The Preparation of Graphene Oxide-Silver Nanocomposites: the Effect of Silver Loads on Gram-Positive and Gram-Negative Antibacterial Activities.

In this work, silver nanoparticles (Ag NPs) were decorated on thiol (-SH) grafted graphene oxide (GO) layers to investigate the antibacterial activities in Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Pseudomonas aeruginosa). The quasi-spherical, nano-sized Ag NPs were attached to the GO surface layers, as confirmed by using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), respectively. The average size of GO-Ag nanocomposites was significantly reduced (327 nm) from those of pristine GO (962 nm) while the average size of loaded Ag NPs was significantly smaller than the Ag NPs without GO. Various concentrations of AgNO3 solutions (0.1, 0.2, and 0.25 M) were loaded into GO nanosheets and resulted in the Ag contents of 31, 43, and 65%, respectively, with 1-2 nm sizes of Ag NPs anchored on the GO layers. These GO-Ag samples have negative surface charges but the GO-Ag 0.2 M sample (43% Ag) demonstrated the highest antibacterial efficiency. At 10 ppm load of GO-Ag suspension, only a GO-Ag 0.2 M sample yielded slight bacterial inhibition (5.79-7.82%). As the GO-Ag content was doubled to 20 ppm, the GO-Ag 0.2 M composite exhibited ~49% inhibition. When the GO-Ag 0.2 M composite level was raised to 100 ppm, almost 100% inhibition efficiencies were found on both Staphylococcus aureus (S.A.) and Pseudomonas aeruginosa (P.A.), which were significantly higher than using pristine GO (27% and 33% for S.A. and P.A.). The combined effect of GO and Ag nanoparticles demonstrate efficient antibacterial activities.

Increased anti-biofilm efficacy of toluidine blue on Staphylococcus species after nano-encapsulation.

BACKGROUND: Photodynamic therapy has been studied as a method for inactivating bacterial growth. Workers have used planktonic bacterial as well as biofilm bacterial cultures to evaluate the potential of photodynamic therapy in inactivating bacteria. However, almost all the studies use a photosensitiser in aqueous solution, which could be detrimental to the efficiency of photodynamic therapy. METHODS: In this study, the photodynamic killing effect of toluidine blue O (TBO) has been investigated on Staphylococcal biofilms in-vitro. The sensitivity of the in-vitro biofilms to photodynamic killing action was compared using different formulations of TBO, different dosages of photosensitiser and different light irradiation strengths. Effect of TBO formulations on bacterial quorum sensing system was evaluated using a colorimetric assay. Finally, dual staining using hoechst and propidium iodide stains was carried out on the photodynamically treated biofilms to visualise and compare the effects of photodynamic therapy. Scanning electron microscope imagery was also carried out to evaluate the photodynamic killing effect on the in-vitro biofilms. RESULTS: The sensitivity of biofilms to the photodynamic killing effect increased proportionally with the photosensitiser dosage and the light irradiation duration. TBO encapsulated in microemulsion was more effective in killing the biofilm bacteria than only TBO in water. The combination of TBO in microemulsion with EDTA was another effective way of increasing the photodynamic killing effect on the bacterial biofilms. Effect of encapsulated TBO on the quorum sensing system of bacteria was greater than the effect of aqueous solution of TBO. The in-vitro Staphylococcal biofilms could thus be inhibited by the photodynamic effect, and TBO encapsulated in microemulsion was much more effective than only TBO in water. CONCLUSIONS: The encapsulation of a photosensitiser is an effective way of increasing the likelihood of the complete and successful inactivation of the biofilm growth. The encapsulated photosensitiser achieves higher inactivation of the bacterial biofilm than that of the aqueous solution of a photosensitiser.

Photosensitizer in lipid nanoparticle: a nano-scaled approach to antibacterial function.

Photosensitization-based antimicrobial therapy (PAT) is an alternative therapy aimed at achieving bacterial inactivation. Researchers use various photosensitizers to achieve bacterial inactivation. However, the most widely used approach involves the use of photosensitizers dispersed in aqueous solution, which could limit the effectiveness of photodynamic inactivation. Therefore, the approaches to encapsulate the photosensitizer in appropriate vehicles can enhance the delivery of the photosensitizer. Herein, Toluidine Blue O (TBO) was the photosensitizer, and lipid nanoparticles were used for its encapsulation. The lipid nanoparticle-based delivery system has been tailor-made for decreasing the average size and viscosity and increasing the formulation stability as well as the wettability of skin. Usage of an appropriate vehicle will also increase the cellular uptake of the photosensitizer into the bacterial cells, leading to the damage on cell membrane and genomic DNA. Evidence of effectiveness of the developed PAT on planktonic bacteria and biofilms was examined by fluorescence microscopy and scanning electron microscopy. Lipid nanoparticles protected the photosensitizer from aggregation and made the application easy on the skin as indicated in data of size distribution and contact angle. The use of lipid nanoparticles for encapsulating TBO could enhance photosensitization-based antimicrobial therapy as compared to the aqueous media for delivering photosensitizers.

Enhancement of photodynamic inactivation against Pseudomonas aeruginosa by a nano-carrier approach.

As pathogens steadily develop resistance to widely used antibiotics, new methodologies for their efficient inactivation must be developed. Photodynamic therapy is an upcoming technique that provides an alternative option for treating pathogenic infections. The efficiency of photodynamic therapy has been limited by the use of aqueous mediums for dispersing photosensitising agents. Toluidine Blue O (TBO) was chosen for this study as a cationic photosensitiser to inhibit Gram-negative bacterium Pseudomonas aeruginosa. Enhanced delivery of the photosensitiser was ensured by utilising an essential oil-based microemulsion. The efficiency of photodynamic therapy was further improved by the use of a chemical penetration enhancer to improve permeability of the bacterial outer membrane. TBO accumulation patterns in neonate pig skin were studied using confocal laser scanning microscopy. The physicochemical properties of the TBO loaded microemulsion, including UV-vis absorbance, size distribution and zeta potential, were analysed to understand the enhanced antimicrobial activity. Confocal laser scanning microscopy confirmed the formation of a TBO reservoir in the skin by the TBO-loaded microemulsions. TBO (5 µg/mL) in the vehicles significantly inhibited the growth of P. aeruginosa. All these efforts resulted in inhibition obtained at a drug concentration and light intensity much lower than what is reported by the works of previous investigators.