Cell culture conditions, incubation with microchips, and image processing. HeLa cell line (CCL-2) was provided from ATCC and was grown in standard DMEM medium supplemented with 10% FBS, 1% penicillin-streptomycin and 1% of glutamine and kept at 37 ºC and 5% CO2 conditions. HeLa cells were incubated with microchips (SOµC-Bdpy1 and SOµC-Bdpy2) in glassbottom p35 plates (Grenier) to be easily observed under the confocal microscope. Typically, 10.000 cells/cm 2 were seeded and after 24h to 48h of growing, SOµC-Bdpy1 or SOµC-Bdpy2 were added. The ratio of microchip:cell used was 0.5:1 or 1:1 and incubation in a DMEM small volume was performed for overnight to improve the contact of the chip with the cells and facilitate their entry. After, more culture medium was added when it was necessary, the cells were incubated with 1mM of BSO (L-buthionine sulfoximine, B2515; MERCK) during 48h. Cell viability was analyzed by incubating cells with Cell Tracker Green (CFDA; Molecular Probes, Invitrogen) for 15 min at 37°C. When stated, 10 mM of GSH (GSHee, G1404; Sigma-Aldrich) or 100 µM of NEM (N-ethylmaleimide (NEM, 203030; ThermoScientific, Pierce) were added during 4 h before CLSM.