Brain sensors and electronic tags that dissolve. Boosting the potential of renewable energy sources. These are examples of the latest research from two pioneering scientists selected as this year’s Kavli lecturers at the 247th National Meeting & Exposition of the American Chemical Society (ACS).
The meeting features more than 10,000 presentations from the frontiers of chemical research, and is being held here through Thursday. Two of these talks are supported by The Kavli Foundation, a philanthropic organization that encourages basic scientific innovation. These lectures, which are a highlight of the conference, shine a spotlight on the work of both young and established researchers who are pushing the boundaries of science to address some of the world’s most pressing problems.
Tackling health and sustainability issues simultaneously, John Rogers, Ph.D., is developing a vast toolbox of materials—from magnesium and silicon to silk and even rice paper—to make biodegradable electronics that can potentially be used in a range of applications. He will deliver “The Fred Kavli Innovations in Chemistry Lecture.”
“What we’re finding is that there’s a robust and diverse palette of material options at every level,” said Rogers, who’s with the University of Illinois, Urbana-Champaign. “For the conductor, for the semiconductor, for the insulating layer and the package and the substrate, one can pick and choose materials depending on the application’s requirements.”
Rogers’ team is working to incorporate some of these elements in sensors that can, for example, detect the early onset of swelling and temperature changes in the brain after head injuries and then vanish when they’re no longer needed. Today, devices designed for these purposes are wired—they have to be implanted and later completely removed once they’re no longer needed. Rogers’ sensor could be implanted but work wirelessly and, after use, “simply disappear.” That eliminates the risk of infection and other complications associated with having to remove devices surgically. Rogers has successfully tested early prototypes of sensors in laboratory animals and envisions that such devices could be used one day in human patients.
His group is also working on biodegradable radio-frequency identification tags, or RFID tags. Currently, RFIDs are produced by the billions and used in everything from jeans for accurately tracking inventory to smart cards and injected into pets. They are also found in product packaging that ends up in landfills. Using cellulose, zinc and silicon, Rogers has successfully made dissolvable RFID tags in the lab. The next step would be figuring out how to scale production up and commercialize it.
“We’re quite optimistic,” Rogers said. “We see the way forward and are about halfway there.”
Delivering the “The Kavli Foundation Emerging Leader in Chemistry Lecture” is Emily Weiss, Ph.D., of Northwestern University. Her lab is focused on getting the most power possible out of mixed and matched nanomaterials that are being developed to maximize renewable energy sources. Scientists can now engineer these materials with unprecedented precision to capture large amounts of energy—for example, from the sun and heat sources. But getting all that energy from these materials and pushing it out into the world to power up homes and gadgets have been major obstacles.
“Electric current originates from the movement of electrons through a material,” Weiss explained. “But as they move through a material or device, they encounter places where they have to jump from one type of material to another at what’s called an interface. By interfaces, I mean places where portions of the material that are not exactly alike meet up. The problem is when an electron has to cross from one material to another, it loses energy.”
As structures in materials get smaller, the interface problem becomes amplified because nanomaterials have more surface area compared to their volume. So electrons in these advanced devices have to travel across more and more interfaces, and they lose energy as heat every time.
But thanks to the latest advances in analytical instruments and computing power, Weiss’ group is poised to turn this disadvantage into a plus. “Rather than seeing all these interfaces as a negative, now we don’t need to consider it a drawback,” she said. “We can design an interface such that we can get rid of defects and get rid of this slowdown. We can actually use carefully designed interfaces to enhance the properties of your device. That sort of philosophy is starting to take hold.”
More information: 1. Biodegradable electronics, John Rogers, Ph.D.:
A remarkable feature of the modern integrated circuit is its ability to operate in a stable fashion, with almost perfect reliability. Recently developed classes of electronic materials create an opportunity to engineer the opposite outcome, in the form of devices that dissolve completely in water, with harmless end products. The enabled applications range from ‘green’ consumer electronics to bio-resorbable medical implants – none of which would be possible with technologies that exist today. This talk summarizes recent work on this physically ‘transient’ type of electronics, from basic advances in materials chemistry, to fundamental studies of dissolution reactions, to engineering development of complete sets of device components, sensors and integrated systems. An ‘electroceutical’ bacteriocide designed for treatment of surgical site infections provides an application example.
