2.4. Surface Modification of NaA Nanozeolites with Silane–PEG

The modification procedure was carried out according to the method described by Hermanson [37]. Briefly, a solution containing 4% ethanol in water (v/v) was prepared, and the pH was adjusted to 5.0 with concentrated acetic acid. Then, 2 mg of silane–PEG-NH₂ (5000 Da) was dissolved in acidic water/ethanol, and the solution was stirred for 5 min. After this time, 1 mg nanozeolite was added, and the mixture was stirred for 24 h at room temperature. The obtained product was washed several times with 99.8% ethanol to remove the excess of silane-PEG 5000 compound and dried at 110 °C for 30–40 min. The functionalization of the surface was carried out by using a silane coupling agent with three ethoxy groups and PEG molecules. The silane-PEG-NH₂ agent was attached to the surface of nanozeolite NaA by the siloxane bonds formation. The surface modification of NaA nanozeolites with silane-PEG is presented in Figure 1.

Steps of the ²²³RaA-silane-PEG-D2B radiobioconjugate synthesis.