A Multifunctional Magnetic Fluorescent Nanoprobe for Copper(II) Using ZnS-DL-Mercaptosuccinic Acid-Modified Fe3O4 Nanocomposites
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
Manuscript of Zeng and co-workers describes the synthesis of fluorescent nanoparticles for the detection and adsorption of copper (II) ion. Although the literature is full of copper sensors, the possibility to use magnetic nanoparticles is intriguing. In addition, manuscript is well written thus can be published after some important revisions:
· Literature needs to be improved, in particular the author should cite important reviews on the topic
· Scheme 1: it is not clear where is the sulphur atom
· Adsorption experiments: how final concentration of copper has been calculated? Following this procedure, adsorption process requires 12 hours, probably this time is too long to find an application. in addition, the comparison with the other works, reported in table 2, must include also the adsorption time
· Figure 1: resolution is poor, thus figure is not clear. In addition, please differentiate SEM by TEM images (up or down). In the caption, c is repeated two times
· TEM and SEM discussion: some comment on the dimensions and dispersion is required
· the uv spectrum of megnatic fluorescent nanoprobes is required
· section 3.2 and 3.3 can be merged
· how LOD was calculated? please, convert concentration limit allowed in drinkign water in molarity
· title of Table 1 is confused. In addition, why these few works have been selected for the comparison? Literature is almost full of copper(II) fluorescent sensors
· Section 3.4: "Specificity and anti-interference capability" are also called "Selectivity" selectivity seems to be good, but why these nanoprobes show this selectivity?
· the comparison of IR spectra before and after the addition of copper highlights some important differences, not only in the -COOH region! Spectra seem to be totally different, at 3500, but also in the regiorn 1000-1500 cm-1. This point needs to be addressed
Comments on the Quality of English Language
none
Author Response
1.Literature needs to be improved, in particular the author should cite important reviews on the topic
Answer: Thanks to the reviewers for their suggestions. The manuscript had been revised carefully and marked yellow in the manuscript.
2.Scheme 1: it is not clear where is the sulphur atom
Answer: Thanks to the reviewers for their suggestions. The ZnS is expressed as a whole, coated on the surface of Fe3O4 and bonded with the sulfhydryl group in the thiol reagent.
3.Adsorption experiments: how final concentration of copper has been calculated? Following this procedure, adsorption process requires 12 hours, probably this time is too long to find an application. in addition, the comparison with the other works, reported in table 2, must include also the adsorption time
Answer: Thanks to the reviewers for their suggestions. The removal and adoption capacity performance of Cu2+ testings were performed in a centrifuge tube, different concentrations of CuSO4 under Shake well on a shaker. The removal activities can be evaluated by the following equation: (1)
C1 is the final concentration of Cu2+, and C0 is the initial concentration of Cu2+ ions. The concentration of Cu2+ ions was analyzed by AAS. The adsorption amount of Cu2+ (Q mg/g) can be calculated according to the following equation:
(2)
Qe is the adsorption capacity (mg·g-1), C0 and Ce are the initial and equilibrium concentrations of Cu2+ (mg·L-1), respectively. V is the volume of the metal ion solution (L), and m is the Fe3O4@ZnS-COOH mass (g)
This probe is mainly for detecting metal ions, and the adsorption time is not the main research content. This probe detected metal ions This probe showed a very fast response time to metal ions, which is also an advantage of this probe.
4.Figure 1: resolution is poor, thus figure is not clear. In addition, please differentiate SEM by TEM images (up or down). In the caption, c is repeated two times
Answer: Thanks to the reviewers for their suggestions. The manuscript had been revised carefully and marked yellow in the manuscript.
The morphologies of Fe3O4, Fe3O4@ZnS and Fe3O4@ZnS@DL-Mercaptosuccinic acid were analyzed by SEM(first line) and TEM(second line).
5.TEM and SEM discussion: some comment on the dimensions and dispersion is required
Answer: Thanks to the reviewers for their suggestions. The manuscript had been revised carefully and marked yellow in the manuscript.