2. Behavior of electrons at nanoscopic organic/inorganic interfaces, Emily Weiss, Ph.D.:
Abstract The behavior of electrons and energy at interfaces between different types or phases of materials is an active research area of both fundamental and technological importance. Such interfaces often result in sharp free energy gradients that provide the thermodynamic driving force for some of the most crucial processes for energy conversion: migration of energy and charge carriers, conversion of excited states to mobile charge carriers, and redox-driven chemical reactions. Nanostructured materials are defined by high surface area-to-volume ratios, and should therefore be ideal for the job of energy conversion; however, they have a structural and chemical complexity that does not exist in bulk materials, and which presents a formidable challenge: mitigate or eliminate energy barriers to electron and energy flux that inevitably result from forcing dissimilar materials to meet in a spatial region of atomic dimensions. Chemical functionalization of nanostructured materials is perhaps the most versatile and powerful strategy for controlling the potential energy landscape of their interfaces, and for minimizing losses in energy conversion efficiency due to interfacial structural and electronic defects. Using metal and semiconductor nanoparticles as model systems, this talk will explore the power of tuning the chemistry at the organic-inorganic interface within colloidal semiconductor and metal nanoparticles as a strategy for controlling their structure and properties.
One of the most promising technologies for the treatment of various cancers is nanotechnology, creating drugs that directly attack the cancer cells without damaging other tissues’ development. The Laboratory of Cellular Oncology at the Research Unit in Cell Differentiation and Cancer, of the Faculty of Higher Studies (FES) Zaragoza UNAM (National Autonomous University of Mexico) developed a therapy to attack cervical cancer tumors.
According to the researcher Rosalva Rangel Corona, head of the project, the antitumor effect of interleukin in cervical cancer is because their cells express receptors for interleukin-2 that “fit together ” like puzzle pieces with the protein to activate an antitumor response .
The scientist explains that the nanoparticle works as a bridge of antitumor activation between tumor cells and T lymphocytes. The nanoparticle has interleukin 2 on its surface, so when the protein is around it acts as a switch, a contact with the cancer cell to bind to the receptor and to carry out its biological action.
Furthermore, the nanoparticle concentrates interleukin 2 in the tumor site, which allows its accumulation near the tumor growth. It is not circulating in the blood stream, is “out there” in action.
The administration of IL-2 using the nanovector reduces the side effects caused by this protein if administered in large amounts to the body. These effects can be fever, low blood pressure, fluid retention and attack to the central nervous system, among others.
It is known that interleukin -2 is a protein (a cytokine, a product of the cell) generated by active T cells. The nanoparticle, the vector for IL-2, carries the substance to the receptors in cancer cells, then saturates them and kills them, besides generating an immune T cells bridge (in charge of activating the immune response of the organism). This is like a guided missile acting within tumor cells and activating the immune system cells that kill them.
A woman immunosuppressed by disease produces even less interleukin. For this reason, the use of the nanoparticle would be very beneficial for female patients. The researcher emphasized that his group must meet the pharmaceutical regulations to carry their research beyond published studies and thus benefit the population.
Knowing this bouncing probability would give scientists an essential understanding of a variety of applications that involve water flow: the movement of water through soil, the formation of clouds and fog, and the efficiency of water-filtration devices.
This last application spurred Karnik and his colleagues — Jongho Lee, an MIT graduate student in mechanical engineering, and Tahar Laoui, a professor at the King Fahd University of Petroleum and Minerals (KFUPM) in Saudi Arabia — to study water’s probability of bouncing. The group is developing membranes for water desalination; this technology’s success depends, in part, on the ability of water vapor to flow through the membrane and condense on the other side as purified water.
By observing water transport through membranes with pores of various sizes, the group has measured a water molecule’s probability of condensing or bouncing off a liquid surface at the nanoscale. The results, published in Nature Nanotechnology, could help in designing more efficient desalination membranes, and may also expand scientists’ understanding of the flow of water at the nanoscale.
“Wherever you have a liquid-vapor surface, there is going to be evaporation and condensation,” Karnik says. “So this probability is pretty universal, as it defines what water molecules do at all such surfaces.”
Getting in the way of flow
One of the simplest ways to remove salt from water is by boiling and evaporating the water — separating it from salts, then condensing it as purified water. But this method is energy-intensive, requiring a great deal of heat.
Karnik’s group developed a desalination membrane that mimics the boiling process, but without the need for heat. The razor-thin membrane contains nanoscale pores that, seen from the side, resemble tiny tubes. Half of each tube is hydrophilic, or water-attracting, while the other half is hydrophobic, or water-repellant.
