*2.9. Cell Culture*

HeLa, T24 or T24/eGFPLuc-200cT (authenticated by DSMZ, Braunschweig, Germany) cells, stably expressing an eGFP-luciferase fusion gene under the control of the CMV promoter and with a target site for miR200c, were cultivated in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% fetal bovine serum (FBS), 100 U mL−<sup>1</sup> penicillin and 100 U mL−<sup>1</sup> streptomycin.

## *2.10. Cell Viability Determined by MTT Assay*

MTT assay was performed in triplicate in 96-well plates. One day prior to transfection, T24 cells were seeded at 3500 cells/well. Before transfection, medium was replaced by 80 μL fresh medium. MSN samples (20 μL) loaded with or without RNA were added at different concentrations in HEPES buffer and incubated for 45 min at 37 ◦C followed by a medium exchange. Subsequently, cells were returned to the incubator and 48 h after transfection a viability assay was performed. For this, an MTT solution (100 μL/well; 0.5 mg mL−<sup>1</sup> in DMEM) was added for 2 h. Then, the supernatant was removed and cells were lysed by freezing at −80 ◦C. DMSO (100 μL) was added and plates were incubated at 37 ◦C under shaking. Absorption at 590 nm against a reference wavelength of 630 nm was measured using a SpectraFluorTM Plus microplate reader S4 (Tecan, Groeding, Austria). Cell viability was calculated as percentage of absorption compared to wells treated with HEPES buffer.

## *2.11. Cellular Adhesion Determined by Flow Cytometry*

T24/eGFPLuc-200cT cells were seeded 24 h before transfection on 24-well plates with a density of 5 × 10<sup>5</sup> cells per well in 1000 μL growth medium. After 24 h, the medium was replaced by 400 μL fresh medium. A total of 100 μL MSN, MSN-454-PEG and MSN-454-GE11 samples loaded with fluorescent dye (500 μg mL−<sup>1</sup> MSN in HEPES buffer) were added and incubated for 45 min at 37 ◦C. After incubation time, the cells were washed three times with PBS, 500 I.U. heparin to remove particles non-specifically associated to the cell surface and were detached with trypsin/EDTA, taken up in growth medium, centrifuged and resuspended in PBS containing 10% FBS. Cellular internalization of the MSN samples was assayed by flow cytometry at an Atto-633 carboxy fluorescent dye excitation wavelength of 635 nm and detection of emission at 665 nm. Cells were gated by forward/sideward scatter and pulse width for exclusion of doublets. DAPI (4,6-diamidino-2-phenylindole) was used to discriminate between viable and dead cells. Data were recorded by BD LSRFortessa™ (BD Biosciences, USA) and analyzed by FlowJo® 7.6.5 flow cytometric analysis software. All experiments were performed in triplicate.
