THE EDITORIAL OFFICE Dated 23-05-2020

PLOS ONE

Corrections in the manuscript entitled “Facile, one-pot biosynthesis and characterization of iron, copper and silver nanoparticles using Syzygium cumini leaf extract: As an effective antimicrobial and aflatoxin B1 adsorption agents (Ms. Ref. No.: PONE-D-20-11741)”

Dear Editor,

First of all, authors are thankful to you for your useful comments and suggestions about our manuscript. The authors have modified the manuscript accordingly and the detailed corrections are listed below point by point. All the changes in manuscript are highlighted using Track Changes.

Response to Editor comments:

Manuscript has been formatted according to the attached guidelines.

Response to Reviewer comments:

Reviewer # 1:

Minor

1. Line number 47 and 55 – they should add “and”.

Response to Reviewer comment no. 1: The word has been added “and” in both lines as mentioned below.

Abstract

The present findings suggests that the green synthesis of metal NPs is a simple, sustainable, non-toxic, economical and energy-effective as compared to the others conventional approaches.

1. Introduction

Apart from recent advancement, pathogenic mould contamination associated in food and feed products are still major threat world-wide.

2. Line number 61 – “Although about 20 AFs have been discovered”; it looks incomplete.

Response to Reviewer comment no. 2: The sentence has been rephrased as mentioned below.

1. Introduction

To date, at least 20 different types of AFs such as aflatoxin B1, B2, G1 and G2 have been identified.

3. Line number 79 – reference format

Response to Reviewer comment no. 3: Correction has been made as per reviewer’s recommendation in text of manuscript as mentioned below.

1. Introduction

Currently, nanotechnology is emerging field with its applications in science and technology. Nanoparticles (NPs) are using in some cosmetics, sunscreens, toothpaste, pharmaceutical and even food products (9).

4. The editor could ask for better resolution or contrast of images. If possible they could add statistical particle distribution of metal – nanoparticles.

Response to Reviewer comment no. 4: The resolution or contrast of each image has been improved. However, in the present study, the SEM and TEM analysis was used to evaluate the particle size distribution. TEM is a direct counting method, which measures a size value for each particle selected for the analysis, thus providing a number-based particle size distribution. The statistical particles distribution in terms of range and mean has been incorporated in Table 1.

5. In FTIR study – they should provide reference for Fe – O stretching.

Response to Reviewer comment no. 5: The missing reference has been added as mentioned below.

5. References

Sun X, Zheng C, Zhang F, Yang Y, Wu G, Yu A, Guan N. Size-controlled synthesis of magnetite (Fe3O4) nanoparticles coated with glucose and gluconic acid from a single Fe (III) precursor by a sucrose bifunctional hydrothermal method. The Journal of Physical Chemistry C. 2009 Sep 10;113(36):16002-8.

6. UV – Visible study should be discussed in details and should provide appropriate reference for absorption peak as it is a signature peak for metal nanoparticles.

Response to Reviewer comment no. 6: The UV-Visible study has been discussed in detail with appropriate references as mentioned below.

The optical property of synthesized Fe-, Cu- and Ag-NPs was assessed by the evaluation of UV-Vis spectra. Before the mixing of FeCl3, CuSO4 or AgNO3 solutions, the mustard or yellow colour of each plant extract don’t produces spectral features in UV/Vis range due to unavailability of surface plasmon resonance (SPR). However, on the addition of precursor solutions an increase in the absorbance arisen that maybe indicated the onset of particle formation. UV-Vis spectrum of Fe-NPs revealed characteristic SPR absorption peak at 262 nm (Fig. 5a) and agreement with the previous study (21). UV/Vis spectrum of Cu-NPs presented maximum SPR absorption peak at 572 nm (Fig. 5b). The strong SPR absorption band might be due to the SPR band of Cu colloids and the formation of NPs (22). UV/Vis spectrum of Ag-NPs showed characteristic SPR absorption peak at 426 nm (Fig. 5c), as compare with the previous study (23). The increases in SPR absorption peak with respect to time indicating polydispersity nature of the Ag-NPs (24). Only one sharp peak appeared in all spectrums, can be attributed to the NPs absorption and validates the NPs formation only. This phenomena was occurred due to the SPR absorption and confirms that the protein of plant leaves act as a template and stabilizing agent during the synthesis of NPs. SPR is an important optical biosensing tool that occurs due to the combined vibration of electrons of metal NPs in resonance with the light wave.

