Highly Sensitive Sensor for the Determination of Riboflavin Using Thionine Coated Cadmium Selenide Quantum Dots Modified Graphite Electrode
Round 1
Reviewer 1 Report
The work “Highly sensitive sensor for the detection of riboflavin using 2 Thionine coated Cadmium Selenide Quantum Dots modified 3 graphite electrode” describes a method for determining a vitamin by a relatively simple electrochemical method.
here are some questions
- Line 44, the title of Quantum dots is capitalized and no abbreviation is introduced.
- Is not very clean is some electrochemical sensors for riboflavin are exist already. What is the advantage to use quantum dots for electrochemical sensors? The introduction does not open the excellence of this method.
- How you can explain H type aggregate between semiconductor crystal and molecule?
- Won't the NH4OH evaporate from the surface?
- TH has a mass of 263.75 g/mol. Compared to the size of a nanoparticle, this is a very small size. This suggests that the layer for coating the nanoparticles should be visually invisible and the amount of TH in the colloid is in large excess, as can be seen from the TEM images. Have collides been diluted to measure RAMAN
- According to the TEM images, there is a feeling that there is no such dot coverage, but a film is formed. Could it be that the TH provides a layer of coating on the electrode with a uniform distribution of QDs, which allows you to see them on a voltammogram?
- How many times was the experiment repeated?
Author Response
Response sheet
Journal Title: Micro
Manuscript Title: Highly sensitive sensor for the detection of riboflavin using Thionine coated Cadmium Selenide Quantum Dots modified graphite electrode
Manuscript Number: Micro-2464517
Dear Editor,
Thank you very much for your valuable and helpful comments about our manuscript. We like to reply for the comments raised by the reviewer’s and editor in support of our work.
The corrections have been carried out in the Revised Manuscript and are highlighted in yellow color.
Comment 1: Line 44, the title of Quantum dots is capitalized and no abbreviation is introduced.
Answer 1: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have abbreviated in the revised manuscript. Thank you for noticing.
Comment 2: Is not very clean is some electrochemical sensors for riboflavin are exist already. What is the advantage to use quantum dots for electrochemical sensors? The introduction does not open the excellence of this method.
Answer 2: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, the integration of redox mediators such as dyes, metal oxides or metal hexacyanoferrates on the surface of QDs have been used to improve the performance of the modified electrode ability by means of lowering the over potential and enhancing the sensitivity because they provide large surface area for them to adsorb on the surface of electrode. Now we have included the advantages of the QDs used as electrochemical sensors in revised manuscript.
Comment 3: How you can explain H type aggregate between semiconductor crystal and molecule?
Answer 3: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, there is a strong electronic coupling between the negatively charged CdSe QDs and the cationic Thionine dye aggregates causes blue shift (H-type) in the absorption band. This often leads to the close packing of dye molecules on a charged particles surface [1], and thus makes the local concentration of TH on particle surfaces increases. The reference was cited in the revised manuscript.
- Liu D, Kamat PV (1996) Dye-Capped Semiconductor Nanoclusters. One-Electron Reduction and Oxidation of Thionine and Cresyl Violet H-Aggregates Electrostatically Bound to SnO2 Colloids. Langmuir 12:2190–2195. https://doi.org/10.1021/la9510994
Comment 4: Won't the NH4OH evaporate from the surface?
Answer 4: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, the NH4OH was not used in the present work. For electrochemical studies, we are using NH4NO3 and NH4Cl electrolytes.
Comment 5: TH has a mass of 263.75 g/mol. Compared to the size of a nanoparticle, this is a very small size. This suggests that the layer for coating the nanoparticles should be visually invisible and the amount of TH in the colloid is in large excess, as can be seen from the TEM images. Have collides been diluted to measure RAMAN.
Answer 5: We agree with the reviewer comment. Giving due respect to the reviewer comment, the powdered sample of Thionine coated CdSe QDs was directly place the sample holder to measure the Raman studies. The water soluble Thionine after coated with CdSe QDs, which makes insoluble Thionine coated CdSe QDs powder sample was prepared. Hence, the powdered sample was dispersed in propanol for TEM sample preparation. Hence, the film showed in the TEM image, it could be a solvent layer.
