Nevertheless, the mean sizes of the particle size distributions from the three individual batches were still in excellent agreement. Mean sizes were recorded at 230.8 ± 7.4 nm for di, 241.7 ± 10.5 nm for dv, 166.3 ± 1.7 nm for dn and 208.6 ± 6 nm for Z-average, which confirms the low variation (see Figure (a-b) and Figure ). Zeta potential measured for aqueous suspensions of samples at pH ~7 was negative with a mean value of -40.7 ± 3 mV (see Figure ), due to deprotonated silanol groups on the unfunctionalized MSN. The TEM images show a population of spherical, monodispersed particles with a mesoporous structure (see Figure ), and a slightly broader, but similar size distribution across batches (Figure ), as also evidenced from DLS. The mean size distribution calculated from these measurements confirms a good reproducibility of batches with a mean particle size of 89.1 ± 3.6 nm (see Figure ). It is worthwhile to mention that the DLS values are larger in this case compared to actual mean particle size from TEM, due to some smaller aggregates or conjoined particles which can additionally skew the DLS results, apart from the other effects discussed above. As evident from the DLS and TEM results (Figure ), the standard deviation of mean sizes produced from the characterization results were very low at 5%.