Modulating Photodissociation and Photobleaching via Plasmon Resonance to Enhance Light-Induced Nitric Oxide Release

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript reports the effect of vicinity to silver islands on the photochemical nitric oxide release utilizing boron dipyrromethene molecules. The plasmonic enhancement on NO release and the role of overlapping absorption and plasmonic absorption spectra of silver islands is reported. The manuscript can be accepted for publication in applied nano after addressing the following.

 

• The introduction section lacks prior work on similar systems and hence needs to be included with relevant works in literature.
• Why does the extinction spectra of silver islands with different SiO₂ thicknesses first shift to shorter wavelength with 0.5 nm SiO₂ and then shift towards longer wavelengths with increase in SiO₂ thickness?
• The rinsing procedure including the volume and time to prepare should be included in detail as it determines the final NO concentration.

Author Response

The manuscript reports the effect of vicinity to silver islands on the photochemical nitric oxide release utilizing boron dipyrromethene molecules. The plasmonic enhancement on NO release and the role of overlapping absorption and plasmonic absorption spectra of silver islands is reported. The manuscript can be accepted for publication in applied nano after addressing the following.

The introduction section lacks prior work on similar systems and hence needs to be included with relevant works in literature.

 

Similar systems have indeed been reported in the literature; however, in most cases they were used primarily for studying singlet oxygen generation. In such systems, island-like metallic films with relatively broad plasmon resonances were typically employed, and the exact position of the plasmon resonance was often not a critical factor. For example, in [10], singlet oxygen yield was enhanced by varying the thickness of a buffer layer, and the effect was mathematically modeled.

 

In our study, we use island silver films with a distinct, narrow plasmon resonance and, for the first time, demonstrate that the metal-enhanced photodissociation rate depends directly on the excitation wavelength. Furthermore, we vary the thickness of a silicon dioxide buffer layer and show how it influences non-radiative processes in dye molecules.

 

We have added the following paragraphs into the Introduction:

 

“For example, in [10], the singlet oxygen yield was improved by varying the buffer layer thickness and modeling the effect theoretically. This dual enhancement enables not only increased singlet oxygen production but also the activation of photodissociation pathways responsible for NO release [13]. This plasmon-enhanced nitric oxide release is a rel-atively new and less explored area. One of the key works in this field is [13], where excitation of the plasmon resonance in silver nanostructured “Quanta Plate” films led to a 2–6-fold increase in NO yield. However, in existing works, island-like metallic films with relatively broad plasmon resonances were used, and the precise position of the plasmon resonance was often not considered a critical factor. In our case, the silver island films (SIFs) used are distinct in that their plasmon resonance can be tuned to match the absorption band of the dye, allowing more precise control over the interaction between the plasmonic field and the photosensitizer.

 

<…>

 

Unlike prior works, our SIFs feature a distinct and narrow plasmon resonance, allowing us to di-rectly demonstrate that the metal-enhanced photodissociation rate depends on the excita-tion wavelength.”

 

Why does the extinction spectra of silver islands with different SiO2 thicknesses first shift to shorter wavelength with 0.5 nm SiO2 and then shift towards longer wavelengths with increase in SiO2 thickness?

• For buffer layers from 0.5 nm to 20 nm, the plasmon resonance consistently red-shifts with increasing SiO₂ thickness, as expected from the increase in the effective local refractive index.
• Regarding the apparent initial blue shift for the 0.5 nm buffer layer compared to the 0 nm: it is due to a difference in the thickness of the deposited silver layer (prior to annealing) between SIFs with and without a buffer layer. This fabrication difference results in distinct initial plasmon resonance positions.

However, the SIF without a buffer layer already has its plasmon resonance near 488 nm, which makes it possible, for example, to directly compare SIFs with 0 nm and 20 nm SiO₂ when their plasmon resonances have a similar degree of spectral overlap with the excitation wavelength.

 

 

The rinsing procedure including the volume and time to prepare should be included in detail as it determines the final NO concentration.

 

As now indicated in the paper, the glass substrates with the sample (8 µL) were placed into a cuvette containing 3 ml of ethanol.

