Supramolecular hybrid assemblies based on gold nanoparticles, amphiphilic cyclodextrin and porphyrins with combined phototherapeutic action

Abstract

Gold nanoparticles (AuNPs), amphiphilic cyclodextrin (SC6NH2) and anionic porphyrin (TPPS₄) spontaneously self-assemble in aqueous basic solution forming nanostructures with controlled size and shape. Spectroscopic techniques such UV-Vis, fluorescence emission and Dynamic Light Scattering (DLS) demonstrate that AuNPs are covered by SC6NH2, and TPPS₄ is strongly entrapped within, forming assemblies with size of 4 and 50 nm. Scanning Near-Field Optical Microscopy (SNOM) and Scanning Near-Field Optical Luminescence (SNOL) assess the presence of luminescent vescicular structures incorporating porphyrin with dimensions of about 150 nm. Transmission electron microscopy (TEM) indicates AuNPs with sizes of 20–30 nm can be located inside the largest cyclodextrin/porphyrin aggregates (≅150 nm) or interact externally with the smallest cyclodextrin/porphyrin vesicles (≅ 40 nm). The generation of an appreciable quantum yield of singlet oxygen (Φ_Δ = 0.25) guarantees the photodynamic action excluding mostly strong interactions between gold and porphyrin. These hybrid systems are fairly stable at physiological conditions (pH = 7.4) and can be taken up by HeLa cancer cells which, upon treatment, show co-localization of gold and porphyrins in the cytoplasm. After intracellular delivery, these assemblies induce low dark toxicity and a combined photothermal–photodynamic effect upon proper irradiation, showing promising properties as dual-action phototherapeutics.