Mobile phones come alive with the sound of music

Working priciple of nanogenerator where the force is exerted in perpendicular to the growing direction of nanowire. (Photo credit: Wikipedia)

Working priciple of nanogenerator where the force is exerted in perpendicular to the growing direction of nanowire. (Photo credit: Wikipedia)

Charging mobile phones with sound, like chants from at football ground, could become a reality, according to a new collaboration between scientists from Queen Mary University of London and Nokia.

Last year, Dr Joe Briscoe and Dr Steve Dunn from QMUL’s School of Engineering and Materials Science found that playing pop and rock music improves the performance of solar cells, in research published with Imperial College London.

Developing this research further, Nokia worked with the QMUL team to create an energy-harvesting prototype (a nanogenerator) that could be used to charge a mobile phone using everyday background noise – such as traffic, music, and our own voices.

The team used the key properties of zinc oxide, a material that when squashed or stretched creates a voltage by converting energy from motion into electrical energy, in the form of nanorods.

The nanorods can be coated onto various surfaces in different locations making the energy harvesting quite versatile. When this surface is squashed or stretched, the nanorods then generate a high voltage.

The nanorods respond to vibration and movement created by everyday sound, such as our voices. Electrical contacts on both sides of the rods are then used to harvest the voltage to charge a phone.

In order to make it possible to produce these nanogenerators at scale, the scientists found innovative ways to cut costs in the production process.

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Let There Be Light: Chemists Develop Magnetically Responsive Liquid Crystals

Top: Scheme showing magnetic control over light transmittance in the novel liquid crystals. B is the alternating magnetic field. The polarized light is seen in yellow. The gray rods represent the polarizers. The magnetic field controls the orientation of the nanorods (seen in orange), which in turn affects the polarization of the light and, then, the amount of light that can pass through the polarizers. Bottom: Images show how a polarization-modulated pattern changes darkness/brightness by rotating the direction of the cross polarizers. The circles and background contain magnetic nanorods aligned at different orientations. Research by the Yin Lab at UC Riverside shows that by combining magnetic alignment and lithography processes, it is possible to create patterns of different polarizations in a thin composite film and control over the transmittance of light in particular areas. IMAGE CREDIT: YIN LAB, UC RIVERSIDE.

The discovery has applications in signage, posters, writing tablets, billboards and anti-counterfeit technology

Chemists at the University of California, Riverside have constructed liquid crystals with optical properties that can be instantly and reversibly controlled by an external magnetic field. The research paves the way for novel display applications relying on the instantaneous and contactless nature of magnetic manipulation—such as signage, posters, writing tablets, and billboards.

Commercially available liquid crystals, used in modern electronic displays, are composed of rod-like or plate-like molecules. When an electric field is applied, the molecules rotate and align themselves along the field direction, resulting in a rapid tuning of transmitted light.

“The liquid crystals we developed are essentially a liquid dispersion, a simple aqueous dispersion of magnetic nanorods,” said Yadong Yin, an associate professor ofchemistry, who led the research project. “We use magnetic nanorods in place of the commercial nonmagnetic rod-like molecules. Optically these magnetic rods work in a similar way to commercial rod-like molecules, with the added advantage of being able to respond rapidly to external magnetic fields.”

Yin explained that upon the application of a magnetic field, the nanorods spontaneously rotate and realign themselves parallel to the field direction, and influence the transmittance of polarized light.

“Prior attempts had been limited to materials with very limited magnetic responses,” Yin said. “We utilized our expertise in colloidal nanostructure synthesis to produce magnetite nanorods that can form liquid crystals and respond strongly to even very weak magnetic fields – even a fridge magnet can operate our liquid crystals.”

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Knowing whether food has spoiled without even opening the container

The green smart tag on the bottle above indicates that the product is no longer fresh. Credit: Chao Zhang, Ph.D.

A color-coded smart tag could tell consumers whether a carton of milk has turned sour or a can of green beans has spoiled without opening the containers, according to researchers.

The tag, which would appear on the packaging, also could be used to determine if medications and other perishable products were still active or fresh, they said.

This report on the color-changing food deterioration tags was presented today as part of the 247th National Meeting & Exposition of the American Chemical Society (ACS), the world’s largest scientific society. A new video, illustrating how the tag works, is available at http://www.youtube.com/watch?v=y-Fpj9bdht4.

The meeting, attended by thousands of scientists, features more than 10,000 reports on new advances in science and other topics. It is being held at the Dallas Convention Center and area hotels through Thursday.

“This tag, which has a gel-like consistency, is really inexpensive and safe, and can be widely programmed to mimic almost all ambient-temperature deterioration processes in foods,” said Chao Zhang, Ph.D., the lead researcher of the study. Use of the tags could potentially solve the problem of knowing how fresh packaged, perishable foods remain over time, he added. And a real advantage, Zhang said, is that even when manufacturers, grocery-store owners and consumers do not know if the food has been unduly exposed to higher temperatures, which could cause unexpected spoilage, “the tag still gives a reliable indication of the quality of the product.”