Comment 6: According to the TEM images, there is a feeling that there is no such dot coverage, but a film is formed. Could it be that the TH provides a layer of coating on the electrode with a uniform distribution of QDs, which allows you to see them on a voltammogram?
Answer 6: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, the water soluble Thionine after coated with CdSe QDs, which makes insoluble Thionine coated CdSe QDs powder sample was prepared. Hence, the powdered sample was dispersed in propanol for TEM sample preparation. Hence, the film showed in the TEM image, it could be a solvent layer. Also, Fig. 4 showed the detailed cyclic voltammogram explanation of bare PIGE (a), CdSe QDs-PIGE (b) TH-PIGE (c) and TH@CdSe QDs-PIGE (d) modified electrodes in 0.1 M NH4NO3 at 50 mV/s.
Comment 7: How many times was the experiment repeated?
Answer 7: We appreciate and comply with the referee’s comment. The determination of riboflavin experiment in cyclic voltammetry was repeated twice to check the consistency.
It is hereby requested that the Revised Manuscript should be considered for publication in Micro.
-AUTHORS
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors reported an interesting work using TH coated CdSe QDs as the sensor. The work is well performed, but there are still some problems that need to be addressed. Therefore, a major revision is needed, and the following questions must be addressed.
1. Figure 1, the name of y axis overlaps with some other texts. Some problem for Figure 4.
2. To show a bigger picture to the readers, the introduction about quantum dots could be expanded and more applications and advantages of QDs need to be discussed. This will let people understand why it is important to study QDs. The following recent example of QDs applications should be cited (https://doi.org/10.1063/5.0051893; https://doi.org/10.1016/j.physleta.2021.127307).
3. The authors claimed that “The decrease in the absorption band of the TH monomer confirms 106 the formation of H-type aggregates with CdSe QDs.”. Any reference for that?
4. Apart from the UV vis, is that possible to also give the photoluminescence spectrum of QDs in the presence of different amount TH? This could help better understand photophysical interaction between two species.
5. I am still quite confused about why TH coated QDs works for the sensor of riboflavin. Is that possible also to add some more discussion or draw a mechanism figure?
6. What is the sensor performance of uncoated QD? The control experiment is needed.
Author Response
Response sheet
Journal Title: Micro
Manuscript Title: Highly sensitive sensor for the detection of riboflavin using Thionine coated Cadmium Selenide Quantum Dots modified graphite electrode
Manuscript Number: Micro-2464517
Dear Editor,
Thank you very much for your valuable and helpful comments about our manuscript. We like to reply for the comments raised by the reviewer’s and editor in support of our work.
The corrections have been carried out in the Revised Manuscript and are highlighted in yellow color.
Comment 1: Figure 1, the name of y axis overlaps with some other texts. Some problem for Figure 4.
Answer 1: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have rectified in the revised manuscript.
Comment 2: To show a bigger picture to the readers, the introduction about quantum dots could be expanded and more applications and advantages of QDs need to be discussed. This will let people understand why it is important to study QDs. The following recent example of QDs applications should be cited
(https://doi.org/10.1063/5.0051893; https://doi.org/10.1016/j.physleta.2021.127307).
Answer 2: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, the above references were included in the revised manuscript.
Comment 3: The authors claimed that “The decrease in the absorption band of the TH monomer confirms 106 the formation of H-type aggregates with CdSe QDs.”. Any reference for that?
Answer 3: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, there is a strong electronic coupling between the negatively charged CdSe QDs and the cationic thionine dye aggregates causes blue shift (H-type) in the absorption band. This often leads to the close packing of dye molecules on a charged particles surface [1], and thus makes the local concentration of TH on particle surfaces increases. The relevant reference was included in the revised manuscript.
