Alternative Platform for COVID-19 Diagnosis Based on AuNPs Modified Lab-On-Paper

Since the SARS-CoV-2 virus was first discovered in 2019, it has spread over the world. Rapid testing is critical to retard the spread of the virus. Herein, a Lab-on-Paper for diagnosis of COVID-19 is developed applying a colorimetric method for screening test, along with high precision SARS-CoV-2 antigen detection on paper using a laser desorption ionization mass spectrometry (LDI-MS). Gold nanoparticles (AuNPs) were modified on paper for both colorimetric and LDI-MS detection. The colorimetric detection is based on the color change occurring on the paper from pink to purple as a result of AuNP aggregation which can be regulated by antigen−antibody bioconjugation. AuNPs on paper can be used directly as an LDI-MS substrate for direct quantitation of SARS-CoV-2 antigen in saliva without sample preparation for SARS-CoV-2 quantitative detection. In comparison to RT-PCR, LDI-MS provides early diagnosis with high sensitivity, rapidity without sample preparation, as well as a lower cost/test, which is crucial for preventing mortality of patients with underlying conditions. This approach demonstrated linearity between 0.01 and 1 µg mL^-1, covering a cut-off value of 0.048 µg mL^-1 for COVID-19 indication in saliva. Hence, this platform might be a potential device for applying as non-invasive diagnosis of COVID-19 Omicron BA.2 variant.