Hollow polymeric micro- and nanoparticles have numerous existing and many anticipated applications in drug delivery, ranging from the controlled release of drugs, cosmetics, inks, pigments or chemical reagents to the protection of biologically active species, and removal of pollutants. Encapsulation also allows drug targeting via cell and tissue-specific ligands. There is a variety of methods available for synthesis of polymer microspheres with hollow interiors. The hollow particles are most commonly prepared by coating the surfaces of colloidal templates with thin layers of the desired material (or its precursor), followed by selective removal of the templates by means of calcination or chemical etching. For polymers, methods such as emulsion polymerization, phase separation, cross-linking of micelles and self-assembly have also been demonstrated for generating hollow structures. The hollow polymer particles produced by these methods present either a closed-core-shell structure or many small pores on their surface. However, these synthetic approaches present limitations on the choice of polymers that can be produced as hollow microspheres. Also, the number, size and shape of the surface pores can not be easily manipulated. When these materials are used for encapsulation-related applications, the encapsulation of the desired functional materials is usually too slow and/or too labor-intense. These problems have motivated scientists to develop the synthesis of a new class of polymer microspheres, which they called microscale fish bowls. Their unique feature consists in the presence of one big pore on their surface that allows easy and fast diffusion of a functional material to be encapsulated. Another new feature is that this newly developed method presents no limitations on the choice of polymers that can be produced as microscale fish bowls.
Sophisticated optical lithography techniques have been developed by the semiconductor industry to pack more and more transistors onto chips. On the road to a billion transistors per chip, Intel has already developed transistors so small that 200 million of them could fit on the head of a pin. As if that wasn't small enough, scientists are pushing further down, hoping to be able one day to reliably (and affordably) control surface features as small as 1 nm. With today's technology, cost-effective fabrication in the sub-50 nm range is a major challenge. Given the advanced development of (nano)lithography it is not surprising that various forms of it are the most common techniques used by nanotechnology researchers for manipulating sub-100 nm surface features. With the current state of optical lithography it appears that traditional commercial lithography techniques will not be cost effective below 30 nm. State-of-the-art electron beam lithography (EBL) has been proved to be capable of delivering resolution in the 10 nm range. Unfortunately, EBL is slow, very expensive and it is very unlikely that it can effectively go below 10 nm. The same limitations hold for x-rays and focused ion beams (FIBs), with additional tremendous difficulties in developing equipment for beam manipulation and focusing on nanometer scales.
Nature has excelled in designing molecular motors, something nanotechnology researchers are still having a hard time with. The potential for nano-actuators (a nanoscale device that creates automatic motion by converting various forms of energy to rotary or linear mechanical energy) is huge - basically any active system that performs some kind of work requires an energy source. Applications reach from simple pumps on lab-on-a-chip devices to move nanoliters of fluid around to nanoscale motors for nanorobotic systems. One of the challenges of designing such a motor for the nano realm is that during the design of a nano-actuator the tradeoffs among range of motion, force, speed (actuation frequency), power consumption, control accuracy, system reliability, robustness, load capacity, etc. must be taken into consideration. Most microscale systems are currently achieved by relatively large external actuators such as syringe pumps, or high voltage power supplies, which negates the advantages of the microfabricated systems. That's why scientists are quite intrigued by the opportunity to use biological organisms to construct mechanical actuators in engineered systems at the micro- or even nanoscale. An extremely powerful biological motor is the bacterial flagellar motor found in organisms such as Escherichia coli or Serratia marcescens. Bacteria draw chemical energy directly from their environment and are able to survive in a wide range of temperature and pH. What makes bacterial propulsion system interesting for nanotechnology researchers is that bacteria are exquisitely sensitive to a wide variety of external stimuli. So far, scientists have managed to control them en masse through light (phototaxis) and chemical (chemotaxis) sensory mechanisms. In a recent example of successful use of live bacteria as mechanical actuators, scientists have built a microfluidic pump powered by self-organizing bacteria.
Biosensors, which incorporate biological probes coupled to a transducer, have been developed during the last two decades for environmental, industrial, and biomedical diagnostics. Typically, signal sizes generated by biomolecular binding tend to be extremely small - this is the limiting factor in reaching high sensitivity for these sensors. The application of nanotechnology to biosensor design and fabrication and therapy at the molecular and cellular level promises to revolutionize bio-diagnostics. By exploiting the large surface-to-volume ratio of nanowires, nanotubes, nanocrystals, nanocantilevers, or quantum dots, researchers were able to build sensors that can measure extremely faint, and otherwise undetectable, signals - for instance a change in electrical conductance - arising from biomolecular binding on the surface of these nanodevices. Highly sensitive nanoprobes and nanosensors have the potential for a wide variety of medical uses at the cellular level. For instance, the potential for monitoring in vivo biological processes within single living cells, e.g. the capacity to sense individual chemical species in specific locations within a cell, will greatly improve our understanding of cellular function, thereby revolutionizing cell biology. One way of enhancing signal strength is on the sensor device itself and researchers have now demonstrated such an on-chip signal amplification using a standard protein on a nanoscale field effect transistor.
