Single-Molecule Surface-Enhanced Raman Spectroscopy

Round 1

Reviewer 1 Report

The authors summarize numerous SM-SERS studies with the aim to inspire further developments in the field. The organization of this article looks good. The subpoints are connected to each other and supported by literature examples. I would suggest a careful revision of the manuscript considering the following issues.    There are several mistakes on the fundamental concepts. For example, in the first sentence, the definition of "Raman scattering" is wrong, it relies on the interaction between photons and molecules. On page 3, it is improper to use the term "Raman polarizability". The authors should clarify the basic theory of Raman scattering regarding Raman activity, molecular vibration, and polarizability. The polarizability is an intrinsic molecular property, so the description regarding the mechanism of "resonance Raman" is improper. The definition of "enhancement factor" is also not clear, it should involve the number of molecules and the relative signal intensity.    The author shows numerous examples of SM-SERS substrates. However, the information on the development trends and the rationals for different designs is missing, because the fundamental mechanism of SM-SERS is not well presented earlier.   Since some important information is wrong or missing, the reader has to spend extra efforts to understand the field of SM-SERS. In addition, the authors could improve the language clarity with the help from academic editing services or native English speakers.

Author Response

Comment 1: The authors summarize numerous SM-SERS studies with the aim to inspire further developments in the field. The organization of this article looks good. The subpoints are connected to each other and supported by literature examples. I would suggest a careful revision of the manuscript considering the following issues.

Response: We really acknowledge the reviewer for the constructive feedback and valuable comments. In the following, we give our response (marked in blue) point by point to the reviewer’s comments and suggestions. The revised portions are marked in red in the revised manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

This review paper is on single-molecule surface-enhanced Raman spectroscopy (SM-SERS). The authors want to give a brief overview of the topic and they reported in a pretty clear way some aspects related to it. In particular they mention the major approaches to obtain experimental evidence of single-molecule event, issues related to spectral fluctuation and data analysis. moreover the discuss on strategy of improving the probability of molecules in hotspots and  non-metallic and hybrid substrate.

Some applications are also mentioned and discussed, in particular the section on In Situ Monitoring of Catalytic Reactions is interesting and rather new with respect to other review papers on SM-SERS.

The paper is good, but considering that in literature several other papers reported on similar discussion I think that some improvements are needed before the publication.

First of all, the authors missed to mention some important results on different aspects discussed in this review.

in particular, TERS. The authors correctly claim that SM-TERS is typically done at low temperature, but several reports on temperature dependent and room-temperatura SERS using nanocavities (very very similar to a TERS configuration) have been reported. for examples:

J. Chem. Phys. 153, 170901 (2020);

Nature Nanotech. 15  105–11 (2020);

J. Phys. Chem. Lett. 2018, 9, 24, 7146–7151; 

Nano Lett. 2016, 16, 1, 479–487

Regarding the different platforms for SM-SERS, the number of examples in literature are pretty large and some are really missing here:

Nanoscale 2014, 6 (15), 8521−8526.; 

ACS Nano 2011, 5 (6), 4407−4413;

Anal. Chem. 2021, 93 (34), 11679−11685;

Anal. Chem. 2019, 91 (9), 6275−6280;

ACS Sens. 2020, 5, 7, 2198−2204

Angew. Chem. Int. Ed. 2020, 59, 2–11

finally, the authors mentioned in ref. 66 a review paper on plasmonic nanopores also for SM-SERS. A more updated review on the topic, also more focused on SM-SERS can be mentioned: Anal. Chem. 2022, 94, 2, 503–514

minor corrections:

-line 80: "It is vital that how much EF is required...." not clear....rephrase please

-ref 97 not working....there is a recent paper exactly on this platform (nanoporous film for single molecule DNA SERS). the authors should replace the ref with it (J. Phys. Chem. C 2020, 124, 41, 22663–22670)

In the "challenges in SM-SERS" section, the authors should consider to mention on new approaches based on ultra-fast SERS to perform SM-SERS. this method could open the way to important improvent in SM-SERS application (see for example Chem. Soc. Rev., 2016,45, 2263-2290 and Analyst, 2015,140, 4922-4931)

Author Response

Comment: This review paper is on single-molecule surface-enhanced Raman spectroscopy (SM-SERS). The authors want to give a brief overview of the topic and they reported in a pretty clear way some aspects related to it. In particular they mention the major approaches to obtain experimental evidence of single-molecule event, issues related to spectral fluctuation and data analysis. Moreover, the discuss on strategy of improving the probability of molecules in hotspots and non-metallic and hybrid substrate.

Some applications are also mentioned and discussed, in particular the section on In Situ Monitoring of Catalytic Reactions is interesting and rather new with respect to other review papers on SM-SERS.

The paper is good, but considering that in literature several other papers reported on similar discussion I think that some improvements are needed before the publication.

Response: We really acknowledge the reviewer for this positive comment. In the following, we give our response (marked in blue) point by point to the reviewer’s comments and suggestions. The revised portions are marked in red in the revised manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors have done a literature survey on the latest in the field of using SERS in single molecule sensing. This review paper could be of an interest to a wide range of readers. However, there are a few issues that need to be revised before suggesting for publication.

-   The first statement in the abstract: “Single-molecule surface-enhanced Raman spectroscopy (SM-SERS) is a non-invasive, label-free, and high-throughput single-molecule detection technology” is not quite right as it could be labelled and depending on the procedure might be invasive. Therefore, it is recommended that the authors revise this statement to maybe “surface-enhanced Raman spectroscopy (SM-SERS) has the potential to detect Single-molecule in a non-invasive, label-free manner with high-throughput”.

-          The overall English needs be improved.

-          The referencing needs to be revised as it is not clear what statement is referenced for examples: Raman scattering [1] …. Thus, the Raman spectrum [2] and many more examples.

-          Could the authors label different section of the figure.1 instead of saying right, left etc.

-          Could the authors name a few examples for the need to measure single molecules, and the importance of doing so.

-          It would be beneficial if the authors include the typical formula used to calculate the EF– in the section 2.1

-          It is not clear in the section 2.1 what type of SERS substrates have been used to obtain the reported EFs.

-          It is worth mentioning what are the differences of SPR and charge transferred mechanism in a separate section.

-   Since this is a review paper, could the authors provide sufficient refences to back up their statements such as “Conventional SERS substrates are dominated by noble metals, such as Au, Ag, and Cu, but suffer from high cost, heterogeneity, lack of stability and biocompatibility.” Also, not all the novel metals are like AU and Ag suffering from lack of biocompatibility.

-          The authors could added the following citations to further strengthen section 3.3 as follows: “Non-metallic materials, such as semiconductor [ 10.1021/acsami.8b10590]”

-          Authors could perhaps add a section to cover organic materials as a SERS substrate as well

Author Response

Comments: The authors have done a literature survey on the latest in the field of using SERS in single molecule sensing. This review paper could be of an interest to a wide range of readers. However, there are a few issues that need to be revised before suggesting for publication.

Response: We really acknowledge the reviewer for the constructive feedback and valuable comments. In the following, we give our response (marked in blue) point by point to the reviewer’s comments and suggestions. The revised portions are marked in red in the revised manuscript.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The new version of the manuscript is very good.

I recommend the publication.