Preparation of Bimetallic Au-Pd/MWCNTs Electrode for Detection of Dopamine

Round 1

Reviewer 1 Report

The authors prepared a functionalized multi-walled carbon nanotubes (AuPd/MWCNT) and applied it to construct an electrochemical sensor for dopamine detection. The tests were well performed and the results were rationally discussed. However, some issues should be addressed before a possible publication:

1\Can the synthesis process of this paper be illustrated by diagrammatic sketch ?

2\ In Figure 7, there are many small peaks in addition to the 0.2V target peak, please explain.

3\ Figure 8 (a): It is observed that there are broken lines in the figure. Please explain the reason, and there is a lack of bare glass data.

4\ Figure 8 (b) lacks separate carbon tube and bare glass data.

5\Figure 9 (a): There are too few pH data and the pH value is irregular.

6\Figure 9 (b): pH is not linear with peak potential. Please explain the reason.

7\It is not clear that the effect of 1%Pd and 5%Au combined with carbon nanotubes is the best, and there is a lack of proportion optimization data.

8\ Real sample detection data should be added.

Author Response

Reviewer #1

Comments and Suggestions for Authors

The authors prepared a functionalized multi-walled carbon nanotubes (AuPd/MWCNT) and applied it to construct an electrochemical sensor for dopamine detection. The tests were well performed and the results were rationally discussed. However, some issues should be addressed before a possible publication:

Response: We are thankful for the appreciation of the reviewer. This manuscript was revised as following.

 

1. Can the synthesis process of this paper be illustrated by diagrammatic sketch?

Response: We are thankful for the kind suggestion of the reviewer.  We have added the Fig. 1A as a diagrammatic sketch and related texts in the revised manuscript. Figure 1A revealed the synthesis the Sensing material and electrode for detecting system.

Fig. 1A Synthesis the sensing material and preparation for sensing electrode to the detecting system

The revised texts in manuscript is showed as following.

“2.2. Electrochemical sensors preparation

Sensing material synthesis: A facile method has been introduced for the fabrication of electrochemical sensors and the fabrication process is as following. Hydrogen tetrachloroaurate (III) trihydrate and sodium nitrate were added into deionized water under constant stirring for 1 h, and then multi-wall carbon nanotube was added to the above solution under stirring for 24 h. Subsequently, the resultant precipitate was collected by centrifugation, washed with deionized water several times and dried at 45 °C for 24 h in an oven to obtain Au/MWCNT. Starch, multi-wall carbon nanotube and palladium chloride were added into deionized water under vigorous stirring for 1 h, and then the resulting Pd/MWCNT was purified by centrifugation, washed with deionized water three times and dried at 45 °C until completely dry. Multi-wall carbon nanotube was impregnated with aqueous solution of trisodium cit-rate dehydrate, palladium chloride and hydrogen tetrachloroaurate (III) trihydrate. After stirring for 1.5 h, the obtained precipitate was collected by centrifugation and purified by repetitive deionized water rinsing. Then, the product was dried at 45 °C overnight to obtain the black powder (denoted as AuPd/MWCNT). Above synthesis the sensing material is showed in Figure 1A (a).

Sensing electrode preparation: Prior to use, the surface of the bare electrode (glass carbon electrode, GCE) was polished with alumina powder and wool, and then the bare GCE was ultrasonically cleaned with ethanol and deionized water for 10 min. Subsequently, the as-prepared sensing material was drip-coated on the surface of freshly prepared GCE and dried in an oven at 60 °C overnight to obtain modified GCE. Above synthesis the sensing material is presented in Figure 1A (b).”

 

2. In Figure 7, there are many small peaks in addition to the 0.2 V target peak, please explain.

Response: We are thankful for the kind suggestion of the reviewer.  We have listed the peaks in Fig. 7a and 7b and explained them in the revised manuscript.

 

“The oxidation and reduction mechanisms of dopamine and relative compounds was sorted out from the CV curves in Fig. 7a and 7b.  In Fig. 7a and 7b, the oxidation reaction from DA to dopaminequinone (DAQ) peak appeared at the potential about 0.24 V and reduction from DAQ to DA at the potential about 0.20 V (Equation 1).  It was another oxidation reaction from leucodopaminechrome (LDC) to DC at the potential -0.2 V and reduction reaction from DC to LDC at the potential -0.25 V (Equation 2).  LDC is cyclization from DAQ (Equation 2).  The 5,6-dihydroxyindole (DHI) was followed by DC rearrangement (Equation 3).  A further reaction resulting in an oxidation peak from DHI to indole quinone (IQ) is at a potential of about -0.1 V (Equation 3).  Gold oxidation and reaction is located at 1.0 V, and gold oxide reduction occurs at 0.5 V.”

 

(a)

(b)

Figure 7 (a). CV curves of the various kinds of sensing material samples. (b) Oxidation-reduction reaction mechanisms of DA and relative compounds.

 

3. Figure 8 (a): It is observed that there are broken lines in the figure. Please explain the reason, and there is a lack of bare glass data.

Response: We are thankful for the kind suggestion of the reviewer.  We replace the Fig. 8a and related texts in the revised manuscript as following.

“To further investigate the electrochemical performances of various kinds sensing material electrodes, the current of detection DA at about 0.2 V was performed in Figure 8a [29,30]. The bare GCE electrode showed very low DPV current signal and near straight line curve. Notably, 1% Pd-5% Au/MWCNT possessed the highest DPV current among various kinds of sensing electrodes in Figure 8a.”

Figure 8. (a) DPV curves of different electrodes in dopamine solution

 

4. Figure 8 (b) lacks separate carbon tube and bare glass data.

Response: We are thankful for the kind suggestion of the reviewer.  We redraw the Fig. 8b and related texts in the revised manuscript as following.

 

(b)

Figure 8. (b) The linear relationship between the peak current intensity and dopamine concentration on various kinds electrodes.

 

5. Figure 9 (a): There are too few pH data and the pH value is irregular.

Response: We are thankful for the kind suggestion of the reviewer.  We replace the Fig. 9a and related texts in the revised manuscript as following.

“The effect of different pH values to the DPV current response of DA over 1% Pd-5% Au/MWCNT has been investigated, as displayed in Figure 9a. It can be found that the anodic peak current of DA increased with the enhancement of pH value and then decreased after reaching the optimum pH value (7.0). “

 

 

 

 

 

 

 

 

 

 

 

 

Figure 9. (a) DPV curve of various pH

 

6. Figure 9 (b): pH is not linear with peak potential. Please explain the reason.

Response: We are thankful for the kind suggestion of the reviewer.  We added the error bar in Fig. 9b and related texts in the revised manuscript as following. The standard deviations from experimental data (for examples: pH buffer solution value, temperature of solution and stability of the electrochemical system…) to combination of uncertainty, so we draw the error bar in Fig. 9b.

Figure 9. (b) Plot of the oxidation peak potentials versus the pH values.

 

“It can be found that the anodic peak current of DA increased with the enhancement of pH value and then decreased after reaching the optimum pH value (7.0). In addition in Figure 9b, the DPV oxidation peak potentials of DA exhibited a linear relationship with pH values, and the slope (-0.0558 V/pH) of the corresponding linear regression line came near the theoretically expected Nernstian value (−0.059 V/pH), suggesting that the electron transfer reactions accompanied by an equal number of protons.”

 

7. It is not clear that the effect of 1%Pd and 5%Au combined with carbon nanotubes is the best, and there is a lack of proportion optimization data.

Response: We are thankful for the kind suggestion of the reviewer. We choose the optimization data by CV method (Figures A, B and C).

The currents of various CV curves were showed in Fig. A.  It was found the highest oxidative current (DA -> DAQ) is the 1%Pd/MWCNT at 0.2 V.  Fig. B. revealed the CV curves on various loading of Au on 1% Pd/MWCNT.  The topmost oxidative current was appearing on 1%Pd-5%Au/MWCNT at 0.2 V.  In Figure C, the linearity was calculated as R² = 0.99936 on 1%Pd-5%Au/MWCNT.  The linearity of 1%Pd-5%Au/MWCNT is the nearest to R² = 1.0000 in Figure C.

Figure A. CV curves on various loading of Pd on MWCNT.

Figure. B. CV curves on various loading of Au on 1% Pd/MWCNT.

  

           Figure C. the calibration curve of loading of Au on 1% Pd/MWCNT.

 

 

8. Real sample detection data should be added.

Response: We are thankful for the kind suggestion of the reviewer. We performed the standard addition method by 6.25 μM to 100 μM DA on the high concentration of AA and UV, and the calibration curve was presented on Figure 10c and 10d.

The DPV diagrams of different concentrations of DA, under 400 μM AA and 1000 μM UA was proceeded.  Standard addition of the DA concentration from 6.25 μM to 100 μM under 400 μM AA and 1000 μM UA in Figure 10 c. Since the concentration of AA and UA in the human body is higher than that of DA (the concentration of AA in body fluids is 100-1000 μM, while the concentration of UA in blood and urine is 100-1000 μM).  We want to know whether AA and UA will interfere with the detection of dopamine at high concentrations. In Figure 10c, it is under 400 μM AA and 1000 μM UA and different concentrations of DA showed that with the increase of DA concentration, the peak current also increased significantly, and the peak potentials of AA and UA were at -0.075 V and 0.35 V, respectively.  In Figure 10d, it is the plot of DA concentration and DPV peak current.  It can be seen that in the case of high concentrations of AA and UA, DA has a good linearity (R²=0.99611) in the range from 6.25 to 100 μM.  It is promising on the real field application.

(c)

(d)

Figure 10. (c) Standard addition of the DA concentration from 6.25 μM to 100 μM under 400 μM AA and 1000 μM UA.

Reviewer #1

Comments and Suggestions for Authors

The authors prepared a functionalized multi-walled carbon nanotubes (AuPd/MWCNT) and applied it to construct an electrochemical sensor for dopamine detection. The tests were well performed and the results were rationally discussed. However, some issues should be addressed before a possible publication:

Response: We are thankful for the appreciation of the reviewer. This manuscript was revised as following.

 

1. Can the synthesis process of this paper be illustrated by diagrammatic sketch?

Response: We are thankful for the kind suggestion of the reviewer.  We have added the Fig. 1A as a diagrammatic sketch and related texts in the revised manuscript. Figure 1A revealed the synthesis the Sensing material and electrode for detecting system.

