One-Step Polylactic Acid Screen-Printing Microfluidic Paper-Based Analytical Device: Application for Simultaneous Detection of Nitrite and Nitrate in Food Samples

Round 1

Reviewer 1 Report

This paper introduced one step polylactic acid screen-printing microfluidic paper-based analytical device. The work is interesting. However, the following comments should be addressed before the paper can be further considered:

Figure 3b, hydrophilic and hydrophobic areas are not clearly shown in SEM image. A scale bar should be clearly shown in the image as well. In result and discussion section, the sensitivity of the proposed device (LOD) should be discussed and compared with that of the existing devices. Relevant publications should be cited and discussed in the text, which include but are not limited to the followings: (a)Electrospin-coating of nitrocellulose membrane enhances sensitivity in nucleic acid-based lateral flow assay (2018). Analytica chimica acta, 1009, 81-88. (b) Hydrophobic Covalent Patterns on Cellulose Paper through Photothiol-X Ligations (2018). ACS Omega, 3(8), 9155-9159. (c) Paper‐based inkjet‐printed microfluidic analytical devices. Angewandte Chemie International Edition (2015), 54(18), 5294-5310.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript entitled "One-step polylactic acid screen-printing microfluidic paper-based analytical device: Application for simultaneous detection of nitrite and nitrate in food samples" described a microfluidic analytical paper-based device prepared using a new patterning method with polylactic acid. The analytical proof-of-concept was demonstrated using the quantification of nitrite and nitrate in different food samples.

The particular devices presented in this work appear novel, aka screen patterning of polylactic acid on paper-based device. However using polylactic acid for hydrophobic patterning is not new, for example it was used in the fabrication of lateral flow paper-devices (the following publication that should be referenced 

"Developing new materials for paper-based diagnostics using electrospun nanofibers by Reinholt, S.J., Sonnenfeldt, A., Naik, A. et al. Anal Bioanal Chem (2014) 406: 3297. https://doi.org/10.1007/s00216-013-7372-5

And screen patterning is relatively common as well.

Different methods of patterning are required for different types of paper-based analytical devices, so it does not devalue the work, but appropriate context of the novelty should be described for an out-of-the-field reader.

The choice of nitrate/nitrite as analyte to test the devices seemed a bit random in the current writing of the manuscript, although those ions are analytically relevant.

In general a careful re-writing of the manuscript is required for some minor language elements, but more importantly to establish the made. The project is interesting and could be relevant for some specific testing, but some critical elements of the results (or experimental design?) are missing. The impact and significance of the work would change with appropriate scientific arguments. The list below indicate some of those elements that to my opinion are required.

 

1) If this manuscript objective is to describe the new device whose novelty relies on the polylactic acid screen patterning, a more detailed description of the patterning method is required (amount of solution, how was it apply to the screen, how was the screen made, manufacturer of the fabric, type of fabric mesh, what was its dimensions, what was the dimensions of the whole sheet, how long did it dry, how was the solution poured, how was it push through the screen, etc...).

2) The SEM picture of Figure 3b is not clear. It does not clearly show a distinctive region for the hydrophillic channel (typo, not cannel) than for the hydrophobic zone (typo, not part). Another picture should be chosen or the results should be described/discussed so the reader can understand what we are suppose to observe/look for.

3) the study of reagents volume and viscosity was interesting, however if needed some of the pictures could be put in supporting information to have more space in the main text as long as results are mentioned and discussed in the main text.

4) The authors based the colorimetric detection of nitrate and nitrite on Griess reactions. The chemical reactions should be cited for a chemsensors journal.

5) Calibration curves for nitrate and nitrite NEED to be added, we cannot only have the tabe indicating the linear range, LOD, LOQ...

6) the precisions intra-day and interday showed are very good <1%, but we do not know how many devices, samples, and/or days this was tested on.

7) The determined LODs are indeed significantly lower than the allowable level, however, the dynamic ranges for nitrite and nitrate should be discussed as well. If the allowable level for nitrate for example is 500 mg/L, how would a device that can only quantify up to 50 mg/L be used? similar for nitrite (linear range up to 10 mg/L, allowable level 125 mg/L).

8) Additionally, if we imagine a sample that would be below the allowable level, but more concentrated than the 50 mg/L tested, there will be a problem as there would not be enough zing to reduced the nitrate to nitrite for detection. (having the reactions would also highlight the amount of zinc per mole of nitrate needed)

9) As the validation of the uPAD is done by comparing the results to those of a spectrophotometric method, the method in question needs to be explicitely described (Results and discussion), including all the parameters used for the experimental tests (in Material and Methods).

10) The preparation of the food sample should be more descriptive in material and methods, as it is known as a critical step when analyzing food. How did the author ensure that all the nitrate/nitrite was indeed recover with their procedure?

11) When analyzing the real samples, some of them were above the linear ranges indicated in the table for both nitrite and nitrate, so how was the concentration determined?

12) As the real samples are still below the allowable levels, it would be useful to generate spiked samples with a dose above the allowable levels, and ensure that they would be accurately detected.

13) In figure 6d, why is the intensity decreasing for a longer (above 12 min) reaction time? Is there a degradation of the  product of the reactions? would that impact the application of the device if the timing of reading the results needs to be very accurately monitored?

 

Language/Typos

1) add reference as mentioned earlier.

2) The manuscript reads like if some paragraphs were cut after writing and half was put in the materials and methods and half in the results and discussion, resulting in superfluous descriptive elements in materials and methods, and key description of the devices and results missing in the results and discussion.

3) page 3 line 97, diameter of the sample zone is probably 8 mm and not 0.8 mm from the figure.

4) page 3 line 97, the word "zones" is missing in two main detection zones for nitrite and nitrate

Author Response

please see attachment

 

 

Author Response File: Author Response.pdf