Charge Transfer on the Surface-Enhanced Raman Scattering of Ag/4-MBA/PEDOT:PSS System: Intermolecular Hydrogen Bonding
and Young Mee Jung 2,*Round 1
Reviewer 1 Report
In this manuscript, the authors present an intermolecular hydrogen bonding could affects SERS enhancement mechanism in sandwich structure. The probe molecule, 4-mercaptobenzoic acid, has a function to show very interesting spectroscopic results. It can be published after minor revision.
I would like to suggest minor revision for clarifying misunderstanding.
1) Page 4, Line 161 : There is no information where the particle size is obtained.
2) Page 4, Line 170 : I think "absorption" is typo. "adsorption" is more adaptable. Please check this word.
3) ρCT : I would like to suggest this symbol the same for consistency.
Author Response
We appreciate Reviewer’s comments on this manuscript which make us revise the manuscript significantly.
According to the comments of Reviewers, we prepared a highlighted revised version documenting all changes made. Our point-by-point response to the Reviewers’ comments is attached.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper investigates the effect/role of charge transfer on the SERS properties of a Ag/4-MBA/PEDOT:PSS hybrid system. The contents of the paper fit well within the journal's scopes, and the investigated area can be of interest to both readers and experts in the field. However, I have several technical issues with the paper, which should be addressed before publication:
- Regarding the synthesis of the Ag NPs, there are many claims that are not supported by any presented data. In section 2.2.1: “Spherical Ag NPs were uniformly dispersed, and the average particle size was approximately 65 nm.” How was it measured? Similarly, in Section 3: “As shown in Figure 1a, prior to the introduction of PEDOT:PSS, the spherical Ag NPs were evenly distributed on the surface of the glass substrate as a monolayer with an average particle size of approximately 65 nm.” First, the quality of the SEM images in Fig. 1 is poor. Secondly, the magnification is not enough to see individual particles. The tiny scalebar represents 100 nm, and some of the visible structures have over 100 nm size, yet the authors claim that the particle size is uniformly distributed 65 nm. Please support these claims.
- 5A should contain the results corresponding to 0% PEDOT:PSS. Why was this omitted in the first place?
- One of the most important claims of the paper is that a 0.8% PEDOT:PSS concentration increases the ρCT value from 0.46 to 0.53, compared to the 0% case. Was the statistical relevance of this claim (difference) tested with any method? Based on Fig. 4B, after baseline correction, the 0% and the 0.8% spectra are quite close to each other, maybe within the standard deviation range (based on Fig. 5A).
- What was the repetition number used for error bar calculation in Fig. 5A? Are these standard deviation or min-max bars?
- The connection between PEDOT:PSS concentration and the obtained ρCT values is not properly discussed in the text. “There is a positive correlation between ρCTand PEDOT:PSS concentration, indicating that the formation of hydrogen bonds is beneficial to the CT process[40, 41].” Compared to the 0% (0.46 ρCT) small amounts of PEDOT:PSS causes a significant drop in ρCT. Below 0.3% the obtained ρCT is lower than without PEDOT:PSS. There are no explanations for this behavior. Also, from 0.8% to 1% there is a significant drop in ρCT, which is again not addressed. The truth is, PEDOT:PSS only yielded a better ρCT than the reference at 0.8%, but the statistical relevance of this should be tested.
- Although the English of the paper is mostly good, there are some poorly formulated sentences, e.g. “When ρCT(κ) was close to 1, the mainly CT effect affected the SERS enhancement” It should be a general term, no such measurements were performed (‘was close to 1’..).
Author Response
We appreciate Reviewer’s comments on this manuscript which make us revise the manuscript significantly.
According to the comments of Reviewers, we prepared a highlighted revised version documenting all changes made. Our point-by-point response to the Reviewers’ comments is attached.
Author Response File: Author Response.pdf
Reviewer 3 Report
- Introduction
- Line 44 - 56
What are other factors rather than intermolecular force?