The commericial Fe3O4 with a diameter distribution from 150 to 250 nm, which reveal that Fe3O4 MNPs have a regular and uniform distribution. The particle diameter of the three samples increased accompanied by more rougher surfaces and more irregular fine particles. In addition, TEM image (Figure 1c second line) of Fe3O4@ZnS-COOH with a diameter distribution from 200 to 300 nm were achieved.
6.the uv spectrum of megnatic fluorescent nanoprobes is required
Answer: Thanks to the reviewers for their suggestions. The application of fluorescence data can detect the presence of hypochlorous acid more intuitively. Compared with UV-visible absorption spectrum, the fluorescence data can give a more obvious reaction at a lower detection concentration. UV-visible absorption spectrum often fails to show obvious changes under low concentration conditions, and higher concentration may be required to observe obvious titration reactions, which is not ideal for some applications that require detection in a low concentration range. Therefore, we use fluorescence detection methods to provide more intuitive and accurate results.
7.section 3.2 and 3.3 can be merged
Answer: Thanks to the reviewers for their suggestions. The manuscript had been revised carefully and marked yellow in the manuscript.
8.how LOD was calculated? please, convert concentration limit allowed in drinking water in molarity
Answer: Thanks to the reviewers for their suggestions. LOD=3δ /k, δ is standard deviation and k is the slope of the standard curve.
9.title of Table 1 is confused. In addition, why these few works have been selected for the comparison? Literature is almost full of copper(II) fluorescent sensors
Answer: Thanks to the reviewers for their suggestions. The work of this paper also belongs to the category of fluorescent probes. Compared with other similar probes, the improvement of this probe is highlighted.
10.Section 3.4: "Specificity and anti-interference capability" are also called "Selectivity" selectivity seems to be good, but why these nanoprobes show this selectivity?
Answer: Thanks to the reviewers for their suggestions. The probe is designed for the detection of Cu2+, so it has specific selection for Cu2+.
11.the comparison of IR spectra before and after the addition of copper highlights some important differences, not only in the -COOH region! Spectra seem to be totally different, at 3500, but also in the regiorn 1000-1500 cm-1. This point needs to be addressed
Answer: Thanks to the reviewers for their suggestions. The manuscript had been revised carefully and marked yellow in the manuscript.
The reason for the change of the infrared absorption peak of the carboxyl group may be that the oxygen atoms in the carboxyl group cooperate with Cu2+ to form a synergistic complex. The oxygen atom of the carboxyl group is negatively charged, indicating that the -COOH group can adsorb Cu2+ through electrostatic interaction. It can be seen that it is speculated that the oxygen atom of the -COOH group provides electrons to Cu2+, resulting in charge transfer, resulting in changes in the infrared spectrum.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments and Suggestions for Authors
Submitted manuscript is devoted to the development of a multifunctional magnetic fluorescent -nanoprobe for Cu(II) using acid modified FeOx composites. The goal is interesting and has practical importance. However? The scientific and technical quality of the manuscript must be significantly improved prior to possible publication.
The main problem is that the initial state of the particles is not really defined. Authors call them Fe3O4 but it is not justified with evidence. It is well known that XRD studies are not sufficient in order to make conclusions about γ- Fe2O3 or Fe3O4 cases, chemical titration is necessary (I. V. Beketov, et al. Iron oxide nanoparticles fabricated by electric explosion of wire: Focus on magnetic nanofluids, AIP Adv., vol. 2, no. 2, pp. 022154-1–022154-18, 2012). Authors do not provide data for lattice parameters and give no data about the crystallite size defined by XRD from the profile adjusting or simply the width of peak estimation. This parameter must be compared with corresponding data obtained from TEM statistics and calculations. Obtained parameter is critically important for the estimation of the results of magnetic measurements as the saturation magnetization of the fine particles depends on the size and state of the surface (O’Handley, R. C. Modern Magnetic Materials: Principles and Application; Wiley: New York, 2000; p 570). In addition, it is impossible to measure powders with such an accuracy as 16.25 emu/g (16.3 ± 0.1 at most).
The same comes from provided XPS data. For Fe2p or Fe2p3/2 the position of the binding peaks are 710.9 and 709.6 (eV) – from the presented data one cannot make proper conclusion (Moulder, J. F.; Stickle, W. F.; Sobol, P. E.; Bomben, K. D. Handbook of X-ray Photoelectron Spectroscopy (XPS); Chastain, J., King, R. C., Jr., Eds.; Physical Electronics Division ULVAC-PHI, Inc.: Chigasaki Japan, 1995; p 261 or Kim, K. J.; Moon, D. W.; Park, C. J.; Simons, D.; Gillen, G.; Jin, H.; Kang, H. J. Quantitative Surface Analysis of FeNi Alloy Films by XPS, AES and SIMS. Surf. Interface Anal. 2007, 39, 665−673.).
Figures are very bad technical quality, they are unreadable. For example, the scales for Figure 1a, b, c are impossible to define. The photographs themselves are distorted being enlarged in vertical direction. Figure captions should be carefully rewritten. For instance, Figure 2 contains 2 curves but the second one is not identified by any way.
The goal of the work cannot be formulated as description of the research task and Scheme for fabrication should be given before it.
English requires careful correction – “These three magnetic nanoparticles were estimated” – it should be three batches or types, etc.
There are to many lost intervals over the text.
Comments on the Quality of English Language
English requires careful correction – “These three magnetic nanoparticles were estimated” – it should be three batches or types, etc.
Author Response
1.The main problem is that the initial state of the particles is not really defined. Authors call them Fe3O4 but it is not justified with evidence. It is well known that XRD studies are not sufficient in order to make conclusions about γ- Fe2O3 or Fe3O4 cases, chemical titration is necessary (I. V. Beketov, et al. Iron oxide nanoparticles fabricated by electric explosion of wire: Focus on magnetic nanofluids, AIP Adv., vol. 2, no. 2, pp. 022154-1–022154-18, 2012). Authors do not provide data for lattice parameters and give no data about the crystallite size defined by XRD from the profile adjusting or simply the width of peak estimation. This parameter must be compared with corresponding data obtained from TEM statistics and calculations. Obtained parameter is critically important for the estimation of the results of magnetic measurements as the saturation magnetization of the fine particles depends on the size and state of the surface (O’Handley, R. C. Modern Magnetic Materials: Principles and Application; Wiley: New York, 2000; p 570). In addition, it is impossible to measure powders with such an accuracy as 16.25 emu/g (16.3±0.1 at most).
Answer: Thanks to the reviewers for their suggestions. The manuscript had been revised carefully and marked yellow in the manuscript.
(1) Comparing Fe3O4 with XRD card, it is in line with the Fe3O4 crystal form.
(2) The saturation magnetization of samples had been corrected in the manuscript (With the external applied magnetic field changed from -20 kOe to 20 kOe, the satura-tion magnetization of samples decreased from 64.5±0.1 emu/g to 34.7±0.1 emu/g and 16.3±0.1 emu/g along with the core-shell structure thickens gradually.)
2.The same comes from provided XPS data. For Fe2p or Fe2p3/2 the position of the binding peaks are 710.9 and 709.6 (eV) – from the presented data one cannot make proper conclusion (Moulder, J. F.; Stickle, W. F.; Sobol, P. E.; Bomben, K. D. Handbook of X-ray Photoelectron Spectroscopy (XPS); Chastain, J., King, R. C., Jr., Eds.; Physical Electronics Division ULVAC-PHI, Inc.: Chigasaki Japan, 1995; p 261 or Kim, K. J.; Moon, D. W.; Park, C. J.; Simons, D.; Gillen, G.; Jin, H.; Kang, H. J. Quantitative Surface Analysis of FeNi Alloy Films by XPS, AES and SIMS. Surf. Interface Anal. 2007, 39, 665−673.).
Answer: Thanks to the reviewers for their suggestions and the references had been cited in the manuscript.
High-resolution XPS is shown below. The elemental composition of the Fe3O4@ZnS-COOH nanoparticle was explored by XPS analysis (Figure a), The five peaks at 1020.2 eV, 710.8 eV, 530.6 eV, 286.6 eV, and 160.2 eV are composed of Zn 2p, Fe 2p, O 1s, C 1s, and S 2p, respectively, confirming the successful synthesis of Fe3O4@ZnS-COOH nanoparticles. Figure b shows that the binding energies of Fe3+ 2p3/2 and Fe3+ 2p1/2 are 710.2 and 724.8 eV, respectively, and the bimodal fitting of Fe 2p can obtain the binding energies of Fe2+ 2p3/2 and Fe2+ 2p1/2 at 709.7 and 722.6 eV, respectively. The results indicate that Fe3O4 exists in the nanoparticle. According to Figure c, the difference in binding energy between Zn 2p3/2 and Zn 2p1/2 is 22.5 eV, indicating that metallic Zn supported by the MFNPs mainly exists in the Zn2+ valence state. Peaks at 158.9 eV and 161.0 eV (Figure d) are attributed to metal sulfides S2- (2p3/2 and S 2p1/2) from ZnS, respectively.
3.Figures are very bad technical quality, they are unreadable. For example, the scales for Figure 1a, b, c are impossible to define. The photographs themselves are distorted being enlarged in vertical direction. Figure captions should be carefully rewritten. For instance, Figure 2 contains 2 curves but the second one is not identified by any way.
Answer: Thanks to the reviewers for their suggestions. The manuscript had been revised carefully and marked yellow in the manuscript. The fluorescence spectra of the magnetic fluorescent nanoprobe (0.2 mg/mL) before and after the addition of Cu2+ (400 μM ).
4.The goal of the work cannot be formulated as description of the research task and Scheme for fabrication should be given before it.
Answer: Thanks to the reviewers for their suggestions. The goal of the work is to designe and synthesize a magnetic fluorescent nanoprobe for the detection of metal ions. The preparation scheme of Fe3O4@ZnS-COOH had been given in Schem 1.
5.English requires careful correction – “These three magnetic nanoparticles were estimated” – it should be three batches or types, etc. There are too many lost intervals over the text.
Answer: Thanks to the reviewers for their suggestions. The manuscript had been revised carefully and marked yellow in the manuscript.
Round 2
Reviewer 1 Report
Comments and Suggestions for Authors
manuscript has been revised in some points raised during the first round, but some important points have not been addressed.
In particular, Literature needs to be strongly revised. There are a huge number of fluorescent Cu2+ sensors (please see Coord. Chem. Rev. 2016, 311, 125-167; Chem. Soc. Rev. 2015, 44, 4400-4414), and table 2 shows a comparison with only 5 papers.
UV spectrum of nanoparticles: I asked a simple UV spectrum of nanoparticles, not the titration
Selectivity for Copper2+: a clear explanation of the selectivity has not been provided. The answer provided by the authors “The probe is designed for the detection of Cu2+, so it has specific selection for Cu2+” is scientifically not significant.
Comments on the Quality of English Language
none
Author Response
(1)In particular, Literature needs to be strongly revised. There are a huge number of fluorescent Cu2+ sensors (please see Coord. Chem. Rev. 2016, 311, 125-167; Chem. Soc. Rev. 2015, 44, 4400-4414), and table 2 shows a comparison with only 5 papers.
Answer: All of the probes in the literature provided by the reviewers are organic fluorescent compounds. Most of these fluorescent probes can not be separated from the detection system, which introduce the further pollution to the environment.
(2)UV spectrum of nanoparticles: I asked a simple UV spectrum of nanoparticles, not the titration.
Answer: The UV spectrum of the nanoparticles had been added
Fig. The UV spectrum of the nanoparticles(Fe3O4@ZnS-COOH).
- Specificity and anti-interference capability" are also called "Selectivity" selectivity seems to be good, but why these nanoprobes show this selectivity?Selectivity for Copper2+: a clear explanation of the selectivity has not been provided. The answer provided by the authors “The probe is designed for the detection of Cu2+, so it has specific selection for Cu2+” is scientifically not significant.
