E normalized efficiency was calculated by subtracting the fluorescent background from each well and normalizing the values corresponding to the highest value of the dataset. To evaluate the transfection efficiencies the cells were prepared and incubated with particles as described above. Then 100 
mM siRNA labeled with AlexaFluor488 (Qiagen, Hilden, Germany) was added to the samples and the cells were laser-treated. Dead cells were stained with ToPro3 (Invitrogen, MedChemExpress Itacitinib Carlsbad, USA). Thetransfection efficiency was measured by flow cytometry (FACS Calibur, BD Bioscience, Heidelberg, Germany).siRNA mediated knock downFor EGFP knock down ZMTH3 cells stably transfected with pd2-EGFP-N1 (Clontech Laboratories, Mountain View, USA) were laser-transfected with anti-GFP siRNA (Qiagen, Hilden, Germany). After 24 h 
EGFP fluorescence was measured at EX475/EM511 nm and viability assessed as described above. To account for possible cell losses, knock down efficiencies were calculated as corF Fs {Fb ?100 Vs corFs ?100 corFc ??KD??with corF = corrected fluorescence, Fs = fluorescence of the sample, Fb = fluorescence of the blank (empty well), Vs = viability of the sample, KD = knock down in and Fc = fluorescence of untreated control cells.Western blot analysis48 h after GNOME laser transfection with anti-GFP siRNA all samples and controls were lysed in 40 ml lysis buffer (150 mM NaCl, 1 Triton X-100, 50 mM Tris, pH 8.0, Roche cOmplete ultra protease inhibitor) per well. Protein contents were determined using the Roti Quant universal Kit (Carl Roth, Karlsruhe, Germany). After electrophoresis and blotting GFP was MedChemExpress Gracillin detected by a 1:4,000 dilution of the Living Colors A.v. Monoclonal Antibody (Clontech Laboratories) and a 1:1,000 dilution of an anti-mouseHRP conjugate (dianova, Hamburg, Germany). b-Actin was detected by a 1:20,000 dilution by a directly HRP linked antibody (dianova).Toxicity testingsTo assess the viability after laser treatment for longer time scales 56103 cells per well were seeded and then laser treated as described above. To measure the impact of AuNP incubation, cells were incubated with 0.5 or 5 mg/cm2 for 3 or 24 h, respectively. Viability was measured using the QBlue viability assay kit. Afterwards the staining solution was replaced by culture medium and cells were further incubated until the next time point. Cells treated with 12 mg/ml Digitonin (Sigma-Aldrich) served as negative control.ESEM ImagingFor ESEM imaging, the cells were grown on cover slides (diameter 12 mm) in a 24 well plate and treated with the indicated concentrations of AuNP for 3 h. The culture medium was removed and the samples were fixed in 4 paraformaldehyde and 2.5 glutaraldehyde (Sigma-Aldrich) for 10 min at room temperature. The samples were carefully rinsed with distilled water and imaged in an electron microscope (Quanta 400 F, FEI, Eindhoven, Netherlands) in wet mode. Images were taken after two purge cycles between 6 and 13 mbar at 2uC, 6 mbar and a high voltage of 15 kV. The cell surface area and particle count were analyzed using ImageJ [31].Figure 2. Experimental procedure for GNOME laser transfection. Cells are incubated with AuNP (1), the molecule to be delivered is added (2) and the sample is irradiated to permeabelize the cell membrane (3). Drawings are not true to scale. doi:10.1371/journal.pone.0058604.gGold Nanoparticle Mediated Laser TransfectionFigure 3. Fluorescence level and viability for different transfection parameters for the delivery o.E normalized efficiency was calculated by subtracting the fluorescent background from each well and normalizing the values corresponding to the highest value of the dataset. To evaluate the transfection efficiencies the cells were prepared and incubated with particles as described above. Then 100 mM siRNA labeled with AlexaFluor488 (Qiagen, Hilden, Germany) was added to the samples and the cells were laser-treated. Dead cells were stained with ToPro3 (Invitrogen, Carlsbad, USA). Thetransfection efficiency was measured by flow cytometry (FACS Calibur, BD Bioscience, Heidelberg, Germany).siRNA mediated knock downFor EGFP knock down ZMTH3 cells stably transfected with pd2-EGFP-N1 (Clontech Laboratories, Mountain View, USA) were laser-transfected with anti-GFP siRNA (Qiagen, Hilden, Germany). After 24 h EGFP fluorescence was measured at EX475/EM511 nm and viability assessed as described above. To account for possible cell losses, knock down efficiencies were calculated as corF Fs {Fb ?100 Vs corFs ?100 corFc ??KD??with corF = corrected fluorescence, Fs = fluorescence of the sample, Fb = fluorescence of the blank (empty well), Vs = viability of the sample, KD = knock down in and Fc = fluorescence of untreated control cells.Western blot analysis48 h after GNOME laser transfection with anti-GFP siRNA all samples and controls were lysed in 40 ml lysis buffer (150 mM NaCl, 1 Triton X-100, 50 mM Tris, pH 8.0, Roche cOmplete ultra protease inhibitor) per well. Protein contents were determined using the Roti Quant universal Kit (Carl Roth, Karlsruhe, Germany). After electrophoresis and blotting GFP was detected by a 1:4,000 dilution of the Living Colors A.v. Monoclonal Antibody (Clontech Laboratories) and a 1:1,000 dilution of an anti-mouseHRP conjugate (dianova, Hamburg, Germany). b-Actin was detected by a 1:20,000 dilution by a directly HRP linked antibody (dianova).Toxicity testingsTo assess the viability after laser treatment for longer time scales 56103 cells per well were seeded and then laser treated as described above. To measure the impact of AuNP incubation, cells were incubated with 0.5 or 5 mg/cm2 for 3 or 24 h, respectively. Viability was measured using the QBlue viability assay kit. Afterwards the staining solution was replaced by culture medium and cells were further incubated until the next time point. Cells treated with 12 mg/ml Digitonin (Sigma-Aldrich) served as negative control.ESEM ImagingFor ESEM imaging, the cells were grown on cover slides (diameter 12 mm) in a 24 well plate and treated with the indicated concentrations of AuNP for 3 h. The culture medium was removed and the samples were fixed in 4 paraformaldehyde and 2.5 glutaraldehyde (Sigma-Aldrich) for 10 min at room temperature. The samples were carefully rinsed with distilled water and imaged in an electron microscope (Quanta 400 F, FEI, Eindhoven, Netherlands) in wet mode. Images were taken after two purge cycles between 6 and 13 mbar at 2uC, 6 mbar and a high voltage of 15 kV. The cell surface area and particle count were analyzed using ImageJ [31].Figure 2. Experimental procedure for GNOME laser transfection. Cells are incubated with AuNP (1), the molecule to be delivered is added (2) and the sample is irradiated to permeabelize the cell membrane (3). Drawings are not true to scale. doi:10.1371/journal.pone.0058604.gGold Nanoparticle Mediated Laser TransfectionFigure 3. Fluorescence level and viability for different transfection parameters for the delivery o.