# Internalization of Phospholipid-Coated Gold Nanoparticles
## 4 Results
### Endocytosis Occurs in C2C12 and A549 Cells and is Cell Type Specific
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **C2C12** & **A549** \\ \hline \(\langle F(\mathit{PCAuNPs}|Rab5\,)\rangle\) & \(0.21\pm 0.03\) \({}^{\ddagger}\) & \(0.64\pm 0.05\) \\ \hline \(\langle F(\mathit{PCAuNPs}|Rab7\,)\rangle\) & \(0.33\pm 0.04\) & \(0.38\pm 0.08\) \\ \hline \(\langle F(\mathit{PCAuNPs}|LAMP-1\,)\rangle\) & \(0.25\pm 0.04\) & \(0.57\pm 0.08\) \\ \hline \(\langle F(\mathit{PCAuNPs}|Rab11\,)\rangle\) & \(0.25\pm 0.07\) & \(0.49\pm 0.04\) \\ \hline \multicolumn{3}{c}{\({}^{\ddagger}\). Standard error.} \\ \end{tabular}
\end{table} 
Table 1: Co-localization of phospholipid-coated gold nanoparticles with endocytic marked compartments in cells. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **C2C12** & **A549** \\ \hline \(\langle F(\mathit{Rab5}|PCAuNPs)\rangle\) & \(0.21\pm 0.03\)\({}^{\ddagger}\) & \(0.06\pm 0.01\) \\ \hline \(\langle F(\mathit{Rab7}|PCAuNPs)\rangle\) & \(0.17\pm 0.02\) & \(0.19\pm 0.04\) \\ \hline \(\langle F(\mathit{LAMP-1}|PCAuNPs)\rangle\) & \(0.22\pm 0.04\) & \(0.03\pm 0.01\) \\ \hline \(\langle F(\mathit{Rab11}|PCAuNPs)\rangle\) & \(0.18\pm 0.04\) & \(0.08\pm 0.01\) \\ \hline \multicolumn{3}{c}{\({}^{\ddagger}\). Standard error.} \\ \end{tabular}
\end{table} 
Table 2: Co-localization of endocytic marked compartments with phospholipid-coated gold nanoparticles in cellsTo quantify the extent of co-localization from the images shown in Figure 4, triple image cross correlation spectroscopy was used to obtain the fractions of PCAuNPs that associate with two markers (Table 3). It is clear that the PCAuNPs co-localize with compartments containing two markers in both cell types. Specifically, the fraction of PCAuNP-containing compartments that also contain two markers range from 8-40% in C2C12 cells and from 24-39% in A549 cells. These numbers are consistent with the fact that between 50 and 80% of these markers co-exist on the same endosome compartments [50]. Triple image cross correlation spectroscopy was also used to quantify the fraction of one marker that also co-localize with PCAuNPs and another marker (Table 4). These fractions are consistent with the data in Table 2 and show that a significant, but small number of the various compartments contain PCAuNPs in C2C12 cells, while very few of these compartments contain PCAuNPs in A549 cells  
Figure 4: PCAuNPs with two endocytic marked compartments in C2C12 cells and A549 Cells. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **C2C12** & **A549** \\ \hline \(\langle F(\,PCAuNPs|Rab5\,Rab11\,)\rangle\) & \(0.18\pm 0.05\)\({}^{\ddagger}\) & \(0.33\pm 0.07\) \\ \hline \(\langle F(\,PCAuNPs|Rab5\,Rab7\,)\rangle\) & \(0.16\pm 0.05\) & \(0.25\pm 0.04\) \\ \hline \(\langle F(\,PCAuNPs|Rab7\, LAMP-1\,)\rangle\) & \(0.40\pm 0.08\) & \(0.24\pm 0.05\) \\ \hline \(\langle F(\,PCAuNPs|Rab5\, LAMP-1\,)\rangle\) & \(0.08\pm 0.02\) & \(0.39\pm 0.08\) \\ \hline \hline \end{tabular} \({}^{\dagger}\). Standard error.  
\end{table} 
Table 3: Fractions of PCAuNPs distribution that co-localize with compartments containing two markers. Uptake of PCAuNP Follows the Same Time Dependent Trend in Both Cell Lines--PCAuNP Aggregate to a Greater Extent in A549 Cells  
C2C12 and A549 cells were incubated with PCAuNPs for two hours, followed by rinsing, and re-incubation to monitor the processing of PCAuNPs in the cells. Figure 5 shows images of PCAuNPs after 1, 2, 4, and 24 h of re-incubation in A549 cells. In Figure 5, PCAuNPs are distributed in similar ways within the cytoplasm with the progression of time in A549 cells. However, the intensity of PCAuNPs appears to be less after 24 h has elapsed. Image correlation spectroscopy (ICS) was used to quantify the intensity, cluster density, and degree of aggregation of PCAuNPs in C2C12 and A549 cells (Figure 6). At short time frames, the intensity, or concentration, of gold nanoparticles in the cells are of the same order of magnitude, suggesting that the relative amount of gold nanoparticles internalized within two hours of initial exposure is comparable for the two cell types.