Gold nanoparticles (NPs) functionalized with L-amino acid-terminated monolayers provide an effective platform for the recognition of protein surfaces. Isothermal titration calorimetry (ITC) was used to quantify the binding thermodynamics of these functional NPs with alpha-chymotrypsin (ChT), histone, and cytochrome c (CytC). The enthalpy and entropy changes for the complex formation depend upon the nanoparticle structure and the surface characteristics of the proteins, e.g., distributions of charged and hydrophobic residues on the surface. Enthalpy-entropy compensation studies on these NP-protein systems indicate an excellent linear correlation between Delta H and T Delta S with a slope (alpha) of 1.07 and an intercept (T Delta S-0) of 35.2 W mol(-1). This behavior is closer to those of native protein-protein systems (alpha = 0.92 and T Delta S-0 = 41.1 kJ mol(-1)) than other protein-ligand and synthetic host-guest systems.