Intracellular Localization of Quantum Dots

For intracellular localization of QDs, QD-Ce₆ complexes and Ce₆, MDA-MB-231 breast cancer cells (ATCC, USA) were seeded on a Nunc LabTek II chamber slide (Thermo Fisher Scientific, Waltham, MA, USA) at a density of 25,000 cells per well using standard cell culture medium (Dulbecco’s modified Eagle’s medium (DMEM), 10% fetal bovine serum (FBS), 1% penicillin/streptomycin antibiotic mix (all from Gibco, Waltham, MA, USA). Upon cell attachment, cells were treated with serum-free cell medium containing 10 nM of either different P-QDs or L-QDs or their QD-Ce₆ complexes for 24 hours. In addition, 1 μM Ce₆ solution was used as a control. Samples for confocal microscopy were prepared as previously described [22 (link)]. Briefly, cells were fixed with 4% paraformaldehyde solution (Sigma Aldrich, USA) and permeabilized with 0.2% Triton-X 100 (Sigma Aldrich, St. Louis, MO, USA). Actin filaments were stained with 15 U/mL Alexa Fluor 488 Phalloidin (Thermo Fisher Scientific, Waltham, MA, USA) and 25 μg/mL Hoechst 33342 (Sigma Aldrich, St. Louis, MO, USA) was used to label nuclei.