From Spontaneous to Stimulated Emission: Quantum Optical Probes for Supramolecular Organization

Quantum statistical properties of fluorescence emitted spontaneously in random directions underpin a variety of experimental methods for determining molecular interactions in both test tubes and biological cells. I will begin this talk with a brief overview of a method developed in my lab, dubbed Fluorescence Intensity Fluctuation (FIF) Spectrometry, which probes spatial fluctuations in fluorescence intensities from fluorescently labeled proteins to determine the number of subunits comprising a complex. I will then present Förster Resonance Energy Transfer (FRET) Spectrometry and its application to determination of the relative distances between and orientation of fluorescent molecules within a complex via energy transfer between their transition dipoles. In the third part of the talk, I will introduce a mathematical framework for quantization of electromagnetic fields emitted by single dipole radiators, which predicts both the directionality of photon emