A study on using gold nanoparticles for naked-eye detection of SARS-CoV-2

Meena Kharatmal, HBCSE

In the current outbreak of COVID-19, the prevailing testing methods for detection of SARS-CoV-2 are real-time reverse transcription-polymerase chain reaction (RT-PCR), and rapid antibody test. The RT-PCR test detects the genetic material i.e. RNA in the current infection, using a swab technique. It takes about 4-6 hours for detection and requires sophisticated instruments and software. Complementing detection of the viral RNA with RT-PCR, rapid antibody tests detect the presence of antibodies using a blood sample, but these indicate past infection and not the presence of viral RNA in the patient, and thus are not useful for large-scale diagnosis of active infection. In the wake of the pandemic, it is preferable to use a testing method that is easy and quick, without using any sophisticated instrument for large-scale diagnosis.

In recent years, gold nanoparticles are being used in colorimetric bioassays to visualize the colour response, as these have simplicity in design, and provide a direct visual output, without the use of sophisticated instruments. A recent study that describes the detection of the SARS-CoV-2 virus with the naked eye uses such gold nanoparticles. The gold nanoparticles are coated with short DNA probes that are complementary to the viral RNA. Thus these nanoparticles aggregate only in the presence of viral RNA through the formation of RNA-DNA hybrids. The aggregation can be detected as a visible color change, and also as a visual sediment at the bottom of the vial when the RNA is digested.

The DNA-coated nanoparticles were tested against the MERS-CoV viral RNA, and showed no distinct change in color, indicating the specificity of the sensor for SARS-CoV-2. The test can work with mutated forms of the virus too as it can simultaneously target two separate regions
of the viral genome.

[Last update 25 June 2020]