- Liu D, Kamat PV (1996) Dye-Capped Semiconductor Nanoclusters. One-Electron Reduction and Oxidation of Thionine and Cresyl Violet H-Aggregates Electrostatically Bound to SnO2 Langmuir 12:2190–2195. https://doi.org/10.1021/la9510994
Comment 4: Apart from the UV-vis, is that possible to also give the photoluminescence spectrum of QDs in the presence of different amount TH? This could help better understand photophysical interaction between two species.
Answer 4: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, in our institution we don’t have the facility of photoluminescence technique. Generally, we send samples to the other universities to analyze the physicochemical characterization. Normally it will take two months to analyze the particular studies. Hence, we are unable to do the photoluminescence spectra analysis. We apologize for not able to provide the data of reviewer requested.
Comment 5: I am still quite confused about why TH coated QDs works for the sensor of riboflavin. Is that possible also to add some more discussion or draw a mechanism figure?
Answer 5: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, The integration of redox mediators such as dyes, metal oxides, metal hexacyanoferrates or polymers on the surface of QDs have been used to improve the performance of the modified electrode ability by means of lowering the over potential and enhancing the sensitivity because they provide large surface area for them to adsorb on the surface. Redox dyes are the best candidates since they exhibit both electrochromic and electrochemical properties. Dyes have been widely applied in the field of catalysis, electrochromic devices, sensors and biosensors. The immobilization of dyes on nanomaterials such as carbon nanotubes, graphene and metal nanoparticles to fabricate modified electrodes showed good electrocatalytic activity towards a variety of biologically, environmentally and industrially important compounds. The mechanism of electroreduction of Riboflavin at modified electrode as scheme 1 was included the revised manuscript.
Comment 6: What is the sensor performance of uncoated QD? The control experiment is needed.
Answer 6: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, we have already included the QD sensor performance in Figure 4b. The control experiment of bare PIGE (a), CdSe QDs-PIGE and (c) mere TH-PIGE were included and discussed in the revised manuscript.
It is hereby requested that the Revised Manuscript should be considered for publication in Micro.
-AUTHORS
Author Response File: Author Response.pdf
Reviewer 3 Report
In this paper, an electrochemical determination of riboflavin was proposed based on its reduction at a graphite electrode modified with thionine-coated cadmium selenide quantum dots. The manuscript is very confusing. It was presented more results of the electrochemical behavior of thionine (modified agent) than riboflavin (analyte). Important studies such as the effect of pH, supporting electrolyte composition, scan rate were performed based on thionine (modified agent). Thus, the method and electrode were not optimized to improve riboflavin sensitivity. The optimization of the analytical method is flawed. The validation of the analytical method is flawed. In my view, there is an overlap of the voltammetric peaks of thionine with riboflavin. So, not the selectivity, precision and accuracy of the method. The manuscript contains serious problems and is very confusing. Thus, as it is being presented, the manuscript must be rejected for publication. But it is possible to do a major revision and resubmit as a new manuscript.
General comments:
1. The authors, like many others, confuse the terms "detection" and "determination". Detection is qualitative by nature, while determination always is quantitative. Qualitative analysis is the detection of the presence of ions or compounds in an unknown sample, for example. The term "determination" refers to quantitative analysis to obtain data on the amount of analyte by weight or by concentration of an element or a compound in a sample. Therefore, most of the words “detection" in the manuscript should be replaced by the term "determination" (or "quantitation" or "assay") if quantitative assays are involved.
2. The novelty of the manuscript needs to be better clarified, since inorganic quantum dots are toxic.
3. There seems to be an overlapping of thionine and riboflavin peaks. Authors need to discuss and clarify this point.
4. An English grammar review is required in this manuscript.
5. It should be indicated on the voltammograms: Potential vs. SCE.
6. The manuscript is not formatted for the MDPI standard. There are different fonts, different margins. The correct symbols are not used. Symbols for multiplication and subtraction must be used correctly.
7. Update the terminologies for the electrochemical methods according to new IUPAC recommendations. See the information in Pure and Applied Chemistry, 92 (2020) 641–694. Current is I (in italics).
8. Voltammograms must be presented according to the IUPAC convention.
9. The manuscript must contain up-to-date references (2020-2023). There are many old references.
Specific comments:
1. Abstract:
a. Line 21. Check the symbols.
