Aqueous Singlet Oxygen Sensitization of Porphyrin-Embedded Silica Particles with Long-Term Stability

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript describes the efficiency of singlet oxygen generation using palladium octaethylporphyrin (PdOEP) embedded silica particles in aqueous media. Although this manuscript provides some interesting scientific results, several deficiencies should be addressed before acceptance for publication in Inorganics from MDPI. Please take into consideration the following points.

 

1. On page 2, line 52;

Why was palladium porphyrin derivative selected as a photosensitizer? The reason using palladium complex should be explained.

 

2. On page 2 (2.1 Preparation and Characterization of Particles)

Can the number of porphyrins embedded in each silica particle be estimated?

 

3. On page 2, line 74;

In the caption of Figure 1, “and (c) and (c)” is wrong.

 

4. On page 3, line 87 and line 115;

Absorbance at 546 nm shows a Q band of porphyrins? Why wasn’t a Soret band selected?

There is no Figures 2b.

 

5. On page 3, line 90 and line 95;

Figures 2b →Figure 1b?

Figures 2c →Figure 1c?

 

6. On page 3, line 94;

The ω values were decreasing with the concentration of surfactant. As the surfactant concentration increased, the c/c₀ values increased, while the ω values of silica particles decreased. A clear explanation on this should be given.

 

7. On page 4, in Figure 2;

Figure 2b should be shown in Figure 2.

 

8. On page 6, line 200;

To determine Φ_Δ values, the linear slopes of the plots of F_t/(F₀·A_PdOEP) vs. irradiation time were used. Why were F_t/(F₀·A_PdOEP) used instead of F_t/F₀ on the Y-axis?

 

9. On page 6, line 254;

In Figure 4d, the linear relationship of F_t/F₀·with irradiation time was confirmed. But for some reason, F_t/(F₀·A_PdOEP) is written in the main text?

 

10. Please check the chapter number, such as “3. Materials and Methods”.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The authors describe the embedding of palladium-octaethylporphyrin into silica nanoparticles through a micelle-based strategy using Tween 20 and Tween 80 as surfactants, for the design of aqueous stable photosensitizers. The work is systematically described and complementary tests such as the addition of cholesterol are performed to support the trends in singlet oxygen generation ability. The manuscript is in general well written, though some concepts could be clarified earlier in the manuscript to make easier the understanding of the whole discussion. The main observations are detailed next.

• Lines 55 and 56: in sentence “Although PdOEP demonstrated good solubility…”, better indicate that the data provided correspond to the micellar system with Tween 80, to make clearer the later comparison (line 61) with that of the embedded analogue.
• Lines 58 and 59: the concept of enhanced stability is repeated
• A brief explanation of the meaning of embedding efficiency (ω) should be provided around line 92, where it is mentioned for the first time, to clarify that this parameter is related to the percent of micelles embedded versus the initial micelle solution. On the other hand, the authors should revise whether the “particle coating efficiency E”, defined in lines 270-271, is indeed the same parameter as the embedding efficiency ω (and, if so, homogenize the nomenclature).
• Lines 96-97: in my opinion, the assertion about the superior embedding efficiency of Tween 80 is dispensable, as it is only clearly higher for Tween 80 at 10 mg/mL (for lower concentrations the two surfactants behave similarly, as evidenced in Figure 1c).

• A brief discussion on the reasons for the lower embedding efficiency at high surfactant concentration should be provided somewhere between lines 94 and 98. Could it be a question of competence between empty and PdOEP-containing micelles? A higher amount of surfactant may lead to the formation of micelles lacking Pd content, and silica would presumably polymerize around these micelles as well

• Sentence in lines 143-145 is confusing and should be redrawn (“corresponds has been shown” appears as a grammar/typo mistake). Also, the “transition” mentioned in line 145 should be detailed in a better way. Finally, the relationship between the density of the packing in micelles and the embedding efficiency omega should be discussed in a deeper way: what is the reason for the differences in packing and how it affects the ability to retain PdOEP?. All these topics are better understood later in the manuscript (section 2.2), so probably a reorganization of the contents to expose the concepts in a sequential way would be enough to make the text easier to follow.

• Plots of nitrogen sorption isotherms, mentioned in line 280, should be better included in the supporting information (Section S2)

Finally, some typo and format issues can be addressed:

• Line 47, The packing structures govern (or The packing structure governs)
• Line 50, better avoid using consecutive similar words (limited, limiting)
• Line 74, “and (c)” is repeated
• Line 88, “which achieved”
• Line 90, “(Figures 2b)” should be either “Figure 1(b)” or “Figure S2 (c) and (d)”
• Lines 93, 269, 271 and equation (3): better homogenize the use of the term “supernatant” and
• “supernate”
• Line 95, “Figures 2c” should be “Figure 1c”
• Line 124: notation “(b)” is missing in the figure (though it is easy to deduce by elimination)
• Lines 168 and 201: font size in Figure 3d and the offcut “energy transfer” in Figure 4a should be increased
• Supporting information: the caption in Figure S2 should be better end as “…coating process. (c) and (d) are the analogous spectra obtained with Tween 20”

Author Response

Please see the attachment.

Author Response File: Author Response.docx