## 3 Results and Discussion
### Characterization of Nanoparticles  
To enhance the cell uptake and overcome the low water solubility of ZnPcBCH\({}_{3}\), the sensitizer was encapsulated in PLGA-b-PEG polymeric nanoparticles using the nanoprecipitation method. The size and shape of the polymeric nanoparticles were determined using dynamic light scattering (DLS) and TEM, respectively (cf. Figure 5). Nanoprecipitation was carried out in different solvents to determine any change in size and zeta potential. The average diameter of polymeric nanoparticles was 90.02 \(\pm\) 0.07 nm using THF and 97.82 \(\pm\) 0.01 nm using acetone. Changing solvent for encapsulation did not have a significant impact on the polydispersity index (PDI) or the zeta potential of the nanoparticles (Table 3). These properties are in agreement with our reported zeta potential for the polymeric nanoparticles using THF or acetone (\(-\)9.74 \(\pm\) 0.01 mV and \(-\)8.93 \(\pm\) 0.04 mV, respectively). Representative TEM images showed that the formed nanoparticles from PLGA-b-PEG are spherical.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Compound** & \(\mathbf{\lambda_{\text{ex}}}\) **(nm)** & \(\mathbf{\varepsilon}\) **(M\({}^{-1}\) cm\({}^{-1}\))** & \(\mathbf{\lambda_{\text{ex}}}\) & \(\mathbf{\varepsilon}\) **(M\({}^{-1}\) cm\({}^{-1}\))** & \(\Phi_{f}\) & \(\mathbf{\tau}_{f}\) & \(\Phi_{\mathbf{\Delta}}\) \\ \hline ZnPc & 672 & \(1.7\times 10^{5}\) & 346 & \(8.58\times 10^{4}\) & \(0.28\pm 0.05\) & \(3.166\times 10^{-9}\) & 0.56 \(\pm\) 0.04 \\ ZnPcBCH\({}_{3}\) & 677 & \(1.6\times 10^{5}\) & 352 & \(6.4\times 10^{4}\) & \(0.52\pm 0.08\) & \(3.132\times 10^{-9}\) & 0.51 \(\pm\) 0.056 \\ \hline \hline \end{tabular} \(\varepsilon\) (M\({}^{-1}\) cm\({}^{-1}\)) is molar extinction coefficient, \(\Phi_{f}\) is relative fluorescence quantum yield, \(\Phi_{f}\) is the emission lifetime, \(\mathbf{\lambda_{\text{ex}}}\) is the excitation lambda max, and \(\Phi_{\Delta}\) is singlet oxygen quantum yield.  
\end{table}
Table 1: Photophysical properties of ZnPc and ZnPcBCH\({}_{3}\) in DMSO obtained in plate reader with correction factor of 0.32.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Compound** & \(\mathbf{\lambda_{\text{abs}}}\) **(DMF)** & \(\mathbf{\varepsilon}\) **(M\({}^{-1}\) cm\({}^{-1}\))** & \(\mathbf{\lambda_{\text{Em}}}\) & **Stokes Shift** \\ \hline ZnPcBCH\({}_{3}\) & 681 nm & 1.60 \(\times\) 10\({}^{5}\) & 697 nm & 16 nm \\  & 612 nm & 3.41 \(\times\) 10\({}^{4}\) & & \\ \hline \hline \end{tabular} \(\lambda_{\text{abs}}\) is the ground state excitation lambda max and \(\lambda_{\text{Em}}\) is the fluorescence emission lambda max.  
\end{table}
Table 2: Absorption data recorded in DMF.  
Figure 4: Absorption and emission spectra of ZnPc and ZnPcBCH\({}_{3}\) in DMSO.  
As indicated in Table 3, regardless of the solvent choice, the zeta potential of the nanoparticles is \(\pm\)10 mV. This range of zeta potential indicates that the formed PLGA-b-PEG nanoparticle is a neutral particle [24] so that it interacts with cell membrane to facilitate the cell uptake. A PDI of less than 0.3 indicates a homogeneous particle distribution. Furthermore, the amount of encapsulated dye was measured using standard absorption curve for ZnPcBCH\({}_{3}\) in THF media, the results of which are summarized in Table 4.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Sample** & **ZnPcBCH\({}_{3}\)** \\ \hline Nanoparticle yield (\%) & 73.76 \\ Dye sensitizer load (\%) & 0.37 \\ Entrapment efficiency (\%) & 28 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Nanoparticles yield, sensitizer load, and entrapment efficiency obtained from nanoprecipitation using THF.  
Figure 5: Diameter size distributions obtained from DLS for encapsulated ZnPcBCH\({}_{3}\) nanoparticles prepared in THF (**A**), acetone (**B**) and acetonitrile (**C**) media in the nanoprecipitation process, and TEM data for nanoparticles in acetonitrile (**D**).