This project was focused on a preparation of silica- and titania-based nanomaterials doped with silver nanoparticles and subsequent characterization of structural, optical and antibacterial properties of the obtained compounds in order to apply in the enhanced antimicrobial photodynamic therapy (APDT).

The main tasks of this work were:

• Synthesis of silica and titania matrices by sol-gel method and examination of their  physical and structural properties.
• Immobilization of silver nanoparticles on the surface of silica and titania matrices and examination of their physical and structural properties.
• Examination of optical and structural properties of nanosilver and photosensitizer doped sol-gel materials.
• Examination of the enhancement of the photodynamic effect in the presence of silver nanoparticles.
• Examination of biological properties of synthesized biomaterials doped with biologically active silver nanoparticles and photosensitizers.

The ceramic powders (silica nanoparticles and titania nanoparticles in amorphous and crystalline form) were prepared by modified sol-gel method, so thus to obtain a homogeneous distribution of particle sizes. Silica and titania nanoparticles were used as support for immobilization of silver nanoparticles.

Structural properties were characterized by TEM and SEM followed by computer aided image analysis. The nanoparticles of the following diameters were synthesized: silica nanoparticles with the diameter 180±30 nm, amorphous titania nanoparticles in two morphological structures with the diameter about 113±20 nm and 205±25 nm and titania nanoparticles in crystalline form with the diameter about 30 nm were obtained. The average size of silver nanoparticles in silica and titania nanopowders were about 14–35 nm.

Atomic Absorption Spectroscopy (ASA) for determination of total metallic silver concentration was used. The results confirmed that the Ag-SiO₂ based materials may contain 8.53% of silver. The average concentration of silver in Ag-TiO₂ nanomaterials in amorphous form can be as high as 11.68% and in crystalline form 6.32%.

Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) for analyze the composition of the synthesized nanomaterials revealed characteristic vibrations of Si–O–Si, Ti–O–Ti bond and hydroxyl groups for appropriate materials were observed.

Chlorine e6 based photosensitizer Photolon in various concentration was used as dopant. The absorption spectrum of silver doped silica and titania nanoparticles had a maximum between 420–445 nm, which is characteristic for silver nanoparticles. It was proved that for certain concentration of metallic silver in Photolon solutions the absorbance is high.

Antibacterial properties of synthesized nanomaterials against Gram-positive and Gram-negative bacteria were tested. Minimal inhibitory concentration of metallic silver was determined. Antimicrobial photodynamic activity against Pseudomonas aeruginosa was examined. Tested samples were non irradiated and irradiated with laser light 662 nm. The silver doped silica and titania nanoparticles had antibacterial activity, but in the presence of Photolon, the antibacterial activity of nanomaterials in APDT was much more effective.

The results of the project showed that it is possible to create a new system to fight with growing number of drug resistant bacteria. APDT efficiency may be enhanced by metallic nanoparticles with antibacterial activity. Photosensitizers combined with nanomaterials can be applied to eliminate bacteria, viruses, fungi and parasites.

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1. BioElectricSurface Project
2. Silica sol-gel matrix doped with photolon molecules for sensing and medical therapy purposes