Combining nanoscale optical phenomena with atomic force microscopy for cellular studies

Evanescent Waves (EWs) and Förster Resonance Energy Transfer (FRET) concepts combined with Atomic Force Microscopy (AFM) have been used for imaging and sensing. For the proposed EW microscopy system, Quantum Dot (QD) embedded Polystyrene microspheres are mounted on AFM cantilevers. When excited by laser, QDs luminescence couples to the Whispering Gallery Modes (WGMs) in the periphery of the microsphere. The resultant EWs extend on the order of 100 nm from the surface of the microsphere. These EWs decay exponentially and are explored as a tool to excite fluorescent labeled trans-membrane and near-membrane proteins. For the FRET system, QD coated silica microspheres are conjugated with fibronectin and mounted on AFM cantilevers. Moving the sphere down to the surface of the RFP-αv integrin tagged cells, fibronectins on the microsphere surface bind to integrins on the cell surface and FRET is observed between the QDs (donor) and RFP (acceptor). The detected fluorescence for the imaging system and the FRET efficiency for the sensing system are both functions of cell surface protein density. These innovative nanoscale imaging and sensing systems can be used to obtain unique dynamic data from living cells to improve understanding of cell adhesion and mechanobiology in cells.