Although dynamic light scattering is usually ABT-888 nmr applied to determine the diameter distribution of spherical particles, it also facilitates the understanding of size distribution of dispersed carbon nanotubes [35–38]. Prior to centrifugation, the average particle size of 5 μg/ml PEI-NH-SWNTs and PEI-NH-MWNTs was the highest among the concentrations tested, due possibly to the inhomogeneous nature of the suspension. After centrifugation, the average particle

size of 5 to 100 μg/ml PEI-NH-SWNTs and PEI-NH-MWNTs in the supernatant was 229 ± 8 to 291 ± 34 and 287 ± 8 to 433 ± 102 nm, which were significantly lower than those before centrifugation (Figure 6). In addition, when the particle size of different concentrations of PEI-NH-SWNTs or PEI-NH-MWNTs was compared, no significant difference was observed. These results indicate that the centrifugation procedure effectively THZ1 concentration reduced the particle size and increased the homogeneity of PEI-NH-CNTs. Figure 6 Average particle size of PEI-NH-SWNTs and PEI-NH-MWNTs before and after centrifugation. The average

particle diameters of 5, 50, and 100 μg/ml of PEI-NH-SWNTs (A) or PEI-NH-MWNTs (B) before and after removal of large aggregates through centrifugation was analyzed by dynamic light scattering. Before centrifugation, PEI-NH-SWNTs or PEI-NH-MWNTs were solubilized in ddH2O at a concentration of 1 mg/ml and sonicated for 15 min; after centrifugation, PEI-NH-SWNTs or PEI-NH-MWNTs were centrifuged at 3,000 rpm for Endonuclease 30 min to remove large aggregates. Error bars represent standard deviations (n ≥ 3). *p < 0.05 and **p < 0.01 compared to PEI-NH-SWNTs or

PEI-NH-MWNTs of the same concentration before centrifugation. Zeta potential of PEI-NH-CNTs The zeta potential of 1 mg/ml pristine or PEI-grafted carbon nanotubes at 25°C and neutral pH was determined through dynamic light scattering. The zeta potential of pristine SWNTs and MWNTs was negative (Figure 7), similar to those reported in the literature [39, 40]. As expected, PEI functionalization increases the positive charge on the surface of PEI-NH-CNTs, resulting in positive zeta potentials, which were higher in PEI-NH-MWNTs compared to PEI-NH-SWNTs (Figure 7). The stability of PEI-NH-CNT suspension may therefore be maintained by electrostatic selleck chemicals repulsion contributed by the cationic PEI. Figure 7 Zeta potential of pristine and PEI-functionalized carbon nanotubes. The zeta potential of 1 mg/ml pristine or PEI-grafted carbon nanotubes at 25°C and neutral pH was determined by dynamic light scattering. Error bars represent standard deviations (n ≥ 3). **p < 0.01 compared to PEI-NH-SWNTs.