Antibody for bird flu detected in 20 min

Japanese researchers have succeeded in detecting anti-avian influenza virus antibody in blood serum within 20 minutes, using a portable analyser they created to conduct rapid onsite bio tests. If a suitable reagent is developed, the technology could be used to detect antibodies against SARS-CoV-2, the causative virus of COVID-19.

Rapid initial response for suspected infection and continuous surveillance are essential to mitigate the damage from highly pathogenic, transmittable pathogens such as avian influenza viruses. Generally the polymerase chain reaction (PCR) method is used to detect the viral genome, but its complicated procedure requires a considerable amount of time. Another method involves detecting antibodies produced in the body in reaction to virus infection; however, widely used antibody detection methods can be inaccurate because the antibodies’ existence is generally determined by eyesight.

Seeking to rectify this, a team led by Hokkaido University researchers set out to develop a new method and analyser capable of rapid, facile and selective detection of antibodies. The method is based on conventional fluorescence polarisation immunoassay (FPIA) but applies a different measurement mechanism to make the analyser smaller and more portable, weighing only 5.5 kg. Their work was published in the journal Sensors and Actuators B: Chemical.

The combined use of liquid crystal molecules, an image sensor and the microfluidic device made it possible to simultaneously examine multiple samples and reduce the volume of each sample required. Liquid crystal molecules are capable of controlling the polarisation direction of fluorescent light, while the microfluidic device has a number of microchannels as a measurement vessel.

The group also developed a reagent to detect anti-H5 avian influenza virus antibody — a fluorescein-labelled protein that binds only with the antibody. The reagent was made by reproducing hemagglutinin (HA) protein fragments, which are expressed on the surface of H5 avian influenza virus, through gene recombination and by labelling fluorescent molecules to the fragments.

To make the measurement, serum collected from birds was mixed with the reagent and left for 15 minutes. The mixture was injected into the microfluidic device and measured with the portable fluorescence polarisation analyser. Molecular movements of the reagent bound with the antibody are smaller in the liquid, producing a different degree of polarisation from the reagent not bound with the antibody. The system can detect anti-H5 avian influenza virus antibody with only 2 μL of serum sample and within 20 minutes.

“Our analyser could be used to conduct other bio tests if suitable reagents are developed,” said Hokkaido’s Professor Manabu Tokeshi, with the group having already successfully detected mycotoxin and drug constituents. “By reproducing fragments of spike proteins expressed in the novel coronavirus, and using them as the reagent, the analyser should be able to detect anti-coronavirus antibodies.”

Image caption: The microfluidic device to which ∼20 μL of samples containing 2 μL of serum will be applied. Image credit: Nishiyama K et al, Sensors and Actuators B: Chemical. April 21, 2020.

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