Magnetism in nanoscale layers only a few tens of atoms thick is one of the foundations of the big data revolution – for example, all the information we download from the internet is stored magnetically on hard disks in server farms dotted across the World. Recent work by a team of scientists working in Singapore, The Netherlands, USA and Ireland, published on 14 August 2015 in ("maging and control of ferromagnetism in LaMnO3/SrTiO3 heterostructures"), has uncovered a new twist to the story of thin-film magnetism. 
Image of the magnetic fields recorded by scanning a tiny superconducting coil over the surface of a LaMnO3 film grown on a substrate crystal. The magnetic left-hand side is seven LaMnO3 blocks thick (about 3 nm), while the nonmagnetic right-hand side is only five (2 nm). The measuring setup is shown on the right. (Image: NUS) (click on image to enlarge) The team from the National University of Singapore (NUS) - Mr Li Changjian, a graduate student from the NUS Graduate School for Integrative Sciences and Engineering, Assistant Professor Ariando and Professor T Venky Venkatesan – led to the discovery of this new magnetic phenomenon by growing perfectly-crystalline atomic layers of a manganite, an oxide of lanthanum and manganese {LaMnO3}, on a substrate crystal of nonmagnetic strontium titanate using a method – pulsed laser deposition – developed many years ago for high-temperature superconductors and multicomponent materials by Prof Venkatesan, who now heads the NUS Nanoscience and Nanotechnology Institute (NUSNNI). The manganite is an antiferromagnet when it is atomically thin and shows no magnetism. The new discovery is that its magnetism is switched on abruptly when the number of Manganese atomic layers changes from 5 to 6 or more. The conjecture is that this arises from an avalanche of electrons from the top surface of the film to the bottom, where the electrons are confined near the substrate. This shift of electric charge occurs as the manganese atomic layers form atomically charged capacitors leading to the build-up of an electric field, known as ‘polar catastrophe’, inside the manganite. As a consequence of this charge transfer, the manganite layer switches to a strongly ferromagnetic state, as could be visualised by a magnetic microscopy technique called Scanning SQUID Microscopy. This was conducted by Dr Xiao Renshaw Wang, who is a PhD graduate from NUSNNI, working with Professor Hans Hilgenkamp at the MESA+ Institute of the University of Twente in The Netherlands. The work validates the polar catastrophe model, and it shows how the addition of just one extra atomic layer can transform the magnetism. The team plans to use local electric fields to controllably turn on/off the magnetism of its 5-layer films, and explore potential applications in microwave devices and magnetic recording. With magnetic memory elements approaching nano dimensions, this technique promises new approaches in magnetic recording and computing.
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Image of the magnetic fields recorded by scanning a tiny superconducting coil over the surface of a LaMnO3 film grown on a substrate crystal. The magnetic left-hand side is seven LaMnO3 blocks thick (about 3 nm), while the nonmagnetic right-hand side is only five (2 nm). The measuring setup is shown on the right. (Image: NUS) (click on image to enlarge) The team from the National University of Singapore (NUS) - Mr Li Changjian, a graduate student from the NUS Graduate School for Integrative Sciences and Engineering, Assistant Professor Ariando and Professor T Venky Venkatesan – led to the discovery of this new magnetic phenomenon by growing perfectly-crystalline atomic layers of a manganite, an oxide of lanthanum and manganese {LaMnO3}, on a substrate crystal of nonmagnetic strontium titanate using a method – pulsed laser deposition – developed many years ago for high-temperature superconductors and multicomponent materials by Prof Venkatesan, who now heads the NUS Nanoscience and Nanotechnology Institute (NUSNNI). The manganite is an antiferromagnet when it is atomically thin and shows no magnetism. The new discovery is that its magnetism is switched on abruptly when the number of Manganese atomic layers changes from 5 to 6 or more. The conjecture is that this arises from an avalanche of electrons from the top surface of the film to the bottom, where the electrons are confined near the substrate. This shift of electric charge occurs as the manganese atomic layers form atomically charged capacitors leading to the build-up of an electric field, known as ‘polar catastrophe’, inside the manganite. As a consequence of this charge transfer, the manganite layer switches to a strongly ferromagnetic state, as could be visualised by a magnetic microscopy technique called Scanning SQUID Microscopy. This was conducted by Dr Xiao Renshaw Wang, who is a PhD graduate from NUSNNI, working with Professor Hans Hilgenkamp at the MESA+ Institute of the University of Twente in The Netherlands. The work validates the polar catastrophe model, and it shows how the addition of just one extra atomic layer can transform the magnetism. The team plans to use local electric fields to controllably turn on/off the magnetism of its 5-layer films, and explore potential applications in microwave devices and magnetic recording. With magnetic memory elements approaching nano dimensions, this technique promises new approaches in magnetic recording and computing.