As water flows from the hydrophilic to the hydrophobic side, it turns from liquid to vapor at the liquid-vapor interface, simulating water’s transition during the boiling process. Vapor molecules that travel to the liquid solution on the other end of the nanopore can either condense into it or bounce off of it. The membrane allows higher water-flow rates if more molecules condense, rather than bounce.
Designing an efficient desalination membrane requires an understanding of what might keep water from flowing through it. In the case of the researchers’ membrane, they found that resistance to water flow came from two factors: the length of the nanopores in the membrane and the probability that a molecule would bounce, rather than condense.
In experiments with membranes whose nanopores varied in length, the team observed that greater pore length was the main factor impeding water flow — that is, the greater the distance a molecule has to travel, the less likely it is to traverse the membrane. As pores get shorter, bringing the two liquid solutions closer together, this effect subsides, and water molecules stand a better chance of getting through.
But at a certain length, the researchers found that resistance to water flow comes primarily from a molecule’s probability of bouncing. In other words, in very short pores, the flow of water is constrained by the chance of water molecules bouncing off the liquid surface, rather than their traveling across the nanopores. When the researchers quantified this effect, they found that only 20 to 30 percent of water vapor molecules hitting the liquid surface actually condense, with the majority bouncing away.
A no-bounce design
They also found that a molecule’s bouncing probability depends on temperature: 64 percent of molecules will bounce at 90 degrees Fahrenheit, while 82 percent of molecules will bounce at 140 degrees. The group charted water’s probability of bouncing in relation to temperature, producing a graph that Karnik says researchers can refer to in computing nanoscale flows in many systems.
“This probability tells us how different pore structures will perform in terms of flux,” Karnik says. “How short do we have to make the pore and what flow rates will we get? This parameter directly impacts the design considerations of our filtration membrane.”
Jan Eijkel, a professor of microfluidics and nanofluidics at the University of Twente in the Netherlands, says the group’s work may be useful in understanding a wide range of phenomena, including the microphysics and chemistry of clouds, fluids, aerosols, and the atmosphere.
“Their main contribution is the introduction of an entirely new method, which has the very nice flexibility of being able to adjust the distance between water surfaces down to very short distances,” says Eijkel, who did not contribute to the work. “Also, the innovation of changing the composition of the two solutions independently is elegant.”
Lee says that knowing the bouncing probability of water may also help control moisture levels in fuel cells.
“One of the problems with proton exchange membrane fuel cells is, after hydrogen and oxygen react, water is generated. But if you have poor control of the flow of water, you’ll flood the fuel cell itself,” Lee says. “That kind of fuel cell involves nanoscale membranes and structures. If you understand the correct behavior of water condensation or evaporation at the nanoscale, you can control the humidity of the fuel cell and maintain good performance all the time.”
The research was funded by the Center for Clean Water and Clean Energy at MIT and KFUPM.
- Jongho Lee, Tahar Laoui, Rohit Karnik. Nanofluidic transport governed by the liquid/vapour interface. Nature Nanotechnology, 2014; DOI: 10.1038/nnano.2014.28
(Phys.org) —In current research related to improving cancer treatments, one promising area of research is the effort to find ways to selectively pinpoint and target cancer cells while minimizing effects on healthy cells.
View of iron-oxide nanoparticles embedded in a polystyrene matrix as seen via a transmission electron microscope. These nanoparticles, when heated, can be applied to cancer cells in order to kill those cells.
In that effort, it’s already been found in lab experiments that iron-oxide nanoparticles, when heated and then applied specifically to cancer cells, can kill those cells because cancer cells are particularly susceptible to changes in temperature. Increasing the temperature of cancer cells to over 43 degrees Celsius (about 109 degrees Fahrenheit) for a sufficient period of time can kill those cells.
So, a University of Cincinnati-led team – along with researchers at Iowa State University, the University of Michigan and Shanghai Jiao Tong University – recently conducted experiments to see which iron-oxide nanoparticle configurations or arrangements might work best as a tool to deliver this killing heat directly to cancer cells, specifically to breast cancer cells. The results will be presented at the March 3-7 American Physical Society Conference in Denver by UC physics doctoral student Md Ehsan Sadat.
In systematically studying four distinct magnetized nanoparticle systems with different structural and magnetic properties, the research team found that an unconfined nanoparticle system, which used an electromagnetic field to generate heat, was best able to transfer heat absorbed by cancer cells.
So, from the set of nano systems studied, the researchers found that uncoated iron-oxide nanoparticles and iron-oxide nanoparticles coated with polyacrylic acid (PAA) – both of which were unconfined or not embedded in a matrix – heated quickly and to temperatures more than sufficient to kill cancer cells.
