Label-Free Free-Solution Single-Molecule Protein–Small Molecule Interaction Observed by Double-Nanohole Plasmonic Trapping

The interaction of proteins with small molecules is fundamental to their function in living organisms, and it is widely studied in drug development. Here we use the double nanohole optical trapping technique to observe real-time label-free free-solution single-molecule dynamics of three complexes: biotin–streptavidin, biotin–monovalent streptavidin, and acetylsalicylic acid–cyclooxygenase 2. Radically different behavior is seen between the protein with and without the small molecule binding. This detection platform is scalable, inexpensive, and highly sensitive, which may transform drug discovery based on protein–small molecule interactions.