Aggregation Tendency, Cellular Uptake, and Viability Effects of Structurally Distinct Carbazole–Phthalocyanine Gold Nanoconjugates

Phthalocyanine-gold nanoparticle (Pc-AuNP) conjugates combine the unique properties of gold with the therapeutic potential of phthalocyanines, offering a promising strategy for cancer therapy. Here, two novel carbazole-containing Pcs, axially disubstituted Si-(IV) and peripherally tetra-substituted Zn-(II) derivatives, were synthesized and conjugated to gold nanoparticles of two core sizes (20 and 40 nm). Characterization was performed using TEM and SEM techniques. Stability assays in complete medium showed a stronger aggregation tendency for SiPc-AuNPs than for ZnPc-AuNPs. Bright-field microscopy revealed that Pc-AuNPs induced detachment of A549 lung adenocarcinoma cells but not HUVEC endothelial cells, highlighting a cell type-dependent effect. Despite this detachment, no significant loss of viability occurred at 72 h, underscoring the resilience of A549 cells to membrane and cytoskeletal stress. Once internalized, both SiPc- and ZnPc-based nanoconjugates displayed similar cytoplasmic and perinuclear localization, suggesting uptake was dominated by the AuNP carrier. Preliminary MTT assays showed dye-particle interference, leading to use of the PrestoBlue assay, which avoids insoluble formazan artifacts. Viability analysis indicated that only <b>Au40/SiPc</b> transiently increased A549 reducing capacity at 24 h, likely due to short-term ROS scavenging, which normalized by 72 h. Overall, these findings demonstrate how metal center, substitution geometry, and particle size collectively affect aggregation, cellular interactions, and cytotoxic profiles, providing insights for optimizing Pc-AuNPs as nanophototherapeutic agents.