Table 3. Mean and median particle sizes (hydrodynamic diameter) determined by NTA.
Based on these direct measurements of hydrodynamic diameter, the volume-weighted median for particles of 32 nm diameter would be the particle number concentration (12×108 particles/ml) times the volume of a single particle (i.e., 4/3Pi r3); or approximately (200 nm3/ml). An example plot of the particle size distribution as hydrodynamic diameter is shown (Figure 2). Note the range of sizes with a few percent of particles as small as 10 nm and as large as around 90 nm for the largest aggregates measured in the samples.
Size distribution of colloidal silver determined using nanoparticle tracking analysis (Nanosight NTA 2.2). The concentration at each size category (nm) in shown as 106 particles/ml. Cumulative percentage undersize is shown in red (%).
Particle size distribution in the dispersions
“Nanoparticle tracking analysis was used to determine the size distribution of the particles in the bottle, using the same methodology as the previous batch that was analysed. Particles were detected in the bottle (Table 1), and the median size was around 29 nm (close to the 32 nm measured in the previous batch). The mean diameter (35 nm) was also close to the previous bottles (34.5 nm). The particle number concentration was 10-11 x 108 particles/ml; almost identical to the previous batch at 11-12 x 108 particles/ml. There appears to be very good reproducibility of the colloidal silver particle size and number concentrations between the bottles of the materials tested by Plymouth University.”