Insecticide Monitoring in Cattle Dip with an E-Nose System and Room Temperature Screen-Printed ZnO Gas Sensors
Round 1
Reviewer 1 Report
The authors have examined two electronic noses, including commercial gas sensors and printed ZnO gas sensors to monitor Taktic levels in dipping pool water. The following comments can help improve the manuscript.
1- Please improve the English grammar and writing skills for this paper.
2- It's better to use "fabrication" instead of "manufacturing".
3- Line 78: Why did you mention metal oxide materials only in the amorphous category?
4- Line 79: The mechanism of gas sensing in metal oxide materials needs a more detailed explanation.
5- Line 84: Add to the article more novel techniques used to increase selectivity. For example high-integrated structures (DOI:10.1016/j.snb.2023.133289) and nanocomposite materials (DOI: 10.1016/j.snb.2022.131418).
6- Line 171: What is the reason for using the relay circuits?
7- It is necessary to indicate the sample holder size.
8- Production specific and the name of the supplier of the materials used in synthesis must be specified.
9- Add scale bar to the fig. 9.
10- The scale bar and text in figure 10 are unclear.
11- It is necessary to specify exactly what the "Normalised sensor output" is.
12- Add a graph or table to compare result of section 3.1 and 3.2.
13- Do you have the same response curve for each testing under a certain temperature and humidity? The reader will expect to have a discussion on the influence of both factors simultaneously on the samples. How they will actually affect each other. It is important to have the same response and recovery shape each time you tested for under different conditions. This meant that there were no serious sensing poisoning to your samples and they were full recoverable to the initial stage. You can put them in the supplementary data.
14- None of the important sensor parameters such as stability, reversibility, response and recovery time, Relative Standard deviation, and ... have been discussed.
Please improve the English grammar and writing skills for this paper.
Author Response
Good day,
We appreciate your feedback and have edited the paper considering all of your comments. Please find our response below.
1- Please improve the English grammar and writing skills for this paper.
English grammar and writing have been reviewed by our authors and care has been taken to correct mistakes.
2- It's better to use "fabrication" instead of "manufacturing".
This is correct, thank you. "Manufacturing" has been replaced with "fabrication" in almost every instance except in the introduction, where large-scale manufacturing was discussed.
3- Line 78: Why did you mention metal oxide materials only in the amorphous category?
This was a mistake and was changed.
4- Line 79: The mechanism of gas sensing in metal oxide materials needs a more detailed explanation.
Complete.
5- Line 84: Add to the article more novel techniques used to increase selectivity. For example high-integrated structures (DOI:10.1016/j.snb.2023.133289) and nanocomposite materials (DOI: 10.1016/j.snb.2022.131418).
In the introduction section, more novel techniques for selectivity are now discussed, but the paper now also makes it more clear that selectivity in a gas sensor array-based e-nose comes from training with a classifier and not individual sensor selectivity. This is how we intend to use the sensors as well.
6- Line 171: What is the reason for using the relay circuits?
The relay circuits activate the valve and pump and protect the microcontroller from back EMF. This has been made more clear in the paper and the trade-offs with using something like a Mosfet with lower power were also discussed.
7- It is necessary to indicate the sample holder size.
This has been changed and is now indicated in the text and in the figure.
8- Production specific and the name of the supplier of the materials used in synthesis must be specified.
We have added all names of suppliers.
9- Add scale bar to the fig. 9.
Complete
10- The scale bar and text in figure 10 are unclear.
Complete
11- It is necessary to specify exactly what the "Normalised sensor output" is.
This is correct and we have added an in-text description, as well as clarification in the figure where it was used.
12- Add a graph or table to compare result of section 3.1 and 3.2.
We will not be comparing the results of Sections 3.1 and 3.2, as 3.1 shows a completed e-nose system, whereas 3.2 only shows gas sensors that respond to the insecticide in a non-e-nose configuration. We realised that this was unclear in the text. We have clarified in the text that the aim of section 3.2 is not to compare to a full e-nose system, but to present a component-level alternative to commercial sensors.
13- Do you have the same response curve for each testing under a certain temperature and humidity? The reader will expect to have a discussion on the influence of both factors simultaneously on the samples. How they will actually affect each other. It is important to have the same response and recovery shape each time you tested for under different conditions. This meant that there were no serious sensing poisoning to your samples and they were full recoverable to the initial stage. You can put them in the supplementary data.
We have added an entirely new section to the results where Taktic fumes are measured at constant humidity and temperature. We then compare this to samples with water and the results are different. We also observe the long-term sensor response when exposed to water vapour, as opposed to air and have discussed the differences. We have added a discussion of the effects of humidity and temperature and have suggested that further comprehensive poisoning of data with humidity should be done in future work, as this is out of the scope of the paper.
14- None of the important sensor parameters such as stability, reversibility, response and recovery time, Relative Standard deviation, and ... have been discussed.
This has also been added.
Thank you for your feedback.
