Teaching Nano to Swim

October 14, 2008

(PhysOrg.com) -- Ayusman Sen, head of the Department of Chemistry at Penn State, makes tiny, metallic objects do something extraordinary -- he makes them swim. Sen's work is driven by catalysis, the chemical phenomenon whereby a substance accelerates a chemical reaction but emerges unchanged at the end of the process.

The chemical reaction upon which he and his team of students and colleagues focus their efforts is the well-known redox reaction, in which electrons and protons are broken away from their parent atoms and are pumped back and forth between substances, resulting in the liberation of energy during the process.

That energy manifests itself as an electrical gradient in the fluid surrounding a micro particle or nanomotor. Frequently, the motor is one of the group's two-micron-long platinum-gold nanorods. In most cases, the fluid starts out as a dilute solution of hydrogen peroxide which, upon being catalytically oxidized by the platinum tip of a nanorod, results in oxygen and also in electrons and protons that flow from bow to stern; electrons inside the rod; and an equal number of protons in the fluid along the outside of the rod. At the stern, the electrons and protons catalytically reduce hydrogen peroxide to water. The protons flowing from stem to stern function like paddles propelling the nanorod toward its platinum forward end, or if the nanorod is stationery, pumping water around it toward the aft end.

While getting metal particles to move under their own power is one thing, getting them to ambulate purposefully toward a specific location is another. In response, the Penn State team has developed three methods of steering their motors: magnetism, chemistry, and light.

The magnetic system employs magnetized nickel segments built into the platinum and gold-layered rods that respond to an external magnetic field by coaxing the rods to swim parallel to it.

The chemical system uses chemotaxis, traditionally defined as the movement of living organisms toward or away from a chemical attractant or toxin. In the first example of chemotaxis in a non-living system, Sen's platinum-gold nanorods propel themselves along a gradient of hydrogen peroxide diffused in water toward a higher concentration of hydrogen peroxide.

Phototaxis uses light to initiate catalytic activity. In a demonstration, silver chloride particles suspended in distilled water do not move until ultraviolet light is shone on them, whereupon they migrate en masse toward the light.

As a practical matter, getting metal particles to move toward specific targets is not very valuable unless they do something like deliver a drug, assemble a structure, sense a material, or pump a liquid once they get there. In order to prove the feasibility of such activities, Sen's group has developed electrostatic and chemical linkers to attach cargo to their nanomotors.

Although at this juncture the group knows how to make the motors, attach cargo to them, and transport them to designated points, off-loading remains a problem. In response, the group is beginning work on a photosensitive linker molecule that will break and drop the cargo when exposed to light.

Provided by Penn State

Explore further: Artificial leaf harnesses sunlight for efficient fuel production

Related Stories

Researchers use 'seafloor gardens' to switch on light bulb

August 6, 2015

One of the key necessities for life on our planet is electricity. That's not to say that life requires a plug and socket, but everything from shrubs to ants to people harnesses energy via the transfer of electrons—the basis ...

Recommended for you

Making nanowires from protein and DNA

September 3, 2015

The ability to custom design biological materials such as protein and DNA opens up technological possibilities that were unimaginable just a few decades ago. For example, synthetic structures made of DNA could one day be ...

Graphene made superconductive by doping with lithium atoms

September 2, 2015

(Phys.org)—A team of researchers from Germany and Canada has found a way to make graphene superconductive—by doping it with lithium atoms. In their paper they have uploaded to the preprint server arXiv, the team describes ...

For 2-D boron, it's all about that base

September 2, 2015

Rice University scientists have theoretically determined that the properties of atom-thick sheets of boron depend on where those atoms land.

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

rodriguc1987
not rated yet Oct 14, 2008
This is cool. I can't wait to see this used to target tumors and cancerous cells and then offloading a dose of chemicals onto these bastards. However, how will the light reach the nanobots from outside the body to trigger the offloading?
thales
not rated yet Oct 15, 2008
Here's your answer:

http://www.physor...163.html

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.