Nanoparticles and nanostructured surfaces offer a new route to
study protein interactions, both protein-ligand and protein-protein. For
example, we have studied the binding of HSA to a series of polymeric
nanoparticles of increasing hydrophobicity in the presence and absence
of oleic acid13, which is one of the key ligands that HSA binds during
its normal functioning44. Very different interaction patterns are
observed with and without oleic acid – HSA in complex with oleic acid
gives an endothermic signal and lower stoichiometry compared with
the exothermic signal from apo-HSA (in the absence of oleic acid),
as shown in Fig. 5. A recent study using semiconductor nanocrystals
(QDs of average diameter less than 2 nm) directly conjugated to HSA has shown that these conjugates can be used as fluorescent biological
labels. Using measurements of fluorescence resonance energy transfer
(FRET) from the amino acid tryptophan (Trp214) to the QD, it is
possible to follow the local and global changes in the HSA structure
during thermal unfolding and refolding processes45.