Proof of Concept Study of an Electrochemical Sensor for Inland Water Monitoring with a Network Approach

Round 1

Reviewer 1 Report

I found the abstract overly long if compared to introduction (which contains similar information). So I suggest to avoid repetitions.

Increased labels dimensions will improve the overall readability of figure 2

In Figure 3, looking ate the legends, “,” should be replaced by “.”

In Figure 4 interpolating lines will be encouraged to improve the overall evaluation of sensors performance.

Please check current unit in Figure 7a since it reports very high current values compared to figure 7b

I found section 3.3 more related to  section 2 rather then the “results” section

Since the electrochemical sensor is base of electro-oxidation of chemical species of interest I found interesting to add a part related to possible interfering molecules in the discussion.

Author Response

I found the abstract overly long if compared to introduction (which contains similar information). So I suggest to avoid repetitions.

 

Thanks to the reviewer for her/his suggestion. The abstract has been shortened by eliminating repetitions after a comparison with the introduction.

 

Increased labels dimensions will improve the overall readability of figure 2.

 

Ok, readability increased. Thanks.

 

In Figure 3, looking ate the legends, “,” should be replaced by “.”

 

Thanks, replaced.

 

In Figure 4 interpolating lines will be encouraged to improve the overall evaluation of sensors performance.

 

Thanks to the reviewer for her/his kind suggestion. As you know this plot is effective in representing the good performance of the system in the prediction of the concentration. At the same time, it is not a calibration curve, but a dispersion of points plotted on the predicted vs measured plane; thus, calculating a curve could increase the visibility of the goodness in prediction, but it should be also confounding for some readers, who could think to observe a calibration curve (which should be plotted on the sensor input vs sensor output plane).

 

Please check current unit in Figure 7a since it reports very high current values compared to figure 7b

 

Thanks, corrected.

 

I found section 3.3 more related to  section 2 rather then the “results” section

 

We understand the reviewer point. This subsection, indeed, introduces some methods on the installation/maintenance costs, but it also presents some results on the utilization of the calculation methods. Thus, some points of section 3.3 have been moved to section 2.

 

Since the electrochemical sensor is base of electro-oxidation of chemical species of interest I found interesting to add a part related to possible interfering molecules in the discussion.

 

We agree with the reviewer. Some lines have been added on this topic in the discussion section.

 

Reviewer 2 Report

The authors compared the performance of their sensor with a commercially available sensor. The objectives of this work is not clear. The novelty is also lacking other than the smaller size of the proposed sensor. The bulk of the content is to justify the proposed design is equal or better than the commercial sensor - this demonstrated a commercial interest and itself is not appropriate for a publication. Below are my specific comments: 1) The abstract needs to be rewritten. It is supposed to be the highlight of the paper, not merely a summary. Many of the sentences were repeated. 2) L34 - "Molecules" should be replaced with "Chemicals" 3) Source of bi-distilled water is required. 4) Results - How are the "input" and "output" obtained? How is the input converted to the output? 5) Fig 3a - c - showed no difference at different concentrations 6) Table 1 - dry residue was measured - Why? 7) The authors used spiked samples (with one contaminant) to test the device. How about a mixture of contaminants? Will the sensor fail? 8) No interference test was performed. 9) What is the detection limits?

Author Response

The authors compared the performance of their sensor with a commercially available sensor. The objectives of this work is not clear. The novelty is also lacking other than the smaller size of the proposed sensor. The bulk of the content is to justify the proposed design is equal or better than the commercial sensor - this demonstrated a commercial interest and itself is not appropriate for a publication.

