Quantum dots and medical research

Nanoscale silicon quantum dots are being developed in New Zealand. They will be able to locate and show up cancerous cells in humans, and deliver drugs to them.

What are quantum dots?

Quantum dots are nanoparticles of semiconductor materials, clusters of atoms only a few nanometres across. A special property of quantum dots is that they fluoresce – when ultra-violet light (invisible to human eyes) is shone on them, they re-emit the light as a visible colour. The colour they give off depends on the size and shape of the quantum dot. It is possible to create quantum dots that emit just about any colour you want. Quantum dots are being developed for use in such things as LEDs and television screens, but they also have medical uses.

Locating cancer using quantum dots

Quantum dots that can be used to find and treat cancer are being developed by Dr Richard Tilley and others at Victoria University of Wellington and the MacDiarmid Institute for Advanced Materials and Nanotechnology.

Many of the quantum dots developed in other countries use chemicals such as cadmium. Cadmium is a highly toxic metal, sitting directly above mercury in the periodic table. Dr Tilley and his team have been able to create non-toxic quantum dots using silicon.

Rights: The University of Waikato Te Whare Wānanga o Waikato

Quantum dots in cells

Silicon quantum dots fluorescing inside cancer cells grown in a laboratory. The bar in the bottom right corner measures 20 micrometres (20,000 nanometres).

These quantum dots can be put into single cells, or lots of cells, in the tissue of living organisms. In future, it is planned to attach specific antibodies to the quantum dots – when injected into a body, the quantum dots will find and bind to cancer cells, and illuminate them when they fluoresce.

Rights: The University of Waikato Te Whare Wānanga o Waikato

Dr Richard Tilley working with silicon

Dr Richard Tilley works with silicon inside a sealed ‘glove box’. The glove box is filled with argon gas to make sure there is no oxygen present. If there was oxygen around, the semiconductor silicon (Si) would oxidise to silica (SiO₂), a mineral with different properties.

Once the silicon quantum dots are made they are stable, but Richard needs to make sure there is no oxygen around when he does make them.

There are advantages to using quantum dots rather than the current organic dyes used to highlight living cells:

• Quantum dots last longer. Organic dye molecules only last for about 30 minutes in a human body. Quantum dots can emit light for days. By following the quantum dots over time, it will be possible to monitor and show if treatment is working.
• Silicon quantum dots are less toxic.
• Quantum dots will be able to detect cancer earlier. Current detection methods, such as magnetic resonance imaging (MRI), can only detect tumours that are well developed. Quantum dots can detect individual cancer cells.

Targeted drug delivery

Eventually, it is intended to attach drug molecules to the quantum dots, which will then be able to deliver the drug just to the cancer cells where it is needed. Current anti-cancer drugs tend to have a range of unpleasant side-effects, because they affect the whole body, not just the cancer. The research is still in its early stages – it is hoped that quantum dots should be available to help treat cancer in about ten years.

Examples of collaboration by scientists

Each of the following scientists make a specific contribution to the research on quantum dots:

• Synthetic chemist (Dr Richard Tilley, MacDiarmid Institute) makes quantum dots.
• Medical scientist (Prof Kenji Yamamoto, International Medical Centre of Japan) carries out toxicity testing.
• Biochemist (Thomas Backstrom, Malaghan Institute) looks at which antibodies and drug molecules to use.
• Theoretical physicist (Shaun Hendy, Industrial Research Ltd) creates computer simulations to make predictions about quantum dot structures and properties.