The Nature of a Hard Protein Corona Forming on Quantum Dots Exposed to Human Blood Serum

Biological responses of cells and organisms to nanoparticle exposure crucially depend on the properties of the protein adsorption layer (“protein corona”) forming on nanoparticle surfaces and their characterization is a crucial step toward a deep, mechanistic understanding of their build‐up. Previously, adsorption of one type of model protein on nanoparticles was systematically studied in situ by using fluorescence correlation spectroscopy. Here, the first such study of interactions is presented between water‐solubilized CdSe/ZnS quantum dots (QDs) and a complex biofluid, human blood serum. Despite the large number of proteins in serum, a protein layer of well‐defined (average) thickness forming on QD surfaces is observed. Both the thickness and the apparent binding affinity depend on the type of QD surface ligand. Kinetic experiments reveal that the protein corona formed from serum is irreversibly bound, whereas the one formed from human serum albumin was earlier observed to be reversible. By using sodium dodecyl sulfate‐polyacrylamide gel electrophoresis and mass spectrometry, the most abundant serum proteins contributing to the formation of a hard corona on the QDs are identified. Protein adsorption onto quantum dots immersed in human blood serum is characterized in situ by using dual‐focus fluorescence correlation spectroscopy, revealing a thin, irreversibly bound protein adsorption layer.