The tags, which are about the size of a kernel of corn, would appear in various color codes on packaging. “In our configuration, red, or reddish orange, would mean fresh,” explained Zhang, who is at Peking University in Beijing, China. “Over time, the tag changes its color to orange, yellow and later green, which indicates the food is spoiled.” The colors signify a range between 100 percent fresh and 100 percent spoiled. For example, if the label says that the product should remain fresh for 14 days under refrigeration, but the tag is now orange, it means that the product is only roughly half as fresh. In that case, the consumer would know the product is edible for only another seven days if kept refrigerated, he explained.

The researchers developed and tested the tags using E. coli (food-spoiling bacteria that cause gastrointestinal problems) in milk as a reference model. “We successfully synchronized, at multiple temperatures, the chemical evolution process in the smart tag with microbial growth processes in the milk,” according to Zhang. The tags could also be customized for a variety of other foods and beverages.

The tags contain tiny metallic nanorods that, at different stages and phases, can have a variety of colors: red, orange, yellow, green, blue and violet, Zhang explained. “The gold nanorods we used are inherently red, which dictates the initial tag color,” he said. “Silver chloride and vitamin C are also in the tags, reacting slowly and controllably. Over time, the metallic silver gradually deposits on each gold nanorod, forming a silver shell layer. That changes the particle’s chemical composition and shape, so the tag color now would be different. Therefore, as the silver layer thickens over time, the tag color evolves from the initial red to orange, yellow, and green, and even blue and violet.”

Although the nanorods are made of gold and silver, a tag would still be very inexpensive, and all the chemicals in the tiny tag cost much less than one cent — $0.002. “In addition, all of the reagents in the tags are nontoxic, and some of them (such as vitamin C, acetic acid, lactic acid and agar) are even edible,” he explained.

This technique has been patented in China, and some preliminary results have been published in ACS Nano, Zhang said. He added that the next step is to contact manufacturers and explain how the tag would be useful for them and their customers.

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Shining a little light changes metal into semiconductor

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By blending their expertise, two materials science engineers at Washington University in St. Louis changed the electronic properties of a new class of materials — just by exposing it to light.

With funding from the Washington University International Center for Advanced Renewable Energy and Sustainability (I-CARES), Parag Banerjee, PhD, and Srikanth Singamaneni, PhD, both assistant professors of materials science, brought together their respective areas of research.

Singamaneni’s area of expertise is in making tiny, pebble-like nanoparticles, particularly gold nanorods. Banerjee’s area of expertise is making thin films. They wanted to see how the properties of both materials would change when combined.

The research was published online in August in ACS Applied Materials & Interfaces

The research team took the gold nanorods and put a very thin blanket of zinc oxide, a common ingredient in sunscreen, on top to create a composite. When they turned on light, they noticed that the composite had changed from one with metallic properties into a semiconductor, a material that partly conducts current. Semiconductors are commonly made of silicon and are used in computers and nearly all electronic devices.

“We call it metal-to-semiconductor switching,” Banerjee said. “This is a very exciting result because it can lead to opportunities in different kinds of sensors and devices.”

Banjeree said when the metallic gold nanorods are exposed to light, the electrons inside the gold get excited and enter the zinc oxide film, which is a semiconductor. When the zinc oxide gets these new electrons, it starts to conduct electricity.

“We found out that the thinner the film, the better the response,” he said. “The thicker the film, the response goes away. How thin? About 10 nanometers, or a 10 billionth of a meter.”

Other researchers working with solar cells or photovoltaic devices have noticed an improvement in performance when these two materials are combined; however, until now, none have broken it down to discover how it happens, Banerjee said.

“If we start understanding the mechanism for charge conduction, we can start thinking about applications,” he said. “We think there are opportunities to make very sensitive sensors, such as an electronic eye. We are now looking to see if there is a different response when we shine a red, blue or green light on this material.”

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Laser-Controlled Molecular Switch Turns Blood Clotting On, Off On Command

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Researchers have designed tiny, light-controlled gold particles that can release DNA controls to switch blood clotting off and on.

The results are reported July 24 in the open access journal PLOS ONE by Kimberly Hamad-Schifferli and colleagues from the Massachusetts Institute of Technology.

The two-way switch for blood clotting relies on the ability of two gold nanoparticles to selectively release different DNA molecules from their surface under different wavelengths of laser excitation. When stimulated by one wavelength, one nanorod releases a piece of DNA that binds the blood protein thrombin and blocks clot formation. When the complementary DNA piece is released from the other nanorod, it acts as an antidote and releases thrombin, restoring clotting activity.

Natural blood clotting is precisely synchronized to occur at the right time and place. Wound healing, surgery and other conditions require manipulation of this process, typically through the use of anticoagulants like heparin or warfarin. However, these drugs are inherently one-sided as they can only block clotting, and reversing their effects depends on removing them from the bloodstream.

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