Silicon retina mimics biology for a clearer view

20 October 2006
NewScientist.com news service
Tom Simonite

A silicon chip that faithfully mimics the neural circuitry of a real retina could lead to better bionic eyes for those with vision loss, researchers claim.

About 700,000 people in the developed world are diagnosed with age-related macular degeneration each year, and 1.5 million people worldwide suffer from a disease called retinitis pigmentosa. In both of these diseases, retinal cells, which convert light into nerve impulses at the back of the eye, gradually die.

Most artificial retinas connect an external camera to an implant behind the eye via a computer (see 'Bionic' eye may help reverse blindness). The new silicon chip created by Kareem Zaghloul at the University of Pennsylvania, US, and colleague Kwabena Boahen at Stanford University, also in the US, could remove the need for a camera and external computer altogether.

The circuit was built with the mammalian retina as its blueprint. The chip contains light sensors and circuitry that functions in much the same way as nerves in a real retina – they automatically filter the mass of visual data collected by the eye to leave only what the brain uses to build a picture of the world.
Fully implanted

"It has potential as a neuroprosthetic that can be fully implanted," Zaghloul told New Scientist. The chip could be embedded directly into the eye and connected to the nerves that carry signals to the brain's visual cortex.

To make the chip, the team first created a model of how light-sensitive neurons and other nerve cells in the retina connect to process light. They made a silicon version using manufacturing techniques already employed in the computer chip industry.

Their chip measures 3.5 x 3.3 millimetres and contains 5760 silicon phototransistors, which take the place of light-sensitive neurons in a living retina. These are connected up to 3600 transistors, which mimic the nerve cells that process light information and pass it on to the brain for higher processing. There are 13 different types of transistor, each with slightly different performance, mimicking different types of actual nerve cells.

"It does a good job with some of the functions a real retina performs," says Zaghloul. For example, the retina chip is able to automatically adjust to variations in light intensity and contrast. More impressively, says Patrick Deganeer, a neurobionics expert at Imperial College London, UK, it also deals with movement in the same way as a living retina.
Changing scene

The mammalian brain only receives new information from the eyes when something in a scene changes. This cuts down on the volume of information sent to the brain but is enough for it to work out what is happening in the world.

The retina chip performs in the same way. The lowest image (right) shows how this allows it to extract useful data from a moving face.

As well as having the potential to help humans with damaged vision, future versions of the retina chip could help robots too, adds Deganeer. "If you can perform more processing in hardware at the front end you reduce demand on your main processor, and could cut power consumption a lot," he explains.

Zaghloul and Boahen are currently concentrating on reducing the size and power consumption of the retina chip before considering clinical trials.

Journal reference: Journal of Neural Engineering (vol 3, p 257)

Clever cars shine at intelligent transport conference

13:39 11 October 2006
NewScientist.com news service
Tom Simonite

Smart vehicles capable of following the flow of traffic, parking themselves and even warning drowsy or distracted drivers to pay attention to the road are among the highlights of the Transport Systems World Congress, which takes place this London, UK, this week.

One of the recurring themes of the show is vehicle intelligence, and the inventions on display range from unfinished prototypes to models already on the market in Japan.

A prototype system developed by German company Ibeo enables a car to automatically follow the vehicle ahead. At the press of a button an infrared laser scanner in the car's bumper measures the distance to the next vehicle and a computer maintains a safe distance, stopping and starting if it becomes stuck in traffic.

The scanner can track stationary and moving objects from up to 200 metres away at speeds of up to 180 kilometres (112 miles) per hour. "It gives a very precise image of what's going on," Max Mandt-Merck of Ibeo told New Scientist.

"Our software can distinguish cars and pedestrians from the distinctive shapes the scanner detects." A video shows the information collected by the scanner (2.1MB, mov format).
Airbag activation

Mandt-Merck says the scanner can also be used to warn a driver when they stray out of lane or try to overtake too close to another vehicle. It could even activate airbags 0.3 seconds before an impact, he says.

