Research on On-Line Detection Method and System for Nitrate in Groundwater
Vladislav Yakovlev
Round 1
Reviewer 1 Report
Figures 3 and 4 are not readable.
Style of references is all over the place.
Figure captions are not informative.
There is no clear identification of novelty, significance and impact of the performed work.
Scientific approach is lacking.
There is no quantifiable assessment metric to evaluate the work.
Error bars are not provided, and the source of errors is not analyzed.
There is no any critical assessment of the data.
The experimental procedure is not describe in the way which allows its full reproducibility.
The manuscript is written in a hard to comprehend language.
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
In this manuscript, the authors developed an electrochemical sensor chip and protocols to achieve consistent and accurate nitrate detection with in-situ working electrode surface regeneration. The authors also developed an online data transmission system for remote water quality monitoring. The authors systematically examined the working electrode bias potentials for the three detection stages, namely, Cu dissolution, Cu deposition, and nitrate detection. Then, they tested the calibration curves and inter-sensor variabilities. Lastly, the authors developed a wireless system for remote monitoring applications. I think the manuscript could be supported with more details. With the minor concern addressed, I believe it is suitable for publication.
1. What is the material and the general fabrication process for the sensor electrodes? As a key part of the detection system, the authors should provide some details about these electrodes: what material was used, were they fabricated in-house or purchased, and how were they electrically connected from the glass to the PCB board.
2. The authors should explain more about the lack of oxidation current for Cu dissolution above + 0.14 V. In a common metal dissolution experiment, the electrode current would further increase as the bias voltage increases. And the low electrode current (~ 100 nA) above + 0.14 V indicates the cease of Cu dissolution, which is very unusual. Could there be impurities from the microelectrodes that formed insoluble substances like CuCO3 that passivate the electrode? Could the copper formed alloys with metals in microelectrodes, causing a 2-phase dissolution process?
3. The author should provide more details about the wireless setup since this is a key part of the work (with the name ‘online’ in the title). Providing information such as block diagrams, key protocols involved, and examples of measured data would be very helpful. For example, the MSP430 controller has an integrated 12-bit ADC (analog to digital converter), and the resolution is much lower than that of ADCs used in potentiostats, so questions about amplifier design would naturally arise. Additionally, it's important to include basic information about wireless transmission, considering that Bluetooth, WLAN, and cellular networks exhibit significantly different ranges, particularly in challenging environments like underground areas. The choice of wireless protocol would affect the deployment range of these sensors.
Grammatical and word choice comments:
Since there is no line count in the manuscript file, please cross-reference with the pdf file I uploaded for these comments (highlighted in the pdf).
4. Abstract, consider removing “of groundwater”.
5. Abstract, the “adopted” and ”an online detection…systems (WS)” are in different fonts.
6. Introduction, paragraph 1, consider removing “normal”.
7. Introduction, paragraph 2, consider changing “high” to stringent.
8. Introduction, paragraph 2, consider changing “it” to this issue.
9. Introduction, paragraph 2, consider changing “solution” to aqueous.
10. Introduction, paragraph 2, consider changing “object” to analyte.
11. Introduction, paragraph 2, consider changing “the objective to be measured can be measured by measuring the response signal” to the analyte can be measured by the response signal.
12. Introduction, paragraph 2, consider changing “sensitive material” to sensing material.
13. Introduction, paragraph 2, consider changing “one-time” to single-use or disposable.
14. Section 2.2 Experimental process, paragraph 1, change “opposing electrode” to counter electrode.
15. Section 2.2 Experimental process, paragraph 1, change “electronic medium” to ions.
16. Section 3.1 Parameter Optimization, paragraph 1, double brackets.
17. Section 3.1 Parameter Optimization, paragraph 1, subscribe the “1” in “E1”.
18. Section 3.1 Parameter Optimization, paragraph 2, typo of “deposition”. I think the authors meant dissolution.
19. Section 3.2 Performance Test, paragraph 2, change “timing current curve” to time current curve.
20. Section 5 Conclusion, remove “quality”.
Comments for author File: 
Comments.pdf
The English quality can be improved. With the grammatical and wording issues addressed, I believe the manuscript would be easy for people to read.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Reviewer 3 Report
In this work the authors develop a specialized sensor to solve the problems of passivation effect, short life, and poor repeatability of electrodes in conventional electrochemical detection by means of a novel method based on the use of a copper solution. The method was combined with a microelectrochemical sensing electrode to detect nitrate in water. The work is novel and with future applications in the industrial and agricultural world. I find its publication appropriate if the observations and comments which I suggest be improved:
1. Line 18 abstract Leave a space after the comma “groundwater, a”
2. Line 24 abstract Why does the word “on-line” appear together and sometimes separately? You have to be uniform.
3. Line 27 abstract. It is a very common mistake in the scientific field to confuse the hyphen sign (-) with the minus sign (-). This leads to confusion. They must change the hyphen sign to the minus sign in the math editor throughout the text.
Let me give a few examples:
Error. 0.031 μA/[μmolL-1]
Good. 0.031 μA/[μmolL-1]
Error. -0.8V
Good. -0.8 V (leave space between the number and its corresponding unit)
4. In section 2 Experimental part appears:
CuSO4•5H2O, Na2SO4, NaNO3 and 98%H2SO4.
There are no numbers in sub-indices. The sign (•) is not bold. It must be CuSO4×5H2O.
Please review the entire text.
5. In section Introduction there is an apostrophe in the word residents. Why?
6. In section Introduction the authors state: “When the electrochemical electrode is applied in the solution environment, the object to be measured will have an electrochemical reaction on the surface of the sensitive material, and the concentration of the object to be measured can be measured by measuring the response signal”.
This work would improve if all the electrochemical reactions that take place in the electrodes at each of the stages were written. In this way the reader can understand the physical chemistry that appears at each stage (E1, E2, E3). Semi-reactions (oxidation-reduction) in which the copper electrodeposition process is observed as the nitrate ion interacts with the electrodes must be written in such a way that the reader can observe everything that happens on the electrodes.
7. In all figures both the units of the axes and the variables are in bold. Do not use this font. Use another type of format. The minus sign should be used the mathematician, not the hyphen sign. In case of doubt, consult the specifications of the journal.
8. Is there any thermodynamic reason why the authors use copper sulfate solution in their experimentation? That is, why this dissolution and not another to avoid the effect passivation? There must be a physical reason why this dissolution is better than others.
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors made some minor improvements to the manuscript; however, they failed to address major deficiencies of manuscript, such as providing a sufficient introduction to the field, providing a clear physical foundation for their measurements, and describing measurements in a logical and consistent manner. The quality of graphs is low, and figure captions do not allow to comprehend the information provided in those figures. What is the most frustrating in reading this manuscript is that the majority of data are provided without clear explanation why such data are important and what one can learn from such data. The most important calibration curve is at the very end of manuscript and doesnt contain data for other ions which are likely to be present in real samples.
The manuscript is barely readable and is very hard to understand.
Author Response
ANSWER:Dear Sir/Madam，Thank you for your advice.These data are obtained from our experiments, specifically for sensor performance data. For example, the data in Figure 6 represents the input output relationship of the sensor, while the other image data represents the data during the sensor preparation process. For readers, it can serve as an important reference when they need to make similar sensors，learn about the application scenarios of the sensors in this article and how to build an online monitoring system.Anyway, thank you for your suggestion!
Author Response File: Author Response.docx
Reviewer 3 Report
The authors have responded correctly to all comments and suggestions. I suggest in the future follow the indications regarding the electrochemical equations that take place at the anode and cathode as well as a deep discussion about the physical reason for the interactions.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
