## 4 Conclusions  
In conclusion, we have investigated the role of AuNPs' concentration in their in vivo kinetics by evaluating the ex vivo biodistribution in mice after their radiolabeling with \({}^{99\text{m}}\)Tc. The high-concentration sample resulted in pronounced lung, liver and spleen uptake, while all the other less concentrated samples also accumulated in the lungs, liver and spleen, albeit at lower percentages. Our experiments demonstrate that AuNPs' concentration alters organ distribution, which may be attributed to the difference in zeta potential of the samples, leading to higher protein adsorption for the increased-surface-charge species, and should be taken into account when designing experimental protocols for radiolabeling nanoparticles. Furthermore, the accumulation of nanoparticles for the most concentrated sample remains sufficiently high in lungs (>50%) even at 24 h, making it a very promising therapeutic candidate for future evaluation in lung cancer when radiolabeled with beta-, alpha- or Auger-emitting therapeutic radioisotopes. Conceptualization: A.A., P.K. and P.B. ; methodology: A.A., E.-A.S., A.C., S.X. and P.K. ; validation: I.C.P., P.K. and P.B. ; investigation: A.A., E.-A.S. and N.N.P. ; resources: I.C.P., P.K. and P.B. ; funding acquisition: P.K. and P.B. ; writing--original draft preparation: A.A. and P.B. ; writing--review and editing, all authors; supervision: P.K. and P.B. All authors have read and agreed to the published version of the manuscript. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & \multicolumn{3}{c}{**4 h**} \\ \hline
**Organ** & **312.5 \(\upmu\)g/mL** & **312.5 \(\times\) 10\({}^{-1}\)\(\upmu\)g/mL** & **312.5 \(\times\) 10\({}^{-2}\)\(\upmu\)g/mL** & **312.5 \(\times\) 10\({}^{-3}\)\(\upmu\)g/mL** \\ \hline
**Lung** & 370.68 \(\pm\) 25.73 & 104.32 \(\pm\) 20.98 & 59.79 \(\pm\) 12.58 & 119.90 \(\pm\) 8.64 \\ \hline
**Bone** & 0.64 \(\pm\) 0.11 & 0.68 \(\pm\) 0.10 & 1.44 \(\pm\) 0.45 & 0.88 \(\pm\) 0.17 \\ \hline
**Pancreas** & 0.50 \(\pm\) 0.26 & 0.60 \(\pm\) 0.41 & 0.66 \(\pm\) 0.19 & 0.90 \(\pm\) 0.29 \\ \hline
**Brain** & 0.28 \(\pm\) 0.07 & 0.24 \(\pm\) 0.11 & 0.16 \(\pm\) 0.04 & 0.37 \(\pm\) 0.12 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: _Cont._ \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & \multicolumn{3}{c}{**24 h**} \\ \hline
**Organ** & **312.5 \(\upmu\)g/mL** & **312.5 \(\times\) 10\({}^{-1}\)\(\upmu\)g/mL** & **312.5 \(\times\) 10\({}^{-2}\)\(\upmu\)g/mL** & **312.5 \(\times\) 10\({}^{-3}\)\(\upmu\)g/mL** \\ \hline
**Blood** & 0.08 \(\pm\) 0.01 & 0.54 \(\pm\) 0.11 & 0.83 \(\pm\) 0.13 & 0.50 \(\pm\) 0.06 \\ \hline
**Liver** & 9.89 \(\pm\) 0.04 & 16.00 \(\pm\) 4.46 & 23.69 \(\pm\) 4.90 & 11.22 \(\pm\) 2.77 \\ \hline
**Heart** & 0.78 \(\pm\) 0.27 & 0.77 \(\pm\) 0.16 & 1.62 \(\pm\) 0.18 & 1.43 \(\pm\) 0.37 \\ \hline
**Kidney** & 2.32 \(\pm\) 0.16 & 3.09 \(\pm\) 0.38 & 5.91 \(\pm\) 0.88 & 2.48 \(\pm\) 0.36 \\ \hline
**Stomach** & 0.30 \(\pm\) 0.12 & 0.48 \(\pm\) 0.01 & 0.73 \(\pm\) 0.22 & 0.56 \(\pm\) 0.18 \\ \hline
**Inestine** & 0.69 \(\pm\) 0.41 & 0.58 \(\pm\) 0.12 & 1.09 \(\pm\) 0.07 & 0.87 \(\pm\) 0.55 \\ \hline
**Spleen** & 9.33 \(\pm\) 2.52 & 8.38 \(\pm\) 3.12 & 6.59 \(\pm\) 2.48 & 16.56 \(\pm\) 4.12 \\ \hline
**Muscle** & 0.07 \(\pm\) 0.02 & 0.12 \(\pm\) 0.01 & 0.29 \(\pm\) 0.04 & 0.18 \(\pm\) 0.04 \\ \hline
**Lung** & 51.58 \(\pm\) 0.54 & 19.56 \(\pm\) 8.01 & 9.75 \(\pm\) 2.63 & 10.27 \(\pm\) 1.94 \\ \hline
**Bone** & 0.31 \(\pm\) 0.07 & 0.46 \(\pm\) 0.05 & 0.72 \(\pm\) 0.16 & 0.73 \(\pm\) 0.26 \\ \hline
**Pancreas** & 0.16 \(\pm\) 0.09 & 0.33 \(\pm\) 0.11 & 0.51 \(\pm\) 0.11 & 0.25 \(\pm\) 0.03 \\ \hline
**Brain** & 0.06 \(\pm\) 0.05 & 0.19 \(\pm\) 0.11 & 0.05 \(\pm\) 0.01 & 0.08 \(\pm\) 0.03 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Ex vivo biodistribution results for all tested concentrations at 24 h (\(n\) = 3 \(\pm\) SD).