The suspected presence of toxins in drinking water, liver paté—or indeed the air—is a serious concern. The ability to provide immediate, reliable testing so authorities can take appropriate action—or reassure citizens after a false alarm—is therefore crucial.
However, many toxic substances are extremely difficult to trace, which is why—together with Israeli colleagues—Professor Anders Kristensen from DTU Nanotech and his research group have invented a sensor that causes bacteria to literally light up when exposed to toxins.
The method employs a nanophotonic chip onto which genetically modified coliform bacteria have been placed, causing the bacteria to emit a faint light when exposed to certain toxic substances. The bacteria, which can be ‘encoded’ to monitor different toxins, are therefore very toxin-specific. In the past, the problem has been that the very faint light emitted by the modified bacteria was easily ‘drowned out’ by the weak light radiated by all the other bacteria surrounding them.
Anders Kristensen’s invention is groundbreaking in that it isolates the bacteria used as detectors—i.e. the bacteria researchers want to see.
He explains that by etching a triangular channel onto a silicon crystal, oxidizing it so that the crystal acquires a glass surface, and finally coating it with a thin aluminium film, it is now possible to isolate the light from the individual coliform bacteria.
In practical terms, this involves making a small groove of only a few micrometres’ width and then concentrating the light from the ‘right’ bacteria onto the groove. This method produces a cleaner image that is easier to read.
Like star gazing in the countryside
Contextualizing his results, Anders Kristensen uses the comparison of gazing up at the stars on a frosty crisp December night far out in the countryside with gazing at the stars from City Hall Square in the centre of Copenhagen.
When there are no other sources of ambient light, the image is significantly stronger, which makes the new method interesting, he explains.
“A major challenge has been boosting the light sufficiently to ensure accurate measurement. We have now solved this challenge by trapping the individual bacteria in a three-micrometre wide V-shaped groove. Here, the manipulated bacteria emit a faint light if they come into contact with certain toxic substances.”
Collaboration with Israel
The sensor is the result of a collaboration between Danish researchers from DTU and research 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 the sensor and carried out sensor measurements.
DTU has subsequently produced the final design and manufactured the chip which houses it all.
In principle, the bacteria can be ‘encoded’ to emit light if they have been in contact with almost anything, and the researchers can create combinations that examine different chemicals containing several elements—e.g. explosives with several chemical elements which must be present at the same time.
Part of IOT
The sensor’s further use must now be investigated in more detail,” explains Anders Kristensen, who is nonetheless delighted to have achieved ‘proof-of-principle’—i.e. ascertained that the technology, as such, works.
Using the technology, it is relatively simple and inexpensive to produce small chips that can trace a wide range of substances and thus safeguard food and drinking water—or trace toxic substances. The technology also provides easily readable result that do not require advanced microscopes.
“We are, of course, surrounded by sensors. It’s part of this trend with the Internet of Things, where you measure everything and then analyse it. For example, production companies keep an eye on everything in order to exploit resources as efficiently as possible, and here the technology holds out great potential,” he says.