Reviewer 2 Report

Comments and Suggestions for Authors

The research article is original and innovative in proposing a platform for photodynamic therapy based on nanotechnology for cancer treatment, using reactive oxygen species to kill cancer cells.

  I recommend including in the title of the article, singlet oxygen production, followed by nitric oxide release, since the article explored the nitric oxide release, but also the enhanced singlet oxygen production.   On the other hand, I would recommend adding more information on the introduction and citations on the effect of NO for cancer treatment, since it is better explained for the case of singlet oxygen.   In the conclusion section, I strongly recommend adding a paragraph commenting on how the nanoplatform developed in this work, be applied by researchers interested in applying this technology on in vitro and in vivo biological models in cancer treatment. This addition will make this article more appealing to researchers in the nano medicine field who are already working on cancer therapy research based on photodynamic therapies.   The methodology and the results are well written, adequate, as well as the figures.

Author Response

The research article is original and innovative in proposing a platform for photodynamic therapy based on nanotechnology for cancer treatment, using reactive oxygen species to kill cancer cells.

I recommend including in the title of the article, singlet oxygen production, followed by nitric oxide release, since the article explored the nitric oxide release, but also the enhanced singlet oxygen production.

 

We thank the Reviewer for this suggestion. However, as the title is already long, we decided not to include additional terms. The singlet oxygen production is mentioned in the abstract.

 

On the other hand, I would recommend adding more information on the introduction and citations on the effect of NO for cancer treatment, since it is better explained for the case of singlet oxygen.

 

This is great point. NO plays a complex and sometimes contradictory role in cancer: its low levels can pro-mote tumor growth, angiogenesis, and metastasis, whereas high concentrations may exert cytotoxic or cytostatic effects, damaging tumor DNA, activating p53, and sensitizing can-cer cells to chemo-, radio-, or immunotherapy. This duality makes NO both a potential tumor promoter and a promising therapeutic agent for resistant cancers. We have included this into the Introduction.

 

In the conclusion section, I strongly recommend adding a paragraph commenting on how the nanoplatform developed in this work, be applied by researchers interested in applying this technology on in vitro and in vivo biological models in cancer treatment. This addition will make this article more appealing to researchers in the nano medicine field who are already working on cancer therapy research based on photodynamic therapies. The methodology and the results are well written, adequate, as well as the figures.

 

We thank the Reviewer for the appreciation of the text and figures.

 

We have added the following paragraph to the Conclusion:

 

“Given the demonstrated ability of this nanoplatform to controllably enhance both NO and singlet oxygen generation, it holds strong potential for biomedical applications. However, these applications require reformulation of the platform into biocompatible system, in vitro studies on established cancer cell lines, and in vivo validation in xenograft tumor models that allow assessment of tumor targeting efficiency and therapeutic outcomes. At the same time, from a fundamental perspective, this hybrid platform provides a useful model for studying plasmon–molecule interactions and controlled modulation of nonradiative processes. Future research may further advance this approach toward more complex hybrid systems, such as nanoparticle–dye constructs with embedded molecules in protective shells, which could facilitate efficient intracellular delivery and activation.”

Reviewer 3 Report

Comments and Suggestions for Authors

In this study, the authors developed hybrid systems combining photosensitive nitric oxide donors with silver island films to investigate how localized surface plasmon resonances influence non-radiative relaxation pathways and reactive oxygen species generation. By varying the thickness of a SiO₂ buffer layer, they identified key factors—spectral overlap and nanoparticle–molecule distance—that significantly enhanced both nitric oxide release and singlet oxygen production.

• While the manuscript briefly mentions existing limitations, the research gap is not explicitly and clearly stated. The introduction would benefit from a concise statement outlining what has not been addressed in previous studies and how the present work specifically aims to fill this gap.
• The authors should strengthen the discussion section to provide a deeper interpretation of the results, relate them more extensively to previous studies, and better highlight the significance and implications of their findings.
• The conclusion is primarily descriptive and should provide deeper interpretation of the results, including their significance in the context of previous studies, the implications for practical applications, and the study’s limitations.
• Future research directions are not explicitly stated.The authors should outline specific next steps to build on these findings, such as improving quantitative measurements, testing in biological models, or exploring other plasmonic configurations.

