Hydrothermally Synthesized Red-Emissive Porphyrin Silicon Nanoparticles (pSiNPs) for Photo-Induced Synergistic Therapy on Cancer Cells

Silicon-based nanoparticles (SiNPs), with low toxicity and good biocompatibility, have been investigated for their applications in a wide variety of cell labeling approaches. However, SiNPs are frequently reported to have a strong blue emission and not the more advantageous red-near-infrared (NIR) emission. Porphyrin and its derivatives with red/NIR emission light properties, which can generate reactive singlet oxygen species and have low dark toxicities, have been applied as photosensitizers in therapeutic applications, such as photodynamic therapy (PDT) and photothermal therapy (PTT). However, the inherent limitation of porphyrin is their poor solubility in aqueous solutions. In this work, Tetrakis (4-carboxyphenyl) porphyrin (TCPP) is incorporated with N-(Trimethoxysilylpropyl) Ethylenediamine, triacetic acid, and trisodium salt 35% (TMS-EDTA) to synthesize porphyrin SiNPs (pSiNPs) with red emission that has the added advantage of aqueous solubility. The obtained pSiNPs were characterized by various analytical methods. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to determine the size distribution of the particles (42.7 ± 1.5 nm) and their ζ potentials (-31.6 ± 2.8 mV). Absorption property analysis revealed that the pSiNPs had a wide absorbance range from visible to NIR, with multiple absorbance peaks at 414, 527, 565, and 651 nm. The optical characterization of pSiNPs revealed two distinct emission peaks at 646 and 705 nm. The <i>in vitro</i> cell imaging indicated that pSiNPs were valuable imaging tools for cell labeling and the fluorescent signal from pSiNPs was distributed throughout the cytoplasm and concentrated in the perinuclear region of the cell. The photothermal performance and photodynamic effect showed that the pSiNPs were able to produce laser-induced heat generation that resulted in the formation of reactive oxygen species (ROS), highlighting their potential to achieve PDT and PTT in the cells. The <i>in vitro</i> photosynergistic results indicated that pSiNPs had enhanced PDT/PTT therapeutic performance in the various cancer cell lines tested, including RAW 264.7 cells, MCF-7 cells, and MDA-MB-231 cells.