Review Reports - A Copper-Based Coating for the Control of Airborne Viable Bacteria in a Prison Environment

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

COMMENTS FOR THE AUTHORS

This work reported an innovative antimicrobial coating that supports copper on an inert carrier such as zeolite, intended to provide cost-effective antimicrobial properties to surfaces. In some cases, the text must be clarified and there are issues that are not accurate. Better and more evidences for some conclusions are required.

1. In introduction section, besides copper, the other antimicrobial metals such as Ag, Au, can also be introduced and give a comparison with copper.

2. Line66-67, please give the reference to illustrate for “The efficacy of copper in reducing pathogenic microorganisms has been the subject of extensive research”.

3. A schematic diagram can be given in Section 2.

4. Why did authors select CuAd? And chemical composition should be given.

5. Are there some impurity in the coating?

6. What is the porosity of micrometric zeolite?

7. The morphologies of coatings should be studied.

8. Error bar should be added.

9. Conclusions are needed.

Author Response

This work reports an innovative antimicrobial coating that supports copper on an inert carrier, such as zeolite, intended to provide cost-effective antimicrobial properties to surfaces. In some cases, the text must be clarified, and there are issues that are not accurate. Better and more evidence for some conclusions is required.

Our response: We thank the referee for the comments on the article, we have considered all the referee´s comments and given the proper answer to all the issues point out by the referee. All changes in the draft have been highlighted.

In the introduction section, besides copper, other antimicrobial metals such as Ag and Au can also be introduced, and a comparison with copper.

We appreciate your suggestion. We have expanded the introduction section to include a brief discussion on other antimicrobial metals, such as silver (Ag) and gold (Au), and made a comparison with the antimicrobial properties of copper (Cu). This addition enhances the overall context of using antimicrobial metals in coatings and highlights the choice of copper. A new paragraph was added to the introduction (Lines 66 to 75) with new references 8 to 12.

Lines 66-67, please provide a reference to illustrate “The efficacy of copper in reducing pathogenic microorganisms has been the subject of extensive research.”

We thank the referee for bringing this to our attention. We have included a relevant reference to support the statement regarding the effectiveness of copper in reducing pathogenic microorganisms. The reference #13 was cited in line 77 and added to the list.

A schematic diagram can be added to Section 2.

We appreciate the suggestion given and we agree with the comment of the referee. Thus in Section 2, we incorporated a schematic diagram illustrating the experimental procedure and the structure of the copper-based coating. This diagram helps to visualize the experimental approach more clearly. The schematic diagram was added as Figure 1, replacing the previous one.

Why did the authors select CuAd? The chemical composition should be provided.

In relation to the referee´s question, we have expanded the discussion to explain the reasoning behind the selection of CuAd in lines 231-239. Additionally, we have included the detailed chemical composition of CuAd according to the Energy Dispersive Spectroscopy (EDS) analysis in lines 204-214. EDS is not quantitative technique since is a superficial measurement, but it is possible to propose a chemical composition based on the relation between the elements of this materials. Based on the chemical formulas, it should be expected that Al³⁺, Si⁴⁺, Na⁺ and Cu²⁺ should have a ratio of 1 : 1.2 : 1 : 1 between them, and as the experimental results shows Al³⁺ and Si⁴⁺ have the correct ratio, but there is low sodium proportion compare to copper that may be due to some exchange between this ions. Therefore, we can propose these general formula: (Na⁺_(1-x)Cu²⁺_xAl₁Si_1.2O_4.5· XH₂O)(Cu₂Cl(OH)₃).

Are there impurities in the coating?

We appreciate the referee question, as it provides an opportunity to clarify an important point. We find it unnecessary to focus on potential impurities in the base commercial paint, given that it is a widely used product subject to rigorous quality controls. In this case, the base paint was a commercial oil paint with an alkyd formulation in turpentine solvent (Glossy Oil) made by one of the most larger painting companies in Chile, Tajamar (https://pinturastajamar.cl), commonly used for routine maintenance of detention cells by the national police “carabineros”. The most relevant aspect would be to focus on the purity of the active antimicrobial agent CuAd (copper additive) incorporated into the paint. The Energy Dispersive Spectroscopy (EDS) analysis revealed that CuAd contains the expected elements; aluminum (10.9%), silicon (9.6%), sodium (4.2%), and copper (14.2%), confirming that the zeolite was appropriately functionalized with copper. This is explained in lines 204-214. Therefore, it makes more sense to ensure the purity of the CuAd, as the antimicrobial performance of the coating primarily depends on this additive rather than the base paint. This approach allows the analysis to focus on the aspects that truly impact the effectiveness of the coating.

What is the porosity of micrometric zeolite?

