Zinc phthalocyanine functionalized with Au-chitosan nanoparticles

Abstract

Zinc phthalocyanine (ZnPc) is a new-generation photosensitizer successfully used in photodynamic therapy (PDT), a modern and minimally invasive method for treating certain forms of cancer and microbial infections. This molecule exhibits strong absorption in the near-infrared (NIR) region, allowing activation deep within tissues, where other treatments often struggle to reach. Upon light activation, ZnPc generates reactive oxygen species (ROS) that selectively destroy tumor cells without damaging healthy tissue. Its chemical stability and preferential accumulation in malignant cells make it an ideal candidate for clinical applications. Recent studies highlight the potential of ZnPc to be combined with various nanoparticles, such as Ag, Au, or different polymers, to enhance biodistribution and photodynamic activity [1]. In this study, ZnPc was functionalized with Au–chitosan nanoparticles and characterized using UV-Vis absorption spectroscopy, X-ray diffraction (XRD), zeta potential measurements, and dynamic light scattering (DLS). The results demonstrated that the reaction temperature plays a crucial role in controlling the size, shape, and crystalline structure of the gold nanoparticles (GNPs). Moreover, it was shown that chitosan can act as a scaffold for the assembly of GNPs, which were successfully used for ZnPc functionalization. The first optical indication of GNP formation was a visible color change over time, from violet to light pink. This visible color arises from the interaction of light with GNPs via surface plasmon rezonance. Since the optical spectrum of GNPs strongly depends on their size, shape, local environment, and electronic coupling, their formation was monitored not only visually but more accurately through UV-Vis spectroscopy, showing a characteristic absorption maximum at 520 nm. The zeta potential was approximately –32.25 mV, and DLS analysis revealed a mean GNP diameter of approximately 272.2 nm. All diffraction peaks are attributed to the (111), (200), (220), (311), and (222) planes of a face-centered cubic (fcc) gold crystal. The UV-Vis spectra of ZnPc(COOH)₄ and ZnPc(COOH)₄:Au showed a well-defined B-band maximum at around 364 nm and only a slight attenuation of the Q-band for ZnPc(COOH)₄:Au compared to the pure phthalocyanine. Additionally, a minor red shift was observed in the Q-band-from 700 nm, characteristic for ZnPc(COOH)₄, to 708 nm for ZnPc(COOH)₄:Au.