The group has already successfully detected mycotoxin and drug constituents," said study researcher Manabu Tokeshi from Hokkaido University in Japan. "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," Tokeshi added. For the findings, the research team conducted this study to develop a new method and analyser capable of rapid, facile and selective detection of antibodies. The method is based on conventional fluorescence polarization immunoassay (FPIA) but applies a different measurement mechanism to make the analyser much smaller and portable. The analyser weighs only 5.5 kilograms. The combined use of liquid crystal molecules, an image sensor and the microfluidic device makes it possible to simultaneously examine multiple samples and reduces the volume of each sample required. 

Liquid crystal molecules are capable of controlling the polarization 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. According to the researchers, the mixture was injected into the microfluidic device and measured with the portable fluorescence polarization analyser. 

Molecular movements of the reagent bound with the antibody will be 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 two microliters of serum sample and within 20 minutes, the researchers said. Recently, another study published in the journal Analytical Chemistry, revealed that Chinese researchers developed a quick, sensitive test of antibodies against coronavirus in human blood, which could help doctors track a person's exposure to the disease, as well as confirm suspected COVID-19 cases which have been tested negative by other methods.