Two of the major challenges of our modern, mobile society are the shrinking of available fossil energy resources on one hand and climate change associated with global warming on the other. Continuing population growth multiplied by the increase in consumption and living standards, especially in developing countries, will require more and more oil, coal and natural gas to 'power' humanity. Notwithstanding efforts like the Kyoto Protocol - which wasn't signed by the two major CO2 polluters China and the U.S. - an ever increasing rate of fossil fuel usage means that the increasing emission of CO2 is likely to cause an acceleration of the climate change that is in progress already. Transportation, in particular passenger cars, is one of the areas where new technology could lead to environmental beneficial change. Never mind that GM is still selling 15-20,000 Hummers a year, or that Tata is planning to sell millions of its new Nano car. One of the much touted technological solutions is to substitute fossil hydrocarbon based energy with the energy from carbon-free sources like the sun, nuclear energy, or the hot interior of the Earth and use hydrogen as an energy carrier. Hydrogen can be produced from water using energy from carbon-free sources and can serve as fuel in fuel cells to generate electricity, either stationary or on board of vehicles. Considerable research efforts are going into the evaluation of various nanostructures, such as carbon nanotubes, to find the most suitable hydrogen storage materials.
Toxicology is an interdisciplinary research field concerned with the study of the adverse effects of chemicals on living organisms. It applies knowledge, methods and techniques from such fields as chemistry, physics, material sciences, pharmacy, medicine and molecular biology. Toxicology established itself in the last 25-30 years as a testing science in the course of efforts of industrial nations to regulate toxic chemicals. Particle toxicology, as a subdiscipline, developed in the context of lung disease arising from inhalation exposure to dust particles of workers in the mining industry. It later expanded to the area of air pollution. With the rapid development of nanotechnology applications and materials, nanotoxicology is emerging as an important subdiscipline of nanotechnology as well as toxicology. Most, if not all, toxicological studies on nanoparticles rely on current methods, practices and terminology as gained and applied in the analysis of micro- and ultrafine particles and mineral fibers. Together with recent studies on nanoparticles, this has provided an initial basis for evaluating the primary issues in a risk assessment framework for nanomaterials. However, current toxicological knowledge about engineered nanoparticles is extremely limited and traditional toxicology does not allow for a complete understanding of the size, shape, composition and aggregation-dependent interactions of nanostructures with biological systems. An understanding of the relationship between the physical and chemical properties of nanostructures and their in vivo behavior would provide a basis for assessing toxic response and more importantly could lead to predictive models for assessing toxicity.
Most people when they hear the word semiconductor will think about their role in computers. However, semiconductors also absorb light, some absorb in the visible, thus appearing colored, e.g. gray silicon, and others in the UV, such as titanium dioxide, thus appearing white (when in microparticulate form) or colorless (when in nanoparticulate form). This light-absorbing feature is used to drive electrons around a circuit in photovoltaic cells, such as the silicon solar cell, but it can also be used to drive chemical reactions at the surface. A good example of the latter is the use of thin (15 nm) titanium dioxide film coatings on self-cleaning glass. These films upon absorbing UV light in sunlight are able to reduce oxygen, present in air, to water and oxidize any organic material on its surface to its minerals, thereby keeping the surface clean. Researchers in the UK have used this oxidation feature to developed an irreversible solvent-based blue ink, which upon activation with UV light, loses all its color and becomes oxygen sensitive; it will only gain its original color upon exposure to oxygen. A major application area for this oxygen ink is in food packaging where it could be used to detect a modified atmosphere inside food containers.
One statement of the second law of thermodynamics is that the efficiency of any heat engine or other thermodynamic process is always less that 100%. There will always be some type of friction or other inefficiency that will generate waste heat. The useful work that a heat engine can perform will therefore always be less than the energy put into the system. Engines must be cooled, as a radiator cools a car engine, because they generate waste heat. While there is no way around the second law of thermodynamics, the performance of today's power generation technology is quite appalling. The average efficiency today for fossil-fired power generation, 35% for coal, 45% for natural gas and 38% for oil-fired power generation. By the way, be skeptical when people tell you that nuclear power is good in the fight against global warming - nuclear power plants have a worse thermal efficiency (30-33%) than fossil-fired plants. Approximately 90% of the world's power is generated in such a highly inefficient way. In other words: every year some 15 billion kilowatts of heat is dumped into the atmosphere during power generation (talk about fueling global warming...). This is roughly the same amount as the total power consumption of the world in 2004. Reducing these inefficiencies would go a long way in solving the coming energy and climate problems. Thermoelectric materials - which can directly convert heat into electricity - could potentially convert part of this low-grade waste heat. Problem is that good thermoelectric materials are scarce and so far solid-state heat pumps have proven too inefficient to be practical. Two papers in this week's Nature describe how silicon devices could in principle be adapted and possibly scaled up for this purpose.