## 3 Results and Discussion
### Stability Studies  
The radiolabeled complexes exhibited very promising in vitro stability not only in cysteine and histidine solutions but also in human serum (>90%), which indicates the satisfactory binding of 99 mTc to the AuNPs, thus enhancing their potential to be investigated for in vivo applications (Tables 3-5).  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Concentration of**} & **Histidine Challenge (\%)** & **Histidine Challenge (\%)** \\ **Radiabeled AuNPs** & **(1 h)** & **(24 h)** \\ \hline
500 \(\upmu\)g/radiolabeling & 98.52 \(\pm\) 1.09 & 98.74 \(\pm\) 0.52 \\
500 \(\times\) 10\({}^{-1}\)\(\upmu\)g/radiolabeling & 94.14 \(\pm\) 4.23 & 97.56 \(\pm\) 1.23 \\
500 \(\times\) 10\({}^{-2}\)\(\upmu\)g/radiolabeling & 94.38 \(\pm\) 2.12 & 93.65 \(\pm\) 3.12 \\
500 \(\times\) 10\({}^{-3}\)\(\upmu\)g/radiolabeling & 96.02 \(\pm\) 3.21 & 95.12 \(\pm\) 1.80 \\ \hline \hline \end{tabular}
\end{table}
Table 4: HPLC results representing the in vitro stability of [99 mTc]Tc-AuNPs in the presence of histidine.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Concentration of**} & **Radiochemical Purity (\%)** & **Radiochemical Purity (\%)** \\ **Radiabeled AuNPs** & **(1 h)** & **(24 h)** \\ \hline
500 \(\upmu\)g/radiolabeling & 98.31 \(\pm\) 1.43 & 98.51 \(\pm\) 2.36 \\
500 \(\times\) 10\({}^{-1}\)\(\upmu\)g/radiolabeling & 97.76 \(\pm\) 2.62 & 97.59 \(\pm\) 0.55 \\
500 \(\times\) 10\({}^{-2}\)\(\upmu\)g/radiolabeling & 94.48 \(\pm\) 3.21 & 96.42 \(\pm\) 1.89 \\
500 \(\times\) 10\({}^{-3}\)\(\upmu\)g/radiolabeling & 97.75 \(\pm\) 1.26 & 97.8 \(\pm\) 1.62 \\ \hline \hline \end{tabular}
\end{table}
Table 2: HPLC results representing the radiochemical purity of [99 mTc]Tc-AuNPs.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Concentration of**} & **Radiochemical Purity (\%)** & **Radiochemical Purity (\%)** \\ **Radiabeled AuNPs** & **(1 h)** & **(24 h)** \\ \hline
500 \(\upmu\)g/radiolabeling & 98.31 \(\pm\) 1.43 & 98.51 \(\pm\) 2.36 \\
500 \(\times\) 10\({}^{-1}\)\(\upmu\)g/radiolabeling & 97.76 \(\pm\) 2.62 & 97.59 \(\pm\) 0.55 \\
500 \(\times\) 10\({}^{-2}\)\(\upmu\)g/radiolabeling & 94.48 \(\pm\) 3.21 & 96.42 \(\pm\) 1.89 \\
500 \(\times\) 10\({}^{-3}\)\(\upmu\)g/radiolabeling & 97.75 \(\pm\) 1.26 & 97.8 \(\pm\) 1.62 \\ \hline \hline \end{tabular}
\end{table}
Table 2: HPLC results representing the radiochemical purity of [99 mTc]Tc-AuNPs.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Concentration of**} & **Histidine Challenge (\%)** & **Histidine Challenge (\%)** \\ **Radiabeled AuNPs** & **(1 h)** & **(24 h)** \\ \hline
500 \(\upmu\)g/radiolabeling & 98.52 \(\pm\) 1.09 & 98.74 \(\pm\) 0.52 \\
500 \(\times\) 10\({}^{-1}\)\(\upmu\)g/radiolabeling & 94.14 \(\pm\) 4.23 & 97.56 \(\pm\) 1.23 \\
500 \(\times\) 10\({}^{-2}\)\(\upmu\)g/radiolabeling & 94.38 \(\pm\) 2.12 & 93.65 \(\pm\) 3.12 \\
500 \(\times\) 10\({}^{-3}\)\(\upmu\)g/radiolabeling & 96.02 \(\pm\) 3.21 & 95.12 \(\pm\) 1.80 \\ \hline \hline \end{tabular}
\end{table}
Table 3: HPLC results representing the in vitro stability of [99 mTc]Tc-AuNPs in the presence of cysteine.