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Nano and Micro Technologies

Nano and Micro Technologies - Poster Session D

Poster Z2 - Broad-Spectrum Photocatalytic Decomposition of Chemical and Biological Species Using Porphyrin-Loaded Porous Silicon Nanoparticles

Friday, October 25, 2024
3:30 PM - 4:30 PM EST
Location: Exhibit Hall E, F & G

Introduction:  The global health crisis caused by the SARS-CoV-2 outbreak has highlighted the urgent need for preparedness against diverse threats, including chemical and biological agents. Porphyrin-based photocatalytic detoxification has emerged as an effective and efficient approach for wide-range threat neutralization due to its ability to rapidly generate singlet oxygen with broad chemical, viral and bacterial threat neutralization activity without requiring a priori knowledge of the agent’s structure and/or mechanism of action.
However, the photo-stability and lipophilic nature of most porphyrins limit their practical application. In this study, we employ porous silicon nanoparticles and a calcium silicate sealing technique as a structural framework to encapsulate a porphyrin while retaining the mesoporous structure needed to allow access of the small-molecule toxicant.
This strategy aims to prevent porphyrin leaching while retaining catalytic efficiency and substrate accessibility. Furthermore, the integration of silicon transforms the hydrophobic nature of the porphyrin into a hydrophilic nano formulation. Prior research has demonstrated the capacity of porous silicon to inhibit photolysis of guest molecules. This presentation will describe the synthesis and characterization of porphyrin-loaded porous silicon nanoparticles, and the ability of the resulting construct to efficiently neutralize 2-chloroethyl ethyl sulfide (2-CEES), a mustard gas simulant, as well as the biological agents influenza A H1N1 and S. aureus.

Materials and

Methods:  Preparation of Porphyrin-pSi and Fabric Coating: Porous silicon nanoparticles (pSi) were prepared by ultrasonication of electrochemically etched silicon layers in ethanol. The resulting particles were then oxidized in hydrogen peroxide, isolated by centrifugation and washed with water and ethanol. Porphyrin (tetrakis(4-carboxyphenyl) porphyrin) was loaded into pSi using calcium silicate sealing method, purified and aged under 420 nm light. The resulting porphyrin-pSi nanoparticles were deposited on a polyester-based fabric via drop casting method. Characterization was performed using FTIR, SEM/EDX, DLS and zeta potential, BET, UV-Vis and fluorescence spectroscopy.

Photocatalytic Reaction for mustard gas simulant 2-CEES: The porphyrin-pSi and 2-CEES was dispersed in methanol, purged with oxygen, stirred, and irradiated with 420 nm light (power density = 20 mW/cm2). 2-CEES and an internal standard were added, with samples taken at intervals and analyzed by GC-MS. Reusability of the photocatalyst was tested by washing the particles with methanol and repeating the procedure. Fabric tests followed the same protocol as for nanoparticles. All tests were conducted with controls including pSi, porphyrin, and porphyrin-pSi, with and without light illumination.

Neutralization Assays: Porphyrin-pSi and free porphyrin were tested against MRSA and Influenza A H1N1 using established viral and bacterial viability-based protocols. In vitro cytotoxicity was evaluated on HEKa cells using the LIVE/DEAD Viability/Cytotoxicity Kit and fluorescence microscopy.

Photolysis Study: Porphyrin or porphyrin-pSi in methanol was illuminated with 420 nm light for 3 hours, with fluorescence measured using an iD5 plate reader. Fabric photolysis was assessed similarly, with reflected light spectra measured by an Ocean Optics spectrometer.

Results, Conclusions, and Discussions: Porphyrin-loaded porous silicon nanoparticles (porphyrin-pSi) were synthesized using a calcium silicate sealing method. Characterization involved FTIR analysis, which confirmed successful porphyrin loading with characteristic peaks at 1586 cm^-1 assigned to pyrrole ring breathing. BET measurements showed a reduction in surface area of the pSi material after the loading process, indicative of pore filling and sealing. DLS analysis revealed an increase in particle size from 213 nm to 245 nm and a change in zeta potential from -20 mV to -12 mV, indicating successful calcium sealing. UV-Vis absorbance measurements showed a porphyrin mass loading of approximately 34%. A methanol leaching test showed less than 2% leakage of porphyrin from the particles after 6 hours. SEM imaging and EDX element mapping confirmed uniform coating of porous silicon nanoparticles on the fabric.

The efficacy of porphyrin-pSi in photocatalytic detoxification was verified through various experiments. The mustard gas simulant (2-CEES) was completely converted to the non-toxic product 2-CEESO (2-Chloroethyl ethyl sulfoxide) within 15 minutes, as monitored by GC-MS. Biological toxin neutralization was tested against Influenza A Virus H1N1 and Staphylococcus aureus using light irradiation protocols, achieving nearly 100% viral and bacterial inhibition.

A photolysis study monitored absorbance and fluorescence spectra under light illumination to assess the effectiveness of porphyrin-pSi in mitigating photobleaching. Porphyrin-pSi retained 100% photoactivity compared to porphyrin alone, which retained only 69% after 3 hrs of continuous illumination by 420nm light of power density 20 mW/cm2. The same photocatalytic assays after light exposure for 2-CEES confirmed that porphyrin-pSi retained 100% catalytic activity, compared to porphyrin alone, which retained only 60.08%.

In conclusion, the study demonstrates the potential of porphyrin-loaded porous silicon nanoparticles as a robust platform for neutralizing chemical and biological threats. The approach yields a high mass loading of porphyrin into the porous silicon nanoparticles, and the porphyrin-nanoparticle constructs retain activity when dispersed on a fabric surface. The results highlight the potential use of porphyrin-loaded porous silicon nanoparticles for tissue protection upon direct skin application or through their prior loading into wearable textiles.

Acknowledgements (Optional):  This research was supported by NSF through the UC San Diego Materials Research Science and Engineering Center (UCSD MRSEC), grant DMR-2011924. This work was also performed in part at the San Diego Nanotechnology Infrastructure (SDNI) of UCSD, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation (Grant ECCS-2025752). The authors acknowledge the use of facilities and instrumentation supported by NSF through the UC San Diego Materials Research Science and Engineering Center (UCSD MRSEC) DMR-2011924. Additional support provided from the Defense Advanced Research Projects Agency (DARPA) and Naval Information Warfare Center Pacific (NIWC Pacific) under Contract No. N66001-21-C-4010. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the DARPA or NIWC Pacific.