In the current decade, the use of plant extracts for the green preparation of metal nanoparticles has garnered increasing attention due to their eco-friendliness, cost-effectiveness, and sustainability. In the current study, silver nanoparticles (AgNPs) were synthesized using the ethanolic extract of Circaea lutetiana for the first time. Thetotal flavonoid content (TFC) and total phenolic content (TPC)of the extract were analyzed by spectrophotometric methods. Fourier transform infrared (FT-IR) spectroscopy was employed to determine the functional groups involved in both the reduction and stabilization processes of AgNPs. The formation and optical properties of AgNPs were confirmed by Ultraviolet–Visible (UV–Vis) spectroscopy. The greenlysynthesized AgNPs were characterized by FT-IR, UV–Vis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), dynamic light scattering (DLS) and zeta potential analyses, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The results confirmed that the AgNPs were spherical in shape with an average size of approximately 3.8 nm and showed a good crystalline nature. Additionally, the AgNPs exhibited significant antimicrobial activity against both Gram-positive and Gram-negative bacteria, demonstrating their potential as green antimicrobial agents.

Photodynamic therapy (PDT) is an established light-based treatment modality that relies on the activation of photosensitizers to generate reactive oxygen species (ROS) and induce localized cytotoxicity. In recent years, microalgae have emerged as a promising and sustainable source of natural photosensitizers due to their ability to biosynthesize structurally diverse pigments with strong light-harvesting capacity. This review provides a comprehensive, application-oriented analysis of microalgae-derived photosensitizers, focusing on chlorophylls and their derivatives, carotenoids, and phycobiliproteins. Particular attention is given to analytical strategies for pigment extraction, purification, and characterization, as well as to photophysical properties, subcellular localization, and ROS-mediated mechanisms underlying photodynamic activity. Recent advances in the chemical modification of algal pigments, including chlorin-based derivatives and 5-aminolevulinic acid–related systems, are critically discussed in relation to structure–activity relationships and translational performance. The accumulated evidence demonstrates that microalgae-derived pigments and their synthetic analogues can achieve efficient singlet oxygen generation, organelle-specific phototoxicity, and favorable therapeutic selectivity. Taken together, these findings highlight microalgae as a renewable and versatile platform for developing next-generation photosensitizers with broad biomedical potential in oncology, dermatology, and antimicrobial photodynamic therapy.