Detecting SARS-CoV-2 with a rapid, cost-effective colorimetric biosensor

The COVID-19 pandemic has emphasized the importance and need for fast, accurate, and cost-effective techniques for mass screening to detect viral infection. Colorimetric biosensors that rely on localized surface plasmon resonance represent a promising approach due to their easy fabrication and quick detection.

To optimize this technique, Minopoli et al. simulated the optical behavior of the colorimetric immunosensor they recently created to detect SARS-CoV-2.

“We decided to carry out the analysis to attain a quantitative description of the colorimetric biosensor we realized to test the presence of SARS-CoV-2 in nasopharyngeal swab or even in saliva,” said author Raffaele Velotta. “The biosensor consists of a colloidal solution of gold nanoparticles whose surface is coated with antibodies that recognize the surface proteins of the virion. These nanoparticles surround the viral particles and change the solution color.”

The researchers aimed to gain insight into the physical processes underlying color change by performing theoretical analysis of the biosensor’s optical response at several viral particle concentrations. They employed the finite-difference time-domain method with different configurations of gold nanoparticles and SARS-CoV-2 virions to optimize the device’s performance.

In the end, two ingredients were essential to reaching an acceptable level of detection. First, the biosensor must include three kinds of functionalized nanoparticles, each targeting spike, membrane, and envelope proteins to ensure the virion is fully covered by nanoparticles. Second, nanoparticle functionalization should be configured so the antibody coating on the nanoparticles is thin enough to attain an optimal plasmonic coupling.

“Currently, virus quantification requires complex procedures, and our results are a significant step towards the possibility to use simple optical methods to address such an issue,” said Velotta.

Source: “Analysis of the optical response of a SARS-CoV-2-directed colorimetric immunosensor,” by Antonio Minopoli, Emanuela Scardapane, Adriano Acunzo, Raffaele Campanile, Bartolomeo Della Ventura, and Raffaele Velotta, AIP Advances (2021). The article can be accessed at http://doi.org/10.1063/5.0050570 .