Under The Weather [+]Enlarge Credit: Nano Lett.

The exhalations of people with the flu can do more than just sicken others. Chinese researchers have developed a quick and noninvasive diagnostic tool that identifies influenza viruses in the breath of sick people (Nano Lett., DOI: 10.1021/nl301516z).

Doctors usually diagnose flu by its symptoms, but misdiagnoses are common. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) can accurately detect the flu by identifying genetic material from viruses, but it takes several hours. To speed virus detection, Maosheng Yao of Peking University and colleagues developed a way to rapidly condense the liquid in breath, and then analyze it with an ultrasensitive silicon nanowire sensor.

The researchers decorated silicon nanowires with antibodies that bind to a specific protein of the common influenza virus subtype H3N2. Then they asked 11 people with flu-like symptoms and eight healthy people to breathe on a very cold hydrophobic film. After one or two minutes of each person breathing, the film captured about 100 μL of breath condensate, Yao says.

Using a microfluidic channel, the researchers delivered the sample to the silicon nanowires. Within minutes, H3N2 particles in the sample bound to the antibodies, causing the nanowire conductance to spike. The researchers could measure the conductance change with as few as 29 viruses per μL. In comparison, Yao says, “the detection limit of RT-qPCR varies.” The method typically detects between 100 and 1000 viruses per μL, he says, though it can go lower too.

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When the conductance remained steady, the researchers concluded a sample didn’t contain H3N2. The nanowire results matched RT-qPCR analyses for 17 of the 19 people’s samples; the remainder tested positive for H3N2 by nanowire but negative by RT-qPCR. The researchers think that these disagreeing results may have been caused by non-specific binding to the antibody or by inaccurate RT-qPCR results.