Microwave-Assisted Synthesis of Amikacin Modified N,S co-Doped Carbon Dots for Escherichia coli Detection

Round 1

Reviewer 1 Report

The work deals with the use of fluorescence emission of amikacin modified  N,S carbon dots (CDs) for the detection of Escherichia coli. Unfortunately, many basic concepts of fluorescence spectroscopy are ignored; the most representative points being:

For using fluorescence spectroscopy in any analytical quantitative determination, the emission spectra should be obtained from diluted solutions, with optical density at the excitation wavelength minor to 0.1; range for which a linear relationship between fluorescence intensity and concentration is maintained. In general, the fluorescence intensity depends on the lamp intensity, temperature, medium so, if a valid quantification is required, a standard (e.g. quinine sulphate) or (better) an integrating sphere must be used, rather than using only the intensity, the fluorescence quantum yield is absolutely necessary to be reported. Authors can revise: Principles of fluorescence spectroscopy, J.R. Lakowicz, 2^nd edition, Kluwer Academic/Plenum publishers (1999), New York. The previous requirements are not taken in account. In particular, in figures 1 and 5, where the absorption spectra are reported, the authors can observe that the absorption at 360 nm is higher than 0.1. Moreover, for a correct assessment of any fluorescence peak, at least the corresponding excitation spectrum should be recorded. So the interpretation of the shift in Figure 4 and 6 must be experimentally supported. If the authors observe the absorption spectra, it is clear that the spectra of Figure 1 with higher content of thiourea do not end at zero, i.e. they do not match the X axis at 500 nm. This means that these samples have large particles in suspension that generate scattering. Moreover, the emission peak is red shifting suggesting agglomeration.  Similar spectral features can be found in Figure 5 for larger amikacin content. For sure, light scattering measurements should be performed to confirm the real size of the particles, particularly after amikacin modification. I suggest the authors revise the paper: Phys. Chem. Chem. Phys. 2016, 18, 28274 as good example of photophysical study of carbon dots. Bacteria always give light scattering, so the fluorescence quenching can be simply due to this effect.

Further to all these issues related to fluorescence, there are also many other deficiencies in the scientific aspect of the work. It would take too much time for explaining each single point; I resume in the following the most important ones:

The discussion of the IR section is really difficult to be understood. I do not see that the vibrations of the precursors are maintained in the final modified CDs. Moreover, I suppose that the authors wanted to write that the vibration at 2060 appears and not disappears. Actually, I do not consider that this section really supports the modification of the carbon dots. I suggest to make XPS for an exact surface modification analysis, particularly as this indeed changes the optical properties of the CDs. More details of the chemical investigation of the modification with (first) thiourea and then amikacin should be performed. NMR and Maldi-TOF could help. A similar work has been recently published by the same group, but instead of amikacin, the authors used colistin sulfate (ORIENTAL JOURNAL OF CHEMISTRY 2019, Vol. 35, No.(1): Pg. 49-55). I realise that this work, it is not included as reference in the present manuscript. In general, I do not understand how amikacin could allow the selective detection of Escherichia coli as it is a wide broad spectral antibiotic. In Figure 7c, the authors compare the case of E.coli with S. aereus but it is not clear from the Figure legend, which spectrum is before or after the treatment with the CDs. There is no information about the bacteria preparation: strain, culture growth, and purification conditions. Finally but not less important, all of the Figures have really poor quality and the redaction presents many English errors (particularly in the verb conjugations) and conjunctive words are often missed. Revision of English grammar is required.

Author Response

Please see the attachment below for the Reviewer's comment.

Thank you

Author Response File: Author Response.docx

Reviewer 2 Report

1, The synthesis of doped CDs has been widely investigated in the past few years, the recent progress is suggested to be introducted, such as Nano-Micro Lett 2013, 5 (4), 247-259; J Mater Chem C 2014, 36(2), 7477-7481;Fullerenes, Nanotubes and Carbon Nanostructures 2017, 25 (12), 704-709.

2, HRTEM image and Raman spectrum are suggested to be provided, and related discussion should be given.

 

Author Response

Please see the attachment below for the Reviewer's comment.

Thank you

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript entitled “Microwave-Assisted Synthesis of Amikacin Modified N,S co-Doped Carbon Dots for Escherichia coli” is an interesting account of CDs having antibacterial property upon modifications. The manuscript is potentially interesting, and the materials are well characterized and concluded. My specific comments are pointed below,

 

In figure 1a the y axis seems not to be correct. Please put the right axis title and values.

 

For the synthesis scheme for the CDs it is difficult to follow in only writing. Please provide a table concerning all the synthetic parameters and variations for the readers to understand easily.

 

In contamination detection section kindly compare with state of the art materials and possibly a table comparing the same.

 

Author Response

Please see the attachment below for the Reviewer's comment.

Thank you

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

please check attached report.

Comments for author File: Comments.pdf

Author Response

Please see the attachment below. 

Thank you

Author Response File: Author Response.docx

Reviewer 2 Report

The author has revised the manuscript.

Author Response

Dear reviewer

 

Thank you.

Author Response File: Author Response.docx

Round 3

Reviewer 1 Report

Dear authors

I appreciate that you have considered all my queries; now that you explained the experimental procedure, I think that all the fluorescence results are quite acceptable (still is important to consider the 0,0 point in the response line as any calibration curve should pass though it). I hope that my comments could have improved your work and you can consider them for future research too.

I consider the present version of the paper adequate for publication.