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Quantum Dot Basics
Quantum dots (QDs) are artificial clusters of semiconductive atoms that have the ability to confine the electrons motion due to their small size. One of the most important properties of Quantum Dots is the ability to tune their bandgap and therefore control their light absorbance and emission frequencies. This is done through the quantization of their energy levels. In this way it is possible for their optical and electrical properties to be adjusted according to their purpose of use.
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Pros of Quantum Dots
The latest advances in technology have shown that QDs can really make valuable contributions to a wide range of applications substituting for many of the bulk, expensive, and inefficient materials.
- Quantum Dot formations absorb photons of light and then re-emit longer wavelength photons for a period of time. The high level of control possible over the size of the dot produced provides very precise control over the wavelength of the re-emitted photon. That means that the color of the light emitted from the QD can actually be manipulated without significant cost or the use of high-end technology. Following this procedure, a full range of QDs can be manufactured, each with a narrow distinct emission spectrum.
- Another great benefit is the fact that they only require a small amount of energy in order to be excited and this can be achieved by a single blue or ultraviolet wavelength beam, regardless of the QD size. Both attributes reduce the costs dramatically.
- The high photostability and brightness of QDs make them suitable for high sensitivity applications like fluorescent tagging and live-cell imaging. Their fluorescence properties and their high resistance to metabolic degradation enable a wider range of experiments to be performed ignoring possible time barriers.
- QDs can be used in various forms, e.g. as small crystals in liquid solutions, as quantum dust, and in bead form. All these existing forms make their range of applications even wider.
- Another great aspect of QD manufacturing is that there are multiple methods to develop them easily and cost effectively. These methods include lithographic techniques, epitaxial techniques, and colloidal synthesis.
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Cons of Quantum Dots
Although the use of QDs is not so extensive yet, potential problems may arise during their application and manufacturing process.
- A potential drawback when used in biological applications is the fact that due to their large physical size, they cannot diffuse across cellular membranes. The delivery process may actually be dangerous for the cell and even result in destroying it. In other cases a QD may be toxic for the cell and inappropriate for any biological application.
- Their quite extended lifetime may be a hindrance to certain applications that require QDs to biodegrade immediately after the experiment has been performed. In certain cases however it is possible to remove the QDs by simply washing the cells with appropriate solutions.
- Additionally, Quantum Dots may blink and become invisible. Certain drawbacks on the QD surface may lead to quantum yield deterioration, meaning that the ratio of the emitted to the absorbed energy is rather low. Their low transmittance may stay undetectable or may demand high-sensitivity detection systems.
- In display and monitor industry, QDs are expected to be used in a new LED (light-emitting diode) variation, the QD-LEDs. However, the manufacturing of blue emitting QDs is a difficult process. It requires smaller sizes than the rest of the color emitting dots and an amplified emission compared to the other colors, so that the human eye can detect the same signal.
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Despite any disadvantages, the versatility and flexibility of QDs have proven to be valuable assets, capable of outweighing any negative aspects. This great advantage alone makes them excellent candidates for the production line and particularly significant for future developments.
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- "Opportunities and Risks Of Nanotechnologies" Allianz Center for Technology
- Fluorescence Imaging with Quantum Dot Nanocrystals, Semrock Inc
- Quantum Dots Explained, Evident Technologies
- Image by Alexander Kleinsorge (de.wikipedia) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons