MXene-Based Fiber-Optic Humidity Sensor for Fast Human Breath Monitoring

Round 1

Reviewer 1 Report

Dear Authors, 

Congratulations on the well-written and interesting manuscript. These are some points for your consideration to review.

Highlight the novelty directly in the introduction. 

Add more quotations for Lines 41 to 48 to substantiate.

Briefly highlight the Natural evaporation method in line 80, so users have an idea of what is different/important.

For Fig 1, it would be interesting to put in the parameters e.g. eV of the SEM and TEM.

Very interesting Fig 2. Keep it up!

Do include how the RH was measured by a commercial hygrometer and the model.

In line 191, do discuss more on "has a fast response due to the superior moisture-sensitive properties".

The data looks promising. Congrats.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The article is an interesting presentation of a new and promising detector for gas humidity. It is however NOT a presentation of a detector for series production, just a first prototype. The research carried out and presented certainly merits publication but has a vast potential for improvement.

Some of the sentences can be written better.

Sentences can be written better.

Author Response

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Reviewer 3 Report

I quite like the idea of this manuscript, which is to monitor the humidity in human breath using fiber-optic sensing. Nonetheless, there are several minor issues (and a few more major ones) that combine to detract from my overall enthusiasm for this manuscript, and will need to be addressed before I can recommend publication. These include:

1.       The abstract provides too many technical experimental details, and not enough of an overview of the main idea and point of this manuscript. The authors should move the experimental detail out of the abstract, and include only the key ideas and main “take-away” messages.

2.       The first sentence of the introduction has an extra phrase “human comfort” at the end of the sentence. This should be deleted.

3.       Overall, this manuscript suffers from a non-trivial number of English language and syntax errors, which make it difficult to focus exclusively on the scientific content of the manuscript. The authors should consider how to best address this issue.

4.       In the introduction, the authors state that the “fiber devices” previously reported in the literature are “only sensitive to physical parameters.” If this is correct, then how are such devices able to measure the relative humidity, since this is not included as one of the physical parameters? More clarification is requested.

5.       The first time that the authors use the phrase “MXene,” they should provide a clear definition of what this material is, in addition to the information that they already provide about the advantages of using such materials. Moreover, in the interest of scientific honesty, the authors should also include any disadvantages/ drawbacks to the use of MXenes, rather than simply providing a list of significant advantages.

6.       Moreover, within the category of MXenes, there are a number of potential metals that can be used. The authors need to acknowledge this fact, and explain why they have chosen to focus on titanium-based MXenes for this work.

7.       Moreover, the authors should provide a clear justification about why a fiber optic sensor is the best choice for relative humidity measurements, and why it provides significant advantages over other potential options.

8.       In section 2 of the manuscript (“experiments”), the language of the text should not state that the authors are “proposing” specific work. Rather, this language should be changed to make it clear that the text is describing work that has already been performed.

9.       There is no discussion in this paper about the selectivity of the sensor, and whether it can also generate a response to alcohol, for example, or other volatile analytes. This is an important feature that has the potential to significantly affect the practical applicability of this sensor, and therefore a discussion about this topic should be added to the manuscript.

There are a non-trivial number of syntax-based and English language errors that need to be corrected.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Dear Authors,

The newer article is a great improvement over the old one. I think it can be published.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The authors have made a reasonable attempt to address the points that I raised on the previous version of their manuscript. Nonetheless, there are a number of outstanding issues that continue to be of concern, including:

The revised abstract has a number of inaccuracies/ ambiguities. For example, the authors state that “fiber optic breath sensors are safer for patients than electrical sensors.” How do the authors determine that these sensors are safer? They list MRI conditions as an explanation for why they claim that the fiber optic sensors are safer, but this is not a sufficient explanation. Are the authors stating that if people want to do breath detection during the MRI that they will need to use fiber optic sensors, and declaring on this basis that the sensors are “safer”? This is a weak rationale and needs to be modified.

Also in the abstract the authors state that fiber optic sensors have “attracted more attention.” More than what? How is such attention being measured? This claim needs to be clarified in order to improve its scientific accuracy.

On the previous version of the manuscript, I questioned how “fiber devices” that respond only to physical parameters are expected to act as effective humidity sensors. In response, the authors write that for such devices, “hygroscopic materials are coated” on their surface. The authors should clarify that these materials are expected to be the part of the device that responds to changes in humidity.

On the previous version of the manuscript, I requested that the authors provide an explanation for why they have chosen to focus on titanium-based MXenes. In response, the authors wrote that titanium-based MXenes are the earliest MXenes that were reported. This does not constitute a sufficient scientific explanation for why they have chosen titanium rather than other metal-based MXenes. I reiterate my request for the authors to include a scientific rationale for the decision to focus on this specific MXene.

On the previous version of the manuscript, I requested that the authors include information about the selectivity of their humidity sensor. In response, they have added information that the sensor is not selective at all! In fact, the same MXene responds to the presence of ethanol, methanol, acetone, and ammonia. It is unclear how the authors expect to account for this complete lack of selectivity in what they claim to be a humidity sensor. More information is required.

The English is better, but would still benefit from additional editing.

Author Response

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Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

The authors have done a reasonable job responding to the vast majority of my comments on the previous version of their manuscript. Nonetheless, I am still concerned about the issue of the lack of selectivity of this sensor. I understand that many Mxene sensors are poorly selective, and appreciate that the authors have indicated that further work can be envisioned that would impart the desired selectivity. Nonetheless, the authors have not yet included information in this manuscript about the fact that the sensor in its current iteration is not selective. The lack of selectivity should be explicitly noted (together with supporting data), together with a note that the lack of selectivity is in line with other reports of Mxene-derived sensors and that further work can be envisioned that would lead to high levels of selectivity.

The English is sufficiently improved at this point in time.

Author Response

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