 

 

Authors appreciate reviewer’s comments, which allow them to better explain (here and in the revised text) the objectives, the novelty and the bulk content of the work. Indeed, authors understand that there is a misunderstanding about the term of comparison for the proposed sensor in the field of inland water monitoring; the comparison is proposed against the state of the art in general, looking at the available transduction principles, at the reproducibility, at the sensor performance: as for a standard scientific work;  but also looking at size, costs, power consumption: as a work of research in engineering must do. Many of the sensors cited in the introduction are not commercially available: authors have now specified this aspect in the revised text. In particular the sensors using an electrochemical transduction mechanism are not properly used for inland water monitoring  in large areas and with multipurpose objectives. And here comes the novelty of this work: multipurpose approach (bacteria, water characterization, pollutants), in a wide scenario (low-power, low size, connectivity). Some of these aspects have been treated in previous publications, but as a single application. Moreover, the necessity of a new version (low-size, low-power) asks for  testing it again, not only for pollutants (which is a new application) but also for the other measurands, which is new because the instrument is new. Authors think it is novel, because the application here proposed (remote monitor of inland water) asks for all the novel characteristics here investigated, thus the small size and small power together with the ability in monitoring the three mentioned aspects (bacteria, characterization, pollutants) is novel because it is not present in the field and because it  is different from the previous ones of the same authors. Coming to the bulk of the work, it consists of demonstrating sensor relevance in monitoring inland water in a remote modality: meaning to demonstrate that the ability in pollutants (new), bacteria (upgrade), characterization (upgrade), is possible with and upgraded version with reduced size and power (new) in a network arrangement (new).

 

 

 

Below are my specific comments: 1) The abstract needs to be rewritten. It is supposed to be the highlight of the paper, not merely a summary. Many of the sentences were repeated.

 

Thanks to the reviewer for her/his suggestion. The abstract has been shortened by eliminating repetitions after a comparison with the introduction.

 

 

2) L34 - "Molecules" should be replaced with "Chemicals"

 

Replaced, thanks.

 

3) Source of bi-distilled water is required.

 

Ok. Added.

 

4) Results - How are the "input" and "output" obtained? How is the input converted to the output?

 

Thanks to the reviewer for this observation. In the results section ita has been added a reference to section 2.1: The sensor used exploit the voltammetric working principle for liquid analysis performed using an electrochemical cell is based on a Screen-Printed Electrode (SPE; DRP-250BT, Metrohm, Herisau, Switzerland) probe (Working: Gold; Counter: Platinum; Reference: Silver); the electronic front-end of the system provides the input signal (a triangular voltage waveform from +1 V to −1 V) and records the output data. The SPE is immersed in the target solution and the applied input voltage induces oxi-reduction phenomena in the liquid sample. The output data is a current generated by the electrons involved in the reactions taking place into the liquid sample as consequence of the applied voltage. This current is converted in voltage by a trans-impedance circuit. The input signal frequency is of 0.01 Hz; the output signal is acquired with a rate of 200 ms (500 samples per measurement).

 

5) Fig 3a - c - showed no difference at different concentrations

 

Not large, but significant differences. They could be observed in the voltammograms reported in the figure but, of course, they are evident by the results of the multivariate model.

 

6) Table 1 - dry residue was measured - Why?

 

Because it accounts for a global picture of salt composition of the sample (Bayabil, Haimanote K., et al. "Potential management practices of saltwater intrusion impacts on soil health and water quality: a review." Journal of Water and Climate Change 12.5 (2021): 1327-1343.; ALCAMO, Joseph. Water quality and its interlinkages with the Sustainable Development Goals. Current opinion in environmental sustainability, 2019, 36: 126-140.; CHEN, Leilei, et al. Distribution, residue level, sources, and phase partition of antibiotics in surface sediments from the inland river: a case study of the Xiangjiang River, south-central China. Environmental Science and Pollution Research, 2020, 27.2: 2273-2286.)

 

 

7) The authors used spiked samples (with one contaminant) to test the device. How about a mixture of contaminants? Will the sensor fail?

 

We agree with the reviewer. This is a pilot study. Authors are confident that the instrument will not fail when measuring complex mixtures, because the voltammogram (formed by 500 points) has enough features (high dimensionality) and an optimal reproducibility, to provide different shapes for different mixtures.  Future development will be devoted to the analysis of mixtures. This experimental step is mandatory for sensor application on field, because it is necessary to create a library of any possible mixture/pollutant, which should be present in any different scenario. Thus, a calibration campaign should be performed for each scenario to be considered.

 

 

8) No interference test was performed.

 

Please, see point 7.

 

 

9) What is the detection limits?