Other systems at the show aim to prevent accidents altogether, by alerting drivers when they become distracted. A video shows one that sounds an audible alarm and vibrates the driver's seat when their head turns away from the road ahead (1.91MB WMV format). "There's an infrared camera just behind the steering wheel," explains Kato Kazuya, from Japanese automotive company Aisin. "It detects the face turning by tracking its bilateral symmetry."

A video shows another system, developed by Japanese company DENSO Corporation, that uses an infrared camera to determine whether a driver is becoming drowsy (2.75MB WMV format). "It recognises the shape of your eyes and tracks the height of that shape to watch if they close," explains Takuhiro Oomi. If a driver shuts their eyes for more than a few seconds their seat vibrates and a cold draught hits their neck.
Gaze following

The same camera system could offer other functions, Oomi says. "It can also allow the headlight beams to follow your gaze, or recognise the face of a driver and adjust the seat to their saved preferences," he says.

In the car park outside the conference centre Toyota demonstrated an intelligent parking system. A video shows the system prompting a driver to identify their chosen parking spot, which is identified using ultrasonic sensors (9.8MB, WMV format).

Once the space has been selected, the wheel turns automatically and the driver needs only to limit the car's speed using the brake pedal. When reversing into a parking bay, a camera at rear of the car is used to recognise white lines on the tarmac.

The system needs 7 metres of space for parallel parking, but can fit into a regular parking bay with just 30 centimetres clearance on either side.

"Future developments will probably see a system that lets you get out and leave the car to park itself," says a Toyota spokesman. The intelligent parking system has been available on some Toyota models in Japan since November 2005 and will be available in Europe and the US from January 2007.

Space elevators to heave themselves skyward

20:07 16 October 2006
NewScientist.com news service
Kelly Young

A few early prototypes for space elevators will try to get off the ground at a competition at the Wirefly X Prize Cup in Las Cruces, New Mexico, US, on 20 and 21 October.

The hope is that one day a space elevator, comprised of a robot that will climb a strong tether about 100,000 kilometres (60,000 miles) long, will be able to send humans or other cargo cheaply into space.

To spur the development of that technology, NASA set up two annual competitions, called the Power Beaming and Tether Challenges. The first competitions were held in 2005 – but no one won either of them (see Space elevators stuck on the first floor).

In the Beam Power Challenge, teams have to send a robotic climber up a crane-mounted tether at a minimum speed of 1 metre per second. The climbers will be judged by their speed and weight, with the top three teams taking home $150,000, $40,000 and $10,000, respectively.

The catch is they cannot be powered by fuel, batteries or an electrical extension cord because a real space elevator could not carry these things on a trip into space. So the robotic climbers must use solar arrays powered by light sent from the Sun, solar reflectors, a spotlight, lasers or microwaves.

A dozen teams will compete in the climber challenge. About six to eight teams may have hardware that could climb all the way to the top, says Ben Shelef, co-founder of the Spaceward Foundation, a space advocacy group in Mountain View, California, US, which administers the competition. Two to three of those could nab the prize money.
Laser source

In 2005, teams had to use a spotlight that was provided for the competition. This year, they can bring their own power source.

A Canadian team from the University of Saskatchewan, which climbed to a record 12 metres (40 feet) in last year's competition, says it is developing a laser power source for its climber.

The laser will probably not be ready in time for the competition, so the team will rely on a powerful search light instead. The spotlight may be cheaper in the short term, but in the long term, using energy beamed from a laser may be a more efficient way to move a space elevator, it says.

If they had been able to use a laser this year, they had planned to climb 61 metres (200 feet), to the top of the tether. Now, they believe they may only reach half that height. "We're kind of thinking we might not be ready this year," admits team president Clayton Ruszkowski. "I'm hoping for 100 feet."

