Quantum Dots

QUANTUM DOTS

A quantum dot is a semiconductor whose excitons are confined in all three spatial dimensions. As a result, they have properties that are between those of bulk semiconductors and those of discrete molecules. Quantum dots (QDs) are a novel class of inorganic fluorophore which are gaining widespread recognition as a result of their exceptional photophysical properties. They are rapidly being applied to existing and emerging technologies, and could have an important role in many areas. Quantum dots (QDs) are nanometer-scale semiconductor crystals composed of groups II–VI or III–V elements, and are defined as particles with physical dimensions smaller than the exciton Bohr radius.When a photon of visible light hits such a semiconductor, some of their electrons are excited into higher energy states. When they return to their ground state, a photon of a frequency characteristic of that material is emitted. Metal and semiconductor nanoparticles in the size range of 2–6nm are of considerable interest, due to their dimensional similarities with biological macromolecules (e.g. nucleic acids and proteins).

Optical properties of QDs            Quantum confinement effects give rise to unique optical and electronic properties in QDs, giving them numerous advantages over current fluorophores, such as organic dyes, fluorescent proteins and lanthanide chelates. Properties that particularly influence fluorophore behaviour, and therefore applicability to different situations, include the width of the excitation spectrum, the width of the emission spectrum, photostability, and the decay lifetime. 

Biological applications

            Optical properties of QDs applied in measuring protein conformational change, monitoring protein interaction and assaying of enzyme activity by (Fluorescence resonance energy transfer analysis) FRET mechanism for use in immunoassays. Apart from DNA technology QDs may find use in RNA technologies, in detection of mRNA molecules using ISH and in combination with siRNA in RNA interference applications. QDs have been successfully used in ISH techniques to study the expression of specific mRNA transcripts. QDs further exploited in Fluorescent labelling of cellular proteins, Cell tracking, Pathogen and toxin detection, in vivo animal imaging and tumour biology investigation.  Tumour vasculature plays an important role in determining tumour pathophysiology, and drug delivery. Combination of QDs imaging with second-harmonic generation (SHG), has been used for collagen imaging in normal and cancer tissue. These results show the potential application of QDs in clinical diagnostics.

References
1.Biomaterials 28 (2007) 4717–4732
2.www.mdpi.org/.../logo-quantumdots.jpg
3.http://en.wikipedia.org/wiki/Quantum_dot