 

Thanks to the reviewer for this question. Indeed, authors have specified the Root Mean Square Error in Cross Validation, but not the detection limits for which the minimum detectable output signal should be calculated. We have added some considerations about possible limit of detection for each pollutant, estimated on the basis of the minimum concentration tested in calibration when compared with the RMSECV.

Reviewer 3 Report

Brief summary

This paper is interesting to those who deal with remote systems for inland water monitoring.

This paper follows previous works from the same authors and presents a new version of a sensor for inland water monitoring. The sensor is ready to detect extraneous compounds (like ethanol, isopropanol, and hexane), bacteria (Pseudomonas aeruginosa, and E-coli) and frequent pollutants (in this case, atrazine, dichloromethane, and tetrachloroethene). This new version of the sensor is smaller, more energy efficient and is adequate for integration in LoRaWAN, Sigfox or NB-IoT communication networks. The goal of this paper was to test the accuracy of the new sensor and compare it with the one from the original version, and the tests performed confirmed that it is accurate enough for its purpose.

The paper follows a traditional structure, it is well written and illustrated, the text is concise, and it has a considerable set of references.

However, I think there are a few minor details that deserve to be viewed/corrected.

In my opinion authors should be encouraged to rewrite the paper, taking into consideration the comments presented below, and afterwards accept it for publication.

 

Specific comments

Authors should avoid using “we” or “our”.

Line 39: suggest changing “capillary” to “widespread”, like in the abstract.

Line 70: suggest changing to “contamination, and pollutant identification”.

Line 81: suggest changing “palce” to “place”.

Line 81: suggest changing “consequance” to “consequence”.

Line 98: suggest changing “experiment” to “experiments”.

Line 124: suggest changing “previious” to “previous”.

Line 126: suggest changing “extraced” to “extracted”.

Line 127: suggest changing to “obtained in current and in voltage”.

Lines 136, 137, 138, 206, 231: suggest changing “concentration” to “concentrations”.

Line 193: suggest changing to “relative to”.

Lines 212, 397: suggest changing “pollutant” to “pollutants”.

Line 216: suggest changing to “dichloromethane, and atrazine”.

Line 217: the meaning of RMSECV should be explicit (like later mentioned in Lines 224-225).

Line 221: suggest changing “efficiency” to “accuracy”.

Line 229: suggest changing “precise” to “accurate”.

Line 242: suggest changing “this” to “these”.

Line 243: suggest changing “Tab. 1” to “table 2”.

Line 244: suggest changing “:” to “.”.

Line 248: suggest changing “Table 1” to “Table 2”.

Line 248: suggest changing “Fig.5 and Fig.6” to “figures 5 and 6”.

Line 257: suggest changing “red in fig.5 / black in fig.6” to “red in figure 5 / black in figure 6”.

Line 258: suggest changing “blue in fig.3 / green in fig.4” to “blue in figure 5 / green in figure 6”.

Lines 263, 269: suggest changing “measurement” to “measurements”.

Line 277: suggest changing “Fig. 7” to “Figure 7”.

Figure 7: suggest changing “Output current[A]” to “Output current [A]” and “Ecoli” to “E-coli”.

Line 286: the meaning of CFU should be explicit.

Line 300: the meaning of SF should be explicit.

Line 314: the meaning of CDF should be explicit.

Lines 318, 332, 343, 345: suggest changing “Where” to “where” without indentation.

Line 357: suggest changing “Figure 9” to “figure 9”.

Line 368: suggest changing “pseudomonas” to “Pseudomonas aeruginosa”.

Line 401: suggest changing “It” to “it”.

Author Response

This paper is interesting to those who deal with remote systems for inland water monitoring.

This paper follows previous works from the same authors and presents a new version of a sensor for inland water monitoring. The sensor is ready to detect extraneous compounds (like ethanol, isopropanol, and hexane), bacteria (Pseudomonas aeruginosa, and E-coli) and frequent pollutants (in this case, atrazine, dichloromethane, and tetrachloroethene). This new version of the sensor is smaller, more energy efficient and is adequate for integration in LoRaWAN, Sigfox or NB-IoT communication networks. The goal of this paper was to test the accuracy of the new sensor and compare it with the one from the original version, and the tests performed confirmed that it is accurate enough for its purpose.