2. Introduction:
a. Line 36. The term "quantitative determination" is redundant. The determination is a quantitative assay.
b. Lines 39-41. It is important to add the advantages of using electrochemical methods. The use of miniaturized and portable sensors is only possible because electrochemical instrumentation is also miniaturized and portable. Thus, add in the sentence the advantages of "miniaturization" and "portability" of electrochemical instruments. Add the reference Materials, 16 (2023) 1024 to validate this information.
2. Materials and methods:
a. A section on samples and sample preparation needs to be created. Indicate the city and country where the samples were acquired.
b. Standardize the description of the equipment: model (company, country).
c. Line 73. Indicate the cuvette used and the optical path.
d. Pay attention to significant figures: use 5.0, for example.
3. Results and discussion:
a. Figure 3. A histogram of the QDs diameter distribution should be presented. Present the mean diameter obtained with the margin of error.
b. Line 167. Check.
c. Line 164. The electrochemical characterization of the modified electrodes must be performed with a redox probe known as [Fe(CN)6]3−/4−, and not with the electrode modifying agent. Too confusing.
d. Figure 4. An abbreviation must be used on all modified electrodes indicating the graphite substrate.
e. Line 191. “electrolytele”? Check.
f. Lines 192-197. Provide a scientific chemistry discussion on the behavior of the modified electrode being superior in NH4NO3 supporting electrolyte.
g. The pH study should be carried out with riboflavin, showing at which values there is no overlap with thionine.
h. The oxidation and reduction potentials of riboflavin should be presented and discussed. Is riboflavin a quasi-reversible or reversible system? A discussion is needed.
i. “…in the presence of 1.6 × 10−5 M RF was investigated by CV at various pHs (4-9) in 0.1 M NH4NO3 and the current response was plotted against pH”. Voltammograms must be shown.
j. Figure 7B. Honestly, where did this calibration curve come from? Which parameters? Which technique? It makes no sense for a calibration curve to appear without being discussed.
k. NH4NO3 solution is not a buffer solution. How do the authors guarantee that by varying the pH values from 4-9 the same nature of the species will be maintained? In addition, a calibration curve must be performed in replicates.
l. The authors claim that they monitored the peak reduction of riboflavin, but nowhere in the text is the need for a nitrogen purge mentioned. Confused.
m. What is catalytic current? The authors have no knowledge of Electroanalytical Chemistry. There is no electrocatalysis of riboflavin because there was no shift in riboflavin peak potentials with electrode modification.
n. A Table with recent electrochemical sensors dedicated to the determination of riboflavin must be presented. Thus, the sensors and LODs obtained must be presented. Use the following references: Talanta, 258 (2023) 124409; Talanta, 252 (2023) 123836; Food Chemistry, 423 (2023) 136283; Sensors, 21 (2021) 1371; Microchemical Journal, 179 (2022) 107588; Journal of Electroanalytical Chemistry, 928 (2023) 117037.
o. Relative error values between the data obtained by the modified electrode and the product label must be presented.
p. The calibration curve for riboflavin must be done in replicates, and the error bars shown at each concentration point.
q. Supporting electrolyte pH studies using a buffer solution should be performed for riboflavin.
r. Why was the amperometry technique selected?
“electrolytele”? Check.
Author Response
Response sheet
Journal Title: Micro
Manuscript Title: Highly sensitive sensor for the detection of riboflavin using Thionine coated Cadmium Selenide Quantum Dots modified graphite electrode
Manuscript Number: Micro-2464517
Dear Editor,
Thank you very much for your valuable and helpful comments about our manuscript. We like to reply for the comments raised by the reviewer’s and editor in support of our work.
The corrections have been carried out in the Revised Manuscript and are highlighted in yellow color.
