Recent advances in point of care testing for COVID-19 detection.

The World Health Organizations declaration of the COVID-19 pandemic was a milestone for the scientific community. The high transmission rate and the huge number of deaths, along with the lack of knowledge about the virus and the evolution of the disease, stimulated a relentless search for diagnostic tests, treatments, and vaccines. The main challenges were the differential diagnosis of COVID-19 and the development of specific, rapid, and sensitive tests that could reach all people. RT-PCR remains the gold standard for diagnosing COVID-19. However, new methods, such as other molecular techniques and immunoassays emerged. Also, the need for accessible tests with quick results boosted the development of point of care tests (POCT) that are fast, and automated, with high precision and accuracy. This assay reduces the dependence on laboratory conditions and mass testing of the population, dispersing the pressure regarding screening and detection. This review summarizes the advances in the diagnostic field since the pandemic started, emphasizing various laboratory techniques for detecting COVID-19. We reviewed the main existing diagnostic methods, as well as POCT under development, starting with RT-PCR detection, but also exploring other nucleic acid techniques, such as digital PCR, loop-mediated isothermal amplification-based assay (RT-LAMP), clustered regularly interspaced short palindromic repeats (CRISPR), and next-generation sequencing (NGS), and immunoassay tests, and nanoparticle-based biosensors, developed as portable instruments for the rapid standard diagnosis of COVID-19.

Detection of SARS-CoV-2 virus via dynamic light scattering using antibody-gold nanoparticle bioconjugates against viral spike protein.

Mass testing for the diagnosis of COVID-19 has been hampered in many countries owing to the high cost of genetic material detection. This study reports on a low-cost immunoassay for detecting SARS-CoV-2 within 30 min using dynamic light scattering (DLS). The immunosensor comprises 50-nm gold nanoparticles (AuNPs) functionalized with antibodies against SARS-CoV-2 spike glycoprotein, whose bioconjugation was confirmed using transmission electron microscopy (TEM), UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), and surface-enhanced Raman scattering spectroscopy (SERS). The specific binding of the bioconjugates to the spike protein led to an increase in bioconjugate size, with a limit of detection (LOD) 5.29 × 103 TCID50/mL (Tissue Culture Infectious Dose). The immunosensor was also proven to be selective upon interaction with influenza viruses once no increase in size was observed after DLS measurement. The strategy proposed here aimed to use antibodies conjugated to AuNPs as a generic platform that can be extended to other detection principles, enabling technologies for low-cost mass testing for COVID-19.