Finite Element Models of Gold Nanoparticles and Their Suspensions for Photothermal Effect Calculation
, Javier Monreal-Trigo 1,2,3,4, Andy Hernández-Montoto 1,4,5,6, Francisco Javier Ibáñez-Civera 1,2,3, Rafael Masot-Peris 1,2,3,* and Ramón MartÃnez-Máñez 1,4,5,6
Round 1
Reviewer 1 Report
The comments on the Manuscript ID: bioengineering-2101479;
Title: Finite Element Models of gold nanoparticles and their
suspensions for photothermal effect calculation
Authors: Hannes Allmaier, David E. Sander, Sophia Bastidas
The paper describes the phenomenological modeling concerning the applicability of plasmonic nanoparticles in photothermal conversion. The report illustrates the validity of this data verified by photothermal experiments conducted on aqueous suspensions of diversely shaped gold nanoparticles. After amending several errors, the paper can be accepted by Bioengineering.
Those questions still allowing for a positive evaluation of the paper are:
• Introduction should be widened, considering other issues of photon-plasmon interaction as the authors' data is not just bio-targeted. I would also recommend at least a small comparative section with Au shortcomings and advantages over cheaper non-metalic plasmonic NPs: see some, e.g., reviews: (10.1002/aenm.202002402;10.1016/j.mtener.2020.100629;10.1039/d2mh00263a). Sections 1.2.1 and 1.2.2 contain well-known formulae and the iconic LSPR illustration. I have not found the appropriate citations there. Please amend. For such a long introductory part, it is still unclear if the stated size/shape control is the only way of LSPR tuning toward the desired wavelength.
• There are mistakes in eqs. (31) and (32). Why I0 and P0 are of the same dimension (W/m2)? Should not be ½ the last power in (32)? How can one exponent meters?
• In the experimental section, the focusing area of the laser beam must be discussed in addition to the power density. How many cells are covered by the spot (1, 2, more?) If the spot covers more than a single cell, is there energy interexchange between them? Fig. 9 is misleading. Are cell irritated from a side direction (for 96-cell well plates is almost impossible to reach the desired cell), or does the sketch illustrate the scattered radiation? The discussion of fig. 8 assumes that the illumination comes from the cell plates' top (surface). If so, amend fig. 9 accordingly. How was the temperature of the suspension then monitored?
• In-vitro requires cell/cell cultures experiments, which is not the case in the present study. Nanoparticle suspensions in water generally differ from those in RPMI or MEM as all the parameters (viscosity, heat, mass transfer coefficient, etc.) are altered. Avoid in-vitro formulation here.
• Scalebars in Fig. 10, 12, and 15 are unreadable.
• What is a.u. for the absorbance? Was it normalized?
• In the discussion section, please clarify whether the result described is of the individual or collective heating mechanism nature.
• Since many LSPR Au NPs photothermal reports exist, the conclusions must state the progress made in the field within the presented study.
Author Response
Please see the attachment
Author Response File: 
Author Response.docx
Reviewer 2 Report
In this work, the authors model the nanoparticle geometry in a finite element method model calculus environment for an optical electromagnetic field and a model of the experimental procedure for measuring the temperature of a suspension of the nanoparticle. This research is of great use in the modeling EM field. Overall, the article is well-written and helpful in modeling the problem of nanoparticle scattering. However, the necessary elucidation of the mechanism and references are absent in the manuscript to explain the obtained results. Therefore, in my opinion, a minor revision is needed to accommodate the high-quality requirements of this Journal.
1. For the reader to follow easily, please mention the version of COMSOL used in this work.
2. Lines 55-58 state, “the nanoparticle diameter and geometry can be adjusted to tune a resonance in the absorption spectrum to the desired wavelength, and thanks to this resonance, the absorption of light is greatly enhanced,” The relevant references (J. Phys. D: Appl. Phys., 2016, 49(47), 475102 and Opt. Commun., 2016, 370, 85–90) should be included in the references to support this statement.
3. The simulation time of the models, as shown in Fig. 4 and Fig. 6, should be described in the text.
4. The mechanism “red-shifting when making the aspect ratio larger.” should be clarified in more detail and include the related references (e.g., Applied Optics, 2009, 48(3), 617–622 and J. Appl. Phys., 2016, 120(9), 093110).
5. Please clarify in more detail the setting in COMSOL regarding the temperature evolution corresponding to Fig. 19.
6. Please briefly clarify the influence on absorption and scattering cross-sections if a substrate (e.g., SiO2) is included in your simulation model.
7. Typos, e.g., line 161, FEM is finite element method. Therefore, the “FEM method” should be “FEM.” In the same manner, please check the typos throughout the manuscript.
Author Response
Please see the attachment
Author Response File: Author Response.docx
Reviewer 3 Report
The authors simulated the nanorod/nanostar in a Finite Element Model calculus environment to calculate the effects that occur as a response to placing it an optical electromagnetic field, and also provided a model of the experimental procedure for measuring temperature rise while irradiating a suspension of nanoparticles.
In general, I think this work could be considered as a good tutorial for researchers who are interested in this area, but it doesn’t meet the criteria of a research article. Finite Element Method numerical models can be easily developed using COMSOL interface, andsimilar work has been done by different groups (e.g. https://doi.org/10.1007/s11051-016-3557-0, https://doi.org/10.3390/nano12101710), I, therefore, could not see the novelty of this work.
Author Response
Thank you for your review and for your observations. We believe that the paper provides a clear and detailed overview of the finite element method (FEM) and its application to the modeling and analysis of nanorods, nanostars, and a suspension of nanostars. While the use of the FEM for modeling and analyzing nanoparticles is not a novel concept in and of itself, we believe that our contribution lies in the development of the FEM for the suspension of nanostars. This model was developed using the data from the individual nanoparticle model and was able to accurately predict the temperature evolution when irradiated with an 808 nm laser, which was consistent with experimental data. The FEM calculations of absorbance and scattering cross-section, as well as electric field enhancement, for the individual nanoparticle models also showed good agreement with both experimental and bibliographic results. We believe that these original research contributions, combined with the clear and detailed presentation of the FEM approach and its application to the study of nanoparticles, meet the criteria for considering this work a research paper, which allows for a more comprehensive understanding of the behavior of nanostars in suspension and has important implications for photothermal therapy. We hope that this information helps to clarify the research contributions of our work and that the reviewers will be able to assess it in a different way. We have added a conclusions section to clearly state the advances to the reader.
Round 2
Reviewer 1 Report
The amended paper is now of acceptable quality.
Author Response
We want to thank you for your possitive assessment. The manuscript has been modified as requested by other reviewers, but your previous comments have been kept as far as possible.
