**2. Experimental section**

*Materials*. 3-aminopropyl-(3-oxobutanoic acid)-functionalized silica *NP*s, termed *APOB*, contain significant amounts of carboxylic acids on their surface. They are given from the purveyor (Sigma Aldrich) as 2.5% (w/v) dispersions in dimethylformamide, *DMF*. Their nominal density is 0.927 g ml-1 at 25°C (14). *NP*s were dialyzed against aqueous Borax (50 millimol, pH 8.5) under stirring, sonicated and recovered. The resulting dispersions are relatively stable, since *APOB* nano-particles bear negative charges on their surface.

Hen yolk lysozyme, *LYS*, (Sigma Aldrich) was dialyzed, crystallized, lyophilized and dried over *P2O5*. Its purity was confirmed by ionic conductance, density and viscosity of the corresponding aqueous solutions, at 25.00 *°C* (15,16).

Sodium dodecylsulfate, *SDS*, cetyltrimethylammonium bromide, *CTAB*, and didodecyldimethylammonium bromide, *DDAB*, (Sigma Aldrich) were individually dissolved in ethanol and precipitated by addition of cold acetone. The products were vacuum dried at 70°C. Their purity was confirmed by conductometric determination of the critical micellar concentration, *CMC*, at 25.00 °C. *Pluronic F-127* (Sigma Aldrich), a surface active block copolymer, forming micelles at high temperatures (17), was used as dispersant, when required.

A water soluble carbodiimide, termed *EDAC*, hydroxysuccynimide, *NHS*, triethylamine, *N(Et)3*, and glycine, (Sigma Aldrich), were used as such.
