Printed Capillary Microfluidic Devices and Their Application in Biosensing
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
This research article is intended to develop a capillary-based microfluidic device for biosensing applications. In this paper, authors detected the glucose using this microfluidic platform and claimed that the proposed fabricated method produced the high-volume low-cost production. Paper is well-written, but I have some major concerns,
1. All images and figures should be replaced with HD images (recommend tiff files), as the attached images are blurry and are of poor quality.
2. Attached SEM images have poor quality and have not mentioned about the image magnification.
3. The author should discuss the limit of detection and detection time for detecting glucose with proper analysis.
4. Figure 7 looks like the 5nM and 10mM have similar sensing. How could you differentiate it. Performa and discuss some solid statistical analysis
5. How about specificity of detection?
6. Clearly differentiate the LOD and detection time results with other researcher in tabular form.
7. The title is clear that is adequate to the content of the article but abstract should be grammar free errors.
8. The purpose or purported significance of the article is explicitly stated.
9. Please extend your introduction section to discuss more about microfluidics. I encourage the authors that they can give these review/research articles as references for this article as follows: “Inkjet printing: a viable technology for biosensor fabrication”, “Point-of-Care Diagnostic Devices for Detection of Escherichia coli O157:H7 Using Microfluidic Systems: A Focused Review”, “A Rapid Diagnosis of SARS-CoV-2 using DNA Hydrogel Formation on Microfluidic Pores”, “Collection and detection of SARS-CoV-2 in exhaled breath using face mask.”
10. Overall, the paper lacks proper discussion of each figure. It required more discussion.
11. There are many spelling/grammars errors, needs to fix them.
These all the mistakes and errors can be corrected so that I can accept this paper.
Author Response
- All images and figures should be replaced with HD images (recommend tiff files), as the attached images are blurry and are of poor quality.
Answer: The images and figures have been modified for their better quality. See 3.1 and 3.1 (Figure1-9)
- Attached SEM images have poor quality and have not mentioned about the image magnification.
Answer: The magnification of some SEM image reached the machine’s limit in order to seem the nano particles. The image magnification produced by SEM machine are generated in white color. Additional scale bars are now added to the images. See 3.1 (Figure 2d, Figure 3d,e)
- The author should discuss the limit of detection and detection time for detecting glucose with proper analysis.
Answer: We followed the procedure in the referred paper and didn’t evaluate the impact of the time on the LOD. The reason is that our focus is on demonstrating the concept of printed capillary microfluidic devices, rather than finding the optimal sensing conditions. We just want to know if our fabricated devices can perform similar function as paper-based microfluidic devices at this stage. We hope the detailed research would be carried in future through a collaboration with a team with expertise in biosensing.
The detection time is now described in 2.3 (Line 139-141)
- Figure 7 looks like the 5nM and 10mM have similar sensing. How could you differentiate it. Performa and discuss some solid statistical analysis
Answer: We run the testing with multiple devices and analyzed the data. The obtained average color change at 5 mM is significantly different from that at 10 mM. Average value should be used for distinguishing between these concentrations. The problem is that the standard deviation is large. Large standard deviation was widely reported in paper-based microfluidic devices when using colorimetric method. The accurate characterization of color intensity of a porous material is a challenge when a simple equipment like scanner and camera is used for image capture. At this stage, our biosensing works is a feasibility study to see if the printed devices can be used in the same fashion as paper-based microfluidic devices. Detailed research on the sensing needs to be done in future for reducing the deviation to a practical level.
A short discussion on the standard deviation is now added in 3.2 (Line 367-369).
- How about specificity of detection?
Answer: We didn’t do it, as our biosensing works is a feasibility study to see if the printed devices can be used in the same fashion as paper-based microfluidic devices. Many researchers are working on colorimetric detection using paper-based microfluidics because of their potential as near-patient point-of-care devices. We hope the specificity of detection was addressed in their studies, and think that their developed technology is applicable in our printed devices
- Clearly differentiate the LOD and detection time results with other researcher in tabular form.
Answer: as answered for Question 3, we are now in the stage of demonstrating the concept of printed capillary microfluidic devices. The biosensing application is to see if they can be used in the same fashion as paper-based microfluidics. We followed a reported procedure which is now provided in 2.3 (Line 128-134).
- The title is clear that is adequate to the content of the article but abstract should be grammar free errors.
Answer: Thank you for your suggestion. The errors have been corrected now (Line 8-17)
- The purpose or purported significance of the article is explicitly stated.
Answer: Thank you for your suggestion. The significance of the article is now restated (Line 8-17)
- Please extend your introduction section to discuss more about microfluidics. I encourage the authors that they can give these review/research articles as references for this article as follows: “Inkjet printing: a viable technology for biosensor fabrication”, “Point-of-Care Diagnostic Devices for Detection of Escherichia coli O157:H7 Using Microfluidic Systems: A Focused Review”, “A Rapid Diagnosis of SARS-CoV-2 using DNA Hydrogel Formation on Microfluidic Pores”, “Collection and detection of SARS-CoV-2 in exhaled breath using face mask.”
