Controlled Precursor Feeding During Synthesis Enhances Silver Nanoparticle Uniformity and Cytotoxicity

Precursor feeding is often treated as a minor procedural detail in wet-chemical silver nanoparticle syntheses, although it can directly influence nucleation, growth, and the resulting nanoparticle population. In this study, two otherwise identical citrate/tannic-acid syntheses were systematically compared, differing only in the mode of AgNO3 addition: slow dropwise addition (AgNP-SA) and rapid one-step addition (AgNP-FA). AgNP-SA exhibited a sharper localized surface plasmon resonance band centered at 407 nm, whereas AgNP-FA showed a broader spectrum with greater long-wavelength contribution. Dynamic light scattering indicated a monomodal population for AgNP-SA (32.3 ± 1.2 nm; PDI = 0.093 ± 0.011) and a bimodal, more polydisperse population for AgNP-FA (30.1 ± 2.4 nm and 44.3 ± 3.1 nm; PDI = 0.512 ± 0.018). Transmission electron microscopy and single-particle ICP-MS further supported the greater size heterogeneity of AgNP-FA. For biological assessment, total silver content was quantified by ICP-OES, and both dispersions were normalized to the same total Ag concentration (850 µg/mL) prior to exposure, enabling comparison under controlled Ag dosing. Under these matched conditions, AgNP-SA showed greater cytotoxicity toward HepG2 cells (IC50 = 61.6 µg/mL), whereas AgNP-FA did not reach 50% loss of viability within the tested range (IC50 > 100 µg/mL). Cell-free controls indicated no significant interference in the MTS assay. Overall, controlling precursor feeding provided a reproducible approach to tune dispersion uniformity and was associated with differences in the biological response observed under controlled Ag dosing.