7. Please provide supporting reference for section 3.4.4 (Effect of contact time) and 3.4.5 (Effect of incubation temperature).

Response to Reviewer comment no. 7: References have been provided for both sections as mentioned below.

5. References

Shar ZH, Fletcher MT, Sumbal GA, Sherazi STH, Giles C, Bhanger MI, et al. Banana peel: an effective biosorbent for aflatoxins Part A Chemistry, analysis, control, exposure & risk assessment. 2016.

Asghar MA, Zahir E, Shahid SM, Khan MN, Asghar MA, Iqbal J, et al. Iron, copper and silver nanoparticles: Green synthesis using green and black tea leaves extracts and evaluation of antibacterial, antifungal and aflatoxin B1 adsorption activity. LWT. 2018;90:98-107.

Zahoor M, Khan FA. Adsorption of aflatoxin B1 on magnetic carbon nanocomposites prepared from bagasse. Arabian Journal of Chemistry. 2018;11(5):729-38.

8. Reference for “the calculation of three isotherm models such as Langmuir, Freundlich and Dubinin–Radushkevich (D-R)”.

Response to Reviewer comment no. 8: References for the calculation of three isotherm models such as Langmuir, Freundlich and Dubinin–Radushkevich (D-R) have been provided as mentioned below.

5. References

Langmuir I. The constitution and fundamental properties of solids and liquids. Part I. Solids. Journal of the American chemical society. 1916;38(11):2221-95.

Freundlich H. Over the adsorption in solution. J Phys Chem. 1906;57(385471):1100-7.

Dubinin M. The potential theory of adsorption of gases and vapors for adsorbents with energetically nonuniform surfaces. Chemical Reviews. 1960;60(2):235-41.

9. More analysis and supporting reference needed for section 3.7 kinetic study.

Response to Reviewer comment no. 9: The detail for the kinetic study has been provided with appropriate references.

3.7. Kinetic study

Furthermore, the electrostatic interface among NPs and AFB1 could also be deliberated in the adsorption manner. The chemisorption is recognized as the rate limiting step and attributed the very fast kinetics to adsorbate being adsorbed onto the adsorbent surface (38). The initial adsorption rate (h) values were found higher due to more mass transfer action from higher initial concentrations. However, the adsorption rate (k2) values designates that the higher AFB1concentration should have caused in more driving forces and quicker rates for AFB1. As a result, the structural arrangement of active sites or functional groups available on the NPs surface was more promising for the binding of AFB1 (13).

10. Kinetic study and thermodynamic parameters needs more explanation.

Response to Reviewer comment no. 10: The more explanation for the kinetic study and thermodynamic parameters has been provided as per reviewer recommendation as mentioned below.

3.7. Kinetic study

In order to examine the rate of sorption process of NPs with AFB1, pseudo-first and pseudo-second order kinetics models were applied. The selection of model existed on the values of experimental and theoretical Qe and R2. The kinetic parameters and R2 values are accessible in Table 5. The sorption data were well verifying the condition by the pseudo-second order kinetics model. The experimental and theoretical values of Qe were agreed to each with the linear plot (R2 close to 1). The data suggested that the environment of the process was a chemical monitoring procedure. Furthermore, the electrostatic interface among NPs and AFB1 could also be deliberated in the adsorption manner. The chemisorption is recognized as the rate limiting step and attributed the very fast kinetics to adsorbate being adsorbed onto the adsorbent surface (38). The initial adsorption rate (h) values were found higher due to more mass transfer action from higher initial concentrations. However, the adsorption rate (k2) values designates that the higher AFB1concentration should have caused in more driving forces and quicker rates for AFB1. As a result, the structural arrangement of active sites or functional groups available on the NPs surface was more promising for the binding of AFB1 (13).