-> Need to add the details including how each factor can be matched with SERS performance
-> Especially, for hydrogen bond, you mentioned that it can help to understand the SERS mechanism. Please rewrite them to make it clear how the mechanism understanding can be directly matched with SERS performance.
- Line 63 -65
Is there any reference to support them? Please add them.
- Line 66 -72
Some sentences are not understandable, and some grammars need to be checked.
- Line 72 - 75
Please add some references to support them.
- Line 96 -100
It needs to be rewritten to make it clear and easier understanding.
- Materials and Methods
- Line 119 – 140 (CH 2.2)
Please rewrite or rearrange this chapter to include all the procedures of fabricating the final form of composite. PEDOT:PSS deposition procedure seems to be suddenly introduced in CH 2.3.
- Results
- Line 152 - 156
Please check and rewrite them again. It seems not to be logical.
* Scheme 1
- Please add negative or positive charge on the scheme.
- Also, please add some important bond like Ag-S or hydrogen bond on the scheme.
- Line 163 - 165
The quality of SEM image here seems not to be good to support your mention. Please update the images so that your mentioning can be supported.
- Line 169 - 172
Your idea why the distribution of the AgNPs can be uniform after the introduction of PEDOT:PSS seems not to be clear for me. Please add some in-detail explanation.
- Line 182 - 189
- In my understanding, when you compare Ag sol with AgNPs deposited on the PDDA decorated substrate, the peak position was changed? Please clarify your explanation of dipole-dipole interaction can cause the shift.
- Please add in-detail explanations to support your result of peak shift and widening.
- Line 201 - 203
- You mentioned that 4-MBA was absorbed on PEDOT:PSS. Is it correct? PEDOT:PSS was finally introduced on the AgNPs modified with 4-MBA? Please clarify it.
- I do not understand that carboxyl group can be bonded to negatively charged PSS chain due to electrostatic interaction. Carboxyl group normally having negative charge as well? Please clarify it.
- Line 245
In table 2, do you have any idea why ρCT was suddenly decreased (from 0.46 -> 0.19) when only 0.05% PEDOT:PSS was added?
- Line 289 - 292
It should be interesting to observe the CT process can enhance the SERS signal. However, I would recommend that you need to consider application side as well. Do you have any other SERS result of other target molecule rather than 4-MBA? At least, you need to describe how your SERS platform can be widely used to detect different kinds of target molecules.
Author Response
We appreciate Reviewer’s comments on this manuscript which make us revise the manuscript significantly.
According to the comments of Reviewers, we prepared a highlighted revised version documenting all changes made. Our point-by-point response to the Reviewers’ comments is attached.
Author Response File: Author Response.pdf
Reviewer 4 Report
The manuscript by Yuenan Pan et al presents the development of an organic semiconductor with a noble metal-probe molecule sandwich structure consisting of Ag nanoparticles (NPs), 4-mercaptobenzoic acid (4-MBA) and different concentrations of poly(sty-15 renesulfonate:poly(3,4-ethylenedioxythiophene) (PEDOT:PSS), prepared by a layer-by-layer assembly method. This system aims to improve the understanding and study of hydrogen bonding by the SERS method.
The objectives in the introduction are well described as well as the materials and methods part. The results obtained seem promising but require the clarification of several points.
- First of all, in the introduction, the author should weigh his remarks when he states line 87 to 90 “Due to the shortcomings of noble metals, such as expense, unstable chemical properties, narrow research fields, and poor biocompatibility, semiconductors have emerged as SERS substrates, greatly expanding the scope of SERS research“.
Indeed, in his organic semiconductor assembly, the author also uses Ag nanoparticles, noble metal.
Now on the results part several comments:
- Line 162-163, the author states from the SEM image figure 1.a that “the spherical Ag NPs were evenly distributed on the surface of the glass substrate as a monolayer with an average particle size of approximately 65 nm“.
However, the SEM image does not show clearly an homogenous distribution of nanoparticles, rather it appears a certain particle size distribution as well as different spacings. I suggest that the author should do a statistical analysis on the SEM images to determine the size distribution of the nanoparticles before giving an average particle size that does not appear clearly on the SEM image.
