F 10 kDa FITC-dextran. A: Fluorescence for different scanning velocities at a constant AuNP concentration of 5 mg/cm2. The scanning velocity was set to values between 10 and 200 mm/s, corresponding to 175 and 9 pulses per point, respectively. For all velocities the same fluorescence level could be achieved by using increasing radiant exposure for higher velocities as indicated by the dotted line. B: The corresponding viability dropped with higher radiant exposure and slower scanning velocities. C, D: 
High AuNP concentrations led to pronounced cell death even at low values of radiant exposure and thus only provide low levels of fluorescence. Most efficient delivery was achieved at 0.5 mg/cm2 and 20 mJ/cm2 as indicated by the dotted line in C. Scanning velocity was kept constant at 50 mm/s. Data points represent the mean of n = 4 experiments. doi:10.1371/journal.pone.0058604.gUV/VIS spectra200 nm AuNP were solved in a concentration of 10 mg/ml in RPMI without phenol red supplied with 10 FCS. For each sample 200 ml AuNP suspension were irradiated in a 96 well. The absorbance was acquired in a UV/VIS spectrometer (UV 1650PC, Shimadzu, Duisburg, Germany) against RPMI without AuNP.Results and Discussion Evaluation of transfection parametersIn order to determine the optimal perforation parameters, cells were perforated with FITC purchase JI-101 labeled dextrans with a molecular weight of 10 kDa. This is comparable to siRNA molecules (,14 kDa), although differences in charge and 3D structure of the molecules must be considered. The fluorescence of a well after treatment was chosen as a marker for successful delivery. Since fluorescence is directly linked to the total amount of molecules delivered to the cell population, it is dependent not only on the efficiency (amount of cells perforated), but also on the number of molecules delivered per cell. Figure 3 represents the normalizedfluorescence and the viability for different scanning velocities (Fig. 3a, b) and for different AuNP concentrations (Fig. 3c, d). Both parameters were evaluated against different values of radiant exposure. For a given scanning velocity the viability dropped with increasing radiant exposure (Fig. 3a). In parallel the fluorescence increased until it reached a maximum, an optimal balance of delivery and cell viability was established. When the radiant exposure was increased above this critical point, the fluorescence dropped because the cell loss surpassed the gain of fluorescence. For increasing scanning velocities the corresponding radiant exposure yielding the maximum fluorescence also increased. All tested scanning velocities revealed a comparable level of fluorescence, indicating that the same efficiency was obtained (dotted line in Fig. 3a). These results imply that the membrane perforation is provoked 1527786 by cumulative effects of single pulses. As the repetition rate of the laser system (20.25 kHz) yields a temporal distance of 50 ms between two pulses and thermal processes are finished on a ns-timescale [28,32] the AuNP can be GHRH (1-29) considered as cooled down to the initial temperature until the next pulse. Therefore no thermal accumulation is likely to occur.Gold Nanoparticle Mediated Laser TransfectionFigure 4. Number of particles per cell. A: Particle count per cell after 3 hours of incubation with different AuNP concentrations. No significant difference in the particle count was observed after irradiation with 20 mJ/cm2 (p = 0.46). Values represent the mean of n = 3 experiments 6SEM.F 10 kDa FITC-dextran. A: Fluorescence 
for different scanning velocities at a constant AuNP concentration of 5 mg/cm2. The scanning velocity was set to values between 10 and 200 mm/s, corresponding to 175 and 9 pulses per point, respectively. For all velocities the same fluorescence level could be achieved by using increasing radiant exposure for higher velocities as indicated by the dotted line. B: The corresponding viability dropped with higher radiant exposure and slower scanning velocities. C, D: High AuNP concentrations led to pronounced cell death even at low values of radiant exposure and thus only provide low levels of fluorescence. Most efficient delivery was achieved at 0.5 mg/cm2 and 20 mJ/cm2 as indicated by the dotted line in C. Scanning velocity was kept constant at 50 mm/s. Data points represent the mean of n = 4 experiments. doi:10.1371/journal.pone.0058604.gUV/VIS spectra200 nm AuNP were solved in a concentration of 10 mg/ml in RPMI without phenol red supplied with 10 FCS. For each sample 200 ml AuNP suspension were irradiated in a 96 well. The absorbance was acquired in a UV/VIS spectrometer (UV 1650PC, Shimadzu, Duisburg, Germany) against RPMI without AuNP.Results and Discussion Evaluation of transfection parametersIn order to determine the optimal perforation parameters, cells were perforated with FITC labeled dextrans with a molecular weight of 10 kDa. This is comparable to siRNA molecules (,14 kDa), although differences in charge and 3D structure of the molecules must be considered. The fluorescence of a well after treatment was chosen as a marker for successful delivery. Since fluorescence is directly linked to the total amount of molecules delivered to the cell population, it is dependent not only on the efficiency (amount of cells perforated), but also on the number of molecules delivered per cell. Figure 3 represents the normalizedfluorescence and the viability for different scanning velocities (Fig. 3a, b) and for different AuNP concentrations (Fig. 3c, d). Both parameters were evaluated against different values of radiant exposure. For a given scanning velocity the viability dropped with increasing radiant exposure (Fig. 3a). In parallel the fluorescence increased until it reached a maximum, an optimal balance of delivery and cell viability was established. When the radiant exposure was increased above this critical point, the fluorescence dropped because the cell loss surpassed the gain of fluorescence. For increasing scanning velocities the corresponding radiant exposure yielding the maximum fluorescence also increased. All tested scanning velocities revealed a comparable level of fluorescence, indicating that the same efficiency was obtained (dotted line in Fig. 3a). These results imply that the membrane perforation is provoked 1527786 by cumulative effects of single pulses. As the repetition rate of the laser system (20.25 kHz) yields a temporal distance of 50 ms between two pulses and thermal processes are finished on a ns-timescale [28,32] the AuNP can be considered as cooled down to the initial temperature until the next pulse. Therefore no thermal accumulation is likely to occur.Gold Nanoparticle Mediated Laser TransfectionFigure 4. Number of particles per cell. A: Particle count per cell after 3 hours of incubation with different AuNP concentrations. No significant difference in the particle count was observed after irradiation with 20 mJ/cm2 (p = 0.46). Values represent the mean of n = 3 experiments 6SEM.