Single-phase silver nanoparticles from white tea: colloidal quality, mass-specific potency and bacterial envelope...

Silver nanoparticles (AgNPs) are broad-spectrum antibacterial materials that remain active against clinically relevant pathogens, but tea-mediated syntheses have focused predominantly on green tea and have generally emphasised potency without linking particle properties to downstream damage of the bacterial envelope. Here, we synthesised AgNPs using white tea (Camellia sinensis) and benchmarked them against a citrate-reduced preparation produced and assayed in parallel. X-ray diffraction identified face-centred-cubic Ag in both preparations; the white-tea product showed no crystalline silver-salt impurity, while the chemical benchmark contained AgCl. The biogenic particles were smaller and less polydisperse, based on electron microscopy and light scattering, and carried a more negative zeta potential (28.3 ± 7.7 nm; ζ = -19.6 ± 0.8 mV; polydispersity index 0.319 versus 0.466). Minimum inhibitory concentrations (MICs), determined independently for Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213 by broth microdilution, were approximately eight-fold lower for the biogenic preparation once normalised to total silver (4.7 versus 38.5 µg mL^-1). At sub-inhibitory exposures, complementary flow-cytometric, electron-microscopic and time-resolved supernatant absorbance measurements were consistent with damage to the bacterial envelope and release of intracellular material in both organisms. An A ₃₂₀ particle-scatter tracer additionally identified a sample-processing-related over-subtraction artefact in the A ₂₆₀ leakage assay. Release was detectable within 1 h, with modest subsequent increases, consistent with early envelope disruption.