Huge Fields of Self-Assembled Molecular Ridges May Help Sensor Design

Scientific American ^ | November 30, 2006 | JR Minkel

[neverdem]

In the nanoworld, three square millimeters is pretty big territory

A droplet of liquid and a few seconds are all that researchers need to produce neatly spaced ridges of molecules that cover a huge area--at least by the standards of nanotechnology. In a feat of so-called self-assembly, a group reports that disk-shaped molecules can stack themselves by the millions into lines of up to a millimeter in length and covering several square millimeters.

The process might help ease the fabrication of sensors such as liquid crystal displays (LCDs) that register the presence of offending chemicals. "You just drop a droplet of the solution on a surface and the molecules arrange themselves," says group member Johannes Elemans, a nano researcher at Radboud University Nijmegen in the Netherlands. "It takes five seconds to make the surface, which is not really labor intensive," he says.

Elemans and his colleagues were looking for a solution of molecules that would cling together just enough to form useful patterns as the solution evaporated but would not clump in the process. They struck on a flat molecule that has three lobes projecting from a central core. The cores have chemically sticky parts that project from the plane of the molecule. Ideally the molecules would line up because the cores would stick to each other and the stacked lobes would stabilize the shape [see image below].

Although the researchers anticipated creating such strings, "we expected to get spaghetti all over the place," Elemans says. Instead, when they allowed a droplet to dry on mica, they found that individual columns also aligned themselves into regularly spaced domains of up to three square millimeters in area. The spacing of the columns varied from 0.5 to one micron depending on the droplet size.

Prior experiments relied on long prefabricated polymers to make such arrays, but these domains tended to cover an area only 10 square micrometers or less, the researchers note in their report published online November 30 by Science.

"This is a pretty impressive piece of work," says materials chemist Jeffrey Moore of the University of Illinois at Urbana-Champaign. "They've nicely demonstrated that they can get nearly defect-free organization over a few microns. This isn't just some highly localized, zoomed-in organization," he says.

Elemans says that the arrays might serve to grow LCDs. The researchers found they could align liquid crystal polymers over large areas by depositing their solution onto a glass slip and then adding the polymers. Currently LCDs are made by etching grooves into a polymer sheet and pouring liquid crystals on top, Elemans explains.

The new technique might work for small sensors, but it would have to be dramatically expanded for an LCD monitor, says physical chemist Mohan Srinivasarao of Georgia Tech.

A further-off idea would be to exploit the columns as wires for transmitting electricity or light, and then link the wires into circuits, Moore says.

For now the procedure is a step toward the dream of plopping a liquid down and letting it form a predetermined pattern, Moore notes, which would make industrial fabrication of many devices much easier. "It's really simplification of fabrication," he says. "That's what it boils down to."

[neverdem]

Image: COURTESY OF JOHANNES ELEMANS
ARRAY YOU GO: Researchers have coaxed specially designed molecules to stack into very long columns, which align themselves into extremely large, regularly spaced arrays.

Image: COURTESY OF JOHANNES ELEMANS
STACK ATTACK: When a solution of a three-lobed compound [left] is allowed to dry, the molecules stack into long twisting columns [right] of up to a millimeter in length.

Macroscopic Hierarchical Surface Patterning of Porphyrin Trimers via Self-Assembly and Dewetting link to abstract

[sageb1]

OT question. Freepmail me if you wish. My daughter's mother-in-law has MS. She is a local guinea pig so to speak as she is taking some sort of chemotherapy. Do you have any info on this?

[timer]

Actually with the explosion in nano-technology, we're discovering alien technology, will we have the maturity and ethics to use it more wisely than they do, as kidnappers?

[neverdem]

ping

[Lokibob]

Are you saying the aliens are using nanotechnology in their anal probes? Nasty little buggers, arn't they?

[neverdem]

OT question. Freepmail me if you wish. My daughter's mother-in-law has MS. She is a local guinea pig so to speak as she is taking some sort of chemotherapy. Do you have any info on this?

I guess that means one time question. I'm just a family practice doc. MS is thought to be a disease with an immune system attacking its own body's myelin sheaths. Chemotherapy usually leaves a patient with a weakened immune system. Enter multiple sclerosis and chemotherapy into PubMed. I'd start with review articles.

High-Dose Immunosuppression and Autologous Transplantation for Multiple Sclerosis (HALT MS) Study

[Jedi Master Pikachu]

If they could expand the area, would this make laptops cheaper?

[aligncare]

In pre med biology, my professor tested us every week on three different articles from Scientific American. We were allowed to bring our notes on the articles in to the test, but not the articles themselves. There was still quite a high failure rate.

My point is Scientific American is terrifically difficult...but I learned more about mutations in RNA viruses in that one bio class than I learned in all of med school.

[AntiGuv]

FutureTechPing!

An emergent technologies list covering biomedical research, fusion power, nanotech, AI robotics, and other related fields. FReepmail to join or drop.

[Wonder Warthog]

http://www.nanosolar.com/

These guys say they are doing the same thing, but on a scale a LOT bigger than a few square millimeters.

[sageb1]

OT is off-topic. I didn't want to hijack the thread, but was thinking about the MS when you posted and thought I'd ask you about it. Thanks for the links.

[Kenny Bunk]

Ping

[indthkr]

nanotech ping for later............

[timer]

Anal probes : been there, done that : gorged on popcorn once : guts hurt like hell : drink this barium-milk stuff and fast tomorrow morning : do x-ray and rectal probe : nothing wrong : bottom line : don't gorge popcorn as too many kernals will scrape your guts...sore! So are aliens checking for popcorn-gut-scrapes with nano-probes?