Detecting dengue antibodies in saliva

The Institute of Bioengineering and Nanotechnology (IBN) at Singapore’s Agency for Science, Technology and Research (A*STAR) has developed a paper-based disposable device that will allow dengue-specific antibodies to be detected easily from saliva within 20 min.

The IBN research team that developed the device comprises Executive Director Professor Jackie Y Ying, Postdoctoral Fellow Dr Yi Zhang and Research Scientist Dr Jianhao Bai (from left to right). Image credit: A*STAR.

According to Singapore’s National Environment Agency, dengue fever and its more severe form, dengue haemorrhagic fever, are the most common mosquito-borne viral diseases in the world and a leading cause of illness and death in tropical and subtropical climates. There are four known serotypes of the dengue virus, and patients with secondary infection (who have previously been infected with other serotypes of dengue virus) stand a higher risk of developing dengue haemorrhagic fever or dengue shock syndrome.

The incubation period before symptoms develop generally ranges from four to 10 days after infection; therefore, early diagnosis would enable the patient to receive prompt medical attention and avoid further complications. Dengue infection is currently diagnosed in the laboratory by testing the patient’s blood sample for the presence of dengue antigens or antibodies, but saliva collection would be an easier and more painless method of rapid point-of-care diagnostics.

However, unlike other body fluids, saliva cannot be applied directly to commercially available test kits as it would cause the sensor nanoparticles to stick haphazardly to the test strip. Writing in the journal Lab on a Chip, the IBN researchers explained that “conventional lateral tests are often complicated by severe non-specific adsorption of detector particles when applied to test samples containing salivary fluid. It is believed that a high concentration of proteinaceous substances in salivary fluid causes particle aggregation and adhesion.”

The team developed a stacking flow design to overcome this issue, through which different flow paths are created for samples and reagents through a multiple stacked system. This allows the saliva sample to flow separately through a fibre glass matrix, which removes the substances that would interfere with the nanoparticle-based sensing system before it mixes with the sensor nanoparticles.

“Stacking flow circumvents the need for separate sample pre-treatments, such as filtration or centrifugation, which are often required prior to testing saliva samples using paper-based immunoassays,” the researchers said. The stacking flow configuration also helps to regulate the flow in the test strip, generating uniform test lines for more accurate results.

IBN’s device is capable of detecting IgG, a dengue-specific antibody found at the onset of secondary infections, directly from saliva in one step. According to IBN Executive Director Professor Jackie Y Ying, “The ability to differentiate between primary and secondary dengue infections makes [the device] a valuable early diagnosis tool that would help to ensure timely treatment and proper care of patients.”

The institute is currently collaborating with ARKRAY, a pioneer in the field of automated analysis systems, to commercialise its paper-based diagnostic technology. It is also investigating the use of other common fluid samples, such as blood, urine and serum, as well as the adaptation of the kit to detect other infectious diseases.