Uncoated iron-oxide nanoparticles increased from a room temperature of 22 degrees Celsius to 66 degrees Celsius (about 150 degrees Fahrenheit).
Iron-oxide nanoparticles coated with polyacrylic acid (PAA) heated from a room temperature of 22 degrees Celsius to 73 degrees Celsius (about 163 degrees Fahrenheit.)
The goal was to determine the heating behaviors of different iron-oxide nanoparticles that varied in terms of the materials used in the nanoparticle apparatus as well as particle size, particle geometry, inter-particle spacing, physical confinement and surrounding environment since these are the key factors that strongly influence what’s called the Specific Absorption Rate (SAR), or the measured rate at which the human body can absorb energy (in this case heat) when exposed to an electromagnetic field.
According to Sadat, “What we found was that the size of the particles and their anisotropic (directional) properties strongly affected the magnetic heating achieved. In other words, the smaller the particles and the greater their directional uniformity along an axis, the greater the heating that was achieved.”
He added the systems’ heating behaviors were also influenced by the concentrations of nanoparticles present. The higher the concentration of nanoparticles (the greater the number of nanoparticles and the more densely collected), the lower the SAR or the rate at which the tissue was able to absorb the heat generated.
The four systems studied
The researchers studied
- uncoated iron-oxide nanoparticles
- iron-oxide nanoparticles coated with polyacrylic acid (PAA)
- a polystyrene nanosphere with iron-oxide nanoparticles uniformly embedded in its matrix
- a polystyrene nanosphere with iron-oxide nanoparticles uniformly embedded in its matrix but with a thin film surface of silica
All four nanoparticle systems were exposed to the same magnetic field for 35 minutes, and temperature measurements were performed at two-minute intervals.
As stated, the PAA iron-oxide and the uncoated iron-oxide samples showed the highest temperature change. The lowest temperature changes, insufficient to kill cancer cells, were exhibited by
- The polystyrene nanosphere, which heated to 36 degrees Celsius (about 96 degree Fahrenheit).
- The polystyrene nanosphere with a silica coating heated to 40 degrees Celsius (104 degrees Fahrenheit).
Explore further: Gold-plated nano-bits find, destroy cancer cells
(Nanowerk Spotlight) By Michael Berger. Copyright © Nanowerk The integration of consumer electronics with advanced imaging and analytical platforms holds great promises for medical point-of-care diagnostics and environmental rapid field testing for pollutants and viruses.
For instance, in a recent Nanowerk Spotlight we reported on the use of smartphones to detect single nanoparticles and viruses. In this work, a research group led by Aydogan Ozcan, a professor in the Electrical and Bioengineering Department at UCLA and Associate Director of the California NanoSystems Institute (CNSI), created a field-portable fluorescence microscopy platform installed on a smartphone for imaging of individual nanoparticles as well as viruses using a light-weight and compact opto-mechanical attachment to the existing camera module of the cellphone.
In new work, Ozcan’s group has now developed a Google Glass application and a server platform for instant, wireless diagnostic testing of a variety of health conditions and diseases. “This technology allows Google Glass wearers to use the hands-free camera on the device to send images of diagnostic tests that screen for conditions such as HIV or prostate cancer,” Ozcan explains to Nanowerk. “Without relying on any additional devices, Google Glass users can upload these images and receive accurate analysis of health conditions in as little as eight seconds.”
Labeled Google Glass and demonstration of imaging a rapid diagnostic test (RDT). (a) Front-profile view of the Google Glass with various hardware components36 labeled. (b) Example of using the Glass for taking an image of an RDT as part of our RDT reader application. (Reprinted with permission from American Chemical Society) (click image to enlarge)
This is the first biomedical sensing application created through Google Glass. This breakthrough technology takes advantage of gains in both immunochromatographic rapid diagnostic tests (RDTs) and wearable computers (such as Google Glass). The team reported their findings in the February 27, 2014 online edition of ACS Nano (“Immunochromatographic Diagnostic Test Analysis Using Google Glass”).
Over the past decade, RDTs – which are in general based on light scattering off surface-functionalized metallic nanoparticles – have emerged as a quick and cost-effective method to screen various diseases and have provided various advantages for tackling public health problems including more effective tracking/monitoring of chronic conditions, infectious diseases and widespread medical testing by minimally trained medical personnel or community healthcare workers. The new Google Glass-based diagnostic technology could improve individual tracking of dangerous conditions or diseases, public health monitoring and rapid response in disaster relief areas or quarantine zones.
