Reply to the questions raised by the DAC member Dr. Aravind Raghavan

We would like to thank the DAC member for constructive comments raised regarding the research proposal. We have tried my best to answer the questions posed by the DAC member and the replies to the comments are appended below.

1) Does the proposed topic reflect the theme propounded in the proposal write up?

Comment: DAC member says NO because the relevance of superparamagnetism is not clear.

Reply: We agree to the fact that the superparamagnetism indicated in the title of the proposal is not explicitly justified in the text. In relevance to the proposal the phenomenon of superparamagnetism is a characteristic of magnetic nanoparticle and not a required condition to observe magneto-optical effects. However, the size requirement of magnetic nanoparticles mentioned in the proposal is justified by the following points: a) The observed data will not depend on the magnetic history of the sample and, b) the proposed investigations are an attempt to prepare magneto-plasmonic nanostructures for bio-sensing applications. In this regard we perceive the coating of gold and further binding of bio-molecules on these nanoparticles will be efficient. We have included the above points in the relevant section (introduction of the proposal). We will remove the word superparamagnetism from the title as the material being superparamagnetic is not an essential condition to observe the effects that is being investigated in the proposal.

2) Is the outcome of the work clearly visualized?

Comment: One of the outcomes of the proposal is patents. It cannot be visualized from the proposal.

Reply: We agree, it is not clear from the proposal. We anticipate that the magnetic-nanoparticles that will be investigated in this proposal could be potentially used for bio-sensing applications.The above mentioned outcome will be removed from the relevant portion of the proposal.

3) Are experimental facilities for research work envisaged clearly?

Comment: Partially yes. It is not clear how the size of core-shell nanoparticles and their shape is going to be determined.

Reply: The physical characterization techniques like XRD, TEM, and SAXS etc. will be used routinely for estimation of the size and shape of nanoparticles. The facilities are not available in the campus and therefore these measurements will be performed elsewhere on

payment/collaborative basis.The samples that will be investigated in the proposal are provided by Dr. Balaji Gopalan and his group from the Department of Chemistry.

4) Comment: The research area to which this proposal belongs is an important frontier. Raj Kumar et al. (Ref. 13) have found FR enhancement in gold coated Fe2O3 nanoparticles at 632 nm. In this context, why research is proposed to be done in Fe3O4 nanoparticles needs better justification. This is quite important for research publications to come out of this research.

Reply: This is a good question and also a valid concern! In fact we have started this project with the aim of optimizing the enhanced magneto-optical effects in ϒ-Fe2O3 nanoparticles, where these effects have been reported in the literature, and then investigate the possibilities of sensing bio-molecules by closely monitoring the changes in surface plasmon enhanced Faraday rotation as the bio-molecules gets attached to the ligands of the magnetic nanoparticles. However, out of curiosity we started investigations in gold coated Fe3O4 nanoparticles initially as no group has reported magneto-optical effects in these systems. Our preliminary investigations revealed two interesting observations in these systems, 1) the Faraday rotation in these nanoparticles are higher than that reported for ϒ-Fe2O3 nanoparticles and, 2) the Faraday rotation appears to be higher at lower magnetic field which is counter intuitive to the conventional understanding of this effect where the rotation is linearly proportional to the magnetic field. Furthermore, we also noticed that the technique used to measure Faraday rotation in the two earlier reports in these systems will not allow an opportunity to probe the effects at different magnetic fields. In our perception, this is an important parameter that needs to be varied to understand the origin of Faraday rotation in these nanostructures in detail. The above observations made us believe that thorough investigations of surface plasmon enhanced Faraday effects in gold coated Fe3O4 nanoparticles itself warrant a Ph.D thesis! Therefore, we have proposed these systems in the research proposal. However, as the DAC member rightly pointed out that this is a frontier area of research and therefore there is a possibility of other groups publishing this work earlier than the group at BITS is really a cause of worry. Therefore we thought that we may be on the safer side if we could also study the effect of the shape of nanoparticles on the enhanced Faraday effects. In this context we are also planning to investigate pyramidal shaped core-shell nanoparticles for enhanced Faraday effects. Before we conclude our reply we would like to point out that we are amused by the fact that the same group who carried out investigations in gold coated ϒ-Fe2O3 nanoparticles did not do so in gold coated Fe3O4 nanoparticles!We will include the above mentioned arguments in the section “Gaps in existing research”.

We hope we have answered the different concerns raised by the DAC member. Once again we thank the DAC member for critical insights and valuable suggestions. We would be happy to include any other valuable suggestions the DAC member may have on the proposal.