## 2 Materials and Methods
### Synthesis of MIP and NIP  
Synthesis of the molecularly imprinted polymer (MIP) and non-imprinted polymer (NIP) was carried out based on the following methodology [67].  
_Synthesis of MIP on lead._ First, 1.656 g (5 mmol) of lead nitrate was dissolved in 10 mL of distilled water and in a certain amount of MAA and 2-VP in a three-necked round-bottom flask using a magnetic stirrer until the salt dissolved. The amount of monomers was determined according to the molar ratio of template/monomer-1/monomer-2/cross-linker (Table 1). Afterwards, 5 mL of toluene and 10 mL of 1% HEC solution were added, and the mixture was stirred for 15 min. Then, 5.697 mL of DVB and AIBN 1% by weight of the monomers were added and the mixture was stirred for 5 min. After that, the reaction mixture was blown up by argon for 5 min. The flask was placed in a water bath and kept for 6 h at 60 \({}^{\circ}\)C with constant stirring at 700-1000 rpm. The resulting mixture was centrifuged and divided into two parts. The upper oil layer was removed and the bottom water part was purified by dialysis using cellulose membranes within 4 days, the first day in ethanol, the second in distilled water, the third in a 0.05 M solution of nitric acid, and the last day in distilled water. Finally, the MIPs were freeze-dried.  
Synthesis of MIP on terbiumFirst, 0.3 g (0.55 mmol) of terbium salt was dissolved in 10 mL of distilled water and in 0.233 mL of MAA and 0.298 mL of 2-VP in a three-necked round-bottom flask using a magnetic stirrer until the salt dissolves. Then, 5 mL of toluene and 10 mL of 1% HEC solution were added, and the mixture was stirred for 15 min. Afterwards, 0.627 mL of DVB and 0.0053 g of AIBN were added, and the mixture was stirred for 5 min. The mixture was blown up by argon for 5 min. Then, the flask was placed in a water bath and kept for 6 h at 60 \({}^{\circ}\)C with constant stirring at 700-1000 rpm. The resulting mixture was centrifuged. The water part was purified by dialysis during 4 days, the first day in ethanol, the second in distilled water, the third in a 0.05 M solution of nitric acid, and the last day in distilled water, and afterwards, freeze-dried.  
Synthesis of NIPThe synthesis of NIP repeated the procedure for the synthesis of MIP but without using a template. In a three-necked round-bottom flask, 10 mL of distilled water and 0.233 mL of MAA and 0.298 mL of 2-VP were mixed using a magnetic stirrer. Then, 5 mL of toluene and 10 mL of 1% HEC solution were added, and the mixture was stirred for 15 min. Afterwards, 0.627 mL of DVB and 0.0053 g of AIBN were added, and the mixture was stirred for 5 min. The mixture was blown up by argon for 5 min. Then, the flask was placed in a water bath and kept for 6 h at 60 \({}^{\circ}\)C with constant stirring at 700-1000 rpm. The resulting mixture was centrifuged. The water part was purified by dialysis during 4 days, the first day in ethanol, the second in distilled water, the third in a 0.05 M solution of nitric acid, and the last day in distilled water. Afterwards, the NIPs were freeze-dried.  
In Figure 1, a methodological scheme of the synthesis of MIP and NIP is shown.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Ratio of Template/MAA/2-VP/DVB**} & \multicolumn{2}{c}{**Amount of Monomers, mL**} & \multirow{2}{*}{**Mass, mg**} \\ \cline{2-3}  & **MAA** & **2-VP** & **AIBN** \\ \hline
1:2:2:8 & 0.848 & 1.085 & 19.1 \\ \hline
1:4:4:8 & 1.696 & 2.17 & 38.2 \\ \hline
1:5:5:8 & 2.12 & 2.712 & 47.7 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The molar ratio of the monomers used for synthesis.  
Figure 1: Synthesis of MIP and NIP.