Steve Jones, captain of a team from the University of British Columbia in Canada, says his team's climber is light enough that it does not need a concentrated beam source, like a laser. Instead, it can run on either the Sun or a spotlight.

"We're pretty sure we can win with either," Jones told New Scientist. Indeed, his team was voted most likely to win in 2006.
Breaking point

The related Tether Challenge aims to spark the development of lightweight materials strong enough to stretch 100,000 kilometres into space without breaking. Space elevator proponents believe a thin rope of carbon nanotubes will ultimately be needed for the task.

For the challenge, 2-metre-long tethers are wrapped in loops and stretched to the breaking point. The tether cannot weigh more than 2 grams and must carry 50% more weight before breaking than the best tether from the previous year.

Three teams will test their tethers' strength this year, including a group from the University of British Columbia. This year, they are using a tether made of Zylon fibres, which were once used in bulletproof vests.

The competitions will be held annually until 2010, so even if no one wins them this year, either, the competitors can try again: "We're definitely just going to keep going and see what we can do for next year," Jones says.

A boost for solar cells with photon fusion

Researchers at the Max Planck Institute for Polymer Research in Mainz have developed a process with which longwave light from a normal light source can be converted to shortwave light.

An innovative process that converts low-energy longwave photons (light particles) into higher-energy shortwave photons has been developed by a team of researchers at the Max Planck Institute for Polymer Research in Mainz and at the Sony Materials Science Laboratory in Stuttgart. With the skillful combination of two light-active substances, the scientists have, for the first time, manipulated normal light, such as sunlight, to combine the energy in photons with particular wavelengths (Physical Review Letters, October 4, 2006). This has previously only been achieved with a similar process using high-energy density laser light. The successful outcome of this process could lay the foundation for a new generation of more efficient solar cells. Fig. 1: Experiment to show the changes in the wavelength. The green light directed into the solution reappears as blue light after it has been converted. Image: Max Planck Institute for Polymer Research The efficiency of solar cells today is limited, among other reasons, by the fact that the longwave, low-energy part of the sunlight cannot be used. A process that increases the low level of energy in the light particles (photons) in the longwave range, shortening their wave length, would make it possible for the solar cells to use those parts of light energy that, up to now, have been lost, resulting in a drastic increase in their efficiency. The equivalent has only been achieved previously with high-energy density laser light which, under certain conditions, combines two low-energy photons into one high-energy photon - a kind of photonic fusion. This is a significant step forward for the scientists at the Max Planck Institute for Polymer Research and at the Sony Materials Science Laboratory. In developing this process, they have succeeded, for the first time, in pairing up photons from normal light, thus altering the wavelength. They used two substances in solution, platinum octaethyl porphyrin and diphenylan-thracene, which converted the longwave green light from a normal light source into shortwave blue light. Similar to the process in laser light, this also pairs up photons, but in a different way. When a molecule is manipulated by laser light to take up two photons, which is only probable if it is literally bombarded with a laser beam of photons, the molecules in this case only receive one photon. Two photon partners are brought together between the molecules via a different mechanism called triplet-triplet annihilation. By selecting different, corresponding "matchmaker" molecules, it is possible to combine the energy from photons from the entire sunlight spectrum. The two substances developed by the researchers as "photon matchmakers" have quite different properties. Whereas one serves as an "antenna" for green light (antenna molecule), the other pairs the photons, connecting the two low-energy green photons into one high-energy blue photon, which it transmits as an emitter (emitter molecule). This is what happens in detail: first the antenna molecule absorbs a green low-energy photon and passes it to the emitter molecule as a package of energy. Both molecules store the energy one after the other in "excited" states. Then, two of the energy-loaded emitter molecules react with each other - one molecule passes its energy package to the other. This returns one molecule to its low-energy state. The other, conversely, achieves a very high-energy state that stores the double energy package. This state rapidly collapses when the large energy package is sent out in the form of a blue photon. Although this light particle is of a shorter wave length and higher in energy than the green light emitted initially, the end effect is that no energy is generated, but the energy from two photons is combined into one. Fig. 2: Schematic representation of the energy transfers. The antenna molecule (green with red platinum) receives the green photons (hv = light energy) and transfers them to the emitter molecule (blue). Subsequently, a blue photon is emitted. Image: Max Planck Institute for Polymer Research The process is very interesting in chemical terms as the molecules must be carefully matched to allow the energy to be transmitted efficiently, and neither the antenna nor the emitter molecules are allowed to lose their energy through shortcuts. The researchers therefore had to synthesize an antenna molecule that absorbed longwave light and store it for so long that the energy could be transferred to an emitter. Only a complex metal organic compound with a platinum atom in a ring-shaped molecule was suitable for this purpose. The emitter molecule, on the other hand, must be able to take the energy package from the antenna and hold on to it until another excited emitter molecule is found for the subsequent photon fusion. As this procedure allows previously unused parts of sunlight to be used in solar cells, the scientists are hoping that it offers the ideal starting point for more efficient solar cells. To optimize the process and to bring it closer to an application, they are testing new pairs of substances for other colors in the light spectrum and are experimenting with integrating them in a polymer matrix. Original work: S. Balouchev, T. Miteva, V. Yakutkin, G. Nelles, A. Yasuda, and G. Wegner Up-Conversion Fluorescence: Noncoherent Ex-citation by Sunlight Physical Review Letters, October 4, 2006 (online)

