α lipoic acid

A549 cells were cultured 48 h before imaging with cell culture medium, using our previously published methods.^{22 (link)} Next the culturing medium was removed and cells were washed with 1× PBS. Twenty-four h prior to incubation with AuNP-capped MSN, cells were placed in a cell culture medium containing 500 µM α-lipoic acid (Sigma-Aldrich).^{23 (link)} Cells were kept in the α-lipoic acid culturing medium for 24 h, and then the AuNP-capped MSN were added. 200 µL of nanoparticles were added to the Petri dish with 1 mL of new culturing medium. Cells were incubated for 2 h to naturally internalize the AuNP-capped MSN.^{24 (link)} After incubation, the culturing medium and nanoparticle solution were removed, and the cells were washed again with 1× PBS. After the cells were washed with PBS, a slide was prepared for imaging. Two pieces of double sided tape were placed across the slide parallel to one another. Between the two pieces of tape some culturing medium was pipetted, and the glass coverslip was secured on the glass slide with the tape. During imaging, the cell sample was scanned vertically with a computer controlled vertical stage scanner (Sigma Koki, model no. SGSP-60YAM) attached to the fine-tune knob of the microscope. A 540 nm (10 nm fwhm) bandpass filter was used to image the cells; the sample was vertically scanned every 10 min for 3 h.