The Sheets/Heikal Group uses approaches from biophysics, biochemistry, cell and molecular biology, analytical and physical chemistry, optics, and materials science to answer questions about how molecules (proteins, lipids) interact with each other to effect functional biological responses. The systems we investigate include fluorescent protein-based sensing of macromolecular crowding and ionic strength sensing. We have also investigated immunoreceptor signaling for the allergic response and biomembrane structure and dynamics in the past. We use fluorescence microscopy and spectroscopy and optical trapping to measure and manipulate these single molecule interactions in live cells and biomimetic systems.