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Roar Sits Down with Professor Mark Green to Talk Quantum Dots and the 2023 Nobel Prize in Chemistry

On 11 October 2023, the King’s College London Natural, Engineering and Mathematical Sciences (NMES) department held an event on research at King’s in the fields awarded the 2023 Nobel Prizes in Physics and Chemistry.

Following the event, Roar had the opportunity to interview Kings academic Professor Mark Green on his related work.

The 2023 Nobel Prize in Chemistry was awarded to Moungi G. Bawendi, Louis E. Brus, and Aleksey Yekimob, “for the discovery and synthesis of quantum dots”. During the event, Professor Mark Green dove into his research connected to this field. His background is in nanotechnology, having focused on quantum dots (QDs), their production, and their applications in biology since 1995.

“Quantum dots are incredibly small particles of semiconductors, and the reason they’re interesting is when you get semiconductors that incredibly small, the laws that govern their optical properties become quantum mechanical in nature,” explains Green, “the actual size of the particle dictates the wavelength and the colour of light given out by these particles. So by playing round with the particle size, [the particle] can give out different colours of light. That’s different to bulk materials or non-nano materials because one material will normally give out one colour of light.”

The unique property of QDs makes them ideal for a plethora of applications, ranging from TV screens, Amazon fires, or in theory even medical applications such as biomarkers. Now that the chemistry has been quite well developed, Green feels that the focus has largely shifted towards the practical application of QDs, and is looking into ways to make them more environmentally friendly. The latter is the subject of ongoing research here at King’s.

“Traditionally, most of the semiconductor quantum dots are made with heavy metals such as cadmium, and these are incredibly high quality”, he says. “They’re no chemical oddity; you can make them, you can buy them, this is all down to Bawendi’s synthesis. But the question remains; what happens once you need to get rid of them all?” Due to EU regulations, there are restrictions on the disposal of QDs, necessitating research into more environmentally friendly routes. “We’ve got to come up with alternatives. Green alternatives to cadmium-containing quantum dots”, he emphasises, “… Now there are other families of semiconductors out there that we can make using the same chemistry pioneered by Bawendi. [These are] more environmentally acceptable, so one of the things that we do, and we’ve been doing for 20 years, is exploring these greener semiconductors for TV screens and biological imaging.”

The difficulties in the chemistry behind them and the hurdles faced int he production of quantum dots make focusing on finding simpler ways to make green QDs a hefty goal. One are of QDs research at King’s is helping to achieve this goal, focussing on using biology to grow quantum dots.

“One of the other things we do this is really quite cool is we use biology to grow quantum dots. We [realized] a few years ago that some of the way animals combat toxic metals is to kick out little quantum dots in their livers. So we realised [that] actually, animals have been making quantum dots for decades before we actually started making them in the lab. And one of the things [that we] do is that we’ve hijacked that process and we’ve started playing around with the chemistry in plants and in animals where we can make these quantum dots really quite simply, but using completely new processes.”

“Quantum dots are really small. They’re roughly the size of proteins, but they glow. They’re like little TV pixels. So if you stick an antibody or a biological molecule on the surface of these, that will recognise a tumour. You can start to target cancers so you can inject them into an animal, hopefully eventually in a human and the idea is that these quantum dots will then go around the body and stick to a tumour, and then you can get it to glow and then a surgeon can cut it out,” says Green. He noted that there remain many complications before this theory can be applied, yet the prospects remain enticing. 

Looking to the future, Green predicts greater diversity in the application of QDs, potentially broaching the realm of quantum computing. 

“Because the chemistry is now so well developed, we can make these materials on an unprecedented scale”, he describes, “nanoscale particles that can hold a binary digit for one or a zero, and also potentially a quantum bit (a quibit). I’m beginning to see that quantum dots have an application there, so I think in the next ten years we’ll see some real applications in quantum computing using [them].” 

Green is excited by how relatively fast the field of research has grown, commenting on the availability of resources now accessible for those interested in QDs. 

“When I started in this field 25 years ago, I think there was one book, one popular science book, and now if you just Google it, there’s tons of options. They’ve got to the point now where they’re so common”, he comments, “they’re so ubiquitous now, there’s even undergraduate experiments you can run… Just a few years ago this was a scientific oddity and now we’re designing experiments for 18 year olds to do!”

For more information on King’s research in photonics and nanotechnology, check out their webpage, and the Nanostrand newsletter. 


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