Porphyrins in nanohybrid assemblies for biological applications

Hybrid nanomaterials have gained growing interest due to their intriguing properties resulting from the combination of organic and inorganic species. The emergence of new functionalities and improved performances have enabled the development of methods and technologies aimed to build devices with multimodal functions and new synergistic effects in terms of optical, electronic, magnetic, sensing and plasmonic properties for a variety of applications. In the plethora of molecular tectons for the construction of multifunctional nanoscale architectures, porphyrins are widely used in virtue of their interesting and finely tunable optical and electronic properties. They have found applications in photovoltaics, light harvesting systems, sensing and energy transport. In particular, porphyrin based nanostructures have been widely explored in biomedicine where porphyrins act as photosensitizers (PS) for photodynamic therapy (PDT) and, in combination with inorganic metal nanoparticles (NPs) for dual photothermal and photodynamic therapies (PTT- PDT), thanks to a synergistic effect deriving from molecular and colloidal properties. In this framework, here we report two cases of porphyrin based nanohybrid assemblies with potential applications in biomedical field. In the first example, we discuss novel nanoconstructs as potential theranostic agents that have been prepared self-assembling meso-tetrakis(N-methylpyridinium-4-yl)porphine H2T4 with Au or Ag nanoparticles (NPs). The NPs have been synthesized by a specific polymer bearing citrate and cyclodextrin (CDs) functionalities. The first species acts as reductant/stabilizer towards metal precursors/ NPs, while the latter entraps PS in virtue of the well know carrier ability of CDs towards drugs. In the second example, we report the formation and the spectroscopic characterization of J-aggregates of tetrakis(4-sulfonatophenyl)porphyrin H2TPPS4 in the presence of multi walled carbon nanotubes. The aggregated system has been investigated through a combination of spectroscopic and microscopy techniques, evidencing some potential use in phototherapy and bio-imaging.