3.8. Thermodynamic parameters

The thermodynamic parameters such as Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) of the AFB1 adsorption with NPs were determined using Van’t Hoff equation at different temperatures (39). The obtained parameters are showing in Table 6. The ΔG° values of process were calculated negative for each tested temperatures, specified that the process was feasible, spontaneous and endothermic. Additionally, as the temperature rises the ΔG° values improved, proposing that the sorption may be more feasible at greater temperature. A similar pattern for the adsorption of AFB1 using grape pomace, banana peel and magnetic carbon nanocomposites obtained from bagasse have been studied and indicates that the adsorption process occurs spontaneously at a higher temperature (33, 40, 41). The positive values of ΔH° showing the endothermic nature of adsorption process and improved the randomness of the solid-solution. The amount of the ΔH° values also offers indication of the environment of the adsorption, values < 20 kj mol-1 reflected indicative of physiosorption rather than chemisorptions. The ΔH° values determined for AFB1 on NPs ranged from 5.66 to 7.42 kj mol-1 suggesting physiosorption process and confirms the endothermic process. Whereas, the ΔS° values were also positive and higher for each NPs, which surmise that the adsorption process was favourable in terms of entropy. The ΔS° values also designated the increased randomness at the adsorbent/solution interface during the adsorption process (42).

11. For supporting document the editor can ask for procedure to estimate parameters in Table – 4 , Table – 5 and Table – 6.

Response to Reviewer comment no. 11: The parameters in Table 4, 5 and 6 shows the adsorption, isotherm, kinetic and thermodynamic study, respectively. All parameters of each study were calculated according to the related equations. All the calculations are based on the previous reported procedures. The references have been provided for procedure to estimate parameters in each table. Furthermore, the authors can provide the calculations for each parameter on the request of reader.

12. Figure captions need to be modified

a. For example Figure I - SEM images of metal nanoparticles (a) iron (b) copper (c) and silver nanoparticles

- (c) should be after ‘and’ (do in all captions)

Response to Reviewer comment no. 12: All figures captions have been modified as per reviewer’s recommendation.

13. Please provide better quality of TEM images (with proper brightness and contrast ration)

Response to Reviewer comment no. 13: The quality of TEM images have been improved as per reviewer’s recommendation.

Reviewer # 2:

The authors presented Facile, one-pot biosynthesis and characterization of iron, copper and silver nanoparticles using Syzygium cumini leaf extract: As an effective antimicrobial and aflatoxin B1 adsorption agents.

The work is okay with minor correction as stated below. The work can be accepted after the minor corrections.

The authors grateful thanks to the reviewer’s for the above mentioned comments. However, minor comments as per reviewer recommendation das been incorporated in the manuscript.

1. Section 2.1, line 1

About 10 g of chopped leaves were accurately weighed and boiled in the presence of 100 mL of

Section 2.3.1, line 2

….a concentration between of 1‒512 µg mL-1 was prepared in 10 mL of 0.8% (w v-1) nutrient broth 133

Response to Reviewer comment no. 1: Corrections have been made in both sentences as mentioned below.

2. Experimental

2.1. Synthesis of metal nanoparticles

Ten grams chopped leaves were accurately weighed and boiled in the presence of 100 mL DI-H2O for 20 min at 80oC, cooled at room environment and filtered using Whatman filter paper no. 1.

2.3.1. Minimum inhibitory concentration (MIC)

Dilution broth method was utilized to evaluate the MIC for each metal NPs. In brief, each NPs in a concentration between 1‒512 µg mL-1 was prepared in 10 mL 0.8% (w v-1) nutri¬ent broth medium separately and sterilized for 15 min at 121oC using Rexall autoclave (Kaohsiung, Taiwan).

