By exploiting the outstanding properties of self-organizing materials, a team of Italian scientists has investigated a new way to build a bridge between two branches of physics: 'hard matter' and 'soft matter'. This allows researchers to address specific issues towards the realization of active-plasmonics devices, where the plasmonic resonance of gold nanoparticles can be finely controlled by means of external perturbations (electrical field, optical field, temperature). In place of a static approach - e.g. varying particles size, materials, etc. - the researchers used liquid crystals as active surrounding medium. This approach represents a 'scientific wedding' between the fascinating worlds of soft matter and plasmonics worlds.
Nanoscale materials like quantum dots, carbon nanotubes, graphene, or nanowires, have intriguing properties, but unless they can be assembled in to larger structures it is difficult to take advantage of these properties. Figuring out how to assemble nanostructures into functional macroscale assemblies is one of the key challenges that nanoscientists around the world are faced with. In the area of nanowires, this has led to researchers exploring various nanowire assembly techniques ranging from Langmuir Blodgett alignment to electrospinning. Researchers have now developed a novel approach for assembling nanowires into macroscopic yarns that consist of millions of nanowires bundled together. The team found that light can be used to charge inorganic semiconducting nanowires. Once charged, the nanowires can be manipulated with electric fields.
The idea of using laser light to trap or levitate small particles goes back to the pioneering work by Arthur Ashkin of Bell Laboratories in the 1970s and 1980s. Ashkin found that radiation pressure - the ability of light to exert pressure to move small objects - could be harnessed to constrain small particles. This discovery has since formed the basis for scientific advances such as the development of optical tweezers, which are frequently used to control the motion of small biological objects. However, optical trapping of nanoparticles remains a challenging task because the forces are often too small when the sizes of the objects are reduced to the nanometer scale. New findings from scientists at Lawrence Berkeley National Laboratory and National University of Singapore fill a gap and also open the door to new discoveries by demonstrating trapping and manipulating nanometer size particles using an electron beam instead of optical forces. It could also lead to new force spectroscopy where nanostructures can be assembled one nanoparticle at a time.
The heating properties of iron oxide nanoparticles have been exploited through the years for use in cancer therapy, gene regulation, and temperature responsive valves. These applications have demonstrated the versatility of iron oxide nanoparticles, but they had rarely, if ever, been used to enhance the activity of thermophilic enzymes. Thermophilic enzymes are highly stable biomolecular systems that are excellent tools due to their thermostability and long-term activity for extended lifetime uses in the field and other applications. New work by researchers in the U.S. addresses the problem of remotely activating biological materials with a higher efficiency than conventional methods such as water baths or convection ovens.
Dip-Pen Nanolithography (DPN) is a scanning probe lithography technique in which the tip of an atomic force microscope is used to 'write' molecules directly onto a substrate, allowing nanostructured surface patterning on scales of under 100 nm. Since the driving force of DPN for transporting materials is molecular diffusion through the sub-micrometer sized water meniscus formed between the AFM tip and the surface, large-sized ink materials are not efficiently transported through this water meniscus. For this reason, bacterial cells (1-2 micrometer or larger in length) patterning with DPN technique is often considered to be impossible. Overcoming this limitation, researchers have developed a 'stamp-on' DPN method that uses a previously developed hydrogel-coated tip and carrier agents to generate micrometer-sized bacterial cells.
Controlling the density of electron carriers - which are essential to the operation of electronic devices such as transistors - is achieved by doping conventional three-dimensional semiconductors. But graphene, a semi-metallic layer that is just one atom thick, has properties very different from traditional materials such as silicon. However, the doping of graphene is a key parameter in the development of graphene-based electronics. Researchers have investigated numerous strategies for doping graphene, including attaching organic or metallic molecules to its hexagonal lattice. Now, researchers have managed to dope graphene with light in a way that could lead to more efficient design and manufacture of electronics, as well as novel security and cryptography devices.
Quick Response Codes, or QR codes for short, are two-dimensional matrix codes that can hold 100 times more data than a traditional barcode. QR codes have rapidly gained popularity and are now very commonly used in various products, because of fast readability and large storage capacity. Applying the concept of QR codes to security printing applications - think banknotes - researchers have now developed an invisible QR code made from nanoparticles. They applied upconverting inks to print QR codes on paper and transparent tape, using an aerosol jet direct writing machine. They produced QR codes with embedded security characters using blue and green upconverting inks. These codes are invisible to the naked eye but produce single- and multi-color upconversion luminescence images under near-infrared excitation which can be read and decoded with an unmodified smart phone.
Reducing the size of photonic and electronic elements is critical for ultra-fast data processing and ultra-dense information storage. The miniaturization of a key, workhorse optical instrument - the laser - is no exception. Coherent light sources at the nanometer scale are important not only for exploring phenomena in small dimensions but also for realizing optical devices with sizes that can beat the diffraction limit of light. Researchers at Northwestern University have now found a way to manufacture single laser devices that are the size of a virus particle and that operate at room temperature. They show that subdiffraction nanoresonators based on metallic bowties, when coupled to a gain material, can generate coherent and directional light emission.