This is how it works: The user takes a photo of the RDT device through the camera system in Google Glass. Using a Quick Response (QR) code identifier, which is custom-designed and attached to each RDT cassette, this custom-written Glass application is capable of automatically finding and identifying the type of the RDT of interest, along with other information (e.g., patient data) that can be linked to the same QR code. The data is transmitted to a central server which has been set up for fast and high-throughput evaluation of test results coming from multiple devices simultaneously. The data is processed automatically and to create a quantitative diagnostic result, which is then returned to the Google Glass user.
“We also developed a centralized database and Web interface for visualizing uploaded data in the form of geo-tagged map data, which can be quite useful for short- and long-term spatiotemporal tracking of the evolution,” says Ozcan. “This web portal allows users to view test results, maps charting the geographical spread of various diseases and conditions, and the cumulative data from all the tests they have submitted over time.” He also points out that the precision of the Google Glass camera system permits quantified reading of the results to a few-parts-per-billion level of sensitivity – far greater than that of the naked eye – thus eliminating the potential for human error in interpreting results, which is a particular concern if the user is a health care worker who routinely deals with many different types of tests.”
Block diagram of the rapid diagnostic test (RDT) imaging and processing workflow (a, c) done by the Google Glass application (red dashed frame) and server processes (green dashed frame). In this case, a single RDT is analyzed. (Reprinted with permission from American Chemical Society) (click image to enlarge)
The team tested their Google Glass-based RDT reader platform through commercially available human immunodeficiency virus (HIV) and prostate-specific antigen (PSA) rapid tests. The researchers took images of tests under normal, indoor, fluorescent-lit room conditions. They submitted more than 400 images of the two tests, and the RDT reader and server platform were able to read the images 99.6 percent of the time. Ozcan notes that, for wide-scale deployment and use of this Google Glass application, the sales price of Glass should be cost-effective enough to compete with mobile phones and low enough to enter developing markets. “We are quite hopeful on this end as Google is very well aware of all these emerging opportunities.”
|Source: NanoHybrids (press release)|
02 Mar 2014
A perfect sieve
Graphene, the sheet of carbon just one atom thick, has already featured a few times on this blog thanks to its unique promise for many applications. Could it even turn seawater into drinking water? Scientists at Manchester University think it may be possible using a filter made from laminates of graphene oxide, a form of graphene with oxygen-containing molecules attached to it.
This laminate can perform a magic trick: in the dry state it doesn’t let any gas molecule through except water and is vacuum-tight. When wet, however, nanoscale channels open up and water flows through rapidly, without any resistance. Any particle, molecule or ion that can’t squeeze through the channels is left behind.
But the nanochannels actually swell a little in water, opening up enough to let through two or three atomic layers of water and some ions. The researchers will try out ways to prevent the swelling, so that the nanochannels are so small that they block small ions while water still flows through quickly: a perfect filter for removing salt from water.
Dr Irina Grigorieva, a co-author of the study, says in a press release from Manchester University: “Our ultimate goal is to make a filter device that allows a glass of drinkable water to be made from seawater after a few minutes of hand pumping. We are not there yet but this is no longer science fiction.”
Graphene’s first text message
Wireless communication has become an essential part of our way of life as electronic gadgets are increasingly used on the move. In the near future, wireless chips will need to transmit data faster and be more compact to enable a wide variety of applications, including in smart tags or wearable electronics.
Graphene, which has ultra-efficient electronic properties, seems an ideal candidate for transistors in fast, wireless circuits, which convert radio-frequency signals into electrical currents. However, the conventional chip-making process damages the thin graphene layers, degrading circuit performance.
Now researchers at IBM have found a solution: they reverse the fabrication process, only introducing graphene at the final fabrication step. To test the chip, they sent a message by radio-signal, which the chip received and converted into a three letter message: I-B-M.
Looking for clues
Finding fingerprints is as important as ever in crime scene investigation. Now researchers from Wuhan, China, have used nanoparticles to reveal the merest smudge of a print, even on difficult surfaces such as plastic and coins.
A common technique to detect fingerprints is to treat surfaces with chemicals that make the residues left behind by a finger light up faintly in ultraviolet light. However, there is also fluorescence from the surface itself so that prints that are too weak remain hidden in the background noise. The researchers have therefore turned to infrared light, which causes hardly any fluorescence.
