Characterizing Nanoparticle Dispersions in Cell Culture Media

Titanium dioxide P25 nanoparticles were received as dry powder. After detailed size, morphology, impurity, and surface area characterization (see Supporting Information for all characterization techniques), the sample was suspended in deionzied water at a concentration of 1 mg mL⁻¹ to form a stock solution. Six different cell culture media including Bronchial Epithelial Growth Medium (BEGM), Dulbecco’s Modified Eagle’s Medium (DMEM), Luria Bertani Broth (LB), Tryptic Soy Broth (TSB), Synthetic Defined medium (SD), and Yeast Extract Peptone Dextrose medium (YPD) were selected for TiO₂ nanoparticle dispersion studies. A systematic water quality analysis was conducted for each medium. All characterization techniques were described in the Supporting information. High throughput dynamic light scattering (HT-DLS, Dynapro^™ Plate Reader, Wyatt Technology) was performed to determine the particle size distribution and state of agglomeration/dispersion of the nanoparticles in water and all different cell culture media. The plate reader is operated based on the same principles as the traditional DLS instruments but in a much more rapid manner. Analysis can be done using standard 96-, 384-, 1536-well plates. Since each measurement takes only a few seconds, ten runs were collected for each well and samples were loaded in at least triplicate. Particle sizes at various nanoparticle concentrations in all six media were determined simultaneously. Agglomeration kinetics measurements in each medium were conducted using the built-in kinetics feature in the HT-DLS instrument. This instrument provides a high throughput characterization method in parallel with the high throughput nanotoxicity studies. In addition to the dispersion characterization, the stability of the nanoparticle dispersions with or without dispersing agents was also evaluated by monitoring a characteristic peak of TiO₂ UV-vis absorbance spectrum as a function of time. Zeta potentials of the TiO₂ nanoparticle suspensions as another indication of the particle stability were also collected.