Uses single-molecule spectroscopy, optical trapping, and advanced imaging to study nanoscale systems. Directions: (1) orientation-resolved single-molecule spectroscopy using polarization-controlled excitation and detection; (2) optical trapping of individual nanoparticles and viruses to study force-dependent dynamics; (3) plasmon-enhanced single-molecule detection and imaging beyond diffraction limit; (4) ultrafast spectroscopy of nanoscale energy transfer.