Surface Plasmon Resonance Sensor of CO2 for Indoors and Outdoors
Round 1
Reviewer 1 Report
This paper concerns a surface plasmon resonance sensor of carbon dioxide for indoors and out-doors. I believe that the obtained results justify publication of the paper in Applied Sciences. However, the authors need to revise the paper with respect to the comments.
1.
Readerships can comprehend contents of this paper in detail if figures showing relations between sensor signal and ppm show. Therefore, the authors need to add figure showing relations between sensor signal and ppm.
2.
What is the relationship between the sensor signal and ppm? Does the sensor signal proportional to the change in ppm? The authors need to describe the effect of the signal when ppm changes.
3.
How long is the size of hemispheric prism?
4.
There are some typographical errors. For example, is "end face end face" on line 143 a mistake of "end face"? Please make sure there are no other typographical errors.
Author Response
In the attached file.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This work described the development of a plasmonic sensor aimed at measuring CO2 concentration both indoors and outdoors. This is an interesting work in which the authors use an hemispheric prism, together with a thin layer of gold and an additional layer of LiIO3 to excite a double plasmon wave. This way, they manage to obtain a high sensitivity and a remarkable resolution, compared to other works present in the literature. In my opinion, this work has potential and is a good match for Applied Sciences but it should be revised carefully, because it is far from being ready to be published. The design is correct, the results are good and the figures and clear and adequate, but there are important aspects that should be addressed before further considering it. Therefore, I suggest to perform a set of major revisions, paying special attention to the following bullets:
- I recommend to perform a full English review, since plenty of typos can be found throughout the text. Examples are "out-doors" in the title, "which could works" in line 99, "set up,2 in line 105 or "Birch y Downs" in line 129, among others. Additionally, please consider reducing the length of the sentences and the amount of information between brackets: consider that the Abstract consists of just two sentences and there are 6 times in which information is written between brackets, which is not a best practice in written English. Please, reconsider a re-write of the manuscript.
- The Introduction is too long and it seems very repetitive every time the authors describe the outcome from a referenced work. I recommend to describe the different technologies used to develop CO2 sensors briefly and to add a table summarizing their key features: this way, the reader will be able to compare them easily. Additionally, I recommend to mention plasmonic optical fiber sensors as well, since they are currently attracting a lot of research interest, as well as to add these two references: Optics Letters 43(10), 2308-2311 (2018) & Advanced Optical Materials 7(24), 1901383 (2019).
- In Figure 2, even if your interrogation setup is based on intensity interrogation, the reflection angle will not be the same as the incidence angle when the CO2 concentration changes. Therefore, you should differentiate between the two angels, instead of calling "theta" to both of them.
- Since you use an intensity-based interrogation scheme, how could you address a fluctuation of the power source, or a fluctuation of any transmitting parameters of the optical fiber used in the optical source?
- The response of the proposed sensor highly depends on the ambient conditions, so I recommend to include an equation describing the sensor response and considering parameters such as temperature, humidity and pressure.
Author Response
In attached file.
Author Response File: Author Response.docx
Reviewer 3 Report
The authors propose a surface plasmon resonance-based (SPR) sensor for detecting the amount of CO2 (real-time) for indoors and outdoor settings. In the previous work, the authors have demonstrated different sucrose concentration detection using a very similar setup. In this work, the author claims that the proposed setup can offer many advantages (in terms of sensitivity, price) compared to the existing ones.
I feel that this work addresses an important topic and represents an advance over previous work that is sufficient enough to be publishable. I recommend publication after a few minor points are considered.
(1) The effect of thickness of the layers of Au and Lithium Iodate in the reflectance curve shown in Fig. 2 and also in the sensitivity.
(2) In Fig.2, it seems there are two surface plasmons excited. So is it possible to have two corresponding dips (minimums) in the reflectance curve?
(3) A few minor corrections are needed: in line 85, the 6 mim should be 6 min, and in lines142, the word end face is repeated twice.
Author Response
In the attached file.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The revised version of the manuscript appears to be slightly improved　compared to an initial submission. Could not the authors describe the relationship between sensor signal and ppm from the simulation results?
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors have properly addressed all the comments and concerns arisen during the first round of peer-review. Being a valuable research, the quality of the manuscript has improved and therefore I recommend its acceptance for publication in Applied Sciences.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
