“Respiratory syncytial virus is a disease which significantly impacts the morbidity and mortality of children around the world,” researcher David Wright told nanotechweb.org. “Early detection of viral infection is important because antivirals are increasingly available for treatment, but are only effective when given early in the course of infection.”

Wright and colleagues used antibodies and protein molecules to attach quantum dots to the fusion (F) and attachment (G) proteins found on the surface of the virus particle (or virion). They linked 605 nm streptavidin quantum dots to the F protein and 525 nm streptavidin quantum dots to the G protein.

To infect a host cell, the RSV particle attaches to its surface and the viral membrane fuses into the host cell membrane. This leaves F and G proteins attached to the surface of the host cell. The infected cell then creates further virions which go on to infect other cells.

Confocal laser-scanning microscopy enabled the scientists to locate infected cells by imaging the quantum dots fluorescing at two different wavelengths attached to their surface. In the same way, they were able to monitor the progress of the infection.

“The properties of fluorescent semiconductor nanocrystals - quantum dots - provide a method for viral detection very early in the course of infection at exceedingly low viral concentrations,” said Wright.

The scientists were able to spot F and G proteins as early as one hour after infection. After 24 hours, the team found that the technique had a detection limit of between 35 and 50 plaque-forming units of RSV.

Labelling the F protein with a conventional organic fluorophore - fluorescein isothiocyanate - enabled the team to detect the F protein after 24 hours. However, this required exposures 46 times higher than for the quantum dot-labelled cells and the molecules only lasted around 15 min before their fluorescent properties degraded.

“In addition, since quantum dots are photostable, the trafficking of viral proteins could be examined in realtime to provide a better understanding of the mechanisms of viral infections,” said Wright. “By understanding these mechanisms, potential new treatments could be developed to stop the virus from taking over host cells.”

Now, the team plans to develop a method for detecting RSV in clinical samples. The scientists also hope to adapt this technique to detect other viral infections. “Using the multiplexing capability of quantum dots, a clinician would be able to test a sample against a panel of reagents - each colour present indicating a type of virus detected,” said Wright. “Additionally, we have begun to use quantum dots to investigate the mode of fusion of the respiratory syncytial virus.”

The researchers reported their results in Nano Letters.