 

Comments on the Quality of English Language

The manuscript would benefit from minor language revisions to improve clarity, precision, and readability. 

Author Response

In this study, the authors developed hybrid systems combining photosensitive nitric oxide donors with silver island films to investigate how localized surface plasmon resonances influence non-radiative relaxation pathways and reactive oxygen species generation. By varying the thickness of a SiO₂ buffer layer, they identified key factors—spectral overlap and nanoparticle–molecule distance—that significantly enhanced both nitric oxide release and singlet oxygen production.

While the manuscript briefly mentions existing limitations, the research gap is not explicitly and clearly stated. The introduction would benefit from a concise statement outlining what has not been addressed in previous studies and how the present work specifically aims to fill this gap. The authors should strengthen the discussion section to provide a deeper interpretation of the results, relate them more extensively to previous studies, and better highlight the significance and implications of their findings.

This point was also raised by Reviewer 1.

Similar systems have indeed been reported in the literature; however, in most cases they were used primarily for studying singlet oxygen generation. In such systems, island-like metallic films with relatively broad plasmon resonances were typically employed, and the exact position of the plasmon resonance was often not a critical factor. For example, in [10], singlet oxygen yield was enhanced by varying the thickness of a buffer layer, and the effect was mathematically modeled.

 

In our study, we use island silver films with a distinct, narrow plasmon resonance and, for the first time, demonstrate that the metal-enhanced photodissociation rate depends directly on the excitation wavelength. Furthermore, we vary the thickness of a silicon dioxide buffer layer and show how it influences non-radiative processes in dye molecules.

 

We have added the following paragraphs into the Introduction:

 

“For example, in [10], the singlet oxygen yield was improved by varying the buffer layer thickness and modeling the effect theoretically. This dual enhancement enables not only increased singlet oxygen production but also the activation of photodissociation pathways responsible for NO release [13]. This plasmon-enhanced nitric oxide release is a rel-atively new and less explored area. One of the key works in this field is [13], where excita-tion of the plasmon resonance in silver nanostructured “Quanta Plate” films led to a 2–6-fold increase in NO yield. However, in existing works, island-like metallic films with relatively broad plasmon resonances were used, and the precise position of the plasmon resonance was often not considered a critical factor. In our case, the silver island films (SIFs) used are distinct in that their plasmon resonance can be tuned to match the absorp-tion band of the dye, allowing more precise control over the interaction between the plasmonic field and the photosensitizer.

 

<…>

 

Unlike prior works, our SIFs feature a distinct and narrow plasmon resonance, allowing us to di-rectly demonstrate that the metal-enhanced photodissociation rate depends on the excitation wavelength.”

 

The conclusion is primarily descriptive and should provide deeper interpretation of the results, including their significance in the context of previous studies, the implications for practical applications, and the study’s limitations. Future research directions are not explicitly stated. The authors should outline specific next steps to build on these findings, such as improving quantitative measurements, testing in biological models, or exploring other plasmonic configurations.

Future research may further advance this approach toward more complex hybrid systems, such as nanoparticle–dye constructs with embedded molecules in protective shells, which could facilitate efficient intracellular delivery and activation.

 

We have added the following paragraph to the Comclusion:

 

“Given the demonstrated ability of this nanoplatform to controllably enhance both NO and singlet oxygen generation, it holds strong potential for biomedical applications. However, these applications require reformulation of the platform into biocompatible system, in vitro studies on established cancer cell lines, and in vivo validation in xenograft tumor models that allow assessment of tumor targeting efficiency and therapeutic outcomes. At the same time, from a fundamental perspective, this hybrid platform provides a useful model for studying plasmon–molecule interactions and controlled modulation of nonradiative processes. Future research may further advance this approach toward more complex hybrid systems, such as nanoparticle–dye constructs with embedded molecules in protective shells, which could facilitate efficient intracellular delivery and activation.”