Nanohands, Fully Controlled Janus Particles and Cell sized Assembly Line


Duke University engineers say they can for the first time control all the degrees of the particle’s motion, opening up broad possibilities for nanotechnology and device applications. Their unique technology should make it more likely that Janus particles can be used as the building blocks for a myriad of applications, including such new technologies as electronic paper and self-propelling micromachines. The researchers have dubbed the unique particles they created “dot-Janus” particles. It may also be possible to control the behavior of cells by manipulating dot-Janus particles attached to cell surfaces. [This will go well with the next item in this article of assembly lines for producing cell sized lipid microspheres.

Using optical traps on dot-Janus particles, researchers controlled three degrees of movement – up and down, left and right, forward and backward, while constraining one degree of rotation – side-to-side tilting. Using magnetic fields, they controlled the remaining two degrees of rotation – forward and backward tilting, and left and right turning. The solution was to create a particle with a small cap of cobalt that covers about a quarter of the particle. This gave the particle just enough of a magnetic handle to allow it to be manipulated by magnetism without interfering with the optical tweezers.

Duke engineers was to devise a fabrication strategy to coat the particle with a much smaller fraction of material. This discovery allows these particles to be compatible with optical traps and external magnetic fields, allowing for total control over the particles’ positions and orientations.

“Past experiments have only been able to achieve four degrees of control using a combination of magnetic and optical techniques,” said Nathan Jenness, a graduate student who completed his studies this year from Duke’s Pratt School of Engineering. He and co-author Randall Erb, also a graduate student, were first authors of a paper appearing online in the journal Advanced Materials. “We have created a novel Janus particle that can be manipulated or constrained with six degrees of freedom.”

2. A production line for uniform lipid-coated microspheres has been created by Japanese scientists.

The team’s high-throughout production method uses a microfluidic device consisting of a main channel lined with small chambers. To prepare the device, it is first filled with an aqueous solution containing the material that will make up the vesicles’ contents. Oil is then flowed through the device’s main channel. This washes the aqueous solution out of the channel, trapping the water in the chambers where a monolayer forms at the interface of the oil and water. The aqueous solution then re-enters the main channel, replacing the oil and pushing some of it down into the top of each of the chambers. A layer of lipid forms here, squashed between the two aqueous layers, with a monolayer at both the ‘water’-oil interfaces.

Next, a continuous stream of another aqueous solution is pushed through the main channel, and a gentle flow of the original aqueous solution allowed to enter from bottom of each of the chambers. The flow across the chamber entrance combined with the gentle flow upwards from bottom of the chamber causes the lipid layer to thin out, and the two monolayers to form one bilayer. The shear force combined with the upwards flow of aqueous solution means the lipid bilayer is pulled/pushed up into the fast flowing stream of aqueous solution in the device’s main channel. The shear force of the flow on the deformed bilayer eventually leads to a vesicle being pulled off from the leading edge of the bilayer. This process then continues, releasing ‘perfectly’ sized and shaped vesicles at regular intervals

2. EU-funded NanoHand project uses mobile microrobots equipped with delicate handling tools. NanoHand builds on the work of ROBOSEM, an earlier EU project that developed the basic technologies that are now being put into effect. The robots, about two centimetres in size, work inside a scanning electron microscope where their activities can be followed by an observer. Each robot has a ‘microgripper’ that can make precise and delicate movements. It works on an electrothermal principle to open and close the jaws, much like a pair of tweezers.
The jaws open to about 2 micrometres and can pick up objects less than 100 nanometres in size. “[It is] really able to grip micro or even nano objects,” Eichhorn says. “We have handled objects down to tens of nanometres.”

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