Synthesis and In Vitro Evaluation of γ-Al2O3: Eu/Cysteine/PpIX Nanoparticles for Photodynamic Therapy Applications

Abstract

Photodynamic therapy (PDT) relies on the light-mediated activation of photosensitizers to generate reactive oxygen species (ROS) and induce cancer cell damage. In this study, γ-Al₂O₃:Eu nanoparticles were synthesized using a sol–gel-assisted chemical route and subsequently functionalized with cysteine for EDC/NHS-mediated conjugation of protoporphyrin IX (PpIX). The resulting γ-Al₂O₃:Eu-cysteine-PpIX nanoparticles were evaluated as a nanoparticle-assisted PpIX platform for PDT-related applications. Structural, morphological, and spectroscopic analyses, including XRD, EDS, FTIR, SEM, TEM, DLS, UV–Vis absorption, and photoluminescence measurements, supported the formation of the γ-Al₂O₃:Eu-cysteine-PpIX nanoconjugate and indicated close photophysical interaction between γ-Al₂O₃:Eu emission and surface-associated PpIX. Probe-based ROS assays showed that cysteine-mediated PpIX conjugation enhanced both singlet oxygen- and hydroxyl radical-related responses under UV irradiation. In C26 mouse colon cancer cells, γ-Al₂O₃:Eu-cysteine-PpIX nanoparticles reduced cell viability in a concentration-dependent manner, with the strongest response observed after UV irradiation. The UV-irradiated γ-Al₂O₃:Eu-cysteine-PpIX nanoparticles showed the lowest IC₅₀ value of 1.38 µM, indicating an enhanced photocytotoxic response compared with free PpIX, γ-Al₂O₃:Eu nanoparticles, and non-irradiated γ-Al₂O₃:Eu-cysteine PpIX nanoparticles. Overall, these findings support γ-Al₂O₃:Eu-cysteine-PpIX nanoparticles as a promising nanoparticle assisted PpIX system for PDT-related anticancer studies