Dynamic Light Scattering and Zeta Potential Analysis of MWNT Suspensions

Dynamic light scattering (DLS) and zeta potential analyses were used as part of a quality control routine for the preparation of all MWNT suspensions, as previously described [50 (link),51 (link),54 (link)]. The particle size distributions, in terms of hydrodynamic diameter, of the BSA-MWNT suspensions were determined by DLS. In brief, aliquots of purified pMWNT or cMWNT suspensions were diluted 1:10 in a 0.10 mg/mL BSA working solution and analyzed with a Zetasizer Nano-ZS 3600 (Malvern Instruments, Worcestershire, UK) using a 633-nm laser and a backscatter measurement angle of 173°. The instrument was calibrated with Polybead^® standards (Polysciences, Warrington, PA, USA) and ten consecutive 30-s runs were taken per measurement at 25 °C. The hydrodynamic diameter was calculated using a viscosity and refractive index of 0.8872 cP and 1.330, respectively for deionized water, and an absorption and refractive index of 0.010 and 1.891, respectively, for MWNTs. Zeta potential values were also determined for purified BSA-coated MWNT suspensions that were diluted 1:10 with deionized water. In addition, DLS and zeta potential analyses were performed periodically on purified MWNT suspensions stored at 4 °C. Typically, MWNT suspensions were stable in storage for months, indicated by the lack of aggregates detected by DLS and constant zeta potential results.