note: biological motors are immersed in water, which will limit their power density and efficiency from fluid drag. Not all molecular motors are immersed in water, but many of them are.)
Chemical motors (non-biological) can generate a force of 200 pN per molecule, from a machine 2-3 nm in size. That's pretty impressive.
Even simple organisms, such as bacteria-targeting viruses (bacteriophages), include molecular motors. These are used to augment self-assembly. For example, the bacteriophage motor can corkscrew DNA into the virus against 10,000 atmospheres of pressure, using ATP for fuel.
Most bacteria have self-assembled flagellar motors: about 40 proteins (multiple copies).
Kinesin: walks along microtubules in cells, again powered by ATP, taking 200-300 steps per minute. If kinesin is fastened to a glass slide, it can make microtubules move.
ATP synthase includes a proton pump, which is connected to a component that synthesizes ATP. In an experiment, the ATP-synthesizing part (which is reversible, as it must be for efficiency--CP) was attached to a glass surface, a fiber (made of actin and fluorescently tagged) was attached to the drive shaft, and adding ATP made the fiber rotate. In another experiment, the proton-pump part was attached to a light-driven proton generator, and an array of these was used to transport a fiber for over 70 microns. So this is quite cool.
It's difficult to attach motors to a surface and have them still work. Translocases bind to DNA at a specific site and then pull it to make it move. Not just one step - many base pairs are pulled through the translocase, making the strand shorter. AFMs can be used to watch the translocase create a loop of DNA. But this is a slow process. Using a magnetic bead, they've measured 564 base pairs per second being pulled.
They're hoping to commercialize this type of motor. If the DNA can pull the bead toward a Hall-effect sensor, then they can detect addition of "fuel" (ATP) that makes the motor move. This could be used as a nanoscale valve, or a toxicity tester: detecting dioxin, which stops the motor from working. One dioxin molecule per 400 bases of DNA will stop the motor. It may also sense DNA-binding drugs. Each molecule can generate an individual signal (each molecule has its own sensor). And different molecules can have different sequences.
My summary: This is very cool work, but not much related to productive nanosystems. The motor they're looking at doesn't seem especially useful for molecular machine applications (though it seems great for sensors). I asked this question, and he said this could be used as a conveyor belt: DNA is a great templating tool to attach objects to. But not in the next 10 years. I'm still not sure how controllable this would be; he mentioned that the motor randomly lets go of the DNA.
Question: If the DNA is functionalized, can it be pulled through the motor? A: If there's a gap in the DNA (a region of just one strand) then it'll pull through. If there's a junction or branch, it'll stop.
Chris Phoenix
Tags: nanotechnology nanotech nano science technology ethics weblog blog
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