A Novel SERS Substrate Based on Discarded Oyster Shells for Rapid Detection of Organophosphorus Pesticide

Round 1

Reviewer 1 Report

This is an interesting work but requires mandatory minor revision.
1. The authors should provide a statistical analysis on the uniformity of enhancement factors across a large area (maybe five or ten spots on the substrate) by calculating the relative standard deviation which is now common in all SERS related work.
2. The role of the oyster shells is not very clear. Such enhancement factors are observed routinely on many surfaces decorated with Ag nanoparticles. What is the particular role of the substrate here?
3. The authors should present SPR data for the Ag nanoparticles. There is a mention of this in the introduction, but nowhere else in the manuscript
With these changes, the paper should be acceptable for publication.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments: The manuscript reports on preparation of calcium oxide-based substrate for use in surface-enhanced Raman scattering (SERS) spectroscopy. Using oyster shells as a starting material, CaO nanoparticles covered by silver nanoparticles were prepared and characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. SERS efficiency of the prepared substrate was tested using 4-aminothiophenol. Finally, the substrate was used for the SERS quantitative analysis of methyl parathion. The overall impression is that the reported research was not clearly described and explained, and the obtained results seem doubtful and not convincing. Hence, I cannot recommend the submitted article in the present state for publication in Coatings.

Remarks:

1. English language should be checked and corrected throughout the text. There are parts of the sentences, such as “we analyzed the detection of 4-ATP…”, which are grammatically incorrect and rather confusing to a reader.
2. Lines 74 and 90: There should be written “4-aminothiophenol” (4-ATP) instead of “4-aminothiophenil”.
3. Line 94: The authors refer to Scheme A1 which is not a part of the article but placed in Appendix.
4. Lines 102-109: Preparation of silver nanoparticles should be described in more details and more clearly. It is not clear how polydopamine was synthesized from dopamine hydrochloride (lines 103-106) and a formed polymer attached to CaO, and how silver ions were reduced to nanoparticles. Oxidation-reduction processes during the synthesis should be clearly described.
5. Line 137: There should be written “modified metal / polymer / CaO NPs” instead of “modified metal oxide / polymer / CaO NPs”.
6. Lines 153-155: These sentences do not describe the research results but seem like instructions for preparation of the article.
7. Lines 190-192: Description of the preparation of samples with 4-ATP was not clear. Was a drop of 4-ATP placed on the substrate and dried, or was the substrate soaked in 4-ATP solution and then dried? Were the samples dried at all or were the wet samples measured?
8. Line 193: The authors refer to Figure A1 in supplementary data which are not attached. The respective figure is shown in Appendix.
9. Line 196: Authors should describe the procedure and expression used for calculation of enhancement factor in more detail.
10. Line 204, Figure 4: Which concentration of 4-ATP was used to test SERS efficiency of CaO and Ag/PDA?
11. Lines 206 and 207: Looking at the spectra in Figure 4, the EF values are not convincing. Which band did the authors use for EF calculation? Again, explanation of the EF calculation is badly missing.
12. Raman spectrum of 4-ATP should be given, the main vibrational bands assigned and the Raman spectrum compared to the SERS spectra. In addition, the most intense SERS spectrum was obtained for the 4-ATP concentration of 10-3 M, which could easily correspond to a normal Raman spectrum.
13. What was the reproducibility of the measurements with methyl parathion?
14. Figure 5: Were the spectra processed in any way before linear regression?
15. Figure 5: The bands in the methyl parathion spectra of concentrations lower than 10-3 M are hardly observable and could be easily associated with the noise.
16. Raman spectrum of methyl parathion should be given and the main vibrational bands assigned.
17. Visible spectra of methyl parathion (10-2 and 10-3 M) in Figure 5 could be again the normal Raman spectra, and not the SERS spectra.

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

The research work on, "A novel SERS substrate based on discarded oyster shells for rapid detection of organophosphorus pesticide" reports novel aspect of synthesizing SERS substrate with excellent properties and detection limit.  I appreciate the work reported here, however, some more improvement in the quality of the manuscript is required as follows:

1. Sufficient literature about  CaO is not included related to its CT ability in introduction section. Recent literature about the semiconductor CT capability should be included for example: DOI: 10.1039/D1TC04886D, DOI: 10.1103/PhysRevB.88.205421
2. End of the introduction part explains about the Ag/CuO nanocomposite but suitable reference is not provided. Clearly mention the role of each components in (Ag/PDA/CaO) contributing to SERS enhancement.
3. Figure 1f is not clearly visible specially the lattice fringes which are proved to be shown  lattice spacing between Ag (111) and CaO (200) planes. Please provide the clear image of the same.
4. In XRD, there are some small peaks in red spectrum which are unidentified. explain please
5. Figure 4: which spectra are related to Ag/PDA/CaO...please indicate
6. Comparable EF has been reported for metal oxide based SERS substrates already. Please explain that even after use of Ag with CaO what is the achievement here in the present work which is better than the literature.

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 4 Report

The manuscript entitled, "A Novel SERS Substrate Based on Discarded Oyster Shells for Rapid Detection of Organophosphorus Pesticide" submitted by Chu et al., proposed a method to detect parathion methyl using silver/polydopamine/calcium-oxide (Ag/PDA/CaO) nanocomposite as a SERS material. The manuscript is well presented and can be published after considering following Major comments:

1. A more detailed introduction to SERS should be given.
2. Rigorous analysis for obtained SERS peak should be given with information with wavenumber and the vibration levels.
3. Figure 4: A few peaks are obtained for Ag/PDA. These peaks are obtained for which vibrations?  
4. Figure 5(c): How are the error bars calculated? Authors should also comment about the reproducibility of the results.
5. Table 1: Author claimed the minimum LOD for their proposed sensing. It would be nice if the author could provide the reason, why his method is giving better LOD as compared to other methods for PM detection.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The paper is now acceptable for publication.

Reviewer 4 Report

The authors have successfully addressed all the comments. Manuscript can be published in the current from.