The paper follows a traditional structure, it is well written and illustrated, the text is concise, and it has a considerable set of references.

 

Thanks to the reviewer for her/his kind and valuable appreciation.

 

However, I think there are a few minor details that deserve to be viewed/corrected.

In my opinion authors should be encouraged to rewrite the paper, taking into consideration the comments presented below, and afterwards accept it for publication.

 

Specific comments

Authors should avoid using “we” or “our”.

 

Thanks, corrected each recurrence of “we” and “our” with other phrasal forms.

 

Line 39: suggest changing “capillary” to “widespread”, like in the abstract.

 

Thanks, changed.

 

Line 70: suggest changing to “contamination, and pollutant identification”.

 

Thanks, changed

 

Line 81: suggest changing “palce” to “place”.

 

Thanks, changed

 

Line 81: suggest changing “consequance” to “consequence”.

 

Thanks, changed

 

Line 98: suggest changing “experiment” to “experiments”.

 

Thanks, changed

 

Line 124: suggest changing “previious” to “previous”.

 

Thanks, changed

 

Line 126: suggest changing “extraced” to “extracted”.

 

Thanks, changed

 

Line 127: suggest changing to “obtained in current and in voltage”.

 

Thanks, changed

 

Lines 136, 137, 138, 206, 231: suggest changing “concentration” to “concentrations”.

 

Thanks, changed

 

Line 193: suggest changing to “relative to”.

 

Thanks, changed

 

Lines 212, 397: suggest changing “pollutant” to “pollutants”.

 

Thanks, changed

 

 

Line 216: suggest changing to “dichloromethane, and atrazine”.

 

Thanks, changed

 

Line 217: the meaning of RMSECV should be explicit (like later mentioned in Lines 224-225).

 

Thanks, explicated.

 

Line 221: suggest changing “efficiency” to “accuracy”.

 

Thanks, changed

 

Line 229: suggest changing “precise” to “accurate”.

 

Thanks, changed

 

Line 242: suggest changing “this” to “these”.

 

Thanks, changed

 

Line 243: suggest changing “Tab. 1” to “table 2”.

 

Thanks, changed

 

Line 244: suggest changing “:” to “.”.

 

Thanks, changed

 

 

Line 248: suggest changing “Table 1” to “Table 2”.

 

Thanks, changed

 

Line 248: suggest changing “Fig.5 and Fig.6” to “figures 5 and 6”.

 

Thanks, changed

 

Line 257: suggest changing “red in fig.5 / black in fig.6” to “red in figure 5 / black in figure 6”.

 

Thanks, changed

 

Line 258: suggest changing “blue in fig.3 / green in fig.4” to “blue in figure 5 / green in figure 6”.

 

Thanks, changed

 

Lines 263, 269: suggest changing “measurement” to “measurements”.

 

Thanks, changed

 

Line 277: suggest changing “Fig. 7” to “Figure 7”.

 

Thanks, changed

 

Figure 7: suggest changing “Output current[A]” to “Output current [A]” and “Ecoli” to “E-coli”.

 

Thanks, changed

 

Line 286: the meaning of CFU should be explicit.

 

Thanks, explicated.

 

Line 300: the meaning of SF should be explicit.

 

Thanks, changed

 

Line 314: the meaning of CDF should be explicit.

 

Thanks, changed

 

Lines 318, 332, 343, 345: suggest changing “Where” to “where” without indentation.

 

Thanks, changed

 

Line 357: suggest changing “Figure 9” to “figure 9”.

 

Thanks, changed

 

Line 368: suggest changing “pseudomonas” to “Pseudomonas aeruginosa”.

 

Thanks, changed

 

Line 401: suggest changing “It” to “it”.

 

Thanks, changed

 

Round 2

Reviewer 2 Report

The authors have revised the manuscript adequately. Although I have doubts the proposed sensor could work in real waters, this paper at least shows the new sensor could work comparably with existing sensor. Hence, the paper can be published.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.