A new approach to cancer therapy using improved photodynamic technology has been developed at Oregon State University. (Graphic courtesy of Oregon State University) (click on image to enlarge) Ovarian cancer has a high mortality rate because it often has metastasized into the abdominal cavity before it’s discovered. Toxicity and cancer-cell resistance can also compromise the effectiveness of radiation and chemotherapy that’s often used as a follow-up to surgery. The new approach being developed by researchers from the OSU College of Pharmacy and the University of Nebraska takes existing approaches to photodynamic therapy and makes them significantly more effective by adding compounds that make cancer cells vulnerable to reactive oxygen species, and also reducing the natural defenses of those cells. “Surgery and chemotherapy are the traditional approaches to ovarian cancer, but it’s very difficult to identify all of the places where a tumor has spread, and in some cases almost impossible to remove all of them,” said Oleh Taratula, an assistant professor in the Oregon State University/Oregon Health & Science University College of Pharmacy. “Photodynamic therapy is a different approach that can be used as an adjunct to surgery right during the operation, and appears to be very safe and nontoxic,” Taratula said. “In the past its effectiveness has been limited, but our new findings may make this technology far more effective than it’s ever been before.” Using the new approach, a patient is first given a photosensitizing compound called phthalocyanine, which produces reactive oxygen species that can kill cells when they are exposed to near-infrared light. In addition, a gene therapy is administered that lowers the cellular defense against reactive oxygen species. Both the phthalocyanine and genetic therapy, composed of “small, interfering RNA,” are attached to what researchers call “dendrimer-based nanoplatforms,” a nanotechnology approach developed by OSU researchers. It delivers the compounds selectively into cancer cells, but not healthy cells. Compared to existing photodynamic therapies, this approach allows the near-infrared light to penetrate much deeper into abdominal tissues, and dramatically increases the effectiveness of the procedure in killing cancer cells. Using photodynamic therapy alone, some tumors in laboratory animals began to regrow after two weeks. But with the addition of the combinatorial genetic therapy to weaken the cancer cell defenses, there was no evidence of cancer recurrence. During the procedures, mice receiving the gene therapy also continued to grow and gain weight, indicating a lack of side effects. “Cancer cells are very smart,” Taratula said. “They overexpress certain proteins, including one called DJ1, that help them survive attack by reactive oxygen species that otherwise might kill them. We believe a key to the success of this therapy is that it takes away those defensive mechanisms.” The overexpression of DJ1, researchers said in their study, is associated with invasion, metastasis, resistance to cancer therapies, and overall cancer cell survival. That excess of DJ1 is silenced by the genetic therapy composed of siRNA. The findings of this research, Taratula said, could also build upon some other recent advances in photodynamic therapy, in which a different compound called naphthalocyanine could be administered prior to surgery, causing the cancer cells to “glow” and fluoresce when exposed to near-infrared light. This provides a literal road map for surgeons to follow, showing which tissue is cancerous and which is not. There’s no reason that approach couldn’t be combined with the newest advance, Taratula said, providing multiple mechanisms to improve surgical success and, with minimal side effects, help eradicate any remaining cancer cells that were not completely removed. “Our study established a prospective therapeutic approach against ovarian cancer,” the researchers wrote in their conclusion. “The tumors exposed to a single dose of a combinatorial therapy were completely eradicated from the mice.”
Illustration: Dr. Eric M.M. Tan A polymer can be compared to a necklace of small molecules that are chemically linked together. Polymers are the basis of a huge variety of natural and artificial materials, from skin, hair and DNA, to the simplest and most advanced plastics. The properties of these polymer materials are largely determined by their spatial structure, also known as ‘conformation’. Polymers can be as straight as uncooked spaghetti, but can also occur as a tangle of cooked spaghetti. Polymer chains resist changes to their conformation, for example when they are stretched. This spring-like effect provides elasticity to rubbers, flexibility to plastics and strength to the cytoskeleton of the cell. Therefore, to change the conformation of a polymer, force must be applied to the molecule. But figuring out the exact conformation of a polymer is particularly difficult, especially if the polymers are surrounded by many other substances, such as in a cell. Fingerprint A team of researchers from the Physical Chemistry and Soft Matter Group of Wageningen University, led by Joris Sprakel, has designed a new kind of polymer that 'reports' its spatial configuration to the researchers through the light it emits. PhD candidate Hande Cingil carried out the work on the water-soluble semiconducting polymers, which the researchers have called conjugated polyelectrolytes (CPEs). Luminescent polymers have existed for some time. They change colour as their conformation changes. A special feature of the CPE polymers is that nuances can be observed in these colour changes. Following irradiation with UV light, the existing polymers emit a colour spectrum that looks like the profile of a mountain with a flat top. But the new polymers have their own ‘fingerprint’: they show specific peaks in the spectrum. In addition, these peaks shift as the spatial structure changes, for example, if the material in which they are incorporated is stretched. As a result, the novel polymers can detect very small forces on the nanoscale. Artificial virus In their publication in the prestigious Journal of the American Chemical Society, the Wageningen chemists demonstrate the functioning of their CPE polymers. For this purpose they used a protein that was designed by their colleagues in Wageningen, Renko de Vries and Martien Cohen Stuart. The protein is a highly simplified version of an artificial virus; like a biological virus, it binds to DNA and subsequently encapsulates it. Sprakel: “In our experiment, the CPE was encapsulated by the simplified artificial virus protein, giving it a rigid layer, which caused the polymer to change shape. Using simple and non-invasive light spectroscopy, this encapsulation process can now be studied in detail.” Rupture The novel polymers can be used for many purposes. For example, groups of molecules can be attached to the polymers for specific applications, such as the detection of proteins or toxins. Thanks to this discovery it is possible to study changes in conformation, also deep inside complex substances and materials, in an entirely new way. For example, it offers an improved method for determining exactly how viral proteins stretch and fold to encapsulate DNA, or how very minor damage to polymeric materials gradually accumulates and eventually causes the materials to rupture. The researchers are currently working on fundamental research that goes beyond showing whether a polymer chain has stretched: they aim to show exactly where in the chain this stretching occurred.