The properties of a quantum dot are not only determined by its size but also by its shape, composition, and structure, for instance if it's solid or hollow. A reliable manufacturing technology that makes use of nanocrystals' properties - for a wide-ranging number of applications in such areas as catalysis, electronics, photonics, information storage, imaging, medicine, or sensing - needs to be capable of churning out large quantities of nanocrystals where each batch is produced according to the exactly same parameters. In a recent review article, Sara Skrabalak from Indiana University and Younan Xia from Washington University in St. Louis, describe recent advances in seeded growth as the ultimate approach to producing metal nanocrystals with precisely controlled sizes, shapes, and compositions - the necessary first step toward their use and assembly for large-scale applications.
Quantum dots are emerging as an important class of nanoparticles with applications ranging from medicine to energy. These nanocrystals possess size tunable optical and electronic properties resulting from quantum confinement which allow them to be suitable candidates for applications in solar cells and light emitting devices. For instance, quantum dots have been identified as important light harvesting material for building highly efficient solar cells - when exposed to light at certain wavelengths they can generate free electrons and create an electrical current. Having a high resistance to photobleaching, quantum dots (QDs) also are attractive materials for optoelectronics and in vivo biosensing. Researchers have now demonstrated that QDs, in addition to being excellent fluorescent probes, can be used as photoacoustic (which combines the advantages of optical absorption contrast with ultrasonic spatial resolution for deep imaging) and photothermal contrast agents and sensitizers, thereby providing an opportunity for multimodal high resolution photoacoustic/photothermal-fluorescent imaging as well as sensitizers in nanotherapeutic applications.
The study of individual live cells is a hugely important scientific task and essential to the field of molecular biology and biomedical research. Among the most significant technical challenges for performing successful live-cell imaging experiments is to maintain the cells in a healthy state and functioning normally on the microscope stage while being illuminated. Especially if scientists want to look into cellular processes that occur inside cells in their natural state and that cannot be observed by traditional cytological methods. Quantum dots (QDs), also called nanocrystals, hold increasing potential for in vitro and in vivo cellular imaging. For instance, we have previously reported about how researchers have used QDs for in vivo imaging of embryonic stem cells in mice, a novel technique that has opened up the possibility of using QDs for fast and accurate imaging applications in stem cell therapy. The usefulness of quantum dots comes from their peak emission frequency's extreme sensitivity to both the dot's size and composition. QDs have been touted as possible replacements for organic dyes in the imaging of biological systems, due to their excellent fluorescent properties, good chemical stability, broad excitation ranges and high photobleaching thresholds.
The way things stand now, nanotechnology products can be sold unlabeled and the FDA regulates sunscreens only based on their sun protection factor. Cosmetic manufacturers, of course, claim that their products, including nanoparticle-based sunscreens are harmless. Indeed, nobody has demonstrated that they are unsafe - but the opposite proof, that they are perfectly safe, is missing as well. This confusing situation is due to the incomplete scientific picture created by a lack of relevant research. For instance, the question of whether or not nanoparticles can penetrate the healthy stratum corneum skin barrier in vivo remains largely unanswered. Furthermore, no studies so far have examined the impact of ultraviolet radiation on nanoparticle skin penetration. Since sunscreen is often applied to sun damaged skin, such a real world scenario, as opposed to in vitro studies in a test-tube, could go a long way in confirming or allaying fears. New research by scientists at the University of Rochester is the first to consider the effects of nanoparticle penetration through normal and barrier defective skin using an in vivo model system.
More than half a century ago, Erwin Schroedinger, nobel laureate in physics, claimed that it is 'impossible to carry out experiments on single molecules or atoms'. Today, the detection, tracking and study of single molecules and atoms has become an omnipresent tool in biology, chemistry and physics alike. For example, sequencing DNA one base pair (or letter) at a time currently provides the most likely solution to fulfill the quest for a $1,000 human genome. Nevertheless, observation of a single molecule, especially with standard light microscopes requires a good deal of laboratory skills. This is mostly due to the fact that a single molecule only gives a miniscule amount of detectable signal. In fact, people using light as a probe have relied exclusively on the use of fluorescence, the emission of lower energy light following absorption of radiation at a certain energy. In this scheme, the signal from the molecule of interest can be easily separated from residual excitation light or background fluorescence simply by filtering the detected light spectrally and only detecting the color that is emitted by the molecule. In this way, it is possible to suppress unwanted signals from the billions of other molecules that are in the vicinity of the molecule of interest. As powerful as this approach has been, it also has one major limitation: it is only possible to study molecules that are highly fluorescent, i.e. emit lower energy light with high efficiency. Scientists from the ETH Zurich have recently demonstrated a major step towards the detection and study of single molecules in absorption.
In recent years, great progress has been made in the synthesis and application studies of hybrid nanomaterial systems involving carbon nanotubes (CNTs). Efforts involve the alteration of physical properties of CNTs via the use of organic, inorganic, and biological species to produce functionalized CNTs for further applications. In one such hybrid system, aligned CNT templates serve as a natural 3D scaffold ('CNT forests'). Preferential assembly of nanoparticles onto targeted locations in this 3D scaffold creates novel hybrid nanomaterial systems with a unique architecture comprised of different functional components. For example, these CNT forests could serve as a template for controlled assembly of various semiconducting nanoparticles such as quantum dots. The resulting hybrid nanomaterial has the effect of changing both optical and electronic properties of the CNTs.
A quantum dot (QD), also called a nanocrystal, is a semiconductor nanostructure that can be as small as 2 to 10 nm. The usefulness of quantum dots comes from their peak emission frequency's extreme sensitivity - quantum mechanical in nature - to both the dot's size and composition. QDs have been touted as possible replacements for organic dyes in the imaging of biological systems, due to their excellent fluorescent properties, good chemical stability, broad excitation ranges and high photobleaching thresholds. By contrast, conventional organic dyes cannot be easily synthesized to emit different colors and have narrow excitation spectra and broad emission spectra that often cross into the red wavelengths, making it difficult to use these dyes for multiplexing. QDs hold increasing potential for cellular imaging both in vitro and in vivo. Researchers have now used QDs for in vivo imaging of embryonic stem cells in mice. This opens up the possibility of using QDs for fast and accurate imaging applications in stem cell therapy.
Recent developments in spectroscopic techniques allow highly sensitive image detection both in vitro and in vivo on the individual cell level. These methods depend on nanometer-size particles as detection probes. One class of such particles, so-called nanocrystals or quantum dots (qdots), is very popular for constructing detection probes for biolabeling. Scientists have discovered that these nanocrystals can enable researchers to study cell processes at the level of a single molecule and may significantly improve the diagnosis and treatment of diseases such as cancers. Qdots are either used as active sensor elements in high-resolution cellular imaging, where the fluorescence properties of the qdots are changed upon reaction with the analyte, or in passive label probes where selective receptor molecules such as antibodies have been conjugated to the surface of the dots. Qdots could revolutionize medicine. Unfortunately, most of them are toxic. Ironically, the existence of heavy metals in qdots such as cadmium, a well-established human toxicant and carcinogen, poses potential dangers especially for future medical application, where qdots are deliberately injected into the body. As the use of nanomaterials for biomedical applications is increasing, environmental pollution and toxicity have to be addressed, and the development of a non-toxic and biocompatible nanomaterial is becoming an important issue. Researchers are now proposing the use of nanoscale diamond particles as a non-toxic alternative to heavy metal qdots.