Rice University

Atom-thick CCD could capture images

Posted by

0


An atomically thin material may lead to the thinnest-ever imaging platform. Synthetic two-dimensional materials based on metal chalcogenide compounds could be the basis for superthin devices.
Rice University researchers fabricated a three-pixel, CIS-based optoelectronic sensor array to test the two-dimensional compound’s ability to capture image information. They started with few-layer exfoliated CIS on a silicon substrate, fabricated three pairs of titanium/gold electrodes on top of the CIS and cut the CIS into three sections with a focused ion beam.
An atomically thin material developed at Rice University may lead to the thinnest-ever imaging platform.

Synthetic two-dimensional materials based on metal chalcogenide compounds could be the basis for superthin devices, according to Rice researchers. One such material, molybdenum disulfide, is being widely studied for its light-detecting properties, but copper indium selenide (CIS) also shows extraordinary promise.

Sidong Lei, a graduate student in the Rice lab of materials scientist Pulickel Ajayan, synthesized CIS, a single-layer matrix of copper, indium and selenium atoms. Lei also built a prototype — a three-pixel, charge-coupled device (CCD) — to prove the material’s ability to capture an image.

The details appear this month in the American Chemical Society journal Nano Letters.

Lei said the optoelectronic memory material could be an important component in two-dimensional electronics that capture images. “Traditional CCDs are thick and rigid, and it would not make sense to combine them with 2-D elements,” he said. “CIS-based CCDs would be ultrathin, transparent and flexible, and are the missing piece for things like 2-D imaging devices.”

The device traps electrons formed when light hits the material and holds them until released for storage, Lei said.

CIS pixels are highly sensitive to light because the trapped electrons dissipate so slowly, said Robert Vajtai, a senior faculty fellow in Rice’s Department of Materials Science and NanoEngineering. “There are many two-dimensional materials that can sense light, but none are as efficient as this material,” he said. “This material is 10 times more efficient than the best we’ve seen before.”

Because the material is transparent, a CIS-based scanner might use light from one side to illuminate the image on the other for capture. For medical applications, Lei envisions CIS being combined with other 2-D electronics in tiny bio-imaging devices that monitor real-time conditions.

In the experiments for the newly reported study, Lei and colleagues grew synthetic CIS crystals, pulled single-layer sheets from the crystals and then tested the ability of the layers to capture light. He said the layer is about two nanometers thick and consists of a nine-atom-thick lattice. The material may also be grown via chemical vapor deposition to a size limited only by the size of the furnace, Lei said.

Because it’s flexible, CIS could also be curved to match the focal surface of an imaging lens system. He said this would allow for the real-time correction of aberrations and significantly simplify the entire optical system.

Co-authors of the paper are Rice graduate students Fangfang Wen and Yongji Gong; postdoctoral researchers Bo Li, Pei Dong, Anthony George and Liehui Ge; undergraduates Qizhong Wang, James Bellah and Yihan Huang; complementary appointee Yongmin He of Lanzhou University, China; Jun Lou, an associate professor of materials science and nanoengineering, and Naomi Halas, the Stanley C. Moore Professor of Electrical and Computer Engineering and a professor of chemistry, biomedical engineering, physics and astronomy and of materials science and nanoengineering. Ajayan is Rice’s Benjamin M. and Mary Greenwood Anderson Professor in Engineering, professor of materials science and nanoengineering and of chemistry and chair of the Department of Materials Science and NanoEngineering.

The research was supported by the Army Research Office Multidisciplinary University Research Initiative, the Function Accelerated nanoMaterial Engineering Division of the Semiconductor Technology Advanced Research Network, the Microelectronics Advanced Research Association, the Defense Advanced Research Projects Agency, the Netherlands Organization for Scientific Research, the Robert A. Welch Foundation, the National Security Science and Engineering Faculty Fellowship and the Office of Naval Research.

Story Source:

The above story is based on materials provided by Rice University. Note: Materials may be edited for content and length.

Journal Reference:

  1. Sidong Lei, Fangfang Wen, Bo Li, Qizhong Wang, Yihan Huang, Yongji Gong, Yongmin He, Pei Dong, James Bellah, Antony George, Liehui Ge, Jun Lou, Naomi J. Halas, Robert Vajtai, Pulickel M. Ajayan. Optoelectronic Memory Using Two-Dimensional Materials. Nano Letters, 2014; 141217153644008 DOI:10.1021/nl503505f

OLDER ADULTS NEARLY TWICE AS LIKELY TO HAVE MEMORIES AFFECTED BY ENVIRONMENTAL DISTRACTION.

Posted by

0


140714182408-large

Older people are nearly twice as likely as their younger counterparts to have their memory and cognitive processes impaired by environmental distractions (such as irrelevant speech or written words presented along with target stimuli), according to a new study from psychologists at Rice University and Johns Hopkins University School of Medicine. Whereas other studies had found that older adults are distracted by memories of prior similar events, this was the first study to convincingly demonstrate across several tasks an impairment from environmental distractions.