2. Section 2.5, line 1&2

The adsorption of aflatoxin B1 (AFB1) with NPs with studied as a were studied following the previously defined method with some modifications (15).

Response to Reviewer comment no. 2: Corrections have been made in the sentence as mentioned below.

2.5. Adsorption of aflatoxin B1

The adsorption of aflatoxin B1 (AFB1) with each NPs was studied according to the previously defined method with some modifications (15).

3. After equation one

Where, where

Response to Reviewer comment no. 3: Correction has been done in both equations 1 and 2.

4. Section 3.1 Line 9&10

The volume of the leaf extracts directly influences on the size of the NPs

Response to Reviewer comment no. 4: Correction has been made as mentioned below.

3.1. Formation and characterization of metal nanoparticles

Consequently, the volume of leaves extract directly effects on the morphology, size and production of NPs.

5. Section 3.1 Paragraph 7 line 3-5

It was occur caused by surface plasmon resonance (SPR) and verifying that the available leaves protein plays a significant role as a template as well as preservative during synthesis route. (This sentence is ambiguous kindly re-cast)

Response to Reviewer comment no. 5: The sentence has been revised as mentioned below.

3.1. Formation and characterization of metal nanoparticles

This phenomena was occurred due to the SPR absorption and confirms that the protein of plant leaves act as a template and stabilizing agent during the synthesis of NPs.

6. Conclusion, line 2&3

Ag-NPs the promising potential to reveal the excellent antibacterial and antifungal effect

and inhibit the AFs production. (This sentence is ambiguous kindly re-cast)

Response to Reviewer comment no. 6: The sentence has been revised in conclusion of manuscript as mentioned below.

4. Conclusion

Ag-NPs displays the more significant antimicrobial activity and reduced the production of AFs contamination as compare to Cu- and Fe-NPs.

7. Conclusion, line 3

In addition, Fe-NPs showed the higher highest adsorption capacity with

Response to Reviewer comment no. 7: Correction has been made as mentioned below.

4. Conclusion

In addition, Fe-NPs showed the higher adsorption capacity with AFB1 in contrast to Cu- and Ag-NPs.

8. Acknowledgement

The authors thankfully are thankful to the Feed and Feed Safety Laboratory, FMRRC, PCSIR Laboratories

Response to Reviewer comment no. 8: Correction has been made as mentioned below.

Acknowledgement

The authors gratefully thanks to the Feed and Feed Safety Laboratory, FMRRC, PCSIR Laboratories Complex, Karachi-Pakistan for the supporting of current research work.

9. The introduction lack current citation. The suggested articles below should be added to the introduction

1. Materials Chemistry and Physics 237:121859 https://doi.org/10.1016/j.matchemphys.2019.121859

2. Polym Res (2019) 26: 225. https://doi.org/10.1007/s10965-019-1897-z

3. Journal of Photochemistry and Photobiology B: Biology Volume 199, October 2019, 111601 https://doi.org/10.1016/j.jphotobiol.2019.111601

4. Appl Nanosci (2019). https://doi.org/10.1007/s13204-019-01099-x

5. Surfaces and Interfaces Volume 17, December 2019, 100359

https://doi.org/10.1016/j.surfin.2019.100359

6. European Polymer Journal 2020, 122:109371. https://doi.org/10.1016/j.eurpolymj.2019.109371

7. Applied Physics A 2020, 126:72. https://doi.org/10.1007/s00339-019-3249-6

8. Surfaces and Interfaces, 18, 100419. https://doi.org/10.1016/j.surfin.2019.100419

9. General English and grammar correction should be done, few has been suggested above

Response to Reviewer comment no. 9: All the above mentioned articles have been cited as per reviewer’s recommendation. Furthermore, the general English and grammar corrections have been also done.

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