Fig. 1A Synthesis the sensing material and preparation for sensing electrode to the detecting system

The revised texts in manuscript is showed as following.

“2.2. Electrochemical sensors preparation

Sensing material synthesis: A facile method has been introduced for the fabrication of electrochemical sensors and the fabrication process is as following. Hydrogen tetrachloroaurate (III) trihydrate and sodium nitrate were added into deionized water under constant stirring for 1 h, and then multi-wall carbon nanotube was added to the above solution under stirring for 24 h. Subsequently, the resultant precipitate was collected by centrifugation, washed with deionized water several times and dried at 45 °C for 24 h in an oven to obtain Au/MWCNT. Starch, multi-wall carbon nanotube and palladium chloride were added into deionized water under vigorous stirring for 1 h, and then the resulting Pd/MWCNT was purified by centrifugation, washed with deionized water three times and dried at 45 °C until completely dry. Multi-wall carbon nanotube was impregnated with aqueous solution of trisodium cit-rate dehydrate, palladium chloride and hydrogen tetrachloroaurate (III) trihydrate. After stirring for 1.5 h, the obtained precipitate was collected by centrifugation and purified by repetitive deionized water rinsing. Then, the product was dried at 45 °C overnight to obtain the black powder (denoted as AuPd/MWCNT). Above synthesis the sensing material is showed in Figure 1A (a).

Sensing electrode preparation: Prior to use, the surface of the bare electrode (glass carbon electrode, GCE) was polished with alumina powder and wool, and then the bare GCE was ultrasonically cleaned with ethanol and deionized water for 10 min. Subsequently, the as-prepared sensing material was drip-coated on the surface of freshly prepared GCE and dried in an oven at 60 °C overnight to obtain modified GCE. Above synthesis the sensing material is presented in Figure 1A (b).”

 

2. In Figure 7, there are many small peaks in addition to the 0.2 V target peak, please explain.

Response: We are thankful for the kind suggestion of the reviewer.  We have listed the peaks in Fig. 7a and 7b and explained them in the revised manuscript.

 

“The oxidation and reduction mechanisms of dopamine and relative compounds was sorted out from the CV curves in Fig. 7a and 7b.  In Fig. 7a and 7b, the oxidation reaction from DA to dopaminequinone (DAQ) peak appeared at the potential about 0.24 V and reduction from DAQ to DA at the potential about 0.20 V (Equation 1).  It was another oxidation reaction from leucodopaminechrome (LDC) to DC at the potential -0.2 V and reduction reaction from DC to LDC at the potential -0.25 V (Equation 2).  LDC is cyclization from DAQ (Equation 2).  The 5,6-dihydroxyindole (DHI) was followed by DC rearrangement (Equation 3).  A further reaction resulting in an oxidation peak from DHI to indole quinone (IQ) is at a potential of about -0.1 V (Equation 3).  Gold oxidation and reaction is located at 1.0 V, and gold oxide reduction occurs at 0.5 V.”

 

(a)

(b)

Figure 7 (a). CV curves of the various kinds of sensing material samples. (b) Oxidation-reduction reaction mechanisms of DA and relative compounds.

 

3. Figure 8 (a): It is observed that there are broken lines in the figure. Please explain the reason, and there is a lack of bare glass data.

Response: We are thankful for the kind suggestion of the reviewer.  We replace the Fig. 8a and related texts in the revised manuscript as following.

“To further investigate the electrochemical performances of various kinds sensing material electrodes, the current of detection DA at about 0.2 V was performed in Figure 8a [29,30]. The bare GCE electrode showed very low DPV current signal and near straight line curve. Notably, 1% Pd-5% Au/MWCNT possessed the highest DPV current among various kinds of sensing electrodes in Figure 8a.”

Figure 8. (a) DPV curves of different electrodes in dopamine solution

 

4. Figure 8 (b) lacks separate carbon tube and bare glass data.

Response: We are thankful for the kind suggestion of the reviewer.  We redraw the Fig. 8b and related texts in the revised manuscript as following.

 

(b)

Figure 8. (b) The linear relationship between the peak current intensity and dopamine concentration on various kinds electrodes.

 

5. Figure 9 (a): There are too few pH data and the pH value is irregular.

Response: We are thankful for the kind suggestion of the reviewer.  We replace the Fig. 9a and related texts in the revised manuscript as following.

“The effect of different pH values to the DPV current response of DA over 1% Pd-5% Au/MWCNT has been investigated, as displayed in Figure 9a. It can be found that the anodic peak current of DA increased with the enhancement of pH value and then decreased after reaching the optimum pH value (7.0). “

 

 

 

 

 

 

 

 

 

 

 

 

Figure 9. (a) DPV curve of various pH

 

6. Figure 9 (b): pH is not linear with peak potential. Please explain the reason.

Response: We are thankful for the kind suggestion of the reviewer.  We added the error bar in Fig. 9b and related texts in the revised manuscript as following. The standard deviations from experimental data (for examples: pH buffer solution value, temperature of solution and stability of the electrochemical system…) to combination of uncertainty, so we draw the error bar in Fig. 9b.

Figure 9. (b) Plot of the oxidation peak potentials versus the pH values.

 

“It can be found that the anodic peak current of DA increased with the enhancement of pH value and then decreased after reaching the optimum pH value (7.0). In addition in Figure 9b, the DPV oxidation peak potentials of DA exhibited a linear relationship with pH values, and the slope (-0.0558 V/pH) of the corresponding linear regression line came near the theoretically expected Nernstian value (−0.059 V/pH), suggesting that the electron transfer reactions accompanied by an equal number of protons.”

 

7. It is not clear that the effect of 1%Pd and 5%Au combined with carbon nanotubes is the best, and there is a lack of proportion optimization data.

Response: We are thankful for the kind suggestion of the reviewer. We choose the optimization data by CV method (Figures A, B and C).

The currents of various CV curves were showed in Fig. A.  It was found the highest oxidative current (DA -> DAQ) is the 1%Pd/MWCNT at 0.2 V.  Fig. B. revealed the CV curves on various loading of Au on 1% Pd/MWCNT.  The topmost oxidative current was appearing on 1%Pd-5%Au/MWCNT at 0.2 V.  In Figure C, the linearity was calculated as R² = 0.99936 on 1%Pd-5%Au/MWCNT.  The linearity of 1%Pd-5%Au/MWCNT is the nearest to R² = 1.0000 in Figure C.

Figure A. CV curves on various loading of Pd on MWCNT.

Figure. B. CV curves on various loading of Au on 1% Pd/MWCNT.

  

           Figure C. the calibration curve of loading of Au on 1% Pd/MWCNT.

 

 

8. Real sample detection data should be added.

Response: We are thankful for the kind suggestion of the reviewer. We performed the standard addition method by 6.25 μM to 100 μM DA on the high concentration of AA and UV, and the calibration curve was presented on Figure 10c and 10d.

The DPV diagrams of different concentrations of DA, under 400 μM AA and 1000 μM UA was proceeded.  Standard addition of the DA concentration from 6.25 μM to 100 μM under 400 μM AA and 1000 μM UA in Figure 10 c. Since the concentration of AA and UA in the human body is higher than that of DA (the concentration of AA in body fluids is 100-1000 μM, while the concentration of UA in blood and urine is 100-1000 μM).  We want to know whether AA and UA will interfere with the detection of dopamine at high concentrations. In Figure 10c, it is under 400 μM AA and 1000 μM UA and different concentrations of DA showed that with the increase of DA concentration, the peak current also increased significantly, and the peak potentials of AA and UA were at -0.075 V and 0.35 V, respectively.  In Figure 10d, it is the plot of DA concentration and DPV peak current.  It can be seen that in the case of high concentrations of AA and UA, DA has a good linearity (R²=0.99611) in the range from 6.25 to 100 μM.  It is promising on the real field application.

(c)

(d)

Figure 10. (c) Standard addition of the DA concentration from 6.25 μM to 100 μM under 400 μM AA and 1000 μM UA.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear editor

The authors presented an electrochemical sensor to detect dopamine by using CNT decorated with Pd and Au nanoparticles. Although some of the results are interesting, however, the results presented in the manuscript are not discussed properly. In my opinion, this manuscript can be considered for publication after applying the comments below:  

 1.     Several electrochemical parameters related to modified electrode should have been reported and compared with a bare electrode such as The electroactive surface area (A_eas) and the roughness factor (RF), well-known kinetic parameter (ψ), heterogeneous electron transfer constant (k₀) of electrodes in a solution containing Fe(CN₆)^4-/3-.

2.     In fig.7, since dopamine oxides are first and then reduce (electrochemically), you should start scanning the potential from the low potential like -0.2 V up to 0.5 V and scan back to -0.2V. Before recording the signal of the dopamine, you should scan the potential of the electrode in PBS until the background gets stable. In this figure that you show, I did see any increase in the signal of dopamine which has a reversible peak around 0.2 V.  On the Au/Pd/MWCNT/electrode, only the background increased. You should not have recorded the signal below the -0.2V because oxygen will be reduced on the surface electrode, giving a big reduction peak for O2. Also, you did not explain what the big peak at 0.5 V is in the Au/Pd/MWCNT/electrode that the other electrodes did not have that signal. I guess, it is the signal of Pd nanoparticles.

3.     In fig.12.b, the author did not report any information about the solution, EIS parameters like applied ac potential, the range of frequency, etc. did you record the signal in Fe(CN₆)^4-/3-.

4.        The analytical performance of the sensor to dopamine should have been compared with the other sensors in the literature.

 

5.     The authors are very good in the characterization of the nonmaterial and discussing them but I can not say the same thing about the electrochemical section and measuring dopamine.  

Author Response

Reviewer #2

Comments and Suggestions for Authors

The authors presented an electrochemical sensor to detect dopamine by using CNT decorated with Pd and Au nanoparticles. Although some of the results are interesting, however, the results presented in the manuscript are not discussed properly. In my opinion, this manuscript can be considered for publication after applying the comments below:  

Response: We are thankful for the comments of the reviewer. This manuscript was revised as following.

 

1. Several electrochemical parameters related to modified electrode should have been reported and compared with a bare electrode such as The electroactive surface area (A_eas) and the roughness factor (RF), well-known kinetic parameter (ψ), heterogeneous electron transfer constant (k₀) of electrodes in a solution containing Fe(CN₆)^4-/3-.

