Context: The 2023 Nobel Prize in Chemistry has been awarded to Alexei Ekimov, Louis Brus, and Moungi Bawendi for their work on quantum dots.

Basic background:

• Fundamental facts of Chemistry:
  • Every element exhibits specific properties determined by the number of electrons in its atoms and the distribution of these electrons around the nucleus.
  • So, every piece of a pure element exhibits the same properties regardless of its size. 

E.g., Pure gold has Properties different from silver or any other element. Also, a large 100-gram piece of Gold will have exact properties like a small 10-milligram piece. 

• Peculiar behaviour at Nanoscale:
  • Particles in the nanoscale range behave slightly differently from larger particles of the same element. E.g., A nanoparticle of gold (sizes in the range of 1 to 100 billionth of a metre) displays properties different in some respects from larger particles of gold. 
  • Reasons for deviation: This is because when the size of the particles is reduced to the nanoscale, electrons in the atoms find themselves squeezed or constrained in a small space giving rise to quantum effects. 

The Nobel-winning research:

• The scientists were independently successful in developing efficient methods to produce nano-sized particles that behaved slightly differently than larger particles of the same element. These nanoparticles with special properties were called quantum dots.

Quantum dots:

• Quantum dots are tiny particles or nanocrystals of semiconducting material with a diameter in the range of 2–10 nm (10–50 atoms).
• QDs are nanosized in all three dimensions and are made from a semiconductor such as Silicon.
• They behave like artificial atoms, as they can have a fixed number of electrons in a confined space, leading to unique properties that are size-dependent.
• QDs exhibit special properties when they interact with light.
  • In general, the colour of any material depends on the wavelengths of the light spectrum absorbed or reflected by the material.
  • However, quantum dots made from the same material will re-emit/give out different colours of light depending on their size. The biggest quantum dots produce the longest wavelengths (and lowest frequencies), while the smallest dots make shorter wavelengths (and higher frequencies). 

Applications:

• Bioimaging: QDs are considered to be superior to traditional organic dyes and can be used in bioimaging.
  • QDs are 20 times brighter and 100 times more stable than traditional fluorescent dyes. 
  • Unlike organic dyes, which operate over a limited range of colours and degrade relatively quickly, quantum dyes are very bright, can be made to produce any colour of visible light, and last indefinitely as they are photostable.
• Bio-sensors: QD sensors can detect the presence of pathogens in food or water, or monitor the levels of pollutants in the environment.
• Targeted Cancer treatment:
  • QDs exhibit specific optoelectronic properties. They can be used for fluorescence imaging where quantum dots are injected into the body, which when encounters a cancer cell, attaches to it. When a light of a certain frequency is shined, QD lights up and doctors can exactly target these cells.
  • QDs can be targeted at single organs much more precisely than conventional drugs, reducing the side effects characteristic of untargeted, traditional chemotherapy.
  • Because of their nano size; they possess a large surface area ensuring higher drug loading capacity and can tag the nanocarriers in biological systems.

• Optical applications:
  • Due to their unique optical properties, QDs could be used to make smaller and more efficient image sensors like CMOS sensors. 
  • QDs can be used in computer screens and displays due to their important advantages: 
    • QLEDs are capable of emitting all colours depending on their size. Thus, they provide high-definition, brighter and more colourful displays. Quantum dots are brighter than organic LEDs (OLEDs).
    • QDs produce light themselves and need no backlight which makes them energy efficient.

• Photovoltaic devices: QDs have the potential to boost the efficiency of silicon photovoltaic cells. 
• Photonics: QDs are best suited for photonics-based computing capable of achieving high speeds.