- Similarly Line 163-165 then 169-172, the author states that after coating the morphology of the Ag NPs did not change and that the composite particles became more uniform or that the absorption of the Ag NPs increased and the number of free NPs decreased, making the distribution of the Ag NPs more uniform. Again, there is nothing in the SEM images to suggest such a conclusion.
Even more so when the author states “As the concentration of PEDOT:PSS increased in the Ag/4-MBA/PEDOT:PSS composite system, the contact between the Ag NPs and PEDOT:PSS increased, the absorption of the Ag NPs increased … making the distribution of Ag NPs more uniform“.
How can we say that this is due to a more uniform distribution and not rather to a more uniform interaction with the Ag NPs?
- Line 193: there is a mistake, it is Figure 3 and not Figure 3 (a).
- Overall on the results in Figure 4:
- I think that the author could easily dissociate the peaks 1395 cm-1 (corresponding to 4-MBA) and 1437 cm-1 (corresponding to PEDOT:PSS) and more particularly on Figure 4.B. Moreover one can notice on Figure 4.A that for a concentration lower than 0.8 % of PEDOT:PSS only the peak at 1395 cm-1 seems to remain. Could the author explain why the peak at 1437 cm-1 of PEDOT:PSS disappears?
- In figure 4.B the author uses the concentration of 0.8% PEDOT:PSS, a concentration for which the overall intensity of the SERS bands corresponding to 4-MBA has increased and where the change in intensity has become stable. The comparison then between the SERS signal of Ag/4-MBA and Ag/4-MBA/0.8% PEDOT:PSS supports the author's statement. One can nevertheless wonder about the differences between these two curves which do not seem to coincide with the same curves of figure 4.A (i.e. the comparison between curve b and i) but are closer to curves b and g (0.075% PEDOT:PSS). To be verified by the author
- To be completely convinced, it seems to me that it would be necessary to have on figure 4.B the result of the Raman spectrum of Ag/0.8% PEDOT:PSS, spectrum which is not given and would make it possible to "guarantee" that the effect is indeed related to the interaction described by the author. This spectrum would certainly be more interesting than spectra c) and d) of figure 4.B.
These points seem to me to need clarification in order to conclude on the value of the device has clearly shown that the change in SERS intensity can be attributed to the molecular hydrogen bond formed by PEDOT:PSS and 4-MBA.
Author Response
We appreciate Reviewer’s comments on this manuscript which make us revise the manuscript significantly.
According to the comments of Reviewers, we prepared a highlighted revised version documenting all changes made. Our point-by-point response to the Reviewers’ comments is attached.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
I reckon that the authors made the necessary corrections in their manuscript. I can now support the publication of the paper in the journal.
Author Response
The authors appreciate very much for the positive comment.
Reviewer 3 Report
Thanks for your efforts to modify your manuscript according to what I suggested.
I am pretty much satisfied with the current version of the manuscript except for some points that need to be clarified further.
1. For the response to my No.11 question,
"According to Reference 1, PEDOT: PSS can be connected with carboxyl group."
-> I am still confusing. Please add this explanation in the manuscript to explain how PEDOT:PSS can be connected with carboxyl group.
2. For the response to my No. 13 question,
"Therefore, we selected the MBA as the probe molecule to monitor the CT process."
I truely understand why you choose the molecule. However, I also would like to know your brief discussion for application aspect how your this mechanism finding can be widely utilized for the detection of various molecules rather than just finding CT mechanism using MBA.
Author Response
We appreciate Reviewer’s comments on this manuscript which make us revise the manuscript significantly.
According to the comments of Reviewers, we prepared a highlighted revised version documenting all changes made. Our point-by-point response to the Reviewers’ comments is included.
Author Response File: Author Response.pdf
Reviewer 4 Report
The recommendations and corrections have been followed. The additional explanations provided are satisfactory.
Author Response
The authors appreciate very much for the positive comment.
