General Cell Culture

All reagents used for cell culture, such as Dulbecco’s modified phosphate buffered saline (DPBS), media, and dissociation reagents, were purchased from Life Technologies (Carlsbad, CA). Only CorningBrand (VWR Scientific, Radnor, PA) cell culture flasks, plates, and sera were used. MDA-MB-231 m-Cherry cells were purchased from the American Type Culture Collection (Manassas, VA). Cells were cultured in phenol red-free alpha minimum essential media (α-MEM) supplemented with 10% fetal bovine serum (FBS), 1% nonessential amino acids, and 1% sodium pyruvate. Cells were grown in a humidified incubator operating at 37 °C and 5.0% CO₂. Cells were allowed to incubate for 24 h before all experiments. For harvesting cells, 0.25% TrypLE was added and cells were incubated for 5 min at 37 °C in a 5.0% CO₂ incubator. For sterilization, Gd@AuNPs suspensions in media were filtered with 0.2 μm sterile filters prior to concentration determination and dosing.