Ag-Functionalized Si Nanowire Arrays Aligned Vertically for SERS Detection of Captured Heavy Metal Ions by BSA

Round 1

Reviewer 1 Report

The author reports the use of Si-nanowire (SiNW) arrays with silver nanoparticles (AgNPs) for detection of Bovine Serum Albumin (BSA) and heavy metal ion, Zn2+, by surface enhanced Raman spectroscopy (SERS).

Please highlight the novelty of your work, since SiNW arrays with AgNPs for detection with BSA and heavy metal ion using SERS has been reported in the literature. For example, Microchimica Acta volume 164, p157–160, 2009; Front. Optoelectron. China 4(4), p378–381, 2011; Plasmonics 13, p1057–1080, 2018. Note that I am not in any way related to the authors of these articles.

Please state the concentrations of BSA and Zn2+ employed in your experiment. The aim is for the comparison with others in the literature to give the reader an understanding of how sensitive is your substrate. For example, BSA of 1 pM was detected in Microchimica Acta volume 164, p157–160, 2009; SO4 2- ion of 1 nM was detected in Front. Optoelectron. China 4(4), p378–381, 2011.

Please also compare the SERS results between Ag-SiNW and Ag. Ag meaning that the Ag is fabricated by the rf magnetron sputtering.

More than one concentration of BSA and Zn2+ should have been tested in order to characterize the performance of the SERS substrate and the dependence between concentrations and SERS intensities. Moreover, inter-and intra-substrate results should have been given to allow the reader to understand the standard deviation for the results.

Please also provide the Raman experimental parameters. For example, the excitation power and wavelength of the laser, the laser spot size, the model of the Raman equipment, and the power of objective used (if any).

Author Response

Thank you for reviewer’s comments and amendments. We have asked professionals to revise manuscript. Reply to comments is attached file (Including revised manuscripts).

Author Response File: Author Response.pdf

Reviewer 2 Report

The article is dedicated to an actual theme and can be interesting for readers. But the text contains a set of drawbacks, which should be corrected.
- The introduction does not allow to understand the advantage of Si-nanowires arrows usage for the Raman analysis. Some information about it is presented in part 3.3 and, may be, should be moved in introduction.
- There is an obvious discrepancy between figs. 1 and 2 concerning Ag. According to fig.1 Ag fills all the space between Si-wires. But on fig.2 we can see Ag mostly on the top of wires and a lot of free space between them. To better understanding the fig.1 should be changed in order to bring it closer to reality.
- The fig.3a is unclear. Is it top view? The conclusion about monolayer is unclear as well. Where is the monolayer and what data allow the authors to talk exactly about the monolayer? What does it mean "SiNW" in fig.3c?
- Why the authors mention FWHM, talking about XRD 2theta diffractograms in fig.4? What does FWHM matter here? Do the authors estimate the peaks width? Exactly FWHM, not the integral one?
- The sentence in lines 153-155 should be reformulated in order to readers can understand it.
- What exactly the authors note in fig.10 at 2924 cm^-1, NH₂ or C-H?
- What is the sence of black and red arrows and concerning pictures in fig.11? What do exactly they indicate? The difference of SERC spectra is clear from the caption.

Author Response

Thank you for reviewer’s comments and amendments. We have asked professionals to revise manuscript. Reply to comments is attached file (Including revised manuscripts).

 

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Author Response File: Author Response.pdf

Reviewer 3 Report

Chiou and coauthors report a plasmonic substrate for SERS analysis of silicon structures functionalized with silver nanoparticles. The latter extended the functional scope of the structures by the ability to generate surface-enhanced Raman scattering and to enable the detection of BSA or heavy metal ions. Sadly the presentation quality is poor and the overall manuscript is lengthy and reads at times more like a technical report. I encourage the authors to decrease the level of detail and to focus on the core findings and the discussion of their scientific significance. In summary, the topic of this paper fits well with the journal Coatings. The topic of this article fits well with the journal Coatings however some open questions remain. For this reason i recommend in-depth revisions for which the comments below should serve as a starting point. 

 

Comments:

