Nano News: 04/15/15

Nanotechnology research finds a way to treat tumors with green tea

Delivering a drug to a targeted site in the body requires a ‘carrier’ — a compound that encases the drug. However, optimizing the drug-to-carrier ratio can be a major challenge. “This ratio is a stumbling block in carrier design because the carrier itself provides no therapeutic effect,” explains Jackie Ying. “Furthermore, high quantities of the carrier may lead to problems associated with drug toxicity and metabolism.”

To overcome this problem, Ying, along with Joo Eun Chung, Motoichi Kurisawa and other co-workers, have designed a drug carrier that possesses therapeutic effects.

The scientists identified a catechin derivative in green tea known as epigallocatechin gallate (EGCG), which has documented anticancer effects, as the most promising carrier candidate. They used EGCG as the basis for 90-nanometer-diameter micellar nanocomplexes to deliver the anticancer protein drug Herceptin directly to tumors. The researchers did this by oligomerizing EGCG and then binding it to Herceptin, which formed the core of the micellar nanocomplexes. Finally, they formed the outer shells of the micellar nanocomplexes by binding polyethylene glycol–EGCG to the cores.

Cancer is not the only potential target for this drug delivery system. “EGCG binds to many biological molecules, such as proteins, peptides and genes, and this is responsible for its many beneficial activities,” notes Kurisawa. In particular, EGCG is known to be beneficial for cardiovascular and metabolic health; it also exhibits anti-HIV effects as well as neuro- and DNA-protective effects. “Our green-tea-based nanocarrier has the potential to deliver a variety of proteins, genes or drugs to improve the treatment of other diseases besides cancer,” remarks Chung.

Sputtering start for flat materials

Two-dimensional materials have a whole host of exotic properties because they are just one atom thick. A*STAR researchers have now developed a method for creating large areas of atom-thin material for use in electronic devices ("Growth of wafer-scale MoS2 monolayer by magnetron sputtering"). Graphene, a single layer of carbon atoms arranged into a honeycomb-like pattern, is the most famous example of a two-dimensional material. It is stronger than steel, has excellent electrical properties, and could be used to make two-dimensional devices that are much smaller than those currently made from bulk or thin-film silicon. However, it is not a semiconductor. And so scientists are turning to other materials that have this essential property for creating transistors.

Transistors made of films of two-dimensional molybdenum disulfide (MoS2) could be integrated with other silicon electronics devices. (Image: A*STAR Institute of Materials Research and Engineering) Shijie Wang from the A*STAR Institute of Materials Research and Engineering and his collaborators have now demonstrated a technique for creating a single atomic layer of molybdenum disulfide — a two-dimensional semiconductor. Molybdenum disulfide belongs to a family of materials called transition-metal dichalcogenides. They have two chalcogenide atoms (such as sulfur, selenium or tellurium) for every transition-metal atom (molybdenum and tungsten are examples). These materials and their wide range of electrical properties provide an excellent platform material system for versatile electronics. But creating high-quality material over areas large enough for industrial-scale production is difficult. “Traditional mechanical exfoliation methods for obtaining two-dimensional materials have limited usefulness in commercial applications, and all previous chemical methods are incompatible for integration with device fabrication,” says Wang. “Our technique is a one-step process that can grow good-quality monolayer films, or few layers of molybdenum disulfide films, at wafer scale on various substrates using magnetron sputtering.” The team fired a beam of argon ions at a molybdenum target in a vacuum chamber. This ejected molybdenum atoms from the surface where they reacted with a nearby sulfur vapor. These atoms then assembled onto a heated substrate of either sapphire or silicon. The team found that they could grow monolayer, bilayer, trilayer or thicker samples by altering the power of the argon-ion beam or the deposition time. They confirmed the quality of their material using a number of common characterization tools including Raman spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. The researchers also demonstrated the excellent electrical properties of their molybdenum disulfide films by creating a working transistor (see image). “Our next step in this work will focus on the application of this technique to synthesize other two-dimensional materials and integrate them with different materials for various device applications,” says Wang.

Lanthanide-organic framework nanothermometers prepared by spray-drying

A work in Advanced Functional Materials shows how spray-drying prepared MOF nanoparticles containing lanthanide metals may be used as nanothermometers operative over a wide range of temperatures, in particular, in the cryogenic range. The work was coordinated from the University of Aveiro (Portugal) and participated by Ramón y Cajal Researcher Dr Inhar Imaz and ICREA Research Prof Daniel Maspoch from the ICN2 Supramolecular NanoChemistry & Materials Group. Members of the ICN2 have collaborated in a new research to get nanothermometersthat can provide accurate, noninvasive and self-referenced temperature measurements at the submicrometer scale. Ramón y Cajal Researcher Dr. Inhar Imaz and ICREA Research Prof Daniel Maspoch from the Supramolecular NanoChemistry & Materials Group have participated in the research which has been coordinated from University of Aveiro (Portugal). The results have been published in in an article entitled "Lanthanide–Organic Framework Nanothermometers Prepared by Spray-Drying". The thermal dependence of the phosphor's luminescence provides high detection sensitivity and spatial resolution with short acquisition times in, e.g., biological fl uids, strong electromagnetic fields, and fast-moving objects. The strategy followed to design this kind of devices relies on the thermal dependence of the phosphor luminescence, which provides high detection sensitivity and special resolution with short acquisition times in, e.g., biological fluids, strong electromagnetic fields, and fast-moving objects. The temperature determination is usually based on the change of the luminescence intensity or decay times. However, the measurements based on a single f–f transition may be much affected by the variation of the sensor concentration and the drift of the optoelectronic systems, namely, the excitation sources and detectors. Recently, authors reported self-reference nanothermometers based on the intensity ratio of two f–f transitions that overcome the drawbacks of temperature determination with a single transition. The article also shows that spray-drying prepared MOF nanoparticles may be used as ratiometric luminescent nanothermometers operative over a wide range of temperatures, in particular, in the cryogenic range. Prof Maspoch and Dr Imaz have contributed in the synthesis of the MOF nanoparticles of Tb(III) and Eu(III), the first lanthanide-organic framework prepared by the spray-drying method. This system is the most sensitive cryogenic nanothermometer reported so far, combining high sensitivity, reproducibility, and low-temperature uncertainty.