Reviewer 2 Report
The work is devoted to an urgent problem - the control of the content of insecticides in the water. The chosen method of analysis using sensors is promising, fast and inexpensive. The manuscript considers in details the main prerequisites for choosing the method of analysis and material for the synthesis of sensors, the design of the device, and the methodology for conducting the analysis. However, to understand the effectiveness of the developed device and sensor, some explanations and additions are needed:
1. There is no description of the calculation and statistical parts in the Materials and methods, for example, what programs were used to process sensor signals using the PCA method? Algorithm, validation method? To confirm the ability to distinguish the odour of Amitraz from other odours, it is necessary to present the results of statistical tests, for example, a comparison of averages according to Student's t-test, considering differences in variances. The choice of a statistical criterion for comparing the obtained values should also be described in this section.
2. The magnitude of the sensor signal is affected by a lot of factors, and one of the most important characteristics is selectivity, which has not been considered. Mineralization of water, the presence of surfactants and other components in the water will significantly affect the sensor signal and may make the obtained differences in the sensor signals insignificant. The Discussion section should include a discussion of the selectivity of the obtained system and the synthesized coating, consider in more detail the influencing factors and ways to reduce their influence.
3. The article does not have a Conclusion section at all. In conclusion, in addition to a possible plan for the development of the research, it is also desirable to include information about the possibilities and limitations of the proposed solutions, a comparison with existing systems of electronic noses, including other types of sensors used for water analysis, for example, Kuchmenko, T.A.; Lvova, L.B. A Perspective on Recent Advances in Piezoelectric Chemical Sensors for Environmental Monitoring and Foodstuffs Analysis. Chemosensors 2019, 7, 39. https://doi.org/10.3390/chemosensors7030039, Alphus Dan Wilson: Identification of insecticide residues with a conducting-polymer electronic nose. Chemical Sensors 2014, 4: 3, Ren, Lili and Kong, Cheng and Weng, Xiaohui and Zhang, Tao and Chang, Zhiyong, A Universal Electronic Nose System for Detecting Various Types of Pesticide Residues in Different Carriers. Available at SSRN: https://ssrn.com/abstract=4425839 or http://dx.doi.org/10.2139/ssrn.4425839
Minor editing of English language required
Author Response
Good day, thank you for your feedback. Please find our response below.
There is no description of the calculation and statistical parts in the Materials and methods, for example, what programs were used to process sensor signals using the PCA method? Algorithm, validation method? To confirm the ability to distinguish the odour of Amitraz from other odours, it is necessary to present the results of statistical tests, for example, a comparison of averages according to Student's t-test, considering differences in variances. The choice of a statistical criterion for comparing the obtained values should also be described in this section.
We have clarified why and how we used PCA in the paper. PCA is a very standard statistical method used in e-nose literature to determine if data is well suited to training with a classifier algorithm. We have clarified the programs and processes used in our PCA and referenced other sources that complete similar PCAs. The data is visually very distinct and the data size is not very large, therefore doing a t-test would not provide additional information.
The magnitude of the sensor signal is affected by a lot of factors, and one of the most important characteristics is selectivity, which has not been considered. Mineralization of water, the presence of surfactants and other components in the water will significantly affect the sensor signal and may make the obtained differences in the sensor signals insignificant. The Discussion section should include a discussion of the selectivity of the obtained system and the synthesized coating, consider in more detail the influencing factors and ways to reduce their influence.
We have clarified in the text that the expected odours at a dipping facility would be dominated by Taktic and farm water contaminants. This is why the complete e-nose device is tested with Taktic and farm water. It is further clarified that the e-nose device is selective to Taktic in the expected farm water samples. The individual gas sensors do not need to be very specific to any chemical compound, as the selectivity in an e-nose configuration comes from training with a classifier and using an array of non-selective sensors. This has been clarified in text and methods to improve individual sensor selectivity were also discussed in more detail.
The article does not have a Conclusion section at all. In conclusion, in addition to a possible plan for the development of the research, it is also desirable to include information about the possibilities and limitations of the proposed solutions, a comparison with existing systems of electronic noses, including other types of sensors used for water analysis, for example, Kuchmenko, T.A.; Lvova, L.B. A Perspective on Recent Advances in Piezoelectric Chemical Sensors for Environmental Monitoring and Foodstuffs Analysis. Chemosensors 2019, 7, 39.https://doi.org/10.3390/chemosensors7030039, Alphus Dan Wilson: Identification of insecticide residues with a conducting-polymer electronic nose. Chemical Sensors 2014, 4: 3, Ren, Lili and Kong, Cheng and Weng, Xiaohui and Zhang, Tao and Chang, Zhiyong, A Universal Electronic Nose System for Detecting Various Types of Pesticide Residues in Different Carriers. Available at SSRN: https://ssrn.com/abstract=4425839or http://dx.doi.org/10.2139/ssrn.4425839
This is very valid and the authors agree that a conclusion section is of great importance. We originally did not add it, as the journal recommended one should not add a conclusion unless completely necessary. We have now added a conclusion section.