“Cognitive Declines in Healthy Aging: Evidence from Multiple Aspects of Interference Resolution” appeared in a recent edition of Psychology and Aging. The study supported previous research that showed memory accuracy and the speed of cognitive processing declines with age. It also revealed that older people were at least twice as likely as younger to have irrelevant memories intrude during memory recall and also showed twice as much slowing in cognitive processing in the presence of distracting information in the environment.

The study included 102 people between the ages of 18 and 32 (average age of 21) and 60 people between the ages of 64 and 82 (average age of 71) who participated in a series of memory and cognitive tasks.

 

For example, when the participants were tested on remembering lists of words, individuals in the young test group remembered words on the list with an average accuracy of 81 percent; in comparison, the old test group’s accuracy was only 67 percent. When irrelevant words were introduced that were to be ignored, the young test group’s accuracy dropped to 74 percent, but the accuracy of the old test group’s performance dropped to 46 percent.

 

“Almost any type of memory test administered reveals a decline in memory from the age of 25 on,” said Randi Martin, the Elma W. Schneider Professor of Psychology at Rice and the study’s co-author. “However, this is the first study to convincingly demonstrate the impact of environmental interference on processing having a greater impact on older than younger adults.”

Martin hopes that the research will encourage further research of how the brain is affected by environmental distractions.

“From our perspective of studying neuroplasticity (the brain’s ability to reorganize itself after traumatic injury or neurological disorders) and testing patients with brain damage, this research is very important,” Martin said. “The tests used in this study are important tools in determining how the brain is affected by environmental interference, which is critical information in treating neurological disorders, including stroke and traumatic brain injuries.”

CT nanoparticle contrast: Good as gold?

Posted by

0


CT nanoparticle-based contrast agents are all investigational — and at this point all preclinical — but they’re out there. In a few years, the tiny contrast agent delivery vehicles, which work well in animals, could greatly affect the diagnosis and treatment of disease in humans.

That’s according to David Cormode, PhD, assistant professor of radiology at the University of Pennsylvania. He spoke on nanoparticle CT contrast media at last month’s International Society for Computed Tomography (ISCT) annual meeting in San Francisco.

The integration of nanoparticle CT contrast into the clinical mainstream will take a while, Cormode said, but the process might be speeded up if elements are developed that are cheaper than gold, which is currently used to make the nanoparticles.

Nanoparticles for CT imaging aren’t so different in design and structure from those built for other imaging modalities such as MRI, except that they contain CT contrast agents in their lipid-based cores. Inside every nanoparticle agent is an inner core surrounded by various layered and scattered components including liposomes, micelles, emulsions, and nanocrystals with biocompatible coatings, Cormode said.

CT contrast agents have bigger cores than, for example MR agents, because they need them. Due to CT’s relative insensitivity to contrast compared to other imaging modalities, high-contrast payloads are required for better sensitivity, Cormode said. Nevertheless, they are still quite small, typically less than 4 nm in diameter.

“If you compare the Earth to the size of a soccer ball, it’s about 58 millionth of the size,” he said. “Going from [the soccer ball] to a nanoparticle, it’s about the same factor of difference in sizes.”

In recent years, interest in imaging nanoparticles has soared, with about 80 peer-reviewed studies being published a year, compared with fewer than 10 as recently as 2006, Cormode said. The reason is, quite simply, their vast potential in diagnosing and treating disease.

Nanoparticles are designed to be long-lasting contrast agents that do not need to be readministered in the case of multiple exams being acquired over several hours or potentially even days, Cormode said.

“Compared to agents we are currently using, nanoparticles have long circulation half-lives,” he said. “They can be targeted to allow molecular imaging or specific cells or specific processes. They can be used with spectral CT, and they can also be multifunctional, providing contrast for more than one imaging technique.”

Although no nanoparticle agents are approved for CT, a couple have been cleared for use with MRI, including Doxil, a liposomal formulation of doxorubicin approved for head and neck cancers in the mid-1990s, and Feridex, an iron-oxide nanoparticle contrast agent.

The tiny structures have become more complex in recent years, featuring multiple layers of different coatings, and an antibody or protein used to direct the agent to a biological target. For example, a 2009 in vitro and rat study by Pan and colleagues examined an iodine-loaded agent targeted to fibrin for thrombus imaging, he said.

Representing a new class of nanoparticles designed for CT, the colloidal, radio-opaque and metal-encapsulated polymeric (cROMP) particle offered severalfold enhancement both in vivo and in a rat model, its authors reported, with sensitivity reaching to the low nanomolar particulate .

Key CT nanoparticle studies

In 2006, Mukundan and colleagues tested a blood-pool contrast nanoparticle encapsulating a high concentration of iodine. They injected the agent into five mice and scanned them with micro-CT. The researchers measured high initial enhancement of about 900 HU in the aorta, which plateaued at about 800 HU when measured again two hours later, and there was excellent contrast discrimination between the myocardium and cardiac blood pool .”I imagine if they had continued the study for a longer time, you would have seen the same amount of contrast,” Cormode said.

