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Researchers invent microscopic toxin detector

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Posted June 14, 2018

A suspicion of toxins in the drinking water, in food, or perhaps in the air, is a serious matter. In such cases, very fast and reliable tests are essential in order for the authorities to take the appropriate precautions – or to calm down citizens after a false alarm.

However, many toxins are very hard to trace.

This is the background for the invention of a sensor in which bacteria literally light up when exposed to toxins. The sensor is the invention of Anders Kristensen, Professor at DTU Nanotech, and his research group in collaboration with colleagues from Israel.

A nano photonic chip gets the job done. Genetically modified coli bacteria are placed in the chip and emit a dim light when exposed to certain toxins. These bacteria can be ‘coded’ to look out for different kinds of toxins and therefore be used for very specific purposes. Until now, the problem has been that they emit very dim light which is lost because the modified bacteria are surrounded by many other kinds of bacteria, which also light up.

What is ground-breaking about Anders Kristensen’s invention is the possibility of isolating a specific bacteria used for detecting, i.e. the bacteria you want to see.

“By etching a triangular groove into silicon crystal and then oxidising it so the crystal gets a glass surface and finally applying a thin film of aluminum, it is possible to isolate the light from separate coli bacteria without light from other bacteria blurring the picture”, he explains.

This can be translated into making a small channel, only a few micrometer wide wherein the light from the ‘right’ bacteria can be concentrated. This gives a clearer and more easily read picture.

Like looking at the night sky in the countryside

Anders Kristensen compares his results to looking at the night sky on a cold clear December night when you are in the countryside, as opposed to looking at the stars while standing in the middle of Copenhagen.

Without other light sources nearby, the picture stands out much clearer – and this is what makes this new method interesting, he explains.

“The ability to amplify the light enough to be able to measure it correctly has been a significant challenge, which has been solved by catching the separate bacteria in a V-shaped cut-out, also only a few micrometers in width. And in there the manipulated bacteria will emit a dim light if they detect certain toxins.”

Collaboration with Israel

The sensor was created in a collaboration between Danish researchers from DTU and their colleagues in Israel.

Professor Shimson Belkin and his research group at the Hebrew University of Jerusalem have modified the bacteria, while Professor Uriel Levy and his research group have designed and made measurements on the sensor.

Finally, DTU has designed and produced the chip, where everything is assembled.

In principle the bacteria can be ‘coded’ to emit light, if they are exposed to pretty much anything, and you can make combinations, making it possible to look for different chemicals, which contain multiple elements – for example explosives, which have several chemical elements that must all be present at the same time.

Part of IOT

Further use is being investigated now, Anders Kristensen explains. He is happy having achieved ‘proof of principle’ – i.e. demonstrating that the technology as such works.

With this technology, it is possible to make small simple chips at relative low cost that can trace a number of substances and be used to secure food and drinking water or to trace toxins. It is even possible to get an easily understandable reading without the use of advanced microscopes.

“Sensors are used all around us. It is part of the Internet of Things trend, where everything is measured and analysed upon. For example in production companies, everything is continuously measured to ensure that resources can be used as effectively as possible, and in this connection our technology holds great possibilities”, he says.

Source: DTU

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