coated coverslips after 24 hours the cells were infected for 12 hrs with a gfp expressing virus in solution in the presence or absence of polybrene 72 hrs later the cells were fixed with 4 paraformaldehyde for 10 minutes and the nuclei were stained with dapi cells were analysed with a fluorescence microscope the infection efficiency and the mean fluorescence intensity were calculated for each sample using an image analysis software the results fig2 a show that the infections via ns tio 2 in the absence of polybrene and on the plastic support in the presence of polybrene respectively have the same efficiency and mean intensity for the u201c reverse infection u201d protocol different substrates were compared for infection efficiency briefly a ns tio 2 coated coverslip a gelatin coated coverslip and a plastic well were incubated with viral preparation gfp expressing virus for 4 hours at 4 c virus peg correspond to a 10 fold concentrated viral preparation virus supernatant correspond to the not concentrated viral preparation after a brief wash with pbs melanocytes were plated on all the samples after 72 hours cells were analysed with a fluorescence microscope the infection efficiency and the mean fluorescence intensity were calculated for each sample using an image analysis software the results fig2 b show that the infections mediated by ns tio 2 in the absence of polybrene are more efficient compared to others.