Stability of transferrin in a preformed corona on SPIOs with or without PEGylation (B). FPLC analyses of 125I activity in fractions. A, transferrin adsorbed; B, transferrin covalently bound. The N-PEGylated SPIOS (N10K) and the fully C-PEGylated SPIOs (C10, C40) do not adsorb 125I-albumin. A, initial transferrin adsorbed; B, initial transferrin covalently bound. The peak at 33 min represents proteins with the size of transferrin (DLS: 9 nm).