Analysis of the optical response of a SARS-CoV-2-directed colorimetric immunosensor

The optical response of different configurations of functionalized gold nanoparticles (f-AuNPs) and SARS-CoV-2 virions is simulated in order to explore the behavior of a colloidal solution containing 10(5)-10(13) virions/ml. The analysis herein reported is carried out for three concentration regimes: (i) low (less than or similar to 10(8) virions/ml), (ii) intermediate (similar to 10(9)-10(10) virions/ml), and (iii) high (greater than or similar to 10(11) virions/ml). Given the high binding effectiveness of f-AuNPs to virions, three different configurations are expected to arise: (i) virions completely surrounded by f-AuNPs, (ii) aggregates (dimers or trimers) of virions linked by f-AuNPs, and (iii) single f-AuNP surrounded by virions. It is demonstrated that 20 nm diameter gold nanoparticles functionalized against all three kinds of SARS-CoV-2 proteins (membrane, envelope, and spike) allow one to reach a limit of detection (LOD) of similar to 10(6) virions/ml, whereas the use of only one kind of f-AuNP entails a ten-fold worsening of the LOD. It is also shown that the close proximity (similar to 5 nm) of the f-AuNP to the virions assumed throughout this analysis is essential to avoid the hook effect, thereby pointing out the importance of realizing an apt functionalization procedure that keeps thin the dielectric layer (e.g., proteins or aptamers) surrounding the gold nanoparticles. (c) 2021 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

The study simulates the optical response of functionalized gold nanoparticles and SARS-CoV-2 virions, revealing different configurations and emphasizing the importance of the proximity between functionalized gold nanoparticles and virions in avoiding the hook effect. Additionally, the study demonstrates the potential to achieve low virus detection limits through appropriate functionalization procedures.