I. Design of the polymer
1. Poly (isobutylene- alt maleic anhydride) is vigorously mixed with dodecylamine in 100 mL tetrahydrofurane, so that the amount of added dodecylamine molecules is sufficient to react with 75% of the maleic anhydride units.
2. The cloudy product is heated for several hours (60 °C) and thereby becomes transparent.
3. The solvent is evaporated (e.g. by means of a rotary evaporator) and redissolved in anhydrous chloroform.
4. If a further functionality (such as better solubility at high salt concentrations, biotinization or fluorescence) of the polymer is desired, an appropriate amount of the respective amino group equipped molecules, such as methoxy-PEG-amine (Mw=5000 g mol-1 or Mw=750 g mol-1) dissolved in chloroform, biotin-PEG-amine (Mw= 5000 g mol-1 or Mw= 720 g mol-1) dissolved in chloroform or THF, aminophenyl β-D-galactopyranoside dissolved in THF, or fluorescein amine dissolved in THF are added dropwise into the diluted polymer solution. Therefore, the amount of added molecules is chosen so that 0.25% to 4% of the maleic anhydride rings of the polymer backbone can react with them.
5. The reaction mixture is stirred overnight.
6. The solvent is evaporated under reduced pressure. Finally the product is re-dissolved in fresh anhydrous chloroform.
II. Polymer coating of the nanoparticles
1. The polymer solution in chloroform is mixed with the solution of hydrophobic ligand stabilized nanoparticles in chloroform. Therefore, 100 monomer units of the polymer per nm2 of the nanoparticle surface are inserted.
2. After 30 min, the solvent is removed under reduced pressure (e.g. by means of a rotary evaporator). The thin solid film forms.
3. The product is dissolved in alkaline sodium borate buffer (SBB) solution at pH 12.
4. The solvent is exchanged with a buffer of moderate pH, such as SBB at pH 9. This is performed by twice repeatedly diluting and reconcentrating the solution by means of a centrifuge filter.
5. Residual polymer is removed by size exclusion chromatography and/or gel electrophoresis.