Viral manoeuvres revealed by surveillance system

Virologists have a new weapon in the war against viruses – a way to tag and track individual viruses that are too small to be viewed with light microscopes.

To infect a cell, viruses have to subvert the cell's proteins in order to survive and replicate inside. But working out exactly how the viruses do that is difficult because they are so small. Most are 10 to 300 nanometres across.

Pin Wang and colleagues at the University of Southern California have come up with a way to track individual viruses. "That is a powerful tool for investigating viral infection routes," he told New Scientist.

Until now only one group of viruses – the lentiviruses, which include HIV – could be tracked as they moved through a cell. In 2002, Thomas Hope and colleagues at the University of Illinois tagged HIV-1 with a fluorescent protein called GFP, revealing that it travels through cells by hitching a ride on the protein struts that make up their "skeleton".

Track and trace

Wang's team says that quantum dots, a kind of nanoscale crystal, can track a larger variety of viruses.

Quantum dots are just a few nanometres in diameter, making them subject to quantum effects that make them shine very brightly for hours after being hit with laser light. That makes them perfect for tagging tiny viruses.

Wang's team labelled HIV-1 viruses by attaching them to molecules of biotin (vitamin B7), which in turn connects to a protein coated onto the quantum dots.

To check this method didn't affect the quantum dots' shine or the way viruses behave, the team simultaneously tracked HIV-1 particles using quantum dots, and GFP.

They found that the viruses labelled with quantum dots infected cells as readily as unlabelled viruses.

None shall escape

Wang says that quantum dots could be used to track a much wider range of viruses, including those that can't be followed using GFP.

"We believe that many kinds of enveloped viruses could be labelled by our method," he says.

Although some viruses can be labelled using dye molecules, the dyes are quickly bleached by the powerful light of microscopes and so the viruses can't be tracked for any length of time. By contrast, quantum dots retain their brightness for several hours.

"Some studies show that quantum dot-labelled proteins could be detected in living cells even after 48 hours," Wang adds.

Maxime Dahan at the Ecole Normale Supérieure in Paris is impressed with the study.

"It unquestionably represents a significant result in terms of using quantum dots as virus markers," he says. "It holds great promise to unravel the infection pathway in a detailed manner."

Journal reference: ACS Nano, DOI: 10.1021/nn8002136

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