## 3 Results and Discussion
### Estimation of Analytical Characteristics  
The simple and rapid analytical technique developed was characterized with the following analytical parameters. The first calibration curve obtained when ions were diluted by the distilled water is shown in Figure 4. Despite the development of positive-negative analysis, this calibration curve can be conditionally described by the four-parameter sigmoidal equation (y = A2 + (A1 - A2)/(1 + (x/x0)'p)) to demonstrate the nonlinear dependence. In accordance with this fitting, the detection limit was estimated as 3.2 ng/mL of antimony ions with a relatively narrow range of detectable concentrations from 4.2 ng/mL to 10.5 ng/mL. Such a narrow distribution is explained by the loss of stability of the applied PAO-GNP conjugate. Color transition is observed by the naked eye when the concentration of antimony reached 10 ng/mL. Similar results were obtained when distilled water was changed to actual drinking water (Figure 8). The detection limit of antimony in the real sample was estimated as 2.0 ng/mL, with the range of determined concentrations from 3.7 ng/mL to 25 ng/mL. The average error of detection is from 0.3% to 3.8% in inter-assay. According to these data, our results are promising in analytical sensitivity (LOD = 10 ng/mL), duration of analysis (2 min), and reproducibility (error of determination is less than 3.8% in three replicates). The present study confirmed the applicability of developed colorimetric techniques to determine Sb\({}^{3+}\) as compared to the known methods. Table 1 shows publications related to Sb\({}^{3+}\) determination by the different analytical techniques. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**N** & \
\begin{tabular}{c} **Heavy** \\ **Metal** \\ \end{tabular} & **Sensing Unit** & **Detection Method** &
\begin{tabular}{c} **LOD, Dynamic** \\ **Range** \\ \end{tabular} & **Probe** & **Ref.** \\ \hline \multicolumn{8}{c}{**Sophisticated Instrumental Methods**} \\ \hline \multirow{3}{*}{1} & \multirow{3}{*}{As\({}^{3+}\), Sb\({}^{3+}\)} & \multirow{3}{*}{Gold film electrode} & & As\({}^{3+}\), 11.2 ng/mL & \multirow{3}{*}{Copper} & \multirow{3}{*}{[42]} \\  & & & & 5.5–0.5 ng/mL & & \\ \cline{1-1} \cline{5-6}  & & & Sb\({}^{3+}\), 0.56 ng/mL & & 2.6–0.6 ng/mL & & \\ \hline \multirow{3}{*}{2} & \multirow{3}{*}{Sb\({}^{3+}\)} & Silver & \multirow{3}{*}{Anodic stripping voltammetry} & 0.083 ng/mL & Seawater samples and & \\  & & & screen-printed electrodes & & 0.012-0.11 ug/mL & & \\ \cline{1-1} \cline{5-6}  & & & Gold nanoparticle-modified & & 0.115 ng/mL & Seawater samples, & \\ \cline{1-1} \cline{5-6}  & & carbon screen-printed electrodes & & 0.012-0.11 ug/mL & drug samples & \\ \hline \multirow{3}{*}{4} & \multirow{3}{*}{Sb\({}^{3+}\)} & Mercury film & 1.54 ng/mL & Pharmaceutical & \multirow{3}{*}{[12]} \\  & & screen-printed electrode & & 1.2–10.1 ng/mL & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Described assays for the determination of antimony. Figure 8: Dependence of optical intensity for detecting Sb\({}^{3+}\) in drinking water (n = 3). The points above and to the right of optical density 0.5 correspond to the blue color of the final reaction mixture, and the points below and left to this level correspond to pink (y = 0.66 + (0.43 - 0.66)/(1 + (x/10.05)’1.38), (R\({}^{2}\) = 0.98)). All experiments were undertaken in three replicates. The Discussion of the Interaction Mechanism of Antimony (III) with poly-A Modified Gold Nanoparticles  
The mechanism of interaction of metals and metalloids with DNA and proteins has been of interest to researchers since the successful use of compounds against tropical diseases began [49]. In particular, antimony preparations were used against leishmaniasis [50]. To understand the interaction mechanism, previous investigations are helpful. In some investigations, antimony acts as a complexation agent when interacting with organic compounds, with the resulting salts as stibogluconate or melumine antimonite due to their properties of providing hydroxyl groups [49].