Full of antioxidants and vitamins, tea is pretty good for you, and green tea extracts have even been used as effective carriers for cancer drugs. New research led by Swansea University has found a novel way to wring more health benefits out of the stuff, by making quantum dots from tea leaves and using them to slow the growth of lung cancer cells.

Quantum dots are semiconductor particles so small they exhibit strange electrical and optical properties, such as the ability to fluoresce in different colors, or help with certain chemical reactions. Their glowing properties mean they're showing up in TVs and solar cells, and in medical applications as biomarkers to help doctors precisely locate tumors. They're also being used to treat cancer, fight antibiotic-resistant bacteria and convert CO2 into liquid fuels.

The problem is, manufacturing them can be a costly and complicated process, and the end results can be toxic. So the Swansea team, along with researchers from Bharathiar University and K. S. Rangasamy College of Technology, set about making quantum dots out of humble tea leaves.

The scientists combined a tea leaf extract with cadmium sulfate (CdSO4) and sodium sulfide (Na2S), and then incubated the mixture until quantum dots formed. The team then exposed lung cancer cells to the tea-derived quantum dots, with the aim of testing how well their fluorescence helped light up the tumor.

"Our research confirmed previous evidence that tea leaf extract can be a non-toxic alternative to making quantum dots using chemicals," says Sudhagar Pitchaimuthu, lead researcher on the project. "The CdS quantum dots derived from tea leaf extract showed exceptional fluorescence emission in cancer cell bioimaging compared to conventional CdS nanoparticles."

But to the team's surprise, the nanoparticles did more than just light up the tumors – they helped destroy them. The researchers observed that the quantum dots penetrated into the cancer cells' nanopores, killing up to 80 percent of them.

"The real surprise, however, was that the dots actively inhibited the growth of the lung cancer cells," says Pitchaimuthu. "We hadn't been expecting this. Quantum dots are therefore a very promising avenue to explore for developing new cancer treatments. They also have other possible applications, for example in anti-microbial paint used in operating theaters, or in sun creams."

In the future, the researchers plan to scale up the production technique and continue to study how else these tea leaf quantum dots can be put to work.

"Building on this exciting discovery, the next step is to scale up our operation, hopefully with the help of other collaborators," says Pitchaimuthu. "We want to investigate the role of tea leaf extract in cancer cell imaging, and the interface between quantum dots and the cancer cell. We would like to set up a 'quantum dot factory' which will allow us to explore more fully the ways in which they can be used."

The research was published in the journal Applied Nano Materials.

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