Metal noble nanoparticles bearing a shell based on cyclodextrin polymer/porphyrin complexes as prospective multimodal tools

At the present time, researchers are focusing their interest on the investigation of multifunctional metal noble nanoparticles (NPs) with high potential in nanobiotechnology. A well- established strategy utilizes reactants which behave simultaneously as reductants and stabilizers of metal nanoparticles. -Cyclodextrin (CD) polymers bearing citrate and cyclodextrin functionalities have been extensively used as coatings of a wide range of biomaterials for drug delivery.1 These polymers have also been reported as efficient stabilizers in colloidal solutions of ruthenium NPs.2 Nanoassemblies based on CD were used as shell entrapping photosensitiser (PS) to cover metal noble NPs for photothermal and photodynamic combined therapy (PTT-PDT).3 Here we report one-pot synthesis of gold and silver NPs, respectively, covered by water-soluble cyclodextrins polymer entrapping porphyrins. CD polymer was produced by condensation between hydroxypropylated CD (HPCD) and citric acid (CTR), named polyCTR-HPCD, according to a previously reported method.4 AuNPs@ polyCTR-HPCD have been prepared by addition of the polymer suspension to a HAuCl4 solution at reflux temperature and under stirring, thus the polymer acts either as reducing and stabilizing agent. The synthesis of AgNPs@ polyCTRHP CD has been carried out at room temperature by addition of NaBH4, as reductant, to a stirred solution of AgNO3 previously mixed to polyCTR-HPCD. In this case polymer acts as capping agent stabilizing NPs. Au and Ag core-shell NPs have been characterized by UV-Vis, DLS, TEM and STEM to elucidate their size and confirm the presence of the polymeric shell. The noncovalent interaction between core-shell NPs and the water-soluble anionic tetrakis(4- sulfonatophenyl)porphyrin (TPPS4) or the positively charged meso-tetrakis(Nmethylpyridinium- 4-yl)porphine (H2T4), respectively, was studied in aqueous solution by complementary techniques such as UV-Vis, fluorescence emission and circular dichroism. Our preliminary data evidence that H2T4 interacts more strongly with the polymeric shell than TPPS4, pointing to both electrostatic and hydrophobic effects in driving porphyrin complexation . This approach allows for a control of the PS content in core-shell NPs aiming to design novel nanophototherapeutics with dual action.