We thank the referee for point out this question. Since we are using the same type of zeolite used in a previous work, reference 30, we have used the values reported in this publication. They report the presence of micropores and mesopores, characteristics we have deemed relevant for our analysis. This information was added to Materials and Methods, lines 117-119. The new reference was added as reference #30.

The morphologies of coatings should be studied.

We appreciate your comment. In this case, the morphology of the coating, which consists of a commercial oil-based matrix, is not relevant to the study's objectives. Actually, the coating could be based on any organic matrix, whether another paint or polymers, without altering the central purpose of the research. The critical aspect is how CuAd influences the functional properties of the final material, as it is the active component responsible for conferring antimicrobial properties. The key focus of the study is to highlight the role of CuAd, which will be reflected in both the abstract and the conclusions. However, it would be interesting to compare different organic matrices in future studies. This aspect will be explored in subsequent research.

Error bars should be added.

We thank the referee for this this observation. We have added error bars to Figure 4.

Conclusions are needed.

We appreciate the comment of the referee, this was a not intentional omission. We have reviewed and crafted the conclusions to provide a clearer and more detailed summary of the results obtained and their relevance within the study context. The conclusions were added as section 4.

Reviewer 2 Report

Comments and Suggestions for Authors

The article is interesting for readers and has novel scientific data. Some comments and suggestions:

1) The measurement unit „200-mm mesh“ is incorrect (line 125). It should be „200 Mesh“. 200 Mesh can be converted to mm, and it is 0.074 mm.

2) „On November 23 and 28, bacterial load was particularly high, but even in these days, cell #1 had a lower load than cell #2.“ (line 216). The text does not clarify why the days (23 and 28) are crucial for the research.

3) There is no comparison with the results obtained by other authors. Maybe the authors can compare copper-based coatings with different materials that also have antimicrobial properties.

4) The authors have considered their work's future impact and directions, but some remarks are overgeneralized. The authors use only coliform load in this study, but other relevant pathogens (viruses, other types of bacteria, fungi), which can also be problematic in prison environments, are not considered. So, the authors should avoid making such wide-ranging generalizations without the obtained data. For example, claiming that copper coatings can solve all hygiene issues in prisons weakens the clarity and accuracy of the conclusions.

5) The text contains several grammatical errors: dots are missing at the end of the sentence (eg. [1]. [2-3].), commas and some articles to nouns are missing.

Author Response

Reviewer 2:

The article is interesting for readers and contains novel scientific data. Some comments and suggestions:

The measurement unit "200-mm mesh" is incorrect (line 125). It should be "200 Mesh." 200 Mesh can be converted to mm, and it is 0.074 mm.

We appreciate the observation. We have corrected the unit "200-mm mesh" to "Mesh 200" and added the corresponding conversion to 0.074 mm for clarity (Line 139).

"On November 23 and 28, bacterial load was particularly high, but even on these days, cell #1 had a lower load than cell #2." (line 216). The text does not clarify why these days (23 and 28) are crucial for the research.

Thank you for requesting clarification. This is due to violent clashes between high school students and the police that occurred between November 15 and 29, primarily concentrated in the metropolitan region, specifically in downtown Santiago. The police cell under study is located in this area, which explains why the bacterial load was particularly high on November 23 and 28, due to the increased number of detainees during these incidents. A brief explanation was added in lines 250-256.

There is no comparison with the results obtained by other authors. Maybe the authors can compare copper-based coatings with different materials that also have antimicrobial properties.

We appreciate the referee´s suggestion, which highlight our own results. We have supplemented the results/discussion section by comparing previous studies that use organic matrices in lines 290-297.

The authors have considered their work's future impact and directions, but some remarks are overgeneralized. The authors use only coliform load in this study, but other relevant pathogens (viruses, other types of bacteria, fungi), which can also be problematic in prison environments, are not considered. So, the authors should avoid making such wide-ranging generalizations without the obtained data. For example, claiming that copper coatings can solve all hygiene issues in prisons weakens the clarity and accuracy of the conclusions.

We agree with the referee that some conclusions may have been expressed too broadly. We have revised the text to avoid generalized statements about the ability of copper coatings to solve all hygiene issues in prisons. Additionally, we have clarified that the study focused solely on coliform load and that future studies could explore the effectiveness against other pathogens, such as viruses, bacteria, and fungi. Please find details in the added “Conclusions” in section 4.

The text contains several grammatical errors: periods are missing at the end of some sentences (e.g., [1]. [2-3].), and some commas and articles are missing.

Thank you for pointing out the grammatical errors. We have carefully reviewed the manuscript to correct the punctuation errors, including missing commas, periods, and articles. Grammar and punctuation have been revised throughout the entire manuscript.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Accept in present form