Comment 1: In this paper, an electrochemical determination of riboflavin was proposed based on its reduction at a graphite electrode modified with thionine-coated cadmium selenide quantum dots. The manuscript is very confusing. It was presented more results of the electrochemical behavior of thionine (modified agent) than riboflavin (analyte). Important studies such as the effect of pH, supporting electrolyte composition, scan rate were performed based on thionine (modified agent). Thus, the method and electrode were not optimized to improve riboflavin sensitivity. The optimization of the analytical method is flawed. The validation of the analytical method is flawed. In my view, there is an overlap of the voltammetric peaks of thionine with riboflavin. So, not the selectivity, precision and accuracy of the method. The manuscript contains serious problems and is very confusing. Thus, as it is being presented, the manuscript must be rejected for publication. But it is possible to do a major revision and resubmit as a new manuscript.
Answer 1: Thank you very much for the expert reviewer for their insightful comment which has assisted us to improve the quality of the manuscript. Giving due respect to the reviewer comment, now we have thoroughly revised the manuscript as per reviewers suggestions. Before we determine the riboflavin analyte, we thoroughly characterized the TH coated CdSe QDs modified PIGE. Further, the sensitivity and selectivity of riboflavin determination were optimized. The TH coated CdSe QDs modified PIGE electrode exhibited a pair of well defined redox peaks with cathodic and anodic peak potentials of -0.2260 V and -0.1547 V, whereas the mere TH electrode modified electrode shows the cathodic and anodic peaks at potentials of -0.32 V and -0.21 V, respectively. When the determination of riboflavin, we have optimized the effect of pH, electrocatalytic studies, hydrodynamic studies and chronoamperometric studies.
General Comments
Comment 1: The authors, like many others, confuse the terms "detection" and "determination". Detection is qualitative by nature, while determination always is quantitative. Qualitative analysis is the detection of the presence of ions or compounds in an unknown sample, for example. The term "determination" refers to quantitative analysis to obtain data on the amount of analyte by weight or by concentration of an element or a compound in a sample. Therefore, most of the words “detection" in the manuscript should be replaced by the term "determination" (or "quantitation" or "assay") if quantitative assays are involved.
Answer 1: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have corrected the term “determination” throughout in the revised manuscript. Thank you.
Comment 2: The novelty of the manuscript needs to be better clarified, since inorganic quantum dots are toxic.
Answer 2: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, the novelty of the manuscript is included in the revised manuscript.
Comment 3: There seems to be an overlapping of thionine and riboflavin peaks. Authors need to discuss and clarify this point.
Answer 3: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, the TH@CdSe QDs-PIGE modified electrode exhibited a pair of well defined redox peaks with cathodic and anodic peak potentials of -0.2260 V and -0.1547 V, respectively. But, the electrocatalytic activity of the TH@CdSe QDs-PIGE modified electrode towards Riboflavin (RF). The current response for the reduction of RF at the bare electrode was poor but the modified electrode showed a better and considerable increase in the current response at -0.50 V. Hence, there is no overlapping of thionine and riboflavin.
Comment 4: An English grammar review is required in this manuscript.
Answer 4: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, the entire manuscript was submitted for thoroughly language check and it is free of grammatical errors and well polished.
Comment 5: It should be indicated on the voltammograms: Potential vs. SCE.
Answer 5: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have corrected figures in the revised manuscript.
Comment 6: The manuscript is not formatted for the MDPI standard. There are different fonts, different margins. The correct symbols are not used. Symbols for multiplication and subtraction must be used correctly.
Answer 6: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have corrected in the revised manuscript. We apologize for the errors.
Comment 7: Update the terminologies for the electrochemical methods according to new IUPAC recommendations. See the information in Pure and Applied Chemistry, 92 (2020) 641–694. Current is I (in italics).
Answer 7: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have corrected in the revised manuscript.
Comment 8: Voltammograms must be presented according to the IUPAC convention.
Answer 8: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have corrected in the revised manuscript.
Comment 9: The manuscript must contain up-to-date references (2020-2023). There are many old references.
Answer 9: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have included the recent references in the revised manuscript.
Specific Comments
Comment 1: Abstract: a. Line 21. Check the symbols.
Answer 1: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have corrected in the revised manuscript. Thank you for noticing.
Comment 2: Introduction: a. Line 36. The term "quantitative determination" is redundant. The determination is a quantitative assay.