To make the fingerprints light up, nanoparticles are applied that convert two low-energy infrared photons into one high-energy UV one. To ensure this only happens at the fingerprints, molecules are attached to the nanoparticles that bind to lysosome, which is found in human sweat and left in fingerprint residue. Researchers used the new method to detect fingerprints on various surfaces and from different people, without any background interference.
Sun, sand and nanoparticles
Official health agencies advise using sunscreen lotion when the sun is out to protect against UV light, which causes sunburn and increases the risk of skin cancer. However, some researchers question whether the overall health benefits are clear enough.
One reason is that several studies over the past decade have reported potential harmful effects from the ingredients of sunblock. In recent years, sunscreens have appeared on the market that contain zinc oxide nanoparticles and, given existing concerns, the possible toxic effects are being closely studied.
There is no conclusive evidence that the nanoparticles could be harmful, but researchers at Harvard reason that it may be better to be safe than sorry. They propose sealing the nanoparticles within a thin shell of silica to minimise any toxic effects. Silica is what sand is made of, and is known to be a safe ingredient of many consumer products, including cosmetics.
The researchers compared how much damage the bare and encapsulated nanoparticles caused to DNA in live cells in a laboratory experiment and report three times less damage for the silica-coated nanoparticles.
This study does not say whether the uncoated nanoparticles are actually harmful inside a human body, but the researchers point out that a safer-by-design approach will reduce any possible risks.
In a heartbeat
Implantable medical devices such as pacemakers need batteries, which are bulky and have to be replaced in risky operations. Researchers at the University of Illinois have now found a way to power such devices using energy from the body itself, such as a beating heart. They use nanoribbons made of a piezoelectric material that produces an electric current when its is bent. The nanoribbons are held in place on a flexible silicone layer that conforms to the shape of the tissue on which it is placed.
The researchers have showed that sufficient power can be generated to operate a cardiac pacemaker. To extend the potential use, the device is also connected to a rechargeable battery.
|Nanowerk News) Researchers from UCLA’s Jonsson Comprehensive Cancer Center have developed an innovative cancer-fighting technique in which custom-designed nanoparticles carry chemotherapy drugs directly to tumor cells and release their cargo when triggered by a two-photon laser in the infrared red wavelength.|
|The research findings by UCLA’s Jeffrey Zink, a professor of chemistry and biochemistry, and Fuyu Tamanoi, a professor of microbiology, immunology and molecular genetics, and their colleagues were published online Feb. 20 in the journal Small (“Two-Photon-Triggered Drug Delivery via Fluorescent Nanovalves”) and will appear in a later print edition.|
|Light-activated drug delivery holds promise for treating cancer because it give doctors control over precisely when and where in the body drugs are released. Delivering and releasing chemotherapy drugs so that they hit only tumor cells and not surrounding healthy tissues can greatly reduce treatment side effects and increase the drugs’ cancer-killing effect. But the development of a drug-delivery system that responds to tissue-penetrating light has been a major challenge.|
|To address this, the teams of Tamanoi and Zink, which included scientists from the Jonsson Cancer Center’s cancer nanotechnology and signal transduction and therapeutics programs, collaborated with Jean-Olivier Durand from France’s University of Montpellier to develop a new type of nanoparticle that can absorb energy from tissue-penetrating light.|
|These new nanoparticles are equipped with thousands of pores, or tiny tubes, that can hold chemotherapy drugs. The ends of the pores are capped with nanovalves that keep the drugs in, like a cork in a bottle. The nanovalves contain special molecules that respond to energy from two-photon light exposure, which prompts the valves to open and release the drugs.|
|The operation of the nanoparticles was demonstrated in the laboratory using human breast cancer cells.|
|Because the effective range of the two-photon laser in the infrared red wavelength is 4 centimeters from the skin surface, this delivery system would work best for tumors within that range, which possibly include breast, stomach, colon and ovarian tumors, the researchers said.|
|In addition to their light sensitivity, the new nanoparticles are fluorescent and can be monitored in the body using molecular imaging techniques. This allows researchers to track the progress of the nanoparticle into the targeted cancer cell before light activation. The ability to track a targeted therapy in this way has been given the name “theranostics” — a portmanteau of therapy and diagnostics — in the scientific literature.|
|“We have a wonderful collaboration,” Zink said. “When the Jonsson Comprehensive Cancer Center brings together totally diverse fields — in this case, a physical chemist and a cell signaling scientist — we can do things that neither one could do alone.”|
|“Our collaboration with scientists at Charles Gerhardt Institute was important to the success of this two-photon–activated technique, which provides controls over drug delivery to allow local treatment that dramatically reduces side effects,” said Tammanoi.|
|Source: By Shaun Mason, UCLA|
For close to two decades, Cornell scientists have developed processes for using polymers to self-assemble inorganic nanoparticles into porous structures that could revolutionize electronics, energy and more.
