DNA cages 'can survive inside living cells'

DNA cages 'can survive inside living cells'

  5:07:00 PM    Science Lover

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Scientists at Oxford University have shown for the first time that molecular cages made from DNA can enter and survive inside living cells.

Human embryonic kidney cells were used to test the DNA cages

The work, a collaboration between physicists and molecular neuroscientists at Oxford, shows that artificial DNA cages that could be used to carry cargoes of drugs can enter living cells, potentially leading to new methods of drug delivery.

A report of the research is published online in the journal ACS Nano.

The cages developed by the researchers are made from four short strands of synthetic DNA. These strands are designed so that they naturally assemble themselves into a tetrahedron (a pyramid with four triangular faces) around 7 nanometres tall.

The Oxford researchers have previously shown that it is possible to assemble these cages around protein molecules, so that the protein is trapped inside, and that DNA cages can be programmed to open when they encounter specific ‘trigger’ molecules that are found inside cells.



In the new experiment they introduced fluorescently-labelled DNA tetrahedrons into human kidney cells grown in the laboratory. They then examined the cells under the microscope and found that the cages remained substantially intact, surviving attack by cellular enzymes, for at least 48 hours. This is a crucial advance: to be useful as a drug delivery vehicle, a DNA cage must enter cells efficiently and survive until it can release its cargo where and when it is needed.

‘At the moment we are only testing our ability to create and control cages made of DNA,’ said Professor Andrew Turberfield of Oxford University’s Department of Physics, who led the work. ‘However, these results are an important first step towards proving that DNA cages could be used to deliver cargoes, such as drugs, inside living cells.’

Professor Turberfield said: ‘Previous studies have shown that the size of particles is an important factor in whether or not they can easily enter cells, with particles with a radius less than 50 nanometres proving much more successful at gaining entry than larger particles. At 7 nanometres across our DNA tetrahedrons are compact enough to easily enter cells but still large enough to carry a useful cargo. More work is now needed to understand exactly how these DNA cages manage to find their way inside living cells.’
Provided by Oxford University

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Novel Nanowires Boost Fuel Cell Efficiency

Novel Nanowires Boost Fuel Cell Efficiency

  12:26:00 AM    Science Lover

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Fuel cells have been touted as a cleaner solution to tomorrow's energy needs, with potential applications in everything from cars to computers.

Taylor and Schroers engineered nanowires out of a novel material called bulk metallic glass in order to make fuel cell catalyst systems more durable and efficient. (Credit: Golden Kumar and Miriam Schroers)

But one reason fuel cells aren't already more widespread is their lack of endurance. Over time, the catalysts used even in today's state-of-the-art fuels cells break down, inhibiting the chemical reaction that converts fuel into electricity. In addition, current technology relies on small particles coated with the catalyst; however, the particles' limited surface area means only a fraction of the catalyst is available at any given time.

Now a team of engineers at the Yale School of Engineering & Applied Science has created a new fuel cell catalyst system using nanowires made of a novel material that boosts long-term performance by 2.4 times compared to today's technology. Their findings appear on the cover of the April issue of ACS Nano.

Yale engineers Jan Schroers and André Taylor have developed miniscule nanowires made of an innovative metal alloy known as a bulk metallic glass (BMG) that have high surface areas, thereby exposing more of the catalyst. They also maintain their activity longer than traditional fuel cell catalyst systems.

Current fuel cell technology uses carbon black, an inexpensive and electrically conductive carbon material, as a support for platinum particles. The carbon transports electricity, while the platinum is the catalyst that drives the production of electricity. The more platinum particles the fuel is exposed to, the more electricity is produced. Yet carbon black is porous, so the platinum inside the inner pores may not be exposed. Carbon black also tends to corrode over time.

"In order to produce more efficient fuel cells, you want to increase the active surface area of the catalyst, and you want your catalyst to last," Taylor said.

At 13 nanometers in scale (about 1/10,000 the width of a human hair), the BMG nanowires that Schroers and Taylor developed are about three times smaller than carbon black particles. The nanowires' long, thin shape gives them much more active surface area per mass compared to carbon black. In addition, rather than sticking platinum particles onto a support material, the Yale team incorporated the platinum into the nanowire alloy itself, ensuring that it continues to react with the fuel over time.