In a 2010 study of a gold high-density lipoprotein nanoparticle targeted at atherosclerosis, Cormode and colleagues showed that nanoparticles can distinguish several different components in a single scan. The group performed spectral imaging on a preclinical CT scanner developed by Philips Healthcare to differentiate gold (Au-HDL), iodine-based contrast, and calcium phosphate in phantoms. The gold nanoparticles were injected in mice and followed 24 hours later by an iodine-based contrast agent.

The gold particles were detected in the aortas of the mice, while the iodine-based contrast agent was highlighted in the blood and the calcium-rich tissue of the skeleton during a single CT scan. Microscopy showed that the gold was primarily localized in macrophages in the aorta, thereby showing that spectral CT also provided information about the macrophage burden 

“You can use nanoparticles … to extract several different parameters at the same time,” Cormode said of the study.

Also in 2010, Cormode collaborated with van Schooneveld et al to examine an all-in-one contrast agent for MRI, CT, and fluorescence imaging. The researchers created a gold/silica nanoparticle agent to enhance macrophage cells in vitro using MRI, CT, and fluoroscopy and mice livers in vivo using MRI and CT. The agent is useful in many applications, including cell tracking and target-specific molecular imaging, and is “a step in the direction of truly multimodal imaging,” the authors wrote.

Diagnostic and therapeutic

Gold nanoparticle-based contrast was also the agent of choice in a study by von Maltzahn et al, who used a gold nanorod agent to visualize and then ablate tumors in mice. The nanomaterials improved the specificity of cancer ablation by homing into tumors and acting as antennas for externally applied radiofrequency ablation, the authors .

The polyethylene glycol (PEG)-protected gold nanorods “actually absorb laser radiation very strongly, and when they do they heat up the surrounding material,” Cormode said of the study. “This can be used as a kind of hyperthermia technique” to completely eradicate the tumors, he noted.

In summary, CT nanoparticle contrast agents “are out there, but gold is sort of expensive and we need to create cheaper agents,” Cormode said. In addition, “extensive clearance and toxicity testing” will be needed before the agents are ready for routine clinical use.

Bismuth-carrying nanotubes track stem cells in CT.

Posted by

0


Texas researchers have succeeded in trapping bismuth in a nanotube cage, and the resultant structure could be used as a CT contrast agent to track stem cells, according to a new study in the Journal of Materials Chemistry B.

Specifically, the investigators from Rice University, in cooperation with the University of Houston and St. Luke’s Episcopal Hospital, are inserting bismuth compounds into single-walled carbon nanotubes to make a more effective CT contrast agent. In tests using pig bone marrow-derived mesenchymal stem cells, the researchers found that the bismuth-filled nanotubes, which they have dubbed Bi@US-tubes, produce CT images of higher attenuation than those with iodine-based contrast agents .

Bismuth has been used before as a contrast agent, but putting it in nanotube capsules allowed the researchers to get the substance inside cells in high concentrations, permitting the acquisition of CT images of the cell. The relatively high contrast is achieved with low bismuth loading (2.66% by weight) within the tubes, without compromising cell viability.

Bismuth is a heavy element and therefore is more effective at diffracting x-rays than almost any substance, according to study co-author Lon Wilson, PhD. Going forward, the nanotube surfaces can be modified to improve biocompatibility and their ability to target certain types of cells. They can also be modified for use with MRI, PET, and electron paramagnetic resonance imaging systems, he said.

The researchers are now working to double the amount of bismuth in each nanotube. They would also like to combine bismuth and gadolinium into a single nanotube to produce a bimodal contrast agent suitable for tracking in both CT and MRI, Wilson said.

Source: auntminnie.com

Carbyne, aka linear acetylenic carbon.

Posted by

0


carbyne

First it was diamond, then graphene. These two structures have previously held the title of the world’s strongest material. Now, one of their family members has taken the crown.

new strongest material on earth

In a research paper published recently on Arxiv, a team from Rice University laid out the molecular schematics for Carbyne, aka linear acetylenic carbon. A supermaterial first theorized in 1967, its legitimacy has been disputed for the last 40 years. This time around the team figured out how to successfully synthesize and stabilize it at room temperature.  

The paper goes on to describe the remarkable atomic chain of Carbyne – a microscopic lattice similar to that of its close cousin, diamond. Carbyne, however, has a Young’s modulus 40 times that of diamond, making it the world’s hardest material. With extensive applications in nanotechnology, it could completely change the way scientists view systems with nanomechanical bases. The polyyne family has a new heavyweight champ.

carbyne strongest material in the world

Above: Carbyne under tension. (a) DFT calculations of energy as a function of strain ɛ. The electronic density of carbyne (polyyne) (b) in equilibrium and (c) under tension shows a more pronounced bond alternation in strained carbyne. (d) Bond length alternation and (e) band gap increase as a function of strain.

The results reveal remarkable tensile stiffness, twice that of graphene and carbon nanotubes, and a specific strength greater than any other known material. Potential mechanical and electrical applications are numerous, including a broad category of possible uses in the realm of super-strong and ultra-lightweight materials.