Our group develops and applies ultrahigh-resolution, ultrahigh-sensitivity fluorescence imaging and spectroscopy tools to solving outstanding problems in biology. The ability to watch one molecule at a time helps us obtain unique information on distribution functions of relevant observables, resolve subpopulations in heterogeneous samples, and record asynchronous time trajectories of observables that would otherwise be hidden. For example, dynamic distance changes between two sites on a macromolecule (or between two different molecules) can be measured via single-pair fluorescence resonance energy transfer (spFRET). Our group developed such tools and uses them to study protein folding of several proteins, transcription by RNA polymerase and the transporter lac permease at the single-molecule level. Single-molecule experiments are currently performed predominantly in in-vitro environments. The ultimate challenge is to image cellular substructures, determine the relationships and dynamics of vesicles and organelles, describe existing conformational dynamics and biomolecular interactions, and localization all of the above in-vivo with single molecule sensitivity and nanometer-accuracy. This will allow the study of enzymes and multi-component molecular machines in their natural environment, with the signaling and regulation circuitry all wired-up. We are developing colloidal fluorescent semiconductor nanocrystals (a class of quantum dots, or qdots) for biological labeling. We are developing organic coatings, bioconjugation schemes, targeting strategies, and unique instrumentation that take advantage of nanocrystals' spectral properties. We use qdots to study lipid rafts, the prion protein and ERBB receptors in membranes of live cells, and as molecular imaging probes in live zebra fish and mice.
Research Interests & Expertise: Understanding the behavior and function of proteins