Answer: We are working on materials and printable electronics, and are trying our printable porous materials for microfluidic application and gas sensing application. We don’t have any biosensing background, and are unable to discuss more about microfluidics unfortunately. To be honestly, we are very interested in collaborating with an expert like the reviewer on devices application. Our labs are well equipped with various advanced printing facilities and other device equipment, and we have strong expertise in materials and device fabrication.
- Overall, the paper lacks proper discussion of each figure. It required more discussion.
Answer: Thank you for your suggestion. Description and discussion for the figures is now added in 3.1 and 3.2. Fig. 1 (Line 186-188); Fig. 2 (Line 202-206); Fig. 3 (L263-270); Fig 4. (Line 277-278, 296-299); Fig. 5 (Line 345-348); Fig. 6 & 7 (Line 362-366).
- There are many spelling/grammars errors, needs to fix them.
These all the mistakes and errors can be corrected so that I can accept this paper.
Answer: Thank you for your suggestion. The spelling/grammar errors are connected now.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript presents a printed microfluidic device with free-standing structures directly on polymer films using functional materials that form interconnected pores. The device was used for the colorimetric determination of glucose. Before publishing the manuscript, please address the following comments:
1. After spotting the solution in each detection zone, please clarify how the solution was stopped from transferring to the other detection zones, considering that these zones are interconnected.
2. In Figure 7, there appears to be an overlap between the responses for 10 and 15 mM. For instance, if a reading of 45 AU is obtained, it is unclear whether the concentration is 10 or 15 mM. Please provide a clear method for distinguishing between these concentrations.
3. Regarding Figure 9, although the standard deviation of all data points is generally low, it is noticeably higher for the 15 mM concentration. It is important to provide an explanation for why the standard deviation is larger for the 15 mM data points.
4. To enhance the manuscript, it is recommended to test the performance of the device with real samples to demonstrate its practical applicability.
Comments on the Quality of English Language
The grammar needs to be improved and there are some typos which are needed to be corrected in the manuscript.
Author Response
- After spotting the solution in each detection zone, please clarify how the solution was stopped from transferring to the other detection zones, considering that these zones are interconnected.
Answer: The solution spotted to each detection zone has very small volume that limits its spreading to only cover the zone and a channel section about 1-2 mm from the zone. The information is now added in 2.3 (Line 137-139).
- In Figure 7, there appears to be an overlap between the responses for 10 and 15 mM. For instance, if a reading of 45 AU is obtained, it is unclear whether the concentration is 10 or 15 mM. Please provide a clear method for distinguishing between these concentrations.
Answer: We run the testing with multiple devices and analyzed the data. The obtained average color change at 10 mM is significantly different from that at 15 mM. Average value should be used for distinguishing between these concentrations. The problem is that the standard deviation is large. Large standard deviation was widely reported in paper-based microfluidic devices when using colorimetric method. The accurate characterization of color intensity of a porous material is a challenge when a simple equipment like scanner and camera is used for image capture. At this stage, our works is a feasibility study to see if our printed devices can be used in the same fashion as paper-based microfluidic devices. Further research needs to be done in future to reduce the deviation down to a practical level.
A short discussion on the standard deviation is provided in 3.2 now (Line 367-369).
- Regarding Figure 9, although the standard deviation of all data points is generally low, it is noticeably higher for the 15 mM concentration. It is important to provide an explanation for why the standard deviation is larger for the 15 mM data points.
Answer: We don’t know the reason that the standard deviation at 15 mM concentration is larger in this experiment done last year. But, in recent study using the devices with a different structure, it was found that many parameters, such as the electrical connection, the age of enzyme solution, mobilization of the spotted enzyme in the devices, could affect the standard deviation. We are conducting a detailed study on this, and hope to report it in near future.
- To enhance the manuscript, it is recommended to test the performance of the device with real samples to demonstrate its practical applicability.
Answer: We are now in the stage of demonstrating the concept of printed capillary microfluidic devices. The application is to see if they can be used in the same fashion as paper-based microfluidics. In the future work, we will follow your suggestion to include this.
Comments on the Quality of English Language
The grammar needs to be improved and there are some typos which are needed to be corrected in the manuscript.
Answer: They have been corrected.
Reviewer 3 Report
Comments and Suggestions for AuthorsSeveral points require the author's revision before publication.
1. Figures are low resolution and poor presentation. Ex) Fig.1 is hard to understand. Also, the resolution is low. Fig. 2a has no scale bar Fig. 2d cannot see the letter "d" and scare bar. The same for Fig. 3. Please revise with a better version.
