Enhanced Gas Sensitivity Characteristics of NO₂ Sensor Based on a Silicon Micropillar Design Strategy at Room Temperature

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this manuscript (sensors-3869014), the authors reported a NO₂ sensor using rGO/SnO₂ with silicon micropillar structure. The method is interesting but there are many problems in the writing, introduction, presentation, results and discussion. As such, a major revision is needed before possible acceptance. My specific comments are as follows:

1. Title: From the results, “high performance” is not appropriate. In terms of gas sensing performance, it does not have significant advantages, and the author did not compare it with previous work. Check for similar issues in main text.
2. “40% relative humidity” instead of “40%RH relative humidity”. The abstract is an independent part; relative humidity only appears once and does not need to be abbreviated.
3. The abstract section lacks key performance indicators.
4. Introduction: (1) The first paragraph lacks relevant reference support. (2) P44-58, 74-80: Why does the author discuss so many NH₃ sensors when studying NO₂ gas sensors in this work? Lack of discussion on NO₂ gas sensitive materials and gas sensors. In fact, many high-performance room temperature NO₂ gas sensors have been developed, and even SnO₂ nanoparticles gas sensors can operate at room temperature based on synergistic effect of electron scattering and space charge transfer.
5. Reference citation numbers do not need to be superscripted.
6. “Currently, gas-sensitive materials for such devices primarily focus on two materials: carbon nanotubes and graphene.”: This statement is obviously untenable. As for gas sensors, graphene and carbon nanotubes do not have good gas sensing performance due to poor selectivity and slow recovery speed. In contrast, oxides, two-dimensional materials (transition metal sulfides and MXenes), and emerging gas sensing materials like Ag₂Te nanowires are widely studied for NO₂ gas sensors.
7. P56: MoS₂-rGO, SnO₂; P70: Reduced graphene oxide (rGO); P83: “tin dioxide (SnO₂)”; P134: 51% reduced graphene oxide… The abbreviation that appears for the first time is spelled in full, and the abbreviation will be used later. Check for similar issues throughout the text.
8. “2. Gas Sensor Fabrication” instead of “2.2. Gas sensor fabrication.” Capitalize the first letter and check for similar issues.
9. “Ultra-High Specific Surface Area”: Lack of corresponding characterization, such as specific surface area analysis.
10. For response and recovery curves, corresponding actual resistance response recovery curves should be provided. The actual resistance is important for evaluating the gas sensing performance of sensors.
11. Figure 6. (a1-a8) rGO/SnO2: Numbers in chemical formulas require subscripts.
12. “Figure 9. Sensitivity of a gas sensor with a…”. Sensitivity and response cannot be mixed. Sensitivity is the slope of a linear equation.
13. “We define the sensitivity improvement rate ∆R as:” Sensitivity is the slope of a linear equation. The definition of sensitivity needs to be limited to the linear response range, and the sensor response must satisfy linear response. In fact, equation (3) is the definition of response, referring to Sens. Actuators B Chem., 2024, 402, 135136.
14. The quality of the images is poor, and it is necessary to improve the line width, font size, and resolution.
15. Check the reference format, for example, authors name and journal names should be abbreviated.
16. Check English writing.

Comments on the Quality of English Language

Check English writing.

Author Response

Please check the file below.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors investigated the silicon interdigital electrodes and silicon micropillar surface deposited with rGO and rGO/SnO2 to detect NO₂ at room temperature. From their experiments, the authors observed that rGO/SnO2 deposited on the silicon micropillars' surface improves the sensitivity, response, and recovery times.

• In the abstract section, the authors refer to the sensor devices as micropillar structures, whereas in the Conclusion section, they refer to them as microcolumn structures. This will create confusion for the readers.
• These sensors' response/recovery times are hundreds of seconds, which is very long. Describe the techniques to improve the sensor's response/recovery times.
• For instance, Figures 2, 4, 7, and 8 are blurry. Figure quality and labels must be improved.
• Figure captions are unclear; for instance, "Figure 3: Characteristics of…" is unclear as to what characteristics the authors are referring to.
• In Figure 9, update the legend for interdigitated electrodes. Verify legends throughout the manuscript and update them wherever necessary.

The manuscript contains numerous grammatical errors and typographical mistakes that significantly affect readability. A thorough proofreading and language revision are necessary before the manuscript is submitted.

Comments on the Quality of English Language

The manuscript contains numerous grammatical errors and typographical mistakes that significantly affect readability. For example, the first sentence of the abstract — 'NO₂ sensing is very important industrial production and daily applications for environment safety' — is grammatically incorrect and should be revised to 'NO₂ sensing is very important in industrial production and daily applications for environmental safety.' Additionally, there are several typos, such as 'Developedpidly' on page 2, line 45, and inconsistent use of chemical notation — for instance, 'N' (e.g., page 3, line 125) is used instead of 'N₂'. A thorough proofreading and language revision are necessary before the manuscript can be evaluated appropriately.

Author Response

Please check the file below

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript presents a comprehensive study on the development of room-temperature NO₂ sensors using rGO/SnO₂ composites on both planar interdigitated electrodes (IDEs) and 3D silicon micropillar structures. The work is experimentally rich and addresses an important challenge in gas sensing. However, several aspects require clarification, deeper analysis, and more precise presentation to strengthen the claims and ensure reproducibility.
Clarity of Contributions: The title and abstract emphasize the "silicon micropillar structure," yet a significant portion of the paper is dedicated to optimizing planar IDEs (channel width, SnO₂ doping). The authors should more clearly state the incremental contribution of the micropillar structure over the optimized planar sensor in the abstract and introduction.
1-  The title and abstract emphasize the "silicon micropillar structure," yet a significant portion of the paper is dedicated to optimizing planar IDEs (channel width, SnO₂ doping). The authors should more clearly state the incremental contribution of the micropillar structure over the optimized planar sensor in the abstract and introduction.
2- The data in tables (e.g., Table 1, 2, 3, 4, 5) and performance metrics appear to be from single devices. To ensure reliability, please report the average and standard deviation of response/recovery times and sensitivity for at least 3 devices per configuration.
3- The core material, SnO₂ nanoparticles (50-70 nm), lacks characterization. A TEM image or XRD analysis of the pristine nanoparticles is essential to confirm their crystallinity, size distribution, and phase, which greatly influence gas sensing properties.
4- The quality of the reduced graphene oxide (rGO) is crucial. Provide the ID/IG ratio from Raman spectroscopy.
5- The description of the micropillar fabrication is incomplete.
6- The baseline resistance (R0) of the different sensors (different widths, different dopings, pillars) is a key parameter that influences signal-to-noise ratio and power consumption.
7- Improve your literature review by adding new references in the field of room temperature gas sensors, such as DOI: 10.1007/s00604-025-07367-8. 
8-  A key parameter for practical application is long-term stability. Provide data on the performance (e.g., baseline drift and sensitivity) of the champion sensor over a period of days or weeks.
9- The sensor response is shown down to 5 ppm. Calculate and report the theoretical limit of detection (e.g., based on 3× standard deviation of the baseline noise) for the best-performing sensor.
10-  Some figures (e.g., Fig. 2, 4, 5, 7) have low resolution.

Author Response

Please check the file below. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Concerns have been considered and addressed properly, and publication is recommended. 

In the proof stage, check the reference format. For example, journal names need to be abbreviated.

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for addressing the reviewer's comments. The authors have done a great job of improving the revised manuscript. Your revisions have significantly improved the manuscript. I'm satisfied with the changes made and recommend this manuscript for publication.

Reviewer 3 Report

Comments and Suggestions for Authors

N/A