The Wonderful NanoWorld

Size matters. In the case of nano-technology, elements broken down into their smallest particles exhibits unique properties in ways that the same elements in bulk sizes cannot. By identifying and measuring those properties, they can be used for applications that can benefit humanity. The National Nanotechnology Initiative indicates that matter or elements on a nano-scale exhibits unusual physical, chemical and biological properties(0). Some are stronger. Some exhibit different magnetic properties. Other saw an improvement in conducting electricity or heat. Others reflect light and change colors as their sizes or structures are altered.

Quantum dots (QDs), also known as nanoscale semiconductor crystals, were first described by Ekimov and Onushenko(1) in a glass matrix, back in 1981, with the first biological imaging application reported in 1998.(2) Since then the field of QDs has been growing steadily and now includes applications in fields of solar cells, photovoltaic devices, light-emitting diode (LED) fabrication, photodetectors, computing, biomedical imaging and so on.

Most conventional organic label dyes do not offer the near-infrared (NIR) (>650 nm) emission possibility; this region is highly desired for biomedical imaging due to its reduced light scattering and low tissue absorption, it is why QDs with their tunable optical properties have gained a lot of interest.(3) These nanometric semiconductors offer unique and fascinating optical properties, such as high quantum yield, size-tunable light emission and good chemical and photo-stability.(4) QDs, with sizes 2–10 nm, are generally composed of elements (such as Cd, Pb, Hg) from groups II–VI, III–IV and IV–VI in the periodic table. More recently, researchers have developed ternary I–III–VI QDs (where I = Cu or Ag, III = Ga or In, VI = S or Se).(5) Different types of QDs can be excited with the same light wavelength, and their narrow emission bands can be detected simultaneously for multiple assays. The fluorescence bands of QDs are dependent on their composition, size and shell thickness.(6) If the particle size is smaller than the bulk materials’ Bohr radius, it causes the energy levels to pose atom-like properties and become discrete compared to the continuum energy levels observed in bulk materials; in other words, these unique properties result from the confinement of the states of charge carriers by the physical reduction in the size of the nanoparticles.(7) In order to use QDs under ambient conditions, they must be stabilized or passivated, because of their high reactivity and surface area. When choosing a stabilizer, one has to take into account the absorption and luminescence spectra profile; also the quantum yield and the lifetime depend on the environment composition.(8)

NanoHarmonics is one of the companies working on QD technology for medical devices. Along with the promise of QD technology for accurate diagnosis, it opens the door for other applications as well. While other uses of Quantum Dots in the medical field particularly in Theranostics (imaging, drug delivery, therapy) are still in the research stage, we believe that some will be available soon.  Early detection paired with a non-privacy invasive contact tracing technology platform may be the future that cannot come soon enough.

(0) Quantum dots in imaging, drug delivery and sensor applications

Cristian T Matea,1,* Teodora Mocan,1,2,* Flaviu Tabaran,1,3,* Teodora Pop,1,4,* Ofelia Mosteanu,1,4,* Cosmin Puia,1,5,* Cornel Iancu,1,5,* and Lucian Mocan1,5,* nano.gov

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