Significance of quantum dots in nanotechnology (GS Paper 3, Science and Technology)
Why in news?
- Alexei I. Ekimov, Louis E. Brus, and Moungi G. Bawendi have been awarded the 2023 Nobel Prize for chemistry “for the discovery and synthesis of quantum dots”.
What is a quantum dot?
- A quantum dot is a really small assembly of atoms around a few nanometres wide.
- The ‘quantum’ in its name comes from the fact that the electrons in these atoms have very little space to move around, so the crystal as a whole displays the quirky effects of quantum mechanics.
- Quantum dots have also been called ‘artificial atoms’ because the dot as a whole behaves like an atom in some circumstances.
Why are they of interest?
- There are two broad types of materials: atomic and bulk. Atomic of course refers to individual atoms and their specific properties. Bulk refers to large assemblies of atoms and molecules.
- Quantum dots lie somewhere in between and behave in ways that neither atoms nor bulk materials do. One particular behaviour distinguishes them: the properties of a quantum dot change based on how big it is. Just by tweaking its size, scientists can change, say, the quantum dot’s melting point or how readily it participates in a chemical reaction.
- When light is shined on a quantum dot, it absorbs and then re-emits it at a different frequency. Smaller dots emit bluer light and larger dots, redder light. This happens because light shone on the dot energises some electrons to jump from one energy level to a higher one, before jumping back down and releasing the energy at a different frequency.
- So, quantum dots can be easily adapted for a variety of applications including surgical oncology, advanced electronics, and quantum computing.
What did the Nobel laureates do?
- For centuries, people have been creating coloured glass by tinting it with a small amount of some compound. How much of the compound, or dopant, is added and how the glass is prepared changed which colour the glass finally had.
- By the late 1970s, scientists had developed techniques to deposit very thin films on other surfaces and observe quantum effects in the films. But they didn’t have a material per se.
- In the early 1980s, Alexei Ekimov added different amounts of copper chloride to a glass before heating it to different temperatures for different durations, tracking the dopants’ structure and properties.
- They found that the glass’s colour changed depending on the size of the copper chloride nanocrystals (which depended on the preparation process).
- In 1983, a group led by Louis Brus in the U.S. succeeded in making quantum dots in a liquid, rather than trapped within glass.
- Both Dr. Brus and Dr. Ekimov further studied quantum dots, working out a mathematical description of their behaviour and how it related to their structure.
- A team led by Moungi Bawendi at the Massachusetts Institute of Technology achieved this in 1993, with the hot-injection method.
- A reagent is injected into a carefully chosen solvent (with a high boiling point) until it is saturated, and heated until the growth temperature, that is, when the reagent’s atoms clump together to form nanocrystals in the solution.
- Larger crystals form if the solution is heated for longer. Their birth within a liquid makes their surfaces smooth. Finally, crystals of the desired size can simply be filtered out. This method accelerated the adoption of quantum dots in a variety of technologies.
What are quantum dots’ applications?
- An array of quantum dots can be a TV screen by receiving electric signals and emitting light of different colours. Scientists can control the path of a chemical reaction by placing some quantum dots in the mix and making them release electrons by shining light on them.
- If one of the energy levels an electron jumps between in a quantum-dot atom is the conduction band, the dot can operate like a semiconductor.
- Also, solar cells made with quantum dots are expected to have a thermodynamic efficiency as high as 66%.
- A quantum dot can also highlight a tumour that a surgeon needs to remove, hasten chemical reactions that extract hydrogen from water, and as a multiplexer in telecommunications.
How was mRNA research used to fight COVID?
(GS Paper 3, Science and Technology)
Why in news?
- Recently, the 2023 Prize in Physiology or Medicine was awarded to Katalin Karikó and Drew Weissman.
- They were awarded the prize for their “discoveries concerning nucleoside base modifications that enabled the development of effective mRNA vaccines against COVID-19”.
What are mRNA vaccines?
- mRNA, which stands for messenger RNA, is a form of nucleic acid which carries genetic information. Like other vaccines, the mRNA vaccine also attempts to activate the immune system to produce antibodies that help counter an infection from a live virus.
- However, while most vaccines use weakened or dead bacteria or viruses to evoke a response from the immune system, mRNA vaccines only introduce a piece of the genetic material that corresponds to a viral protein.
- This is usually a protein found on the membrane of the virus called spike protein. Therefore, the mRNA vaccine does not expose individuals to the virus itself.
Why mRNA?
- RNA as a therapeutic was first promoted in 1989 after the development of a broadly applicable in vitro transfection technique. A couple of years later, mRNA was advocated as a vaccine platform.
- mRNA offers strong safety advantages. As the minimal genetic construct, it harbours only the elements directly required for expression of the encoded protein.
- A common approach by vaccine makers during the pandemic was to introduce a portion of the spike protein, the key part of the coronavirus, as part of a vaccine. Some makers wrapped the gene that codes for the spike protein into an inactivated virus that affects chimpanzees, called the chimpanzee adenovirus.
- The aim is to have the body use its own machinery to make spike proteins from the given genetic code. The immune system, when it registers the spike protein, will create antibodies against it.
How are these vaccines different?
- A piece of DNA must be converted into RNA for a cell to be able to manufacture the spike protein. While an mRNA vaccine might look like a more direct approach to getting the cell to produce the necessary proteins, mRNA is very fragile and will be shred apart at room temperature or by the body’s enzymes when injected.
- To preserve its integrity, the mRNA needs to be wrapped in a layer of oily lipids, or fat cells. One way to think of this is that an mRNA-lipid unit most closely mimics how a virus presents itself to the body, except that it cannot replicate like one.
- DNA is much more stable and can be more flexibly integrated into a vaccine-vector. In terms of performance, both are expected to be as effective.
- A challenge with mRNA vaccines is that they need to be frozen from -90 degree Celsius to -50 degree Celsius. They can be stored for up to two weeks in commercial freezers and need to be thawed at 2 degrees Celsius to 8 degrees Celsius at which they can remain for a month.
Advantages:
- But a major advantage of mRNA and DNA vaccines is that because they only need the genetic code, it is possible to update vaccines to emerging variants and use them for a variety of diseases.
- Viral vector vaccines, like Covishield, carry DNA wrapped in another virus, but mRNA are only a sheet of instructions to make spike proteins wrapped in a lipid (or a fat molecule) to keep it stable.
- In the case of COVID-19, mRNA vaccines developed by Moderna, Pfizer and Pune-based Gennova Biopharmaceuticals, these instructions alone are capable of producing the spike protein, which the immune system then uses to prepare a defence.
Outcome:
- In 2015, Dr. Weissman and Dr. Karikó figured how to deliver mRNA into mice using a fatty coating called “lipid nanoparticles” that protected the mRNA from degradation.
- Both her innovations were key to the development of COVID-19 vaccines developed by Pfizer and its German partner BioNTech.