MIT material stops bleeding in seconds

Work could significantly impact medicine

CAMBRIDGE, Mass.--MIT and Hong Kong University researchers have shown that some simple biodegradable liquids can stop bleeding in wounded rodents within seconds, a development that could significantly impact medicine.
When the liquid, composed of protein fragments called peptides, is applied to open wounds, the peptides self-assemble into a nanoscale protective barrier gel that seals the wound and halts bleeding. Once the injury heals, the nontoxic gel is broken down into molecules that cells can use as building blocks for tissue repair.
"We have found a way to stop bleeding, in less than 15 seconds, that could revolutionize bleeding control," said Rutledge Ellis-Behnke, research scientist in the MIT Department of Brain and Cognitive Sciences.
This study will appear in the online edition of the journal Nanomedicine on Oct. 10 at http://www.nanomedjournal.com/inpress. It marks the first time that nanotechnology has been used to achieve complete hemostasis, the process of halting bleeding from a damaged blood vessel.
Doctors currently have few effective methods to stop bleeding without causing other damage. More than 57 million Americans undergo nonelective surgery each year, and as much as 50 percent of surgical time is spent working to control bleeding. Current tools used to stop bleeding include clamps, pressure, cauterization, vasoconstriction and sponges.
In their experiments on hamsters and rats, the MIT and HKU researchers applied the clear liquid containing short peptides to open wounds in several different types of tissue - brain, liver, skin, spinal cord and intestine.
"In almost every one of the cases, we were able to immediately stop the bleeding," said Ellis-Behnke, the lead author of the study.
Earlier this year, the same researchers reported that a similar liquid was able to partially restore sight in hamsters that had had their visual tract severed. In that case, the self-assembling peptides served as an internal matrix on which brain cells could regrow.
While experimenting with the liquid during brain surgery, the researchers discovered that some of the peptides could also stop bleeding, Ellis-Behnke said. He foresees that the material could be of great use during surgery, especially surgery that is done in a messy environment such as a battlefield. A fast and reliable way to stop bleeding during surgery would allow surgeons better access and better visibility during the operation.
"The time to perform an operation could potentially be reduced by up to 50 percent," said Ellis-Behnke.
Unlike some methods now used for hemostasis, the new materials can be used in a wet environment. And unlike some other agents, it does not induce an immune response in the animals being treated.
When the solution containing the peptides is applied to bleeding wounds, the peptides self-assemble into a gel that essentially seals over the wound, without harming the nearby cells. Even after excess gel is removed, the wound remains sealed. The gel eventually breaks down into amino acids, the building blocks for proteins, which can be used by surrounding cells.
The exact mechanism of the solutions' action is still unknown, but the researchers believe the peptides interact with the extracellular matrix surrounding the cells. "It is a completely new way to stop bleeding; whether it produces a physical barrier is unclear at this time," Ellis-Behnke said.
The researchers are confident, however, that the material does not work by inducing blood clotting. Clotting generally takes at least 90 seconds to start, and the researchers found no platelet aggregation, a telltale sign of clotting.
Other MIT researchers who are co-authors on the paper are Gerald Schneider, professor of brain and cognitive sciences, and Shuguang Zhang, associate director of MIT's Center for Biomedical Engineering. Collaborators at the University of Hong Kong Li Ka Shing Faculty of Medicine, Department of Anatomy, include Yu-Xiang Liang, David Tay, Wutian Wu, Phillis Kau and Kwok-Fai So, an MIT alumnus.

