Researchers suggest quantum dots as a potential skin cancer treatment

Posted: October 1, 2009

(Nanowerk News) Resolving questions surrounding nanoparticle toxicity has led North American researchers to suggest the particles as a potential skin cancer treatment ("Photosensitization of CdSe/ZnS QDs and reliability of assays for reactive oxygen species production" – free access paper).

Dopamine-conjugated quantum dots release cytotoxic reactive oxygen species when treated with light

Jay Nadeau from McGill University, Montreal, and colleagues in the US and Canada are investigating using semiconductor nanoparticles, called quantum dots, as photosensitisers - compounds that release reactive oxygen species, such as singlet oxygen, when exposed to light. Photosensitisers can be used in photodynamic therapy, which applies the reactive oxygen species to kill cancer cells. Nadeau's team has measured the reactive oxygen species produced by quantum dots and observed their subsequent effects on mammalian cells using a series of assays.

Currently there is a lot of controversy whether quantum dots do produce reactive oxygen species, and if so which ones. Nadeau says she believes her team has finally been able to resolve the issue by standardising experiments. 'Figuring out which assays are best to use will allow you to screen compounds in a way that is valid, so will allow different groups to at least coordinate their results,' she says.

"Similar conjugated nanoparticles could potentially be used in photodynamic therapy for skin cancer treatment." According to Nadeau 'some nanoparticles don't make singlet oxygen but they do when they are connected to small molecules like [the neurotransmitter] dopamine. That opens up a whole other avenue for investigation,' she says. Her team also found that the dopamine-conjugated quantum dots can be used to kill mammalian cells but only on irradiation with UV-to-blue light. This means the quantum dots are unlikely to be toxic in the body, where the light cannot penetrate, but could have an effect on skin, the researchers claim. They suggest that similar conjugated nanoparticles could potentially be used in photodynamic therapy for skin cancer treatment.

Juan Mareque-Rivas, an expert in fluorescent nanoparticles, from the University of Edinburgh, UK, says 'this is a long overdue investigation. It is nice to see a study in which generation of different reactive oxygen species is demonstrated, quantified and rationalised, and linked to interactions with dopamine - it warns that biomolecules can enhance the phototoxicity of quantum dots.'

Nadeau's team next plans to move the project into an in vivo melanoma model, to see if dopamine-conjugated quantum dots collect in tumours. Further plans include using quantum dots to develop a cream for healing surgical wounds as well as in water decontamination.

Source: Reprinted with permission from Chemistry World (Jennifer Newton)

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Atom-thick material runs rings around silicon

19:00 17 April 2008

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Chunks of this atom-thick material just one nanometre across can function as transistors - the devices central to computing power (Image: Manchester University Mesoscopic Physics Group)

A leading contender to replace silicon as the basis for computing has made another step forward.

Transistors one atom thick and ten atoms wide have been made by UK researchers. They were carved from graphene, predicted by some to one day oust silicon as the basis of future computing.

For 40 years computing has been dominated by a rule of thumb named Moore's law, which predicts that the number of transistors on a chip will double roughly every two years.

Yet silicon, the material that has so far been used to keep up with Moore's law cannot form stable structures below 10 nanometres in size. And today's newest chips already have features just 45 nm across. The hunt is on for a replacement for silicon.

Graphene, a material made from flat sheets of carbon in a honeycomb arrangement is a leading contender. A team at the University of Manchester, UK, have now used it to make some of the smallest transistors ever. Devices only 1 nm across that contain just a few carbons rings.

Previous graphene transistors were significantly bigger – ribbons 10 nm across and many times longer.

Small proportions

"A big question has been which material to use for smaller transistors," says Kostya Novoselov, who with project co-leader Andre Geim discovered graphene in 2004. "This is one of the smallest transistors at the moment."

Graphene's carbon-carbon bonds are among the strongest in nature, and its honeycomb-like structure (see image, right) allows electrons to travel very rapidly. It also exhibits bizarre electrical properties that have fuelled an explosion of interest in the material.

Yet making transistors from graphene has proved difficult. The material usually lacks the switchable conductivity that transistors need to control electric current.

Novoselov and colleagues found that cutting small "quantum dots" of graphene can give it that property. Dots just a few nanometres across trap electrons thanks to quantum effects that become dominant at such small scales.

Tiny transistor

Applying a magnetic field to the smallest dots lets current flow again, making a switchable transistor. The smallest dots that worked as transistors contained as few as five carbon rings – around 10 atoms or 1nm wide.

There are other kinds of prototype transistors in this size range. But they usually need supercooling using liquid gas, says Novoselov. The new graphene devices work at room temperature.

Such prototypes are typically made by building one atom at a time, or wiring up individual molecules. Those approaches are complex and impractical, Novoselov says.

By contrast, the graphene transistors were made in the same way that silicon devices are, by etching them out of larger pieces of material. "That's their big advantage," he says.

Amazing result

"The most amazing result for me is that they were able to obtain quantum dots as small as 1 nm," says Antonio Castro Neto of Boston University, US. "This is shocking." "If you try to reduce the dimensions of any other structure, the structure would disintegrate before you reach these dimensions," Neto adds.

"There is no doubt in my mind that these structures can be used for technological applications," he says. "The electronic flexibility and structural stability, fundamental for modern device development, are unmatched in any other material on Earth." But working out how to manufacture graphene devices on a practical scale remains a challenge, he concludes.

Journal reference: Science (DOI: 10.1126/science.1154663) Link

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