2. Figs. 2 and 3 have 5 and 3 small figs. but there is no detail explaining each a, b, etc. in the text which is hard to read for the reader.
3. What is the design and result of the Y-channel? Since Fig.. 2b shows the printed Y channel the channel boundary is relatively poor in resolution. It is better to compare design and results in these very important points. Which is the smallest size of the channel that can be printed using this method. The authors recommend discussing this point where applicable.
4. The refs are too old which are only 5 refs. published from 2018 to the present among 33 refs. The authors are recommended to replace with the new refs. to increase the need for this work.
5. The thickness of the printed structure is recommended to AFM for a qualification which is a reliable method for measuring the thickness of the structure.
6. In the abstract, the authors claimed that this developed method is low-cost and can handle smaller sample volumes as compared with paper-based devices. For this point, it is better to add a table for comparisons in terms of prices, volumes, adv, and dis of these proposed methods with the existing ones.
7. The authors are suggested to draw an overall process of this proposed method which helps the reader to better understand the flow.
Author Response
- Figures are low resolution and poor presentation. Ex) Fig.1 is hard to understand. Also, the resolution is low. Fig. 2a has no scale bar Fig. 2d cannot see the letter "d" and scare bar. The same for Fig. 3. Please revise with a better version.
Answer: New Fig. 1 is now provided with good resolution and clear structure. Additional scale bar is now provided in Fig. 2d and Fig. 3d,e. ‘d” letter is now visible in Fig. 2d
- 2 and 3 have 5 and 3 small figs. but there is no detail explaining each a, b, etc. in the text which is hard to read for the reader.
Answer: Explanation is now provided for Fig. 2 (Line 202-206) and Fig 3 (Line 263-270).
- What is the design and result of the Y-channel? Since Fig. 2b shows the printed Y channel the channel boundary is relatively poor in resolution. It is better to compare design and results in these very important points. Which is the smallest size of the channel that can be printed using this method. The authors recommend discussing this point where applicable.
Answer: The designed channel width in Fig. 2b is 3 mm in the main section and 2 mm in the branch section. The narrowed lines in our design are 0.5 mm wide, and can be printed with the type two materials. 3 mm is the typical width in paper-based microfluidic devices.
Discussion on the dimension is now added in 3.1 (Line 204-205, 227-228).
- The refs are too old which are only 5 refs. published from 2018 to the present among 33 refs. The authors are recommended to replace with the new refs. to increase the need for this work.
Answer: Paper-based microfluidic devices are popular now. This manuscript is to report an alternative capillary microfluidic device platform. As the fabrication methods for paper-based devices and the initial application of the devices in biosensing were reported many years ago, the important references that have to be included are not new. To follow your suggestion, we have tried our best to arrange the references.
Now, there are 14 references published from 2018 to present.
- The thickness of the printed structure is recommended to AFM for a qualification which is a reliable method for measuring the thickness of the structure.
Answer: We used the Vecco Detak 150 profilometer that is a standard instrument in semiconductor industry for analyzing structure thickness in micrometer scale and up. This tool is a suitable for analysing the channel that is 3 mm wide and over 30 mm thick. AFM is more suitable for analyzing much small feature within a much smaller area.
- In the abstract, the authors claimed that this developed method is low-cost and can handle smaller sample volumes as compared with paper-based devices. For this point, it is better to add a table for comparisons in terms of prices, volumes, adv, and dis of these proposed methods with the existing ones.
Answer: Printing is well recognized as an effective method in low-cost device fabrication. The whole industry of printable electronics has been developed for fabricating electronics devices through printing for high volume and low cost. In addition, as our devices are directly printed on PET polymer films, there is no need to use an additional step to attach a backing substrate to the devices as required by paper-based microfluidic device. In principle, our reported method is qualified as low-cost device fabrication. But, since both our process and the process for paper-based devices are still in lab level, it is difficult to have a practical comparison. Now, we provide more information in 3.1 to explain this (Line 317-327).
In 3.1, we compared the unit sample volume of our devices and paper-based devices. This comparison is independent of device structure. In 3.2, we compared the sample volume of two types of devices with the reported paper-based devices with same devices structure. It all showed that the sample volume of our devices is much smaller. We think that these two types of comparison are sufficient. Follow your question, we now use “typical paper-based microfluidic devices” to limit the comparison in the abstract and conclusion (Line 11).
- The authors are suggested to draw an overall process of this proposed method which helps the reader to better understand the flow.
Answer: Thank you for your suggestion, we now provide an overall process description in 2.2 (Line 82-84)
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsAttached pictures are still not good, need to imporve them.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe Manuscript can be published in it's present form.
Reviewer 3 Report
Comments and Suggestions for AuthorsMost of the questions are revised.