1. On point which is left in the dark is the importance of the SiNW substrate structure. How does the morphology contribute to the SERS performance apart from providing a larger surface area? What is the significance of the vertical alignment? Please explain in the manuscript.
2. Minor issues: L.53 typo „atalytic“; L. 30: non-destructive measuring methods. Could it be that the authors intended to refer to „non-invasive“ methods? L. 239 The term "Raman diffraction analysis“ seems very odd. 
3. The language of the manuscript is not correct at times and should be revised with the help of a native speaker.
4. The manuscript states “Silver has been reported as the dominate SERS substrate.“ This statement lacks support as in this generalised form it is hard to claim that silver is always the best choice. Please revise.
5. Figure 1 gives procedural details which is inappropriate and preferably this information should be moved to the caption of the figure or the main text. Please make better use of the limited space.
6. Please clarify if the SERS analysis is quantitative or qualitative? This point is often disregarded. Please explain in the manuscript.
7. Please give details about the immobilisation of BSA (experimental details such as concentration, etc.) which are lacking in the manuscript.
8. The SERS capabilities of the presented system should critically depend on the optical properties. In fact, the optical properties allow to judge on the efficiency of light-matter interactions. What are the optical properties? And, how do these changes during the various modification steps? Does the plasmon band match with the wavelength of the Raman excitation line?
9. BSA was adsorbed onto the plasmonic SERS substrate. How well do the spectral features detected agree with the reference values given by Tebbe et al. (ACS Applied Materials Interfaces 2015)? Please discuss in detail which vibrational signals could be detected and which could not. Please give reasons for this apparent selectivity.
10. The authors might wish to put their work in better context to the current state of the art of plasmonic sensing and SERS analytics (compare e.g. DOI: 10.5772/intechopen.79055). There is broad range of systems reported to allow sensitive SERS detection. What are the specifics advantages, challenges and limitations of the authors approach?

Author Response

Thank you for reviewer’s comments and amendments. We have asked professionals to revise manuscript. Reply to comments is attached file(Including revised manuscripts).

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Due to fact that this work is difficult to demonstrate novelty/advantage (point 1), and hard to prove the aim of study is realized as claimed by the title (addition experiment needed, point 3 and 4), regret that this manuscript is unable to be published in this journal.

Response to point 1: Agree with you that those points that you give may be the advantages of your method. However, those are not the novelty, that is how your work is different from others (something that is new, and original). Moreover, these advantages are not demonstrated in your results/manuscript. For example, if the author stated that their method to detect heavy metal ions is faster, concrete evidence should be provided because at least 12 hours is needed for incubation prior for detection (step 6 in fig.1). This timing should be included into the sample detection timing required, in which the reader may be difficult to be convinced that their method is faster than ICP-MS (less than 12 hours, e.g., Molecules. 25(21): 5178, 2020). Please also refer to point 2 for the sensitivity when compared with other similar SERS methods in the literature (seems that the sensitivity is better by results reported in other groups). 

Response to point 2: Please understand that the title of this publication is “…detection of BSA and heavy metal ions”. Note that detection of BSA is also one of the analytes to be detected, unless the author did not mean it. Thus, the author probably did not demonstrate/realize the statement claimed in the title, based on their response in point 2, “The main purpose of this study is to capture heavy metals, not BSA.” Otherwise, the title should be modified to “BSA capturer heavy metal ion”.

If the author is using some similar method for BSA/metal detection (back to point 1), the reader may be hard to see the advantage in using this method over others, since the sensitivity/concentration in the literature for detection of BSA (1pM) and Zn2+ (1nM) is better compare to 500 uM and 0.1uM, respectively.

Response to point 3: If experimental results on Ag is unavailable, the reader will have difficulty to comprehend if the SERS action resulted is originated to the formation of the Ag film formed on top, or from the structure as planned by the author (that is the SERS is originated from the functionalized Ag films (30nm-75nm) only even without the SiNWs).

Response to point 4: If experiment results for repeatability is unavailable, the purpose/reason for having SiNWs cannot be justified because the author claimed that “However, the signal intensity and reproducibility of SERS are highly dependent on the preparation of substrates and substrate morphology…. these methods are also irreproducible, unstable, and unsuitable for high volume production.” Agree with the author that repeatability is important in SERS studies. But the author did not show the repeatability results, and thus, difficult to convince about the repeatable performance of this strategy, in particular for performance to be dependent on hotspots, (or localized effect as claimed by author in point 3).  

Please also note that detection of various concentrations is also helpful because if the detection range is small, the investigation may not be worth the effort for further examinations. Moreover, relationship (not necessarily linear) between the SERS intensities and concentrations could be found to prove that SERS action is really taking place.

Author Response

Thank you for reviewer’s comments and amendments. Reply to comments is attached file .

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors have corrected mistakes through the text and improved it. The article can be published in present form.

Author Response

Thank you for affirmation. Once again, thank you very much for your comments and suggestions.

Reviewer 3 Report

The authors have revised their contribution and I am almost completely satisfied with the revisions. In addition to an improvement in the illustrations, the scientific discussion has also been extended. I am convinced that the manuscript can now be accepted for publication. However, as a last small change, I recommend to revise the title. Here, the abbreviation SiNW should be omitted and replaced by „Si Nanowire" (in the title). In addition, the SI abbreviation for hour is "h" nor "hr" (see e.g. in Fig. 1). Please use SI units throughout the manuscript.

Author Response

Thank you for affirmation. We have revised title. (in lines 2). We have confirmed that the manuscript uses the international system of units. (For example, Line 123,127). Once again, thank you very much for your comments and suggestions.

Author Response File: Author Response.pdf