First quantum teleportation between light and matter

The concept of quantum teleportation - the disembodied complete transfer of the state of a quantum system to any other place - was first experimentally realised between two different light beams. Later it became also possible to transfer the properties of a stored ion to another object of the same kind. A team of scientist headed by Prof. Ignacio Cirac at MPQ and by Prof. Eugene Polzik at Niels Bohr Institute in Copenhagen has now shown that the quantum states of a light pulse can also be transferred to a macroscopic object, an ensemble of 10 to the power of 12 atoms (Nature, 4 October 2006).

This is the first case of successful teleportation between objects of a different nature - the ones representing a "flying" medium (light), the other a "stationary" medium (atoms). The result presented here is of interest not only for fundamental research, but also primarily for practical application in realising quantum computers or transmitting coded data (quantum cryptography).

Since the beginning of the nineties research into quantum teleportation has been booming with theoretical and experimental physicists. Transmission of quantum information involves a fundamental problem: According to Heisenberg's uncertainty principle two complementary properties of a quantum particle, e.g. location and momentum cannot be precisely measured simultaneously. The entire information of the system thus has to be transmitted without being completely known. But the nature of the particles also carries with it the solution to this problem: the possibility of "entangling" two particles in such a way that their properties become perfectly correlated. If a certain property is measured in one of the "twin" particles, this determines the corresponding property of the other automatically and with immediate effect.

With the help of entangled particles, successful teleportation can be achieved roughly as follows: An auxiliary pair of entangled particles is created, the one being transmitted to "Alice" and the other to "Bob". (The names "Alice" and "Bob" have been adopted to describe the transmission of quantum information from A to B.) Alice now entangles the object of teleportation with her auxiliary particle and then measures the joint state (Bell measurement). She sends the result to Bob in the classical manner. He applies it to his auxiliary particle and "conjures up" the teleportation object from it.

Are "such "instructions for use" merely mental games? The great challenge to theoretical physicists is to devise concepts which can also be put into practice. The experiment described here has been conducted by a research team headed by Prof. Eugene Polzik at Niels Bohr Institute in Copenhagen. It follows a proposal made by Prof. Ignacio Cirac, Managing Director at MPQ, and his collaborator Dr. Klemens Hammerer (also at MPQ at that time, now at University of Innsbruck, Austria).

First the twin pair is produced by sending a strong light pulse to a glass tube filled with caesium gas (about 1012 atoms). The magnetic moments of the gas atoms are aligned in a homogenous magnetic field. The light also has a preferential direction: It is polarised, i.e. the electric field oscillates in just one direction. Under theses conditions the light and the atoms are made to interact with one another so that the light pulse emerging from the gas that is sent to Alice is "entangled" with the ensemble of 10 to the power of 12 caesium atoms located at Bob's site.

Alice mixes the arriving pulse by means of a beam splitter with the object that she wants to teleport: a weak light pulse containing very few photons. The light pulses issuing at the two outputs of the beam splitter are measured with photo-detectors and the results are sent to Bob.

