According to the Allied Market Research report, the global market for quantum dots will grow from about $300 million to over $5 billion dollars in the period from 2013-2020 period. So, what exactly is a quantum dot and how are they useful?
In 1988, the term “quantum dot” (or “QD” for short) was introduced by Dr. Mark Reed at Yale University to describe nanocrystalline semiconducting fluorophores. Fluorophores are chemical materials that re-emit light when excited by a light pulse. QDs are usually core-shell systems with a semiconductor core enclosed within a shell of another semiconductor material. They usually have confined diameters in the range of 2-20 nanometers (a nanometer is 1 x 10-9 meters) in all three spatial dimensions, resulting in size quantization effects. This size quantization means the band gap (the electron and hole excitation energy levels) of the QD can be “tuned” to provide different light emission frequencies by changing the composition of the QDs and varying their diameters. For example, the larger the QD, the redder, i.e.the lower the energy, emission. Researchers have utilized QDs as efficient materials for advanced photoelectric devices and solar cells. Dr. Arthur Nozik is one of the great leaders in this field (US 4,634,641). During his tenure at the National Renewable Energy Laboratory (NREL), he led a research group to discover variant semiconductor QDs for novel optical and energy systems (US 8,685,781 and US 9,324,562 ). Additionally the surfaces of QDs can be conjugated to various molecules to vary their physical properties, for example, to increase water solubility, reduce cytotoxicity, and resist reactive oxygen formation. The QDs can also be conjugated with specific molecules to target tumor biomarkers. These unique physical properties and the surface chemical modification of QDs have attracted increasing attention to applications in bio-imaging (reviewed in Part VI), bio-analytical assays and diagnostics, as well as the development of new therapeutic agents.