Functional Imaging Through Dark State Dynamics

This thesis harnesses the environmental sensitivity of the dark states of molecular fluorophores, both endogeneous in cells/tissue and externally introduced for mapping of chemical micro-environments including factors such as ion concentration and microviscosity. A novel technique for directly detecting the dynamics and population of dark states, such as the lowest triplet state, was developed and called FAPA, Fluorescence Anomalous Phase Advance. This technique is a sensitive and fast reporter of dark state dynamics and can be used for imaging. In addition, a genetically-encoded microviscosity and micro-environmental mapping ability with high protein-specific specificity was developed by using a TMP-tag and Fluorescence Lifetime Imaging

Mapping protein-specific micro-environments in live cells by fluorescence lifetime imaging of a hybrid genetic-chemical molecular rotor tag

The micro-viscosity and molecular crowding experienced by specific proteins can regulate their dynamics and function within live cells. Taking advantage of the emerging TMP-tag technology, we present the design, synthesis and application of a hybrid genetic-chemical molecular rotor probe whose fluorescence lifetime can report protein-specific micro-environments in live cells

Mapping protein-specific micro-environments in live cells by fluorescence lifetime imaging of a hybrid genetic-chemical molecular rotor tag

The micro-viscosity and molecular crowding experienced by specific proteins can regulate their dynamics and function within live cells. Taking advantage of the emerging TMP-tag technology, we present the design, synthesis and application of a hybrid genetic-chemical molecular rotor probe whose fluorescence lifetime can report protein-specific micro-environments in live cells

Observation of Frequency-Domain Fluorescence Anomalous Phase Advance Due to Dark-State Hysteresis

Frequency-domain fluorescence spectroscopy, commonly referred to as phase fluorometry, is a classic approach to study the lifetime dynamics of fluorescent systems. Here we report an interesting phenomenon: unlike conventional fluorescence lifetime phase fluorometry in which the fluorescence trace always lags behind the modulated excitation source, the detected signal from certain fluorophores can actually exhibit fluorescence anomalous phase advance (FAPA) as if the fluorescence is emitted “ahead” of the source. FAPA is pronounced only within a range of modulation frequencies that are outside quasi-static and quasi-equilibrium conditions. We attribute FAPA to photoinduced dark state hysteresis, supported by both simulations of photodynamic transitions and experiments with dark-state promoters and quenchers. Being a fast and straightforward frequency-domain reporter, FAPA offers a unique and specific contrast mechanism for dark state dynamics sensing and imaging

Large Enhancement of Nonlinear Optical Phenomena by Plasmonic Nanocavity Gratings

Enhancing nonlinear processes at the nanoscale is a crucial step toward the development of nanophotonics and new spectroscopy techniques. Here we demonstrate a novel plasmonic structure, called plasmonic nanocavity grating, which is shown to dramatically enhance surface nonlinear optical processes. It consists of resonant cavities that are periodically arranged to combine local and grating resonances. The four-wave mixing signal generated in our gold nanocavity grating is enhanced by a factor up to ≈2000, 2 orders of magnitude higher than that previously reported.Physic