Hydrofluoric acid

Chloroauric acid (HAuCl₄), (3-Aminopropyl)triethoxysilane (APTES), doxorubicin (Dox) and paclitaxel(PTX) were purchased from Sigma-Aldrich (St. Louis, MO). P-type (100) silicon wafers with resistivity of 0.005 Ω-cm were purchased from Silicon Quest (Santa Clara, CA). Polydimethylsiloxane (PDMS) and curing agent were obtained from Dow Corning (Midland, MI). Phosphate buffered saline (PBS, pH 7.2) was obtained from Gibco (Thermo-Fisher, Waltham, MA). Hydrofluoric acid was from Honeywell International Inc. N-maleimidobutyryl-oxysuccinimide ester (GMBS) and thiol functionalized streptavidin were purchased from Nanocs Inc. (Woburn, MA). The biotinylated anti-CD63 antibody and control IgG was purchased from Abcam Co. (Boston, MA). Human breast cancer cell line MDA-MB-231 cells were purchased from the American Type Culture Collection (Rockville, MD, USA). The multidrug resistant MDA-MB-231/MDR cell line was cultured in our lab. All the cells were cultured in DMEM (Thermo-Fisher, Waltham, MA) supplemented with 10% FBS. The exosome Labelling Kit (Exo-Glow^™) was purchased from System Bioscience (Palo Alto, CA). Amphiphilic copolymer methoxy-poly (ethylene glycol)-poly (ε-caprolactone) (mPEG-PCL, Mw: 5000:5000) was purchased from Polymer Source Inc. (Canada).