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Live Bacteria Bang Out Solos on Graphene Drum

Dead bugs don’t, giving researchers a new way to assess antibiotic efficacy

3 min read
An artist’s impression of a graphene drum detecting nanomotion of a single bacterium

In this artist’s impression, a graphene drum detects the nanomotion of a single bacterium.

Irek Roslon/TU Delft

The two-dimensional material graphene is basically all surface. This makes it highly sensitive to atoms or molecules because its entire volume can serve as a sensor surface. This has led researchers and industry to exploit graphene as both a biosensor and an electronic sensor for detecting the smallest changes to an environment.

Now researchers at Delft University of Technology (TU Delft) in the Netherlands have used graphene sheets to serve as a kind of drum for detecting the movements of a single bacterium. In research published in the journal Nature Nanotechnology, the TU Delft researchers created a device that can sense an object, such as a bacterium, sticking to the surface of the graphene drum and creating oscillations with nanoscale amplitudes.

“When a single bacterium is adhered on the graphene drum, it can transduce a time-dependent deflection on the graphene that is then detected by laser light,” said Farbod Alijani, assistant professor at TU Delft and lead researcher on the project.

The researchers performed experiments in a cuvette containing live E. coli bacteria in a growth medium. In the TU Delft teams’ first measurements, they were immediately able to detect the movements of the bacteria, according to Alijani.

These movements were manifested as a noisy signal within a spectrum that was consistent with biological processes. This observation is the first time that the sound generated by a single bacterium in its aqueous growth environment could be detected, according to Alijani.

The sensor is detecting oscillations that primarily come from the motion of flagella, the tail-like structures that propel the bacterium through its environment. To get a sense of how lightly these flagella beat on the graphene drums, take the force of a boxer punching a bag and divide it by 10 billion, says Alijani.

“When a single bacterium is adhered on the graphene drum, it can transduce a time-dependent deflection on the graphene that is then detected by laser light.” —Farbod Alijani

Alijani believes that the technique’s ability to trace changes in a bacterium’s motion on the nanoscale could help in the administration of antibiotics and could make it a valuable tool in monitoring antibiotic resistance.

Antibiotic resistance is determined by monitoring the oscillations levels. Persistent oscillations indicate that the bacterium is alive and resisting the antibiotic. A decrease in oscillations would indicate that the antibiotics are killing the bacteria.

Alijani points out that while there are many semi-automated antibiotic sensitivity tests currently on the market, the bacteria need to grow, which takes time. This new test provides clear indicators of antibiotic resistance within just 1 or 2 hours as compared to current antibiotic sensitivity tests that require at least 24 to 48 hours, according to Alijani.

“Our technology stands out in terms of sensitivity and speed as it can perform antibiotic susceptibility at the single-cell level using many parallelized sensors,” said Alijani, who notes that one chip can host up to 10,000 sensors.

This graphene sensor falls into the category of a biosensor as opposed to an electronic sensor. The use of graphene in biosensors is gaining broad commercial use, while electronic sensors based on graphene remain at an early stage, with companies like U.K.-based Paragraf beginning to roll out Hall-effect sensors based on graphene.

“We are picking up vibrations optically, not electrically and the actuation of the drums is simply by the bacterium itself (no electrical actuation),” Alijani added. “It is the bacterium that vibrates the sensor.”

The graphene that the TU Delft team used is what’s known as chemical vapor deposition (CVD) bilayer graphene. CVD graphene is markedly cheaper to produce than mechanically exfoliated graphene that needs to be stripped off of graphite one atomic layer at a time in a process known as the “scotch tape” method. This makes the raw material for making the device somewhat more affordable.

While raw-material considerations are always an important factor, “the immediate next step in development is to validate the technology against a variety of bacteria and antibiotics with different modes of action,” said Alijani. “As we bring the technology closer to market, we will very soon launch a startup in collaboration with our vaporization partners.”

In these next steps, Alijani said the team will look to further optimize the readout system, as well as better understand the relation between biophysical processes of a single bacterium and the nanoscale vibrations detected.

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Europe Expands Virtual Borders To Thwart Migrants

Our investigation reveals that Europe is turning to remote sensing to detect seafaring migrants so African countries can pull them back

14 min read
A photo of a number of people sitting in a inflatable boat on the water with a patrol ship in the background.

Migrants in a dinghy accompanied by a Frontex vessel at the village of Skala Sikaminias, on the Greek island of Lesbos, after crossing the Aegean sea from Turkey, on 28 February 2020.


It was after midnight in the Maltese search-and-rescue zone of the Mediterranean when a rubber boat originating from Libya carrying dozens of migrants encountered a hulking cargo ship from Madeira and a European military aircraft. The ship’s captain stopped the engines, and the aircraft flashed its lights at the rubber boat. But neither the ship nor the aircraft came to the rescue. Instead, Maltese authorities told the ship’s captain to wait for vessels from Malta to pick up the migrants. By the time those boats arrived, three migrants had drowned trying to swim to the idle ship.

The private, Malta-based vessels picked up the survivors, steamed about 237 kilometers south, and handed over the migrants to authorities in Libya, which was and is in the midst of a civil war, rather than return to Malta, 160 km away. Five more migrants died on the southward journey. By delivering the migrants there, the masters of the Maltese vessels, and perhaps the European rescue authorities involved, may have violated the international law of the sea, which requires ship masters to return people they rescue to a safe port. Instead, migrants returned to Libya over the last decade have reported enslavement, physical abuse, extortion, and murders while they try to cross the Mediterranean.

If it were legal to deliver rescued migrants to Libya, it would be as cheap as sending rescue boats a few extra kilometers south instead of east. But over the last few years, Europe’s maritime military patrols have conducted fewer and fewer sea rescue operations, while adding crewed and uncrewed aerial patrols and investing in remote-sensing technology to create expanded virtual borders to stop migrants before they get near a physical border.

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