This process has now been driven to an unprecedented level of precision using metal nanoparticles, and is supported by rigorous analysis of the theoretical details behind why and how these particles assemble with polymers. Such a deep understanding of the complex interplay between the chemistry and physics that drive complex self-assembly paves the way for these new materials to enter many applications, from electrocatalysis in fuel cells to voltage conductance in circuits.
A: A schematic of the block copolymer synthesis method which includes gold and platinum nanoparticle self-assembly. B. Molecular structure of the block copolymer used. C. Molecular structure of stabilizing ligands attached to gold and …more
Ulrich Wiesner, the Spencer T. Olin Professor of Materials Science and Engineering, led what is probably the most comprehensive study to date of block copolymer nanoparticle self-assembly processes. The study was published online Feb. 21 in Nature Communications.
From the outside, the process looks simple enough. Begin with platinum and gold particles that grow from a precursor. A chemical called a ligand coats the particles and precisely controls their size. Add to this designed molecules called block copolymers – long chains of two or three organic materials. The polymers combine with the platinum and gold nanoparticles, all of which assemble into ordered, cubic, three-dimensional structures. Etch away the polymer, and what’s left are scores of nanoparticles forming porous 3-D cubic networks.
Each step – from the exact structure of the ligands, to the synthesis of the polymers – requires precise chemistry and detailed understanding of each material’s role. The Nature Communications analysis drew on the expertise of collaborators in electron tomography, energy dispersive microscopy and percolation theory. For example, collaborators from the Japan Science and Technology Agency used electron tomography to map the location of every single particle in the samples, which then could be compared with theoretical predictions. The result is a comprehensive set of design criteria that could lead to readying these particle networks for larger scale solution processing.
“Not only can we make these materials, but through electron tomography in particular, we can analyze these structures at a depth that just has not been done before,” Wiesner said. “The comparison with theory allows us to fully understand the physical mechanisms by which these structures are formed.”
Why pay such attention to these self-assembled nanoparticle networks? They’re made in a way that would never happen in nature or by conventional laboratory means. They are uniformly porous with high surface area and, therefore, are highly catalytic and potentially useful for energy applications.
Perhaps best of all, working with polymers means cost-effective, large-scale processing could be a snap.
Several decades of polymer science has given the world efficient scalability unsurpassed in the materials world – think plastics production. Wiesner and colleagues have proven the concept of self-assembled metal nanoparticles using block copolymer-based solution processing that goes beyond the “glass vial in a lab,” Wiesner said.
“Now that we understand how it all works, our process lends itself easily to larger-scale production of such materials,” he said.
Conductive nanomaterials for printed electronics applications
By Michael Berger. Copyright © Nanowerk
(Nanowerk Spotlight) The term printed electronics refers to the application of printing technologies for the fabrication of electronic circuits and devices, increasingly on flexible plastic or paper substrates. Printed electronics has its origins in conductive patterns printed as part of conventional electronics, forming flexible keyboards, antennas and so on.
Then came fully printed testers on batteries, electronic skin patches and other devices made entirely by printing, including batteries and displays (read more: “Printed electronics widens its scope”). Traditionally, electronic devices are mainly manufactured by photolithography, vacuum deposition, and electroless plating processes. In contrast to these multistaged, expensive, and wasteful methods, inkjet printing offers a rapid and cheap way of printing electrical circuits with commodity inkjet printers and off-the-shelf materials.
All inkjet technologies are based on digitally controlled generation and ejection of drops of liquid inks using one of two different modes of operation: continuous and drop-on-demand printing. Conductive inkjet ink is a multi-component system that contains a conducting material in a liquid vehicle (aqueous or organic) and various additives (such as rheology and surface tension modifiers, humectants, binders and defoamers) that enable optimal performance of the whole system, including the printing device and the substrate. The conductive material may be dispersed nanoparticles, a dissolved organometallic compound, or a conductive polymer.
