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

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 (WD = 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.