It's the nanowires' unique chemical composition that makes it possible to shape them into such small rods using a hot-press method, said Schroers, who has developed other BMG alloys that can also be blow molded into complicated shapes. The BMG nanowires also conduct electricity better than carbon black and carbon nanotubes, and are less expensive to process.

So far Taylor has tested their catalyst system for alcohol-based fuel cells (including those that use ethanol and methanol as fuel sources), but they say the system could be used in other types of fuel cells and could one day be used in portable electronic devices such as laptop computers and cell phones as well as in remote sensors.

"This is the introduction of a new class of materials that can be used as electrocatalysts," Taylor said. "It's a real step toward making fuel cells commercially viable and, ultimately, supplementing or replacing batteries in electronic devices."

Other authors of the paper include Marcelo Carmo, Ryan C. Sekol, Shiyan Ding and Golden Kumar (all of Yale University).

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Smaller Particles Could Make Solar Panels More Efficient

Smaller Particles Could Make Solar Panels More Efficient

  1:24:00 AM    Science Lover

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Studies done by Mark Lusk and colleagues at the Colorado School of Mines could significantly improve the efficiency of solar cells. Their latest work describes how the size of light-absorbing particles--quantum dots--affects the particles' ability to transfer energy to electrons to generate electricity.

Illustration of multiple-exciton generation (MEG), a 
theory that suggests it is possible for an electron that has 
absorbed light energy, called an exciton, to transfer that 
energy to more than one electron, resulting in more electricity 
from the same amount of absorbed light. The left side shows an 
electron promoted to a high energy state (blue) plus the "hole" 
vacated by the electron (red). The right side shows the original 
exciton (now dark green/red) and a new exciton (light green
 /orange) after MEG. The top image shows a conceptualized 
version of the idea, while the bottom shows an actual exciton 
and bi-exciton using the same color scheme. (Credit: Mark 
T. Lusk, Department of Physics, Colorado School of Mines)

The results are published in the April issue of the journal ACS Nano.
 
The advance provides evidence to support a controversial idea, called multiple-exciton generation (MEG), which theorizes that it is possible for an electron that has absorbed light energy, called an exciton, to transfer that energy to more than one electron, resulting in more electricity from the same amount of absorbed light.

Quantum dots are human-made atoms that confine electrons to a small space. They have atomic-like behavior that results in unusual electronic properties on a nanoscale. These unique properties may be particularly valuable in tailoring the way light interacts with matter.

Experimental verification of the link between MEG and quantum dot size is a hot topic due to a large degree of variation in previously published studies. The ability to generate an electrical current following MEG is now receiving a great deal of attention because this will be a necessary component of any commercial realization of MEG.

For this study, Lusk and collaborators used a National Science Foundation (NSF)-supported high performance computer cluster to quantify the relationship between the rate of MEG and quantum dot size.

They found that each dot has a slice of the solar spectrum for which it is best suited to perform MEG and that smaller dots carry out MEG for their slice more efficiently than larger dots. This implies that solar cells made of quantum dots specifically tuned to the solar spectrum would be much more efficient than solar cells made of material that is not fabricated with quantum dots.


According to Lusk, "We can now design nanostructured materials that generate more than one exciton from a single photon of light, putting to good use a large portion of the energy that would otherwise just heat up a solar cell."

The research team, which includes participation from the National Renewable Energy Laboratory, is part of the NSF-funded Renewable Energy Materials Research Science and Engineering Center at the Colorado School of Mines in Golden, Colo. The center focuses on materials and innovations that will significantly impact renewable energy technologies. Harnessing the unique properties of nanostructured materials to enhance the performance of solar panels is an area of particular interest to the center.

"These results are exciting because they go far towards resolving a long-standing debate within the field," said Mary Galvin, a program director for the Division of Materials Research at NSF. "Equally important, they will contribute to establishment of new design techniques that can be used to make more efficient solar cells."

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