In response to the increasingly widespread resistance of fungi to traditional treatment, we have reported successful photodynamic inactivation of Candida albicans planktonic cells using di-(AlPcS2) and trisulfonated (AlPcS3) hydroxyaluminum phthalocyanines in combination with Au/Ag alloy nanoparticles synthesized by the cell-free filtrate of Trichoderma koningii. These nanostructures with Au:Ag molar ratios 2:1, 1:1 and 1:2 have individual plasmonic band at 513-515 nm, 505-509 nm and 486-489 nm, respectively. XPS analysis of the ratio of gold to silver on the surface of these alloys indicated that Au and Ag formed a bimetallic system, wherein Au was coated with Ag. The XRD pattern revealed the angles at 38.2, 44.5, 64.9 and 78.0°. TEM analysis indicated that the average diameter of the synthesized alloys was 9 ± 3 nm, 8 ± 3 nm and 16 ± 3 nm for structures with Au:Ag molar ratios 1:1, 1:2 and 2:1, respectively. The FTIR band absorption, SEM-EDS analysis and basic elemental composition obtained by XPS confirmed that these nanostructures are stabilized by protein(s). Diode laser with the peak-power wavelength ʎ = 650 nm (output power of 40 mW; power density of 105 mW cm-2) was used as a light source. The mixture of AlPcS2+Au/Ag-NPs (Au:Ag = 2:1) can be considered as an effective photosensitizer, because eradication of C. albicans, as required by the American Society of Microbiology (99.9 %), was achieved at a low dose of light of 31.5 J cm-2. It was postulated that this low dose of light applied to the photo-induced fungicidal effect may be painless for potential patients.
Keywords: Antimicrobial Photodynamic therapy; Bimetallic nanoparticles; Candida; Gold; Light dose; Photodynamic inactivation; Phthalocyanines; Silver.
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