PEGylation reaction

For PEGylation of nanoparticles ≥100 nm, 60 mg Methoxypolyoxyethylene amine (mPEG-amine, MW = 5,000) was dissolved into 500 μl polystyrene nanoparticle solution. 500 μl 0.2 M borate buffer (pH 8.2) was added and the pH was adjusted to 7.8 using 0.5 N NaOH. 14 mg Sulfo-NHS was added, mixed for 5 minutes, and 100 μl carbodiimide (EDC) (20 mg/ml in 50 mM MES buffer, pH 6.0) was added. The resulting solution was then mixed for 6 hours in the dark. Free mPEG-amine was removed using Amicon ultracentrifuge filters (MWCO 30/50 KDa) and the PEGylated nanoparticle solution was resuspended with deionised water pH 7.0 and quantified by HPLC. For 20 nm polystyrene nanoparticles, the procedure was modified slightly. Nanoparticles were first concentrated by ultracentrifugation and resuspended with 1 ml 50 mM MES buffer pH 6.0. 90 mg methoxy-PEG5000-NH2 was added and the solution was stirred for 15 minutes followed by the procedure as described above.