Answer 2: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have rectified the statement in the revised manuscript.
Comment 3: Introduction: b. Lines 39-41. It is important to add the advantages of using electrochemical methods. The use of miniaturized and portable sensors is only possible because electrochemical instrumentation is also miniaturized and portable. Thus, add in the sentence the advantages of "miniaturization" and "portability" of electrochemical instruments. Add the reference Materials, 16 (2023) 1024 to validate this information.
Answer 3: We appreciate and comply with the referee’s comment. Now we have added the text in the introduction section of revised manuscript.
Comment 4: Materials and methods: a. A section on samples and sample preparation needs to be created. Indicate the city and country where the samples were acquired.
Answer 4: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have modified the experimental section and included the detail purchase details in the revised manuscript.
Comment 5: Materials and methods: b. Standardize the description of the equipment: model (company, country).
Answer 5: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have modified the experimental section and included the detail purchase details in the revised manuscript
Comment 6: Materials and methods: c. Line 73. Indicate the cuvette used and the optical path.
Answer 6: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, we have indicated the cuvette used and the optical path in the revised manuscript.
Comment 7: Materials and methods: d. Pay attention to significant figures: use 5.0, for example.
Answer 7: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have changed to significant figures in the revised manuscript. Thank You.
Comment 8: Results and discussion: a. Figure 3. A histogram of the QDs diameter distribution should be presented. Present the mean diameter obtained with the margin of error.
Answer 8: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, unfortunately we don’t the data of histogram of the QDs diameter distribution. We apologize for not providing the data.
Comment 9: Results and discussion: b. Line 167. Check.
Answer 9: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, we have corrected the error in the revised manuscript.
Comment 10: Results and discussion: c. Line 164. The electrochemical characterization of the modified electrodes must be performed with a redox probe known as [Fe(CN)6]3−/4−, and not with the electrode modifying agent. Too confusing.
Answer 10: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, If we are using non redox material (i.e., direct electron transfer material is essential to check the electrochemical characterization of the modified electrode with a redox probe known as [Fe(CN)6]3−/4−. But in our present studies, the Thionine (redox dye) itself acts as a redox mediator in the electrode surface, hence we have checked the effect of varying supporting electrolytes on the electrochemical performance of the modified electrode was evaluated as shown in Figure 5. Based on these studies, we conclude NH4NO3 is a suitable electrolyte for further electrochemical studies. There are some of the references were previously published in the literature.
Comment 11: Results and discussion: d. Figure 4. An abbreviation must be used on all modified electrodes indicating the graphite substrate.
Answer 11: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have abbreviated all the modified electrode in the revised manuscript as paraffin wax impregnated graphite electrode (PIGE).
Comment 12: Results and discussion: e. Line 191. “electrolytele”? Check.
Answer 12: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have corrected in the revised manuscript. We apologize for the error. Thank you for noticing.
Comment 13: Results and discussion: f. Lines 192-197. Provide a scientific chemistry discussion on the behavior of the modified electrode being superior in NH4NO3 supporting electrolyte.
Answer 13: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, the modified electrode exhibits a relatively better CV response in NH4NO3 compared to other electrolytes. The ammonium ions are favorable for proton transfer (redox reaction) of Thionine molecule in the electrode surface compare to other K+, Na+ or Ba2+ ions.
- Thenmozhi, S. Sriman Narayanan, Surface renewable sol–gel composite electrode
derived from 3-aminopropyl trimethoxy silane with covalently immobilized thionine,
Biosensors and Bioelectronics 23 (2007) 606-612.
- Electrochemical sensor for H2O2 based on thionin immobilized 3- minopropyltrimethoxy silane derived sol–gel thin film electrode, Sensors and Actuators B 125 (2007) 195-201.
Comment 14: Results and discussion: g. The pH study should be carried out with riboflavin, showing at which values there is no overlap with thionine.
Answer 14: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, in the pH study, the CV curves of thionine and riboflavin oxidation or reduction peak has no overlapping as shown in the Figure 1.
