Protein coronas provide the biological identity of nanomaterials in vivo. Here we have used dynamic light scattering (DLS) and transmission electron microscopy (TEM) to investigate the adsorption of serum proteins, including bovine serum albumin (BSA), transferrin (TRF) and fibrinogen (FIB), on gold nanoparticles (AuNPs) with different surface modifications (citrate, thioglycolic acid, cysteine, polyethylene glycol (PEG, M_w = 2 k and 5 k)). AuNPs with PEG(5 k) surface modification showed no protein adsorption. AuNPs with non-PEG surface modifications showed aggregation with FIB. AuNPs with citrate and thioglycolic acid surface modifications showed 6–8 nm thick BSA and TRF coronas (corresponding to monolayer or bilayer proteins), in which the microscopic dissociation constants of BSA and TRF protein coronas are in the range of 10^–8 to 10^–6 M.