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Salmon DNA used to create more precise photonic devices

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Researchers at Yonsei University, South Korea, are using DNA extracted from salmon to develop photonic devices based on organic thin films. These devices have the capabilities of silicon-based devices, with the added benefit of being biocompatible.

Thanks to its abundance and ease of manipulation, silicon has long since been the go-to material to use in inorganic photonic devices. Perhaps surprisingly, DNA could be an appealing material for organic photonic devices for similar reasons.

“DNA is the most abundant organic material and it is a transparent dielectric [insulator], comparable to silica,” said Professor Kyunghwan Oh of Yonsei University, who led the research.

According to Professor Oh and his colleagues, DNA has potential as the basis for more flexible, environmentally friendly photonic devices. The team demonstrated that this was feasible by creating DNA-based waveguides (optical fibres) to carry light to targets within the human body.

When manufacturing photonic devices such as waveguides, it is vital to be able to control the refractive index of the materials, which describes how light travels through the material. The core of a waveguide must have a significantly different refractive index to the coating, in order to guide the reflected light through the fibre without leakage.

Professor Oh and his team set about using DNA to create thin films for the devices: layers of material which can be used to channel light in photonic devices, such as the silvering coating deposited onto glass sheets to create mirrors.

They began by mixing DNA extracted from salmon with a soap-like substance, CTMA, and dissolving it in water. This solution was dissolved into an organic solvent, and then spun on a surface. As the liquid evaporates, a thin film is left behind.

By altering the ratios of water and CTMA mixed with the DNA in the initial stage of the process, Professor Oh and his colleagues succeeded in controlling the refractive indexes of the thin films, achieving a range far wider than that available in silicon.

Control the index of refraction in organic thin films

Kyunghwan Oh, Yonsei University

Image credit: Kyunghwan Oh, Yonsei University

This allowed them to create much thinner optical fibres, which can more precisely direct light towards a small target.

A device like this could have applications in photodynamic therapy: a particular type of cancer treatment. A drug binds to cells in a tumour and is activated with light, causing just the cancerous cells to be destroyed. Such a fine light beam could also be used to control the activity of individual brain cells, or as the basis of sensors which could be worn comfortably for extended periods of time, due to their organic basis.

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