Figure 1. Effect of pH on the reduction o 1.6 x 10-5 M RF at TH coated CdSe QDs modified electrode
Comment 15: Results and discussion: h. The oxidation and reduction potentials of riboflavin should be presented and discussed. Is riboflavin a quasi-reversible or reversible system? A discussion is needed.
Answer 15: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have included the oxidation and reduction potentials of riboflavin. Riboflavin is a quasi-reversible system.
Comment 16: Results and discussion: i. “…in the presence of 1.6 × 10−5 M RF was investigated by CV at various pHs (4-9) in 0.1 M NH4NO3 and the current response was plotted against pH”. Voltammograms must be shown.
Answer 16: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have included in the revised manuscript.
Comment 17: Results and discussion: j. Figure 7B. Honestly, where did this calibration curve come from? Which parameters? Which technique? It makes no sense for a calibration curve to appear without being discussed.
Answer 17: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, Figure 7A shows the electrocatalytic reduction of RF in higher concentration using cyclic voltammetry. The corresponding calibration curve of electrocatalytic reduction of riboflavin by cyclic voltammetry was plotted. Now we have rewritten in the revised manuscript.
Comment 18: Results and discussion: k. NH4NO3 solution is not a buffer solution. How do the authors guarantee that by varying the pH values from 4-9 the same nature of the species will be maintained? In addition, a calibration curve must be performed in replicates.
Answer 18: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, the buffer solution is used for pH studies and included in the revised manuscript.
Comment 19: Results and discussion: l. The authors claim that they monitored the peak reduction of riboflavin, but nowhere in the text is the need for a nitrogen purge mentioned. Confused.
Answer 19: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have mentioned in the revised manuscript.
Comment 20: Results and discussion: m. What is catalytic current? The authors have no knowledge of Electroanalytical Chemistry. There is no electrocatalysis of riboflavin because there was no shift in riboflavin peak potentials with electrode modification.
Answer 20: We agree with the referee’s comment. Giving due respect to the reviewer comment, the current response for the reduction of RF at the bare electrode was poor and higher formal potential but the modified electrode showed a better and considerable increase in the current response at -0.52 V. The oxidation and reduction potentials of RF is -0.44 V and -0.52 V, respectively and showing quasi-reversible system.
Comment 21: Results and discussion: n. A Table with recent electrochemical sensors dedicated to the determination of riboflavin must be presented. Thus, the sensors and LODs obtained must be presented. Use the following references: Talanta, 258 (2023) 124409; Talanta, 252 (2023) 123836; Food Chemistry, 423 (2023) 136283; Sensors, 21 (2021) 1371; Microchemical Journal, 179 (2022) 107588; Journal of Electroanalytical Chemistry, 928 (2023) 117037.
Answer 21: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, the comparative table and respective references were included in the revised manuscript.
Comment 22: Results and discussion: o. Relative error values between the data obtained by the modified electrode and the product label must be presented.
Answer 22: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have added in the revised manuscript.
Comment 23: Results and discussion: p. The calibration curve for riboflavin must be done in replicates, and the error bars shown at each concentration point.
Answer 23: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, now we have added in the revised manuscript.
Comment 24: Results and discussion: q. Supporting electrolyte pH studies using a buffer solution should be performed for riboflavin.
Answer 24: We appreciate and comply with the referee’s comment. The buffer solution was used for pH studies and now included in the revised manuscript.
Comment 25: Results and discussion: r. Why was the amperometry technique selected?
Answer 25: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, the main idea is Riboflavin (biomolecules) determination in flow conditions. Hence, we choose amperometric technique was selected.
Comment 26: Results and discussion: Comments on the Quality of English Language
“electrolytele”? Check.
Answer 26: We appreciate and comply with the referee’s comment. Giving due respect to the reviewer comment, the entire manuscript was submitted for thoroughly language check and it is free of grammatical errors and well polished.
It is hereby requested that the Revised Manuscript should be considered for publication in Micro.
-AUTHORS
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The revised version is very good and can be published as it is
Reviewer 3 Report
The authors endeavored to answer the reviewer's questions, and the manuscript was improved. Therefore, I recommend that it be accepted for publication.
