Tokyo, Sep 10 (IANS): To fight against Covid-19, Japanese scientists have developed a rapid, reliable and low-cost antibody test, that uses portable lab-on-a-chip technology to accurately measure the concentration of antibodies present in diluted blood plasma.

Previous studies have found that Covid-19 antibodies, or proteins produced by the immune system to neutralize the virus, are present in the later stages of infection and can linger in the blood after the infection has cleared, allowing previously infected individuals to be identified, the study published in the journal Biosensors and Bioelectronics said.

Antibody tests are, thus, an important means of determining the full spread of the coronavirus - information that is crucial to guide public health policies, it said.

"Many existing platforms for antibody tests are accurate and reliable, but they are costly and need to be carried out in a lab by trained operators. This means that it can take hours, or even days, to obtain results," said study author Riccardo Funari from the Okinawa Institute of Science and Technology Graduate University (OIST).

The researchers avoided this trade-off between accuracy and accessibility by developing an alternative antibody testing platform that combines powerful light-sensing technology with a microfluidic chip.

The chip provides results within 30 minutes and is highly sensitive, detecting even the lowest clinically-relevant antibody concentration.

Each chip is cheap to manufacture and negates the need for a lab or trained operators, increasing the feasibility of nation-wide testing.

And there's another distinctive advantage of this newly-developed platform.

"The test doesn't just detect whether the antibodies are present or absent - it also provides information about the number of antibodies produced by the immune system. In other words, it's quantitative," said study author Amy Shen.

The antibody testing platform consists of a microfluidic chip that is integrated with a fibre optic light probe. The chip itself is made from a gold-covered glass slide with an embedded microfluidic channel.

Using an electric voltage, the team fabricated tens of thousands of tiny spiky gold structures, each one smaller than the wavelength of light, on a glass slide.

The researchers then modified these gold nano spikes by attaching a fragment of the SARS-CoV-2 spike protein. This protein is crucial for helping the coronavirus infect cells and causes a strong reaction from an infected person's immune system.

In this proof-of-concept study, the scientists demonstrated the principle behind how the test detects antibodies by using artificial human plasma samples spiked with Covid-19 antibodies that are specific to the spike protein.

Using a syringe pump, the sample is drawn through the chip. As the plasma flows past the protein-coated gold nano spikes, the antibodies bind to the spike protein fragments. This binding event is then detected by the fibre optic light probe.

"The detection principle is simple but powerful," said the study authors wrote.