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Review 1: "Colorimetric Test for Fast Detection of SARS-CoV-2 in Nasal and Throat Swabs"

Reviewer: Chayan Kanti Nandi (Indian Institute of Technology Mandi) | 📒📒📒 ◻️◻️

Published onMay 07, 2022
Review 1: "Colorimetric Test for Fast Detection of SARS-CoV-2 in Nasal and Throat Swabs"
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key-enterThis Pub is a Review of
Colorimetric Test for Fast Detection of SARS-CoV-2 in Nasal and Throat Swabs

AbstractMass testing is fundamental to face the pandemic caused by the coronavirus SARS-CoV-2 discovered at the end of 2019. To this aim, it is necessary to establish reliable, fast and cheap tools to detect viral particles in biological material so to identify the people capable to spread the infection. We demonstrate that a colorimetric biosensor based on gold nanoparticle (AuNP) interaction induced by SARS-CoV-2 lends itself as an outstanding tool for detecting viral particles in nasal and throat swabs. The extinction spectrum of a colloidal solution of multiple viral-target gold nanoparticles – AuNPs functionalized with antibodies targeting three surface proteins of SARS-CoV-2 (spike, envelope and membrane) – is redshifted in few minutes when mixed to a solution containing the viral particle. The optical density of the mixed solution measured at 560 nm was compared to the threshold cycle (Ct) of a Real Time-PCR (gold standard for detecting the presence of viruses) finding that the colorimetric method is able to detect very low viral load with a detection limit approaching that of RT-PCR. Since the method is sensitive to the infecting viral particle rather than to its RNA, the achievements reported here open new perspective not only in the context of the current and possible future pandemics, but also in microbiology as the biosensor proves itself to be a powerful though simple tool for measuring the viral particle concentration.

RR:C19 Evidence Scale rating by reviewer:

  • Potentially informative. The main claims made are not strongly justified by the methods and data, but may yield some insight. The results and conclusions of the study may resemble those from the hypothetical ideal study, but there is substantial room for doubt. Decision-makers should consider this evidence only with a thorough understanding of its weaknesses, alongside other evidence and theory. Decision-makers should not consider this actionable, unless the weaknesses are clearly understood and there is other theory and evidence to further support it.



The authors have used a “colorimetric test for fast detection of SARS-CoV-2 in Nasal and Throat swabs. I must admit that the authors have taken a nice approach to the virus-detection using the most well-known technique the use of gold nanoparticles (AUNP). AUNP is one of the most commonly used nanoparticles, which is known for decades as a high-quality nanoparticle-based sensor because of its easy synthesis process, very low toxicity, and ease to functionalize. The authors have successfully synthesized the AUNP within the size range of 20nm and then functionalized it with the specific antibody for the three different virus proteins namely spike, membrane, and envelope proteins. The data also presented nicely. However, in terms of technology transfer and utilizing the developed sensor for the mass detection of the SARS-CoV-2 virus, the following few comments may be useful.

  1. Although the data represented in Figure 1 suggested the possible binding of AUNP to the SERS-CoV-2 virus, the specificity and selectivity should be checked in presence of other viruses or similar strains so that it is not giving any false-positive results.

  1. In addition, the efficiency of detection of the individual virus proteins should be checked, so that the real efficiency of the AUNP for a particular virus protein could be verified. Finally, based on the result it could be concluded whether the AUNP is equally efficient for all the proteins detection or not. This will really help to modify the sensor according to the need. The quantification of a load of individual antibodies to the AUNP may be helpful in this case.

  2. The color change shown in Figures 1a and 1b upon binding to the virus will not be enough when one has a very less amount of virus signal.

4. The real quantification of the virus to a single AUNP should be verified. I may be wrong, however, the scheme shown in Figure 1 represents the number of AUNP attached to a single virus particle, I was expecting the reverse i.e. the number of virus particles to a single AUNP. I think it will help to understand the sensitivity of the AUNP sensor. These are all my suggestion. The authors may or may not take these works to be carried forward. However, It would be really nice, if a sensor like the authors presented in this manuscript, to have in the market. It will really be beneficial for society in the most difficult situation.


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