Thank you for your well-appreciated feedback.
Reviewer 3 Report
The authors report on a technique to determine Taktic concentration in gas sensors. It is very interesting as it proposes a solution to a pinpointed and important problem, but several points need to be verified, including the following:
1. The vapour pressure of Taktic is reported to be 0.000002 mmHg at 25°C (for example, https://haz-map.com/Agents/3637). Therefore, even for pure components, the volume concentration of volatile components is about 2.6 ppb by simple calculation. Furthermore, the concentrations used in this experiment, e.g. 1000 ppm, are three orders of magnitude lower than this, and furthermore, as these concentrations such as 1000 ppm are those of aqueous solutions, the volatile components from such solutions are generally two to three orders of magnitude lower, depending on the physicochemical properties of the solute components. Accordingly, the concentration of the volatile component of Taktic from aqueous solutions is well below the ppt level, and it is almost impossible to measure this accurately. It is therefore considered that the signals obtained in this experiment are not in response to Taktic itself, but to another component. To confirm this, quantitative analysis using e.g. GC-MS should be performed to validate that the Taktic component is indeed evaporated at a certain concentration level from the aqueous solution. Otherwise, this kind of repot would not only be misleading to the community and industry, but would also undermine the credibility of the authors.
2.Figure 6, which shows the gas sensor system during measurement, is a photograph with very little information. It should be easier to understand what the system looks like, such as the signal read-out part, the gas control system or the system as a whole.
3. The chamber of the gas sensor and the sample holder are both made using a 3D printer, but it is known that these materials generally absorb a lot of gas components. It is necessary to verify how much the gas components are affected compared to the apparatus made of inert materials such as glass, inert-treated SUS, or Teflon.
Author Response
Good day,
Please see our response to your comments below.
1. The vapour pressure of Taktic is reported to be 0.000002 mmHg at 25°C (for example, https://haz-map.com/Agents/3637). Therefore, even for pure components, the volume concentration of volatile components is about 2.6 ppb by simple calculation. Furthermore, the concentrations used in this experiment, e.g. 1000 ppm, are three orders of magnitude lower than this, and furthermore, as these concentrations such as 1000 ppm are those of aqueous solutions, the volatile components from such solutions are generally two to three orders of magnitude lower, depending on the physicochemical properties of the solute components. Accordingly, the concentration of the volatile component of Taktic from aqueous solutions is well below the ppt level, and it is almost impossible to measure this accurately. It is therefore considered that the signals obtained in this experiment are not in response to Taktic itself, but to another component. To confirm this, quantitative analysis using e.g. GC-MS should be performed to validate that the Taktic component is indeed evaporated at a certain concentration level from the aqueous solution. Otherwise, this kind of repot would not only be misleading to the community and industry, but would also undermine the credibility of the authors.
Thank you for the feedback. We realised that we mistakenly used Taktic and Amitraz interchangeably in the introduction and results sections and this caused a lot of confusion and is a mistake on our part. The vapour pressure mentioned is for Amitraz and does not apply to the full mixture of Taktic, which is a brand-named mixture used in this work. However, we have made sure to clarify exactly what we are smelling for in the paper. Amitraz is the active ingredient in Taktic and only comprises 12.5% of the contents. Taktic is a proprietary mixture of chemicals and a GC-MS of Taktic is not in the scope of this paper. We have also clarified in the paper that the purpose of an e-nose is to detect an odour and not a specific chemical. The odour of Taktic is very strong and most likely a mixture of components. The results clarify that the paper aims to detect the odour of Taktic and not Amitraz.
2.Figure 6, which shows the gas sensor system during measurement, is a photograph with very little information. It should be easier to understand what the system looks like, such as the signal read-out part, the gas control system or the system as a whole.
Thank you. We have made adjustments and annotated the image to serve as a system-level description.
3. The chamber of the gas sensor and the sample holder are both made using a 3D printer, but it is known that these materials generally absorb a lot of gas components. It is necessary to verify how much the gas components are affected compared to the apparatus made of inert materials such as glass, inert-treated SUS, or Teflon.
We have added a section in the paper where we measure and discuss the out-gassing of the 3D printed material.
Thank you for your well-appreciated comments.
Round 2
Reviewer 2 Report
The quality of paper was improved by addition valuable information and clarification . I believe that manuscript could be accept for publication.
check the articles and punctuation in the large sentences. may be it should be better to rewrite them into several sentences.
Author Response
Thank you for your review.
Reviewer 3 Report
It is impossible to judge how the changes have been made if the changes are not described in the response letter or highlighted in the revised text.
no comment
Author Response
Good day,
We have highlighted all the changes relevant to your queries in the submitted PDF.
Kind regards,
Round 3
Reviewer 3 Report
The manuscript is now ready for publication.
For minor grammatical errors, please contact the editor.