Answer:The Cu2+ binding mechanism was schematically illustrated in Scheme 2. The analysis of functional groups and morphological features were examined using SEM, FTIR and XPS spectra to confirm how Cu2+ ions were detected by the magnetic fluorescent nanoprobe. The reason for the change of the infrared absorption peak of the carboxyl group may be that the oxygen atoms in the carboxyl group cooperate with Cu2+ to form a synergistic complex. The oxygen atom of the carboxyl group is negatively charged, indicating that the -COOH group can adsorb Cu2+ through electrostatic interaction. It is speculated that the oxygen atom of the -COOH group provides electrons to Cu2+, resulting in charge transfer, resulting in changes in the infrared spectrum.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors
Authors must carefully answer all asked questions.
The main problem is that the initial state of the particles is not really defined. Authors call them Fe3O4 but it is not justified with evidence. It is well known that XRD studies are not sufficient in order to make conclusions about γ- Fe2O3 or Fe3O4 cases, chemical titration is necessary (I. V. Beketov, et al. Iron oxide nanoparticles fabricated by electric explosion of wire: Focus on magnetic nanofluids, AIP Adv., vol. 2, no. 2, pp. 022154-1–022154-18, 2012). Authors do not provide data for lattice parameters and give no data about the crystallite size defined by XRD from the profile adjusting or simply the width of peak estimation. This parameter must be compared with corresponding data obtained from TEM statistics and calculations. Obtained parameter is critically important for the estimation of the results of magnetic measurements as the saturation magnetization of the fine particles depends on the size and state of the surface.
Figures are very bad technical quality, they are unreadable. For example, the scales for Figure 1a, b, c are impossible to define. The photographs themselves are distorted being enlarged in vertical direction. Figure captions should be carefully rewritten. For instance, Figure 2 contains 2 curves but the second one is not identified by any way.
The goal of the work cannot be formulated as description of the research task.
Futhors must provide careful characterization of the initial state and reconsider their way of the revision.
Comments on the Quality of English Language
Still is not fine.
Author Response
(1)Their material is poorly characterized from the point of view of the phase composition, average size of the particles, and particle size distribution. Magnetic analysis of ZFC-FC curves and correspondence of the magnetization value to the obtained average size. XRD is not sufficient for making the difference between gamma-F2O3 and Fe3O4.
Answer: Many thanks to the reviewers for their advice. Based on the references provided by the reviewers, we checked the XRD data carefully. And the XRD data that matched the green line in Figure 4 proved that the synthesized material is indeed magnetic materials. In addition, the key point of this manuscript is to use the unique magnetism of magnetic materials to synthesize a magnetic nano-fluorescent probes for the detection and quantification of heavy metal ions. The purpose is to establish a multi-functional fluorescence probe with enrichment, separation and detection function, rather than focusing on the structural composition of magnetic materials, so no lattice parameters are provided.We had cited the references as (26).
(2)Figures are very bad technical quality, they are urreadable. For example, the scales for Figure 1a, b,c are impossible to define. The photographs themselves are distorted being enlarged in vertical direction.Fiqure captions should be carefully rewritten.For instance,Fiqure 2 contains 2 curves but thesecond one is not identified by any way.
The goal of the work cannot be formulated as description of the research task.
Answer: The figures had been corrected.
(3)In addition, the goal of the study is not a description of technological steps or employed techniques (it is not a technical report). The goal must describe the scientific problem itself and the way of solving it in a systematic scientific way."
Answer: The goal had been revised and yellow marked in the manuscript.(Considering that most fluorescent probes will bring secondary pollution to the environment when recognizing copper, we applied Fe3O4 as the core structure of the probe for the magnetic separation property and ZnS as the shell structure of the probe, and then a fluorescence probe with multiple functions of enrichment, separation and detection was designed to solve the problem. (Scheme 1).)(The magnetic fluorescent nanoprobe could enrich, detect and separate the heavy metal ions at the same time, and reduce the secondary pollution caused by the probe with an environmentally friendly way and high selectivity.)
