Excellent Antimicrobial, Antioxidant, and Catalytic Activities of Medicinal Plant Aqueous Leaf Extract Derived Silver Nanoparticles
Round 1
Reviewer 1 Report
This paper aimed to study the antimicrobial, antioxidant and catalytic activities of silver nanoparticles synthesized from the aqueous leaf extract of the plant Cascabela thevetia. While the green synthesis of nanoparticles (from the leaf extract of C.thevetia) and catalytic activity of this plant extract has been done before (information in literature), this study also showed the antibacterial, antifungal and antioxidant potential of the AgNPS.
In my opinion, it is a relevant and worthwhile study; and was well-carried out. The study design was appropriate. The authors have followed all scientific protocols well, however results for the positives controls are not stated but mentioned as a discussion point. It is important to include this data (i.e. the actual quantification of the growth inhibition by Ciprofloxacin especially) and then discuss it in comparison to the inhibition by the AgNPs.
Table 1 caption is The estimation of the zone of inhibition diameters formed by C-AgNPs against the seven 407 tested bacterial pathogens, but also contains data of the two fungi strains C.albicans and C.parapsilos... the caption must be changed accordingly.
There is also no mention of the positive control used in the antifungal study.
The positive control experiments should be on the same agar plate as the test substances; this does not seem to be the case - according to the pictures included, only the three replicates of the AgNP has been used in each plate. The positive control must be shown on the plate pictures, and the data included in the tables and discussion.
There is no actual "statistical analysis" done; just expressing the inhibition zones as mean +/- standard deviation.
The manuscript does require English editing for minor grammatical errors.
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Reviewer 2 Report
This paper deals with the "Excellent antimicrobial, antioxidant and catalytic activities of medicinal plant aqueous leaf extract derived silver nanoparticles".
This work is interesting and reported the silver nanoparticles which were synthesized by a green method using an aqueous extract of Cascabela thevetia leaves. The structures were investigated from morphologic, structural, optic and photocatalytic point of view. Also, the AgNPs were tested against seven bacterial strains and used to scavenge DPPH radical for antioxidant activity.
Based on the revision, I would like to rise few comments and recommendations:
- The authors should introduce the scales in the images of figure 4, thus, it is easier for the reader to estimate the size of the nanoparticles directly on picture. Figure 4e being useful only to see the dispersion of nanoparticle sizes.
- authors fails to address the exact reasons for enhanced the catalyst mechanism for C-AgNPs. The active species that degrade the dyes used should be specified.
- What was the pH value of the methylene blue and rhodamine B solution?
Thus, the manuscript cannot be accepted for publication in Processes, without elucidating all the above issues.
Author Response
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Reviewer 3 Report
The manuscript titled “Excellent antimicrobial, antioxidant and catalytic activities of medicinal plant aqueous leaf extract derived silver nanoparticles” describes fabrication, characterization and applications of biosynthesized AgNPs. It possesses some merits for applications. However, I worry about some characterization data of the synthesized AgNPs which could not support their conclusions. It should be just considered to publish in Processing when the problems are solved. The authors should follow the below comments:
1. Some previous studies have synthesized AgNPs from aqueous extract of Cascabela thevetia leaf. The authors should mention these references and show the novelty of this work.
2. The authors have mentioned in abstract “UV-Visible and FTIR analysis demonstrated the presence of flavonoids in aqueous extract and solution of C-AgNP”. However, this conclusion is unacceptable. The flavonoids need to be determined via more accurate data such as HPLC-MS. In UV-Vis spectra, peaks at 280 and 327 nm is only absorption of excitation region of π to n* or n to n*. It cannot conclude that the extract contains flavonoids.
3. Also, the authors should focus on the determination of the flavonoid structure (e.g. quercetin) in the extract used to describe the mechanism of Ag+ reduction. If the authors cannot find an exact flavonoid, please remove this mechanism.
4. The author concluded that the size of nanoparticles is in range of 20-30 nm. However, the size of nanoparticles cannot estimate from SEM images. They should use TEM images which can evaluate exactly size and shape of nanoparticles. Moreover, the Bar of SEM images should be provided in Figure 4.
5. The crystalline size of AgNPs should be calculated from XRD data.
6. Please check typos and English thoroughly.
Author Response
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Round 2
Reviewer 2 Report
The authors have improved the manuscript and therefore it can be accepted for publication in Processes. However, I would like that the magnification scale to appear in figure 5a as well, before publication.
Author Response
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Reviewer 3 Report
The reviewer recognizes the efforts for revision of the manuscript including HPLC data supplied and mechanism corrected. However, TEM images are refused. This data is particularly important to get accurate size of nanoparticles. The estimation of size used only SEM images possesses significant deviation. As we known, most applications of the nanomaterials are dependent on particle size. Thus when it is not identified accurately, all applications are meaningless. If the authors refuse to provide this data, I recommend that the manuscript should be rejected.
Author Response
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