A review article in Small (“Conductive Nanomaterials for Printed Electronics”) by Alexander Kamyshny and Shlomo Magdassi from The Hebrew University of Jerusalem, provides a state-of-the-art overview of the synthesis of metal nanoparticles; preparation of stable dispersions of metal nanoparticles, carbon nanotubes (CNTs) and graphene sheets; ink formulations based on these dispersions, sintering of metallic printed patterns for obtaining high electrical conductivity; and recent progress in the utilization of metal nanoparticles, carbon nanotubes, and graphene for the fabrication of various functional devices.
Requirements and challenges for printable dispersions of conductive nanomaterials The use of nanomaterials for the formulation of conductive inkjet inks poses several challenges:
- – the nanoparticles in the ink should be stable against aggregation and precipitation in order to provide reproducible performance
- – nanoparticle-based conductive inks should provide good electrical conductivity of printed patterns
- – there is a need need for a post-printing process in order to sinter the nanoparticles for obtaining continuous metallic phase, with numerous percolation paths between metal particles within the printed patterns
- – when using carbon nanotubes or graphene, the challenge is to prevent aggregation into CNT bundles or graphene layers.
In their article, Kamyshny and Magdassi address these challenges in great detail and then go on to describe preparation methods for metal, graphene, and CNT-based inkjet inks, which are suitable for printed electronics, and post-printing processing methods for obtaining high electrical conductivities.
Printing of a conductive 3D structure with the use of ink composed of an UV-curable emulsion and a dispersion of metal nanoparticles. Inset is a 3D profile of a 200 µm width lines composed of 1, 3, 6, 10, and 20 printed layers.(© The Royal Society of Chemistry)
Applications of conductive nanomaterials The authors also discuss several applications of conductive nanomaterials for the fabrication of printed electronic devices. This includes fabrication and properties of transparent conductive electrodes, which are nowadays essential features for many optoelectronic devices, and inkjet-printed devices, such as RFID tags, light emitting devices, thin-film transistors (TFTs) and solar cells.
Transparent electrodes The market for transparent electrodes has grown tremendously due to wide proliferation of LCD displays, touch screens, thin-film solar cells, and light emitting devices. The most widely used material is indium tin oxide (ITO) with a market share of more than 97% of transparent conducting coatings. ITO coatings have some major drawbacks, though, and many efforts to find alternatives are based on nanomaterials – metal nanoparticles, metal nanowires, carbon nanotubes, and graphene – which can be printed directly on various substrates without etching processes.
RFID tags The main elements of an RFID (Radio Frequency Identification) tag are a silicon microchip and an antenna, which provide power to the tag and are responsible for communication with a reading device. Direct inkjet printing of antennas on plastic and paper substrates with the use of metal nanoparticles inks is a promising approach to the production of low-cost RFID tags.
Thin-film transistors Conductive nanomaterials are used to produce the conductive features on both inorganic and organic TFTs. See for instance our recent Nanowerk Spotlight on inkjet printing of graphene for flexible electronics or the report on inkjet printing of single-crystal films of organic semiconductors.
Light-emitting devices Light emitting devices (or electroluminescent devices, ELDs) are composed of a semiconductor layer placed between two electrodes, and emit light in response to electric current. LEDs to be used for lighting, require a highly conductive grid (“shunting lines”) for homogeneous distribution of current around the lighting device. These circuits can be fabricated on various substrates including plastic, by various printing processes using conductive nanomaterials.
Solar cells The first demonstration of inkjet-printed solar cells was already made in 2007 using fullerene-based ink. The results were discussed in this paper: “High Photovoltaic Performance of Inkjet Printed Polymer:Fullerene Blends”. In recent years, metal nanoparticles as well as nanowires and CNTs have been also used in solar cells fabrication as well.
Concluding their review, the authors note that, in spite of the remarkable scientific progress in preparation processes and applications of conductive nanomaterials, they are still not widely used by the industry in significant quantities:
“The current high price of commercially available inks, which are based mainly on the high cost silver, impedes their wide use for large area printed electronics. Therefore, research should be focused on the development of new nanomaterials and ink formulations based on low cost metals with high electrical conductivity such as copper, nickel, and aluminum.”
They also note that in recent years, many scientific activities have been focusing on graphene and that we can expect future developments in printed electronics that will combine CNTs with graphene. Successive utilization of graphene for printed electronics requires ink formulations with high graphene loading, which are stable against flakes aggregation.
One final thought is the application of conductive nanomaterials in 3D printing of conductive patterns which opens some important perspectives for materials science. Although, this field is at its very early stages of research and development, and the search for new nanomaterials as well as suitable 3D fabrication tools based on wet deposition, it is a stimulating challenge for materials scientists.