The measured results tell Bob what has to be done to complete teleportation and transfer the selected quantum states of the light pulse, amplitude and phase, onto the atomic ensemble. For this purpose he applies a low-frequency magnetic field that makes the collective spin (angular momentum) of the system oscillate. This process can be compared with the precession of a spinning top about its major axis: the deflection of the spinning top corresponds to the amplitude of the light, while the zero passage corresponds to the phase.

To prove that quantum teleportation has been successfully performed, a second intense pulse of polarised light is sent to the atomic ensemble after 0.1 milliseconds and, so to speak, "reads out" its state. From these measured values theoretical physicists can calculate the so-called fidelity, a quality-factor specifying how well the state of the teleported object agrees with the original. (A fidelity of 1 is equivalent to a perfect agreement, while the value zero indicates that there has been no transfer at all.) In the present experiment the fidelity is 0.6, this being well above the value of 0.5 that would at best be achieved by classical means, e.g. by communicating measured values by telephone, without the help of entangled particle-pairs.

Unlike the customary conception of "beaming", it is not a matter here of a particle disappearing from one place and re-appearing in another. "Quantum teleportation constitutes methods of communication for application in quantum cryptography, the decoding of data, and not new kinds of transportation", as Dr. Klemens Hammerer emphasizes. "The importance of the experiment is that it is now possible for the first time to achieve teleportation between stationary atoms, which can store quantum states, and light, which is needed to transmit information over great distances. This marks an important step towards accomplishing quantum cryptography, i.e. absolutely safe communication over long distances, such as between Munich and Copenhagen."

Citation: Jacob F. Sherson, Hanna Krauter, Rasmus K. Olsson, Brian Julsgaard, Klemens Hammerer, Ignacio Cirac and Eugene S. Polzik Quantum teleportation between light and matter Nature 443, 557-560(5 October 2006).

Source: Max Planck Institute of Quantum Optics




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Archon X PRIZE for Genomics

On October 4, 2006, the X PRIZE Foundation announced the launch of its second prize — the Archon X PRIZE for Genomics. The $10 million cash prize has been created to revolutionize the medical world. The launch was attended by visionaries and entrepreneurs from around the globe who recognize the significance and impact that the Archon X PRIZE for Genomics will have on the fields of medicine and research.

Intelligent Nanoscale Bioreactors for Drug Delivery

In a powerful demonstration of how to build a multifunctional, smart nanoscale drug delivery system, researchers at the University of Basel have created a drug-loaded nanocontainer that targets specific cells and releases its payload when receiving a specific physiological signal.

These smart nanocontainers can serve as a model for creating anticancer drug delivery vehicles that will target tumors and release their contents only when they receive a tumor-specific biochemical signal.

Writing in the journal Nano Letters, a group of investigators led by Patrick Hunziker, M.D., describe its development of a polymer nanoparticle that incorporates a biological receptor in its outer shell and a biological effector inside the cell. This receptor and effector duo provides the means of detecting a specific biochemical signal that then has an effect on the nanocontainer and its contents. That effect can include drug release or the generation of a diagnostic signal.

In the proof-of-concept experiments described in their paper, the investigators used a bacterial pore protein that can transport a specific non-fluorescent molecule into the nanocontainer.

Once inside the nanocontainer, this molecule then serves as a substrate for an enzyme loaded into the nanocontainer, producing a fluorescent molecule that can be seen using fluorescence microscopy. The researchers used the appearance of a fluorescent signal as proof that their smart nanocontainer was functioning as designed. The investigators note that the enzyme chosen could be one that converts an inactive drug into its active form for release only inside a diseased cell.

This work is detailed in a paper titled, “Toward intelligent nanosize bioreactors: a pH-switchable, channel-equipped, functional polymer nanocontainer.” This paper was published online in advance of print publication. An abstract of this paper is available at the journal’s website.

Source: National Cancer Institute

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