Response: We are thankful for the comments of the reviewer. This research studies are as following.

 

The diffusion adsorption between the modified electrode and the object to be tested can be understood through the change of the scan rate, and the CV is used to test and change the scan rate range from 20 to 200 mVs^-1 in Figure D.  From Fig. D, the current intensity of the electrodes modified by 1%Pd-5% Au/MWCNT increases with the increase of scan rate. Then, the scan rate and the current intensity are plotted, and the relationship between the electrode and dopamine can be known.

Figure E shows the relationship between scan rate and current. When the scan rate is proportional to the current intensity, it means that the electrode and dopamine are controlled by adsorption. If the square root of the scan rate is proportional to the current intensity, it means that the process is diffusion control. Therefore, in this study, 1%Pd-5%Au/MWCNT was used for electrode modification, and the electrochemical reaction of dopamine on the modified electrode was an adsorption-controlled process, indicating that dopamine directly transfers charge on the electrode surface.

 

Figure D. CV current versus the scan rate from 20 to 200 mVs^-1

 

Figure E. The relationship between CV current and scan rate

 

2. In fig.7, since dopamine oxides are first and then reduce (electrochemically), you should start scanning the potential from the low potential like -0.2 V up to 0.5 V and scan back to -0.2V. Before recording the signal of the dopamine, you should scan the potential of the electrode in PBS until the background gets stable. In this figure that you show, I did see any increase in the signal of dopamine which has a reversible peak around 0.2 V.  On the Au/Pd/MWCNT/electrode, only the background increased. You should not have recorded the signal below the -0.2V because oxygen will be reduced on the surface electrode, giving a big reduction peak for O2. Also, you did not explain what the big peak at 0.5 V is in the Au/Pd/MWCNT/electrode that the other electrodes did not have that signal. I guess, it is the signal of Pd nanoparticles.

Response: We are thankful for the kind suggestion of the reviewer.  We have listed the peaks in Fig. 7a, Fig. 7b and explained them in the revised manuscript.

 

“The oxidation and reduction mechanisms of dopamine and relative compounds was sorted out from the CV curves in Fig. 7a and 7b.  In Fig. 7a and 7b, the oxidation reaction from DA to dopaminequinone (DAQ) peak appeared at the potential about 0.24 V and reduction from DAQ to DA at the potential about 0.20 V (Equation 1).  It was another oxidation reaction from leucodopaminechrome (LDC) to DC at the potential -0.2 V and reduction reaction from DC to LDC at the potential -0.25 V (Equation 2).  LDC is cyclization from DAQ (Equation 2).  The 5,6-dihydroxyindole (DHI) was followed by DC rearrangement (Equation 3).  A further reaction resulting in an oxidation peak from DHI to indole quinone (IQ) is at a potential of about -0.1 V (Equation 3). Gold oxidation and reaction is located at 1.0 V, and gold oxide reduction occurs at 0.5 V.”

 

(a)

(b)

Figure 7 (a). CV curves of the various kinds of sensing material samples. (b) Oxidation-reduction reaction mechanisms of DA and relative compounds.

 

 

3. In fig.12.b, the author did not report any information about the solution, EIS parameters like applied ac potential, the range of frequency, etc. did you record the signal in Fe(CN₆)^4-/3-.

Response: We are thankful for the comments of the reviewer. The texts related Fig.12b and this manuscript was revised as following.

“Electrochemical impedance spectroscopy (EIS) is used to measure the resistance value of the electrode to analyse the electrode performance after material modification.  In this research, 1 mM K₃Fe(CN)₆ solution prepared with 0.1 M KCl was used as the electrolyte solution, a sine-wave with an amplitude of 10 mV was applied to the working electrode of the frequency range from 0.1 to 10⁷ Hz.”

 

4. The analytical performance of the sensor to dopamine should have been compared with the other sensors in the literature.

 Response: We are thankful for the comments of the reviewer. The literature studies are added in the revised manuscript as following.

 

“In Table 1, the electrochemical detection of DA on various sensing electrodes was summarized. PtNi bimetallic naoparticles loaded MoS₂ nansheets (PtNi@MoS₂) is prepared by a co-reduction method for the DPV detection of DA concentration, and the linear detection range is from 0.5-150 μM and the detection limit is obtained as 0.1 μM [31]. The electrochemical sensor of platinum nanochains-Multi-walled carbon nanotubes-graphene nanoparticles composite (PtNCs-MWCNTs-GNPs) electrode for determination of dopamine [32]. It presents DA concentration range is from 0.5-150 μM and the detection limit is gained as 0.5 μM [32]. Pd-Au-P composites were supported on poly(diallyldimethylammonium chloride)-functionalized reduced graphene oxide (Pd-Au-P/PDDA/RGO) for DA detection [33]. Using DPV method, the Pd-AuP/PDDA/RGO sensor has detection limit of 0.7 μM with linear range of 3.5-125 μM [33]. Silver-gold nanoparticles on CNT (Ag-Au/CNT) electrode possess high response to dopamine, it is within 1–173 μM range under detection limit of 0.052 μM [34]. Pd₃Pt₁/PDDA-RGO nanomaterials were synthesized for DPV detection with detection limit of 0.04 μM and linear range of 4-200 μM [35]. It is fabricated with reduced graphene oxide-supported Au@Pd (Au@Pd-RGO) for DA detection, and DA is the concentration ranges from 0.01 to 100 μM with detection limits of 0.024 μM.”

 

5. The authors are very good in the characterization of the nonmaterial and discussing them but I cannot say the same thing about the electrochemical section and measuring dopamine.  

Response: We are thankful for the ki

Reviewer #2

Comments and Suggestions for Authors

The authors presented an electrochemical sensor to detect dopamine by using CNT decorated with Pd and Au nanoparticles. Although some of the results are interesting, however, the results presented in the manuscript are not discussed properly. In my opinion, this manuscript can be considered for publication after applying the comments below:  

Response: We are thankful for the comments of the reviewer. This manuscript was revised as following.

 

1. Several electrochemical parameters related to modified electrode should have been reported and compared with a bare electrode such as The electroactive surface area (A_eas) and the roughness factor (RF), well-known kinetic parameter (ψ), heterogeneous electron transfer constant (k₀) of electrodes in a solution containing Fe(CN₆)^4-/3-.

Response: We are thankful for the comments of the reviewer. This research studies are as following.

 

The diffusion adsorption between the modified electrode and the object to be tested can be understood through the change of the scan rate, and the CV is used to test and change the scan rate range from 20 to 200 mVs^-1 in Figure D.  From Fig. D, the current intensity of the electrodes modified by 1%Pd-5% Au/MWCNT increases with the increase of scan rate. Then, the scan rate and the current intensity are plotted, and the relationship between the electrode and dopamine can be known.

Figure E shows the relationship between scan rate and current. When the scan rate is proportional to the current intensity, it means that the electrode and dopamine are controlled by adsorption. If the square root of the scan rate is proportional to the current intensity, it means that the process is diffusion control. Therefore, in this study, 1%Pd-5%Au/MWCNT was used for electrode modification, and the electrochemical reaction of dopamine on the modified electrode was an adsorption-controlled process, indicating that dopamine directly transfers charge on the electrode surface.

 

Figure D. CV current versus the scan rate from 20 to 200 mVs^-1

 

Figure E. The relationship between CV current and scan rate

 

2. In fig.7, since dopamine oxides are first and then reduce (electrochemically), you should start scanning the potential from the low potential like -0.2 V up to 0.5 V and scan back to -0.2V. Before recording the signal of the dopamine, you should scan the potential of the electrode in PBS until the background gets stable. In this figure that you show, I did see any increase in the signal of dopamine which has a reversible peak around 0.2 V.  On the Au/Pd/MWCNT/electrode, only the background increased. You should not have recorded the signal below the -0.2V because oxygen will be reduced on the surface electrode, giving a big reduction peak for O2. Also, you did not explain what the big peak at 0.5 V is in the Au/Pd/MWCNT/electrode that the other electrodes did not have that signal. I guess, it is the signal of Pd nanoparticles.

Response: We are thankful for the kind suggestion of the reviewer.  We have listed the peaks in Fig. 7a, Fig. 7b and explained them in the revised manuscript.

 

“The oxidation and reduction mechanisms of dopamine and relative compounds was sorted out from the CV curves in Fig. 7a and 7b.  In Fig. 7a and 7b, the oxidation reaction from DA to dopaminequinone (DAQ) peak appeared at the potential about 0.24 V and reduction from DAQ to DA at the potential about 0.20 V (Equation 1).  It was another oxidation reaction from leucodopaminechrome (LDC) to DC at the potential -0.2 V and reduction reaction from DC to LDC at the potential -0.25 V (Equation 2).  LDC is cyclization from DAQ (Equation 2).  The 5,6-dihydroxyindole (DHI) was followed by DC rearrangement (Equation 3).  A further reaction resulting in an oxidation peak from DHI to indole quinone (IQ) is at a potential of about -0.1 V (Equation 3). Gold oxidation and reaction is located at 1.0 V, and gold oxide reduction occurs at 0.5 V.”

 

(a)

(b)

Figure 7 (a). CV curves of the various kinds of sensing material samples. (b) Oxidation-reduction reaction mechanisms of DA and relative compounds.

 

 

3. In fig.12.b, the author did not report any information about the solution, EIS parameters like applied ac potential, the range of frequency, etc. did you record the signal in Fe(CN₆)^4-/3-.

Response: We are thankful for the comments of the reviewer. The texts related Fig.12b and this manuscript was revised as following.

“Electrochemical impedance spectroscopy (EIS) is used to measure the resistance value of the electrode to analyse the electrode performance after material modification.  In this research, 1 mM K₃Fe(CN)₆ solution prepared with 0.1 M KCl was used as the electrolyte solution, a sine-wave with an amplitude of 10 mV was applied to the working electrode of the frequency range from 0.1 to 10⁷ Hz.”

 

4. The analytical performance of the sensor to dopamine should have been compared with the other sensors in the literature.

 Response: We are thankful for the comments of the reviewer. The literature studies are added in the revised manuscript as following.

 

“In Table 1, the electrochemical detection of DA on various sensing electrodes was summarized. PtNi bimetallic naoparticles loaded MoS₂ nansheets (PtNi@MoS₂) is prepared by a co-reduction method for the DPV detection of DA concentration, and the linear detection range is from 0.5-150 μM and the detection limit is obtained as 0.1 μM [31]. The electrochemical sensor of platinum nanochains-Multi-walled carbon nanotubes-graphene nanoparticles composite (PtNCs-MWCNTs-GNPs) electrode for determination of dopamine [32]. It presents DA concentration range is from 0.5-150 μM and the detection limit is gained as 0.5 μM [32]. Pd-Au-P composites were supported on poly(diallyldimethylammonium chloride)-functionalized reduced graphene oxide (Pd-Au-P/PDDA/RGO) for DA detection [33]. Using DPV method, the Pd-AuP/PDDA/RGO sensor has detection limit of 0.7 μM with linear range of 3.5-125 μM [33]. Silver-gold nanoparticles on CNT (Ag-Au/CNT) electrode possess high response to dopamine, it is within 1–173 μM range under detection limit of 0.052 μM [34]. Pd₃Pt₁/PDDA-RGO nanomaterials were synthesized for DPV detection with detection limit of 0.04 μM and linear range of 4-200 μM [35]. It is fabricated with reduced graphene oxide-supported Au@Pd (Au@Pd-RGO) for DA detection, and DA is the concentration ranges from 0.01 to 100 μM with detection limits of 0.024 μM.”

 

5. The authors are very good in the characterization of the nonmaterial and discussing them but I cannot say the same thing about the electrochemical section and measuring dopamine.  

Response: We are thankful for the kind suggestion of the reviewer.  We have added the CV peaks explanation (Fig. 7a and 7b), calibration curves (Fig. 8a and 8b) and EIS experimental (Table 2) data in electrochemical section in the revised manuscript.

nd suggestion of the reviewer.  We have added the CV peaks explanation (Fig. 7a and 7b), calibration curves (Fig. 8a and 8b) and EIS experimental (Table 2) data in electrochemical section in the revised manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

 

The manuscript is about the modification of the electrode in order to develop a sensor for dopamine. The manuscript is attractive, however, it is unaccomplished for publication. Moreover, the manuscript is out of the scope of “Minerals”.

General comments:

1. Procedures in Experimental are not precise enough, i.e. without numbers.
2. Figure captions are too laconic.
3. Abbreviations need revision. The abbreviations need to be indicated in brackets only when they are mentioned for the first time. Abbreviations in some cases are different for the same term.
4. EIS is not described in Experimental. 

Detailed comments:

1. Please change “liner relationship” to “calibration curve” and add the full curve not only the linear part. But the trendline should stay only in the linear range.
2. Fig. 11a): please explain with numbers (seconds, minutes, etc.) the meaning of “different times”.
3. Fig. 12b): the spectra should be “squared”. Now they are a little bit misshaped. But this might be a computer screen effect. If this is the case, please ignore this comment.
4. EIS part is totally unclear because it is not discussed at all. How it was performed in what solutions at what potential? Please discuss fitting to the equivalent circuit. According to the shape of the spectra, it is very doubtful that the fitting is successful (with low error) within the whole frequency range.
   
5. Conclusions are too descriptive without illustrations with some numbers.

Author Response

Reviewer #3

The manuscript is about the modification of the electrode in order to develop a sensor for dopamine. The manuscript is attractive, however, it is unaccomplished for publication. Moreover, the manuscript is out of the scope of “Minerals”.

Response: We are thankful for the comments of the reviewer. This manuscript was revised as following.

 

General comments:

1. Procedures in Experimental are not precise enough, i.e. without numbers.

Response: We are thankful for the valuable suggestion of the reviewer.  We have added the Fig. 1A as a diagrammatic sketch and related texts in the revised manuscript. Figure 1A revealed the synthesis the Sensing material and electrode for detecting system.

 

Fig. 1A Synthesis the sensing material and preparation for sensing electrode to the detecting system

The revised texts in manuscript is showed as following.

“2.2. Electrochemical sensors preparation

Sensing material synthesis: A facile method has been introduced for the fabrication of electrochemical sensors and the fabrication process is as following. Hydrogen tetrachloroaurate (III) trihydrate and sodium nitrate were added into deionized water under constant stirring for 1 h, and then multi-wall carbon nanotube was added to the above solution under stirring for 24 h. Subsequently, the resultant precipitate was collected by centrifugation, washed with deionized water several times and dried at 45 °C for 24 h in an oven to obtain Au/MWCNT. Starch, multi-wall carbon nanotube and palladium chloride were added into deionized water under vigorous stirring for 1 h, and then the resulting Pd/MWCNT was purified by centrifugation, washed with deionized water three times and dried at 45 °C until completely dry. Multi-wall carbon nanotube was impregnated with aqueous solution of trisodium cit-rate dehydrate, palladium chloride and hydrogen tetrachloroaurate (III) trihydrate. After stirring for 1.5 h, the obtained precipitate was collected by centrifugation and purified by repetitive deionized water rinsing. Then, the product was dried at 45 °C overnight to obtain the black powder (denoted as AuPd/MWCNT). Above synthesis the sensing material is showed in Figure 1A (a).

Sensing electrode preparation: Prior to use, the surface of the bare electrode (glass carbon electrode, GCE) was polished with alumina powder and wool, and then the bare GCE was ultrasonically cleaned with ethanol and deionized water for 10 min. Subsequently, the as-prepared sensing material was drip-coated on the surface of freshly prepared GCE and dried in an oven at 60 °C overnight to obtain modified GCE. Above synthesis the sensing material is presented in Figure 1A (b).”

 

• Figure captions are too laconic.

Response: We are thankful for the valuable suggestion of the reviewer.  We have revised some figure captions in the revised manuscript by followings.

 

“Figure 1A Synthesis the sensing material and preparation for sensing electrode to the detecting system, B. The electrochemical dopamine detection system.

Figure 2. XRD patterns of the various kinds of sensing materials samples.

Figure 4. TEM images of as-synthesized sensing material samples (a-b) low to high resolution TEM images of MWCNT, (c-d) low to high resolution TEM images of 1% Au/MWCNT, (e-f) low to high resolution TEM images of 1% Pd/MWCNT, (f) 1% Pd/MWCNT, (g) 1% Pd-5% Au/MWCNT.

Figure 6. XPS spectra of the sensing material 1% Pd-5% Au/MWCNT (a) survey spectrum, (b) C 1s, (c) O 1s, (d) Au 4f, (e) Pd 3d, (f) Mo 3d, (g) Si 2p.

Figure 7. CV curves of the various kinds of sensing material samples.

Figure 9. (a) DPV curve of various pH, (b) Plot of the oxidation peak potentials versus the pH values.”

 

3. Abbreviations need revision. The abbreviations need to be indicated in brackets only when they are mentioned for the first time. Abbreviations in some cases are different for the same term.

Response: We are thankful for the valuable suggestion of the reviewer.  We have corrected the texts in the revised manuscript.

 

 

4. EIS is not described in Experimental. 

Response: We are thankful for the valuable suggestion of the reviewer.  We have added the related texts in “2.3. Characterization apparatus” of the revised manuscript.

“The evolution of the electric conductivity transport process in the electrochemical cell is investigated using the electrochemical impedance spectroscopy (EIS), and the measurement is using an electrochemical analyzer (Won A Tech/ZIVE LAB). Electrochemical impedance spectroscopy (EIS) is used to measure the resistance value of the electrode to analyse the electrode performance after material modification.  In this research, 1 mM K3Fe(CN)6 solution prepared with 0.1 M KCl was used as the electrolyte solution, a sine-wave with an amplitude of 10 mV was applied to the working electrode of the frequency range from 0.1 to 10⁷ Hz.”

 

Detailed comments:

1. Please change “liner relationship” to “calibration curve” and add the full curve not only the linear part. But the trendline should stay only in the linear range.

Response: We are thankful for the valuable suggestion of the reviewer.  We have changed the wordy from “liner relationship” to “calibration curve” in the revised manuscript. We also redraw the Fig. 8b and related texts in the revised manuscript as following. The trend-line and the linear range is shown in Figure D.

(b)

Figure 8. (b) The linear relationship between the peak current intensity and dopamine concentration on various kind electrodes.

 

 

      Figure D. the calibration curve of DA concentration from 0.098 μM to 50 μM.

 

2. 11a): please explain with numbers (seconds, minutes, etc.) the meaning of “different times”.

Response: We are thankful for the suggestion of the reviewer. We revised the texts as followings.

“As illustrated in Figure 11a, it can be found that the 1% Pd-5% Au/MWCNT has been measured continually with total ten experiments, and the relative standard deviation (RSD) was 0.41%, revealing satisfactory reproducibility.”

 

3. 12b): the spectra should be “squared”. Now they are a little bit misshaped. But this might be a computer screen effect. If this is the case, please ignore this comment.

Response: We are thankful for the suggestion of the reviewer. We revised this part in the revised manuscript.

 

4. EIS part is totally unclear because it is not discussed at all. How it was performed in what solutions at what potential? Please discuss fitting to the equivalent circuit. According to the shape of the spectra, it is very doubtful that the fitting is successful (with low error) within the whole frequency range.

Response: We are thankful for the suggestion of the reviewer. We revised the Table 2 and related texts as followings.

“Electrochemical impedance spectroscopy (EIS) is used to measure the resistance value of the electrode to analyse the electrode performance after material modification.  In this study, 1 mM K₃Fe(CN)₆ solution prepared with 0.1 M KCl was used as the electrolyte solution, a sine wave with an amplitude of 10 mV was applied to the working electrode in the frequency range of 0.1-10⁷ Hz.”

“The diameter of the semicircle in the high frequency region was measured to calculate charge transfer resistance (Rct), then show the results of the EIS in a Nyquist plot in Fig. 12b, and the simulated elements value of the equivalence circuits of different sensing electrodes was showed in Table 2 (error of the equivalence circuits < 8%). The equivalent circuit in Fig. 12b is divided into ohmic resistance (Rs), charge transfer resistance (Rct), constant phase element (CPE) and Warburg impedance (Wz). Where Rs is the equivalent series resistance, Rct is the charge transfer resistance at the electrode-electrolyte interface, and then the electric double layer capacitance is replaced by CPE, and the Warburg impedance is the representative as Wz. According to the phenomenon of material transport, the mass transfer resistance can be known. From Table 2, it can show that the calculated data of each element shows that Rs, Rct and Wz take the bimetallic AuPd/MWCNT as the smallest value, indicating that the resistance of active ions to diffuse to the electrode is small, and the charge transfer between dopamine and the surface is fast.”

 

Table 2.  The simulated the elements value of the equivalence circuits of different sensing electrodes.

electrode	Rs (Ω)	Rct (Ω)	CPE (F)	CPE (F)
Bare GCE	20.78	106.72	8.24×10-12	69.94
MWCNT	85.74	94.26	4.00×10-20	47.88
1%Au/MWCNT	33.05	90.98	1.20×10-3	58.67
1%Pd/MWCNT	31.13	91.42	8.70×10-4	102.3
1%Pd-5%Au/MWCNT	18.82	83.21	5.54×10-4	41.36

 

1. Conclusions are too descriptive without illustrations with some numbers.

Response: We are thankful for the suggestion of the reviewer. We revised the conclusion as followings.

“In this work, a serial of AuPd/MWCNTs have been successfully synthesized using sonochemistry method and applied to detect dopamine. Energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), transmission electron microscope (TEM), field emission-scanning electron microscopy (FE-SEM), as well as X-ray photoelectron spectroscopy (XPS) have been employed for characterizing morphology, composition and structure of AuPd/MWCNT, suggesting that Au and Pd nanoparticles have been deposited on the surface of MWCNT. 1% Pd-5% Au/MWCNT showed a wide linear detection range from 0.98 to 200 μM, and a low detection limit of 0.014 μM for dopamine. It reveals long-term stability (16 days), low operating temperature and real-time detection of trace-level dopamine, revealing that the application of AuPd/MWCNTs as an effective electrode material for dopamine detection.”

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

All the suggestions have been addressed. Accept!

Author Response

Dear Editor of Minerals

Manuscript ID: Minerals-1831560

Type: Article

Title: Preparation of Bimetallic Au-Pd/MWCNTs Electrode for Detection of Dopamine

         

We are thankful for your kindness suggestions and appreciate the reviewers’ and editor’ valuable comments.  Also we carefully considered the comments, so we only revised parts of the manuscript according to the reviewers #3 suggestions and mark blue color in the revised manuscript and response letter by the files.

 

Reviewer #1 comment

All the suggestions have been addressed. Accept!

Response: We are thankful for the appreciation of the reviewer.

 

Reviewer #2 comment

In my opinion, the manuscript can be published. Congratulation 

Response: We are thankful for the appreciation of the reviewer.

 

Reviewer #3 comments

1. The authors have replied to all questions, however, they did not improve much the manuscript, e.g. did not add concentrations to the procedures; EIS explanation is not yet clear enough (how capacitance was replaced with CPE, what kind of Warburg element (short or open) was used, etc.

Response: We are thankful for the kind suggestion of the reviewer.  We revised some texts and Figure 12 (b) in the revised manuscript.

“Constant phase element (CPE) means the constant phase-angle element relating to the nonideal characteristic of the double layer.“ CPE is an equivalent electrical circuit component that models the behavior like a double layer, that is an imperfect capacitor. A constant phase element also currently appears in modeling the imperfect dielectrics' behavior.

“For simulation the electrochemical cell sensing system, we used Warburg element (short) to represent diffusion.” (Fig. A and Fig. 12b)

Fig. A

Figure 12. (b) Electrochemical impedance spectroscopy (EIS) of the electrochemical behavior of different electrodes.

 

 

2. The added results show that this material is not suitable for dopamine sensing because it is not sensitive and calibration curve has so high intercept that it is not possible to calculate LOD.

Response: We are thankful for the kind suggestion of the reviewer.  We revised the texts, Figure 8c and Table 1.  The detection limit (DL) is measured by DL = (3×SD)/m by Table A, the SD presents the standard deviation of blank sample signal and the m is revealed the slope of the response versus DA concentration curve.

“Notably, 1% Pd-5% Au/MWCNT possessed the highest DPV current among various kinds of sensing electrodes in Figure 8a. The calibration curves between the peak current and concentration of dopamine has been studied by DPV method. From Figure 8b, it can be found that all of the electrodes exhibited peak currents changed proportional with the increasing concentration of dopamine. It revealed the DPV currents within the detection concentration range of 0.098‐200 μM.  In Table 1, the calculation LOD of DA concentration linear range from 0.098 μM to 6.8 μM of 1% Pd/MWCNT and 1%Pd-5%Au/MWCNT are 0.045 μM and 0.058 μM from Figure 8 (c).”

Figure. 8 (c) The DPV current versus DA concentration from 0.098 μM to 6.8 μM.

 

         Table A. LOD of linear DA concentration range from 0.098 μM to 6.8 μM

 

	SD : standard deviation of blank sample (μA)	Slope: m (μA/μM)	LOD= 3×SD/m     (μM)
1% Au/MWCNT	0.012	0.5314	0.068
1%Pd/MWCNT	0.011	0.7281	0.045
MWCNT	0.010	0.4776	0.063
1%Pd-5%Au/MWCNT	0.011	0.5661	0.058

 

 

 

      Table 1. Comparison of different electrodes for the determination of dopamine (DA).

electrode	Linear Range (μM)	LOD(μM)	References (Ω)
PtNi@MOS2	0.5-150	0.1	[31]
PtNCs-MWCNTs-GNPs	2-50	0.5	[32]
Pd-Au-P/PDDA/rGO	3.5-125	0.7	[33]
Ag-Au/CNT	1-173	0.052	[34]
Pd3Pt1/PDDA-RGO	4-200	0.04	[35]
Au@Pd-RGO	0.01-100	0.024	[36]
1%Pd/MWCNT	0.098-6.8	0.045	This work
1%Pd-5%Au/MWCNT	0.098-6.8	0.058	This work

 

 

 

 

3. The biggest problem is that the paper is not suitable for this journal. It has nothing related to materials.

Response: We are thankful for the kind suggestion of the reviewer.  This manuscript is the invited paper and we think there are some technologies in the manuscript relating to this journal.

• The subject areas of this journal including metallic minerals, and the noble metals Au, Pd and Au-Pd are in the field. This manuscript described the preparation of Bimetallic Au-Pd process.

The related publications 

“The Gold–Palladium Ozernoe Occurrence (Polar Urals, Russia): Mineralogy, Conditions of Formation, Sources of Ore Matter and Fluid” Minerals 2022, 12(6), 765; https://doi.org/10.3390/min12060765

“Recovery of Palladium and Gold from PGM Ore and Concentrate Leachates Using Fe₃O₄@SiO₂@Mg-Al-LDH Nanocomposite” Minerals 2021, 11(9), 917; https://doi.org/10.3390/min11090917

 

• This manuscript is Invited paper: the special Issue (SI) in Minerals is Green Synthesis and Application of Multimetallic Nanoparticles.

This manuscript described the simple, easy and green preparation process of Bimetallic Au-Pd on MWCNT (Fig. 1A) and applied to biosensor field, so it is fitting to the goal of the special Issue (SI) in Minerals is Green Synthesis and Application of Multimetallic Nanoparticles

Figure 1A Synthesis the sensing material and preparation for sensing electrode to the detecting system

 

 

We hope this revised paper could be acceptable in the journal.    

                               

With best regards and your kind help

Sincerely yours,

Ren-Jang (Isaac) Wu

Professor of Applied Chemistry

/Providence University/Taiwan

Dear Editor of Minerals

Manuscript ID: Minerals-1831560

Type: Article

Title: Preparation of Bimetallic Au-Pd/MWCNTs Electrode for Detection of Dopamine

         

We are thankful for your kindness suggestions and appreciate the reviewers’ and editor’ valuable comments.  Also we carefully considered the comments, so we only revised parts of the manuscript according to the reviewers #3 suggestions and mark blue color in the revised manuscript and response letter by the files.

 

Reviewer #1 comment

All the suggestions have been addressed. Accept!

Response: We are thankful for the appreciation of the reviewer.

 

Reviewer #2 comment

In my opinion, the manuscript can be published. Congratulation 

Response: We are thankful for the appreciation of the reviewer.

 

Reviewer #3 comments

1. The authors have replied to all questions, however, they did not improve much the manuscript, e.g. did not add concentrations to the procedures; EIS explanation is not yet clear enough (how capacitance was replaced with CPE, what kind of Warburg element (short or open) was used, etc.

Response: We are thankful for the kind suggestion of the reviewer.  We revised some texts and Figure 12 (b) in the revised manuscript.

“Constant phase element (CPE) means the constant phase-angle element relating to the nonideal characteristic of the double layer.“ CPE is an equivalent electrical circuit component that models the behavior like a double layer, that is an imperfect capacitor. A constant phase element also currently appears in modeling the imperfect dielectrics' behavior.

“For simulation the electrochemical cell sensing system, we used Warburg element (short) to represent diffusion.” (Fig. A and Fig. 12b)

Fig. A

Figure 12. (b) Electrochemical impedance spectroscopy (EIS) of the electrochemical behavior of different electrodes.

 

 

2. The added results show that this material is not suitable for dopamine sensing because it is not sensitive and calibration curve has so high intercept that it is not possible to calculate LOD.

Response: We are thankful for the kind suggestion of the reviewer.  We revised the texts, Figure 8c and Table 1.  The detection limit (DL) is measured by DL = (3×SD)/m by Table A, the SD presents the standard deviation of blank sample signal and the m is revealed the slope of the response versus DA concentration curve.

“Notably, 1% Pd-5% Au/MWCNT possessed the highest DPV current among various kinds of sensing electrodes in Figure 8a. The calibration curves between the peak current and concentration of dopamine has been studied by DPV method. From Figure 8b, it can be found that all of the electrodes exhibited peak currents changed proportional with the increasing concentration of dopamine. It revealed the DPV currents within the detection concentration range of 0.098‐200 μM.  In Table 1, the calculation LOD of DA concentration linear range from 0.098 μM to 6.8 μM of 1% Pd/MWCNT and 1%Pd-5%Au/MWCNT are 0.045 μM and 0.058 μM from Figure 8 (c).”

Figure. 8 (c) The DPV current versus DA concentration from 0.098 μM to 6.8 μM.

 

         Table A. LOD of linear DA concentration range from 0.098 μM to 6.8 μM

 

	SD : standard deviation of blank sample (μA)	Slope: m (μA/μM)	LOD= 3×SD/m     (μM)
1% Au/MWCNT	0.012	0.5314	0.068
1%Pd/MWCNT	0.011	0.7281	0.045
MWCNT	0.010	0.4776	0.063
1%Pd-5%Au/MWCNT	0.011	0.5661	0.058

 

 

 

      Table 1. Comparison of different electrodes for the determination of dopamine (DA).

electrode	Linear Range (μM)	LOD(μM)	References (Ω)
PtNi@MOS2	0.5-150	0.1	[31]
PtNCs-MWCNTs-GNPs	2-50	0.5	[32]
Pd-Au-P/PDDA/rGO	3.5-125	0.7	[33]
Ag-Au/CNT	1-173	0.052	[34]
Pd3Pt1/PDDA-RGO	4-200	0.04	[35]
Au@Pd-RGO	0.01-100	0.024	[36]
1%Pd/MWCNT	0.098-6.8	0.045	This work
1%Pd-5%Au/MWCNT	0.098-6.8	0.058	This work

 

 

 

 

3. The biggest problem is that the paper is not suitable for this journal. It has nothing related to materials.

Response: We are thankful for the kind suggestion of the reviewer.  This manuscript is the invited paper and we think there are some technologies in the manuscript relating to this journal.

• The subject areas of this journal including metallic minerals, and the noble metals Au, Pd and Au-Pd are in the field. This manuscript described the preparation of Bimetallic Au-Pd process.

The related publications 

“The Gold–Palladium Ozernoe Occurrence (Polar Urals, Russia): Mineralogy, Conditions of Formation, Sources of Ore Matter and Fluid” Minerals 2022, 12(6), 765; https://doi.org/10.3390/min12060765

“Recovery of Palladium and Gold from PGM Ore and Concentrate Leachates Using Fe₃O₄@SiO₂@Mg-Al-LDH Nanocomposite” Minerals 2021, 11(9), 917; https://doi.org/10.3390/min11090917

 

• This manuscript is Invited paper: the special Issue (SI) in Minerals is Green Synthesis and Application of Multimetallic Nanoparticles.

This manuscript described the simple, easy and green preparation process of Bimetallic Au-Pd on MWCNT (Fig. 1A) and applied to biosensor field, so it is fitting to the goal of the special Issue (SI) in Minerals is Green Synthesis and Application of Multimetallic Nanoparticles

Figure 1A Synthesis the sensing material and preparation for sensing electrode to the detecting system

 

 

We hope this revised paper could be acceptable in the journal.    

                               

With best regards and your kind help

Sincerely yours,

Ren-Jang (Isaac) Wu

Professor of Applied Chemistry

/Providence University/Taiwan

Dear Editor of Minerals

Manuscript ID: Minerals-1831560

Type: Article

Title: Preparation of Bimetallic Au-Pd/MWCNTs Electrode for Detection of Dopamine

         

We are thankful for your kindness suggestions and appreciate the reviewers’ and editor’ valuable comments.  Also we carefully considered the comments, so we only revised parts of the manuscript according to the reviewers #3 suggestions and mark blue color in the revised manuscript and response letter by the files.

 

Reviewer #1 comment

All the suggestions have been addressed. Accept!

Response: We are thankful for the appreciation of the reviewer.

 

Reviewer #2 comment

In my opinion, the manuscript can be published. Congratulation 

Response: We are thankful for the appreciation of the reviewer.

 

Reviewer #3 comments

1. The authors have replied to all questions, however, they did not improve much the manuscript, e.g. did not add concentrations to the procedures; EIS explanation is not yet clear enough (how capacitance was replaced with CPE, what kind of Warburg element (short or open) was used, etc.

Response: We are thankful for the kind suggestion of the reviewer.  We revised some texts and Figure 12 (b) in the revised manuscript.

“Constant phase element (CPE) means the constant phase-angle element relating to the nonideal characteristic of the double layer.“ CPE is an equivalent electrical circuit component that models the behavior like a double layer, that is an imperfect capacitor. A constant phase element also currently appears in modeling the imperfect dielectrics' behavior.

“For simulation the electrochemical cell sensing system, we used Warburg element (short) to represent diffusion.” (Fig. A and Fig. 12b)

Fig. A

Figure 12. (b) Electrochemical impedance spectroscopy (EIS) of the electrochemical behavior of different electrodes.

 

 

2. The added results show that this material is not suitable for dopamine sensing because it is not sensitive and calibration curve has so high intercept that it is not possible to calculate LOD.

Response: We are thankful for the kind suggestion of the reviewer.  We revised the texts, Figure 8c and Table 1.  The detection limit (DL) is measured by DL = (3×SD)/m by Table A, the SD presents the standard deviation of blank sample signal and the m is revealed the slope of the response versus DA concentration curve.

“Notably, 1% Pd-5% Au/MWCNT possessed the highest DPV current among various kinds of sensing electrodes in Figure 8a. The calibration curves between the peak current and concentration of dopamine has been studied by DPV method. From Figure 8b, it can be found that all of the electrodes exhibited peak currents changed proportional with the increasing concentration of dopamine. It revealed the DPV currents within the detection concentration range of 0.098‐200 μM.  In Table 1, the calculation LOD of DA concentration linear range from 0.098 μM to 6.8 μM of 1% Pd/MWCNT and 1%Pd-5%Au/MWCNT are 0.045 μM and 0.058 μM from Figure 8 (c).”

Figure. 8 (c) The DPV current versus DA concentration from 0.098 μM to 6.8 μM.

 

         Table A. LOD of linear DA concentration range from 0.098 μM to 6.8 μM

 

	SD : standard deviation of blank sample (μA)	Slope: m (μA/μM)	LOD= 3×SD/m     (μM)
1% Au/MWCNT	0.012	0.5314	0.068
1%Pd/MWCNT	0.011	0.7281	0.045
MWCNT	0.010	0.4776	0.063
1%Pd-5%Au/MWCNT	0.011	0.5661	0.058

 

 

 

      Table 1. Comparison of different electrodes for the determination of dopamine (DA).

electrode	Linear Range (μM)	LOD(μM)	References (Ω)
PtNi@MOS2	0.5-150	0.1	[31]
PtNCs-MWCNTs-GNPs	2-50	0.5	[32]
Pd-Au-P/PDDA/rGO	3.5-125	0.7	[33]
Ag-Au/CNT	1-173	0.052	[34]
Pd3Pt1/PDDA-RGO	4-200	0.04	[35]
Au@Pd-RGO	0.01-100	0.024	[36]
1%Pd/MWCNT	0.098-6.8	0.045	This work
1%Pd-5%Au/MWCNT	0.098-6.8	0.058	This work

 

 

 

 

3. The biggest problem is that the paper is not suitable for this journal. It has nothing related to materials.

Response: We are thankful for the kind suggestion of the reviewer.  This manuscript is the invited paper and we think there are some technologies in the manuscript relating to this journal.

• The subject areas of this journal including metallic minerals, and the noble metals Au, Pd and Au-Pd are in the field. This manuscript described the preparation of Bimetallic Au-Pd process.

The related publications 

“The Gold–Palladium Ozernoe Occurrence (Polar Urals, Russia): Mineralogy, Conditions of Formation, Sources of Ore Matter and Fluid” Minerals 2022, 12(6), 765; https://doi.org/10.3390/min12060765

“Recovery of Palladium and Gold from PGM Ore and Concentrate Leachates Using Fe₃O₄@SiO₂@Mg-Al-LDH Nanocomposite” Minerals 2021, 11(9), 917; https://doi.org/10.3390/min11090917

 

• This manuscript is Invited paper: the special Issue (SI) in Minerals is Green Synthesis and Application of Multimetallic Nanoparticles.

This manuscript described the simple, easy and green preparation process of Bimetallic Au-Pd on MWCNT (Fig. 1A) and applied to biosensor field, so it is fitting to the goal of the special Issue (SI) in Minerals is Green Synthesis and Application of Multimetallic Nanoparticles

Figure 1A Synthesis the sensing material and preparation for sensing electrode to the detecting system

 

 

We hope this revised paper could be acceptable in the journal.    

                               

With best regards and your kind help

Sincerely yours,

Ren-Jang (Isaac) Wu

Professor of Applied Chemistry

/Providence University/Taiwan

Author Response File: Author Response.pdf

Reviewer 2 Report

In my opinion, the manuscript can be published. Congratulation 

Author Response

Dear Editor of Minerals

Manuscript ID: Minerals-1831560

Type: Article

Title: Preparation of Bimetallic Au-Pd/MWCNTs Electrode for Detection of Dopamine

         

We are thankful for your kindness suggestions and appreciate the reviewers’ and editor’ valuable comments.  Also we carefully considered the comments, so we only revised parts of the manuscript according to the reviewers #3 suggestions and mark blue color in the revised manuscript and response letter by the files.

 

Reviewer #1 comment

All the suggestions have been addressed. Accept!

Response: We are thankful for the appreciation of the reviewer.

 

Reviewer #2 comment

In my opinion, the manuscript can be published. Congratulation 

Response: We are thankful for the appreciation of the reviewer.

 

Reviewer #3 comments

1. The authors have replied to all questions, however, they did not improve much the manuscript, e.g. did not add concentrations to the procedures; EIS explanation is not yet clear enough (how capacitance was replaced with CPE, what kind of Warburg element (short or open) was used, etc.

Response: We are thankful for the kind suggestion of the reviewer.  We revised some texts and Figure 12 (b) in the revised manuscript.

“Constant phase element (CPE) means the constant phase-angle element relating to the nonideal characteristic of the double layer.“ CPE is an equivalent electrical circuit component that models the behavior like a double layer, that is an imperfect capacitor. A constant phase element also currently appears in modeling the imperfect dielectrics' behavior.

“For simulation the electrochemical cell sensing system, we used Warburg element (short) to represent diffusion.” (Fig. A and Fig. 12b)

Fig. A

Figure 12. (b) Electrochemical impedance spectroscopy (EIS) of the electrochemical behavior of different electrodes.

 

 

2. The added results show that this material is not suitable for dopamine sensing because it is not sensitive and calibration curve has so high intercept that it is not possible to calculate LOD.

Response: We are thankful for the kind suggestion of the reviewer.  We revised the texts, Figure 8c and Table 1.  The detection limit (DL) is measured by DL = (3×SD)/m by Table A, the SD presents the standard deviation of blank sample signal and the m is revealed the slope of the response versus DA concentration curve.

“Notably, 1% Pd-5% Au/MWCNT possessed the highest DPV current among various kinds of sensing electrodes in Figure 8a. The calibration curves between the peak current and concentration of dopamine has been studied by DPV method. From Figure 8b, it can be found that all of the electrodes exhibited peak currents changed proportional with the increasing concentration of dopamine. It revealed the DPV currents within the detection concentration range of 0.098‐200 μM.  In Table 1, the calculation LOD of DA concentration linear range from 0.098 μM to 6.8 μM of 1% Pd/MWCNT and 1%Pd-5%Au/MWCNT are 0.045 μM and 0.058 μM from Figure 8 (c).”

Figure. 8 (c) The DPV current versus DA concentration from 0.098 μM to 6.8 μM.

 

         Table A. LOD of linear DA concentration range from 0.098 μM to 6.8 μM

 

	SD : standard deviation of blank sample (μA)	Slope: m (μA/μM)	LOD= 3×SD/m     (μM)
1% Au/MWCNT	0.012	0.5314	0.068
1%Pd/MWCNT	0.011	0.7281	0.045
MWCNT	0.010	0.4776	0.063
1%Pd-5%Au/MWCNT	0.011	0.5661	0.058

 

 

 

      Table 1. Comparison of different electrodes for the determination of dopamine (DA).

electrode	Linear Range (μM)	LOD(μM)	References (Ω)
PtNi@MOS2	0.5-150	0.1	[31]
PtNCs-MWCNTs-GNPs	2-50	0.5	[32]
Pd-Au-P/PDDA/rGO	3.5-125	0.7	[33]
Ag-Au/CNT	1-173	0.052	[34]
Pd3Pt1/PDDA-RGO	4-200	0.04	[35]
Au@Pd-RGO	0.01-100	0.024	[36]
1%Pd/MWCNT	0.098-6.8	0.045	This work
1%Pd-5%Au/MWCNT	0.098-6.8	0.058	This work

 

 

 

 

3. The biggest problem is that the paper is not suitable for this journal. It has nothing related to materials.

Response: We are thankful for the kind suggestion of the reviewer.  This manuscript is the invited paper and we think there are some technologies in the manuscript relating to this journal.

• The subject areas of this journal including metallic minerals, and the noble metals Au, Pd and Au-Pd are in the field. This manuscript described the preparation of Bimetallic Au-Pd process.

The related publications 

“The Gold–Palladium Ozernoe Occurrence (Polar Urals, Russia): Mineralogy, Conditions of Formation, Sources of Ore Matter and Fluid” Minerals 2022, 12(6), 765; https://doi.org/10.3390/min12060765

“Recovery of Palladium and Gold from PGM Ore and Concentrate Leachates Using Fe₃O₄@SiO₂@Mg-Al-LDH Nanocomposite” Minerals 2021, 11(9), 917; https://doi.org/10.3390/min11090917

 

• This manuscript is Invited paper: the special Issue (SI) in Minerals is Green Synthesis and Application of Multimetallic Nanoparticles.

This manuscript described the simple, easy and green preparation process of Bimetallic Au-Pd on MWCNT (Fig. 1A) and applied to biosensor field, so it is fitting to the goal of the special Issue (SI) in Minerals is Green Synthesis and Application of Multimetallic Nanoparticles

Figure 1A Synthesis the sensing material and preparation for sensing electrode to the detecting system

 

 

We hope this revised paper could be acceptable in the journal.    

                               

With best regards and your kind help

Sincerely yours,

Ren-Jang (Isaac) Wu

Professor of Applied Chemistry

/Providence University/Taiwan

Dear Editor of Minerals

Manuscript ID: Minerals-1831560

Type: Article

Title: Preparation of Bimetallic Au-Pd/MWCNTs Electrode for Detection of Dopamine

         

We are thankful for your kindness suggestions and appreciate the reviewers’ and editor’ valuable comments.  Also we carefully considered the comments, so we only revised parts of the manuscript according to the reviewers #3 suggestions and mark blue color in the revised manuscript and response letter by the files.

 

Reviewer #1 comment

All the suggestions have been addressed. Accept!

Response: We are thankful for the appreciation of the reviewer.

 

Reviewer #2 comment

In my opinion, the manuscript can be published. Congratulation 

Response: We are thankful for the appreciation of the reviewer.

 

Reviewer #3 comments

1. The authors have replied to all questions, however, they did not improve much the manuscript, e.g. did not add concentrations to the procedures; EIS explanation is not yet clear enough (how capacitance was replaced with CPE, what kind of Warburg element (short or open) was used, etc.

Response: We are thankful for the kind suggestion of the reviewer.  We revised some texts and Figure 12 (b) in the revised manuscript.

“Constant phase element (CPE) means the constant phase-angle element relating to the nonideal characteristic of the double layer.“ CPE is an equivalent electrical circuit component that models the behavior like a double layer, that is an imperfect capacitor. A constant phase element also currently appears in modeling the imperfect dielectrics' behavior.

“For simulation the electrochemical cell sensing system, we used Warburg element (short) to represent diffusion.” (Fig. A and Fig. 12b)

Fig. A

Figure 12. (b) Electrochemical impedance spectroscopy (EIS) of the electrochemical behavior of different electrodes.

 

 

2. The added results show that this material is not suitable for dopamine sensing because it is not sensitive and calibration curve has so high intercept that it is not possible to calculate LOD.

Response: We are thankful for the kind suggestion of the reviewer.  We revised the texts, Figure 8c and Table 1.  The detection limit (DL) is measured by DL = (3×SD)/m by Table A, the SD presents the standard deviation of blank sample signal and the m is revealed the slope of the response versus DA concentration curve.

“Notably, 1% Pd-5% Au/MWCNT possessed the highest DPV current among various kinds of sensing electrodes in Figure 8a. The calibration curves between the peak current and concentration of dopamine has been studied by DPV method. From Figure 8b, it can be found that all of the electrodes exhibited peak currents changed proportional with the increasing concentration of dopamine. It revealed the DPV currents within the detection concentration range of 0.098‐200 μM.  In Table 1, the calculation LOD of DA concentration linear range from 0.098 μM to 6.8 μM of 1% Pd/MWCNT and 1%Pd-5%Au/MWCNT are 0.045 μM and 0.058 μM from Figure 8 (c).”

Figure. 8 (c) The DPV current versus DA concentration from 0.098 μM to 6.8 μM.

 

         Table A. LOD of linear DA concentration range from 0.098 μM to 6.8 μM

 

	SD : standard deviation of blank sample (μA)	Slope: m (μA/μM)	LOD= 3×SD/m     (μM)
1% Au/MWCNT	0.012	0.5314	0.068
1%Pd/MWCNT	0.011	0.7281	0.045
MWCNT	0.010	0.4776	0.063
1%Pd-5%Au/MWCNT	0.011	0.5661	0.058

 

 

 

      Table 1. Comparison of different electrodes for the determination of dopamine (DA).

electrode	Linear Range (μM)	LOD(μM)	References (Ω)
PtNi@MOS2	0.5-150	0.1	[31]
PtNCs-MWCNTs-GNPs	2-50	0.5	[32]
Pd-Au-P/PDDA/rGO	3.5-125	0.7	[33]
Ag-Au/CNT	1-173	0.052	[34]
Pd3Pt1/PDDA-RGO	4-200	0.04	[35]
Au@Pd-RGO	0.01-100	0.024	[36]
1%Pd/MWCNT	0.098-6.8	0.045	This work
1%Pd-5%Au/MWCNT	0.098-6.8	0.058	This work

 

 

 

 

3. The biggest problem is that the paper is not suitable for this journal. It has nothing related to materials.

Response: We are thankful for the kind suggestion of the reviewer.  This manuscript is the invited paper and we think there are some technologies in the manuscript relating to this journal.

• The subject areas of this journal including metallic minerals, and the noble metals Au, Pd and Au-Pd are in the field. This manuscript described the preparation of Bimetallic Au-Pd process.

The related publications 

“The Gold–Palladium Ozernoe Occurrence (Polar Urals, Russia): Mineralogy, Conditions of Formation, Sources of Ore Matter and Fluid” Minerals 2022, 12(6), 765; https://doi.org/10.3390/min12060765

“Recovery of Palladium and Gold from PGM Ore and Concentrate Leachates Using Fe₃O₄@SiO₂@Mg-Al-LDH Nanocomposite” Minerals 2021, 11(9), 917; https://doi.org/10.3390/min11090917

 

• This manuscript is Invited paper: the special Issue (SI) in Minerals is Green Synthesis and Application of Multimetallic Nanoparticles.

This manuscript described the simple, easy and green preparation process of Bimetallic Au-Pd on MWCNT (Fig. 1A) and applied to biosensor field, so it is fitting to the goal of the special Issue (SI) in Minerals is Green Synthesis and Application of Multimetallic Nanoparticles

Figure 1A Synthesis the sensing material and preparation for sensing electrode to the detecting system

 

 

We hope this revised paper could be acceptable in the journal.    

                               

With best regards and your kind help

Sincerely yours,

Ren-Jang (Isaac) Wu

Professor of Applied Chemistry

/Providence University/Taiwan

Dear Editor of Minerals

Manuscript ID: Minerals-1831560

Type: Article

Title: Preparation of Bimetallic Au-Pd/MWCNTs Electrode for Detection of Dopamine

         

We are thankful for your kindness suggestions and appreciate the reviewers’ and editor’ valuable comments.  Also we carefully considered the comments, so we only revised parts of the manuscript according to the reviewers #3 suggestions and mark blue color in the revised manuscript and response letter by the files.

 

Reviewer #1 comment

All the suggestions have been addressed. Accept!

Response: We are thankful for the appreciation of the reviewer.

 

Reviewer #2 comment

In my opinion, the manuscript can be published. Congratulation 

Response: We are thankful for the appreciation of the reviewer.

 

Reviewer #3 comments

1. The authors have replied to all questions, however, they did not improve much the manuscript, e.g. did not add concentrations to the procedures; EIS explanation is not yet clear enough (how capacitance was replaced with CPE, what kind of Warburg element (short or open) was used, etc.

Response: We are thankful for the kind suggestion of the reviewer.  We revised some texts and Figure 12 (b) in the revised manuscript.

“Constant phase element (CPE) means the constant phase-angle element relating to the nonideal characteristic of the double layer.“ CPE is an equivalent electrical circuit component that models the behavior like a double layer, that is an imperfect capacitor. A constant phase element also currently appears in modeling the imperfect dielectrics' behavior.

“For simulation the electrochemical cell sensing system, we used Warburg element (short) to represent diffusion.” (Fig. A and Fig. 12b)

Fig. A

Figure 12. (b) Electrochemical impedance spectroscopy (EIS) of the electrochemical behavior of different electrodes.

 

 

2. The added results show that this material is not suitable for dopamine sensing because it is not sensitive and calibration curve has so high intercept that it is not possible to calculate LOD.

Response: We are thankful for the kind suggestion of the reviewer.  We revised the texts, Figure 8c and Table 1.  The detection limit (DL) is measured by DL = (3×SD)/m by Table A, the SD presents the standard deviation of blank sample signal and the m is revealed the slope of the response versus DA concentration curve.

“Notably, 1% Pd-5% Au/MWCNT possessed the highest DPV current among various kinds of sensing electrodes in Figure 8a. The calibration curves between the peak current and concentration of dopamine has been studied by DPV method. From Figure 8b, it can be found that all of the electrodes exhibited peak currents changed proportional with the increasing concentration of dopamine. It revealed the DPV currents within the detection concentration range of 0.098‐200 μM.  In Table 1, the calculation LOD of DA concentration linear range from 0.098 μM to 6.8 μM of 1% Pd/MWCNT and 1%Pd-5%Au/MWCNT are 0.045 μM and 0.058 μM from Figure 8 (c).”

Figure. 8 (c) The DPV current versus DA concentration from 0.098 μM to 6.8 μM.

 

         Table A. LOD of linear DA concentration range from 0.098 μM to 6.8 μM

 

	SD : standard deviation of blank sample (μA)	Slope: m (μA/μM)	LOD= 3×SD/m     (μM)
1% Au/MWCNT	0.012	0.5314	0.068
1%Pd/MWCNT	0.011	0.7281	0.045
MWCNT	0.010	0.4776	0.063
1%Pd-5%Au/MWCNT	0.011	0.5661	0.058

 

 

 

      Table 1. Comparison of different electrodes for the determination of dopamine (DA).

electrode	Linear Range (μM)	LOD(μM)	References (Ω)
PtNi@MOS2	0.5-150	0.1	[31]
PtNCs-MWCNTs-GNPs	2-50	0.5	[32]
Pd-Au-P/PDDA/rGO	3.5-125	0.7	[33]
Ag-Au/CNT	1-173	0.052	[34]
Pd3Pt1/PDDA-RGO	4-200	0.04	[35]
Au@Pd-RGO	0.01-100	0.024	[36]
1%Pd/MWCNT	0.098-6.8	0.045	This work
1%Pd-5%Au/MWCNT	0.098-6.8	0.058	This work

 

 

 

 

3. The biggest problem is that the paper is not suitable for this journal. It has nothing related to materials.

Response: We are thankful for the kind suggestion of the reviewer.  This manuscript is the invited paper and we think there are some technologies in the manuscript relating to this journal.

• The subject areas of this journal including metallic minerals, and the noble metals Au, Pd and Au-Pd are in the field. This manuscript described the preparation of Bimetallic Au-Pd process.

The related publications 

“The Gold–Palladium Ozernoe Occurrence (Polar Urals, Russia): Mineralogy, Conditions of Formation, Sources of Ore Matter and Fluid” Minerals 2022, 12(6), 765; https://doi.org/10.3390/min12060765

“Recovery of Palladium and Gold from PGM Ore and Concentrate Leachates Using Fe₃O₄@SiO₂@Mg-Al-LDH Nanocomposite” Minerals 2021, 11(9), 917; https://doi.org/10.3390/min11090917

 

• This manuscript is Invited paper: the special Issue (SI) in Minerals is Green Synthesis and Application of Multimetallic Nanoparticles.

This manuscript described the simple, easy and green preparation process of Bimetallic Au-Pd on MWCNT (Fig. 1A) and applied to biosensor field, so it is fitting to the goal of the special Issue (SI) in Minerals is Green Synthesis and Application of Multimetallic Nanoparticles

Figure 1A Synthesis the sensing material and preparation for sensing electrode to the detecting system

 

 

We hope this revised paper could be acceptable in the journal.    

                               

With best regards and your kind help

Sincerely yours,

Ren-Jang (Isaac) Wu

Professor of Applied Chemistry

/Providence University/Taiwan

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors have replied to all questions, however, they did not improve much the manuscript, e.g. did not add concentrations to the procedures; EIS explanation is not yet clear enough (how capacitance was replaced with CPE, what kind of Warburg element (short or open) was used, etc.

The added results show that this material is not suitable for dopamine sensing because it is not sensitive and calibration curve has so high intercept that it is not possible to calculate LOD.

The biggest problem is that the paper is not suitable for this journal. It has nothing related to materials.

Author Response

Dear Editor of Minerals

Manuscript ID: Minerals-1831560

Type: Article

Title: Preparation of Bimetallic Au-Pd/MWCNTs Electrode for Detection of Dopamine

         

We are thankful for your kindness suggestions and appreciate the reviewers’ and editor’ valuable comments.  Also we carefully considered the comments, so we only revised parts of the manuscript according to the reviewers #3 suggestions and mark blue color in the revised manuscript and response letter by the files.

 

Reviewer #1 comment

All the suggestions have been addressed. Accept!

Response: We are thankful for the appreciation of the reviewer.

 

Reviewer #2 comment

In my opinion, the manuscript can be published. Congratulation 

Response: We are thankful for the appreciation of the reviewer.

 

Reviewer #3 comments

1. The authors have replied to all questions, however, they did not improve much the manuscript, e.g. did not add concentrations to the procedures; EIS explanation is not yet clear enough (how capacitance was replaced with CPE, what kind of Warburg element (short or open) was used, etc.

Response: We are thankful for the kind suggestion of the reviewer.  We revised some texts and Figure 12 (b) in the revised manuscript.

“Constant phase element (CPE) means the constant phase-angle element relating to the nonideal characteristic of the double layer.“ CPE is an equivalent electrical circuit component that models the behavior like a double layer, that is an imperfect capacitor. A constant phase element also currently appears in modeling the imperfect dielectrics' behavior.

“For simulation the electrochemical cell sensing system, we used Warburg element (short) to represent diffusion.” (Fig. A and Fig. 12b)

Fig. A

Figure 12. (b) Electrochemical impedance spectroscopy (EIS) of the electrochemical behavior of different electrodes.

 

 

2. The added results show that this material is not suitable for dopamine sensing because it is not sensitive and calibration curve has so high intercept that it is not possible to calculate LOD.

Response: We are thankful for the kind suggestion of the reviewer.  We revised the texts, Figure 8c and Table 1.  The detection limit (DL) is measured by DL = (3×SD)/m by Table A, the SD presents the standard deviation of blank sample signal and the m is revealed the slope of the response versus DA concentration curve.

“Notably, 1% Pd-5% Au/MWCNT possessed the highest DPV current among various kinds of sensing electrodes in Figure 8a. The calibration curves between the peak current and concentration of dopamine has been studied by DPV method. From Figure 8b, it can be found that all of the electrodes exhibited peak currents changed proportional with the increasing concentration of dopamine. It revealed the DPV currents within the detection concentration range of 0.098‐200 μM.  In Table 1, the calculation LOD of DA concentration linear range from 0.098 μM to 6.8 μM of 1% Pd/MWCNT and 1%Pd-5%Au/MWCNT are 0.045 μM and 0.058 μM from Figure 8 (c).”

Figure. 8 (c) The DPV current versus DA concentration from 0.098 μM to 6.8 μM.

 

         Table A. LOD of linear DA concentration range from 0.098 μM to 6.8 μM

 

	SD : standard deviation of blank sample (μA)	Slope: m (μA/μM)	LOD= 3×SD/m     (μM)
1% Au/MWCNT	0.012	0.5314	0.068
1%Pd/MWCNT	0.011	0.7281	0.045
MWCNT	0.010	0.4776	0.063
1%Pd-5%Au/MWCNT	0.011	0.5661	0.058

 

 

 

      Table 1. Comparison of different electrodes for the determination of dopamine (DA).

electrode	Linear Range (μM)	LOD(μM)	References (Ω)
PtNi@MOS2	0.5-150	0.1	[31]
PtNCs-MWCNTs-GNPs	2-50	0.5	[32]
Pd-Au-P/PDDA/rGO	3.5-125	0.7	[33]
Ag-Au/CNT	1-173	0.052	[34]
Pd3Pt1/PDDA-RGO	4-200	0.04	[35]
Au@Pd-RGO	0.01-100	0.024	[36]
1%Pd/MWCNT	0.098-6.8	0.045	This work
1%Pd-5%Au/MWCNT	0.098-6.8	0.058	This work

 

 

 

 

3. The biggest problem is that the paper is not suitable for this journal. It has nothing related to materials.

Response: We are thankful for the kind suggestion of the reviewer.  This manuscript is the invited paper and we think there are some technologies in the manuscript relating to this journal.

• The subject areas of this journal including metallic minerals, and the noble metals Au, Pd and Au-Pd are in the field. This manuscript described the preparation of Bimetallic Au-Pd process.

The related publications 

“The Gold–Palladium Ozernoe Occurrence (Polar Urals, Russia): Mineralogy, Conditions of Formation, Sources of Ore Matter and Fluid” Minerals 2022, 12(6), 765; https://doi.org/10.3390/min12060765

“Recovery of Palladium and Gold from PGM Ore and Concentrate Leachates Using Fe₃O₄@SiO₂@Mg-Al-LDH Nanocomposite” Minerals 2021, 11(9), 917; https://doi.org/10.3390/min11090917

 

• This manuscript is Invited paper: the special Issue (SI) in Minerals is Green Synthesis and Application of Multimetallic Nanoparticles.

This manuscript described the simple, easy and green preparation process of Bimetallic Au-Pd on MWCNT (Fig. 1A) and applied to biosensor field, so it is fitting to the goal of the special Issue (SI) in Minerals is Green Synthesis and Application of Multimetallic Nanoparticles

Figure 1A Synthesis the sensing material and preparation for sensing electrode to the detecting system

 

 

We hope this revised paper could be acceptable in the journal.    

                               

With best regards and your kind help

Sincerely yours,

Ren-Jang (Isaac) Wu

Professor of Applied Chemistry

/Providence University/Taiwan

Author Response File: Author Response.pdf