Application of a Terahertz System Combined with an X-Shaped Metamaterial Microfluidic Cartridge
Round 1
Reviewer 1 Report
This manuscript introduced a x-shaped metamaterial microfluidic channel device for chemical and bio-sample sensing and detection. Overall, the manuscript is well written in terms of the English especially the introduction part, and the pictures. However, as a scientific paper the manuscript has lots of space to be improved regarding the depth of result analysis and data processing.
In the section of 2.1 – Design of a metamaterial
The simulation condition was not stated clear enough. For example, what is the material and permittivity of the substrate? What is the polarization of the incident wave? Moreover, the simulation is for metamaterial only. I would suggest the author to study the frequency response for the actual device with all the microfluidic channel parts including the PDMS and channel media.
In the section of 2.5 – Effect of XPS in an actual measurement
I suggest the authors to normalize the measured spectrum to a substrate only measurement. By doing this the measured spectrum can be translated to a S parameter as that in Figure 2c, so that the experiment results can be compare with a simulation results to gain deeper understanding of the design. This is usually how the experiment results are processed and studied.
The measurements were done to four designs. Please explain the details of each design.
In the section of 3 – Results
Please normalize the measured spectrum for the IPA solution and cancer cell measurements. Please also run the simulation and compare the results to the measurements.
How was the post processing done to remove the interference?
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
The submitted manuscript "Application of a terahertz system combined with a X-shaped metamaterial microfluidic cartridge” presented a bio-sensor that is able to detect cancer cells based on microfluidic metamaterial. An X-shaped plasmonic metamaterial is used for the generation of quadrupole resonance. The dip amplitude or frequency would shift due to the change of the refractive index of the environment, so that a bio-sensor is achieved. I would suggest to accept after the following concerns are well addressed.
Please remove Figure 1, since it is a copy from Ref. 5. What is the angle orientation of the two arms of X-shaped structure? Please add a coordinate in Figure 2 to indicate the direction of x-component. What is the thickness of the PDMS? Since the PDMS is quite absorptive in THz region, the author should consider the PDMS in their simulation. For the PDMS based microfluidic metamaterials, it is suggested to add the following papers into the reference: (a) APL Materials 5, 066103 (2017); Doi.org/10.1063/1.4985288 (b) Appl. Phys. Lett. 114, 151105 (2019); Doi.org/10.1063/1.5084329 (c) Advances in Physics, X 3, 1417055 (2018); Doi.org/10.1080/23746149.2017.1417055 In Figure 5, what is the exact dimension of Designs A, B, C, and D? It is suggested to add the simulation results for the water absorption, diabetes decease detection and cancer cells detection. For references, please check the format to match the standard of the journal.In conclusion, the manuscript can be accepted after the above questions are well addressed.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The results look much better in this revision. I only have two comments for the authors to address before recommending for acceptance.
It is possible to include the PDMS and silicon substrate in the simulation. Please refer to the following publication. X. Zhao, and et al. "Nonlinear terahertz metamaterial perfect absorbers using GaAs", Photonics Research, Vol. 4, No.3, 2016. I hope the authors can conduct the study and add the simulation results into the manuscript, and compare the simulation to the experiment results. In the figure of "Effect of four XPS designs in an actual situation" the upper left plot has some ringing effect due to multiple reflection, can the author remove the ringing effect by using the same method as that used in the next figure - the figure for the spectrum of IPA solution?
Author Response
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Author Response File: 
Author Response.docx
