Colloidal Gold Dietary Supplements as Nanomaterials: Physicochemical Evaluation, Estimated Oral Exposure, and Preliminary Biological Assessment

Colloidal gold dietary supplements intended for oral consumption are increasingly marketed as nano-enabled products, yet their physicochemical characteristics and biological effects remain insufficiently documented. In this study, commercially available colloidal gold supplements produced and marketed in Romania (30, 55, and 110 mg/L) were investigated to determine their classification as nanomaterials and to assess their preliminary biological effects in the context of oral exposure. Transmission electron microscopy revealed a narrow particle size distribution (4–11 nm), while SAED and EDX confirmed the presence of metallic gold nanoparticles. UV-VIS spectroscopy showed the characteristic surface plasmon resonance, supported by comparison with citrate-stabilized reference AuNPs (5–20 nm). DLS and zeta potential measurements indicated stable electrostatically stabilized colloids. According to the current EU definition, the number-based size distribution supports classification as nanomaterials. Manufacturer-recommended daily intakes were compared with doses reported in the literature using HED conversion to contextualize oral exposure. In vitro assays showed no pronounced acute cytotoxic or antitumoral effects on HCT-8 cells and no inhibitory effects on selected LAB. However, increased cytotoxicity was observed in HEK293 cells exposed to the dietary supplement formulation compared with the corresponding standard AuNP formulation. These results underscore the importance of considering cell-specific responses when evaluating the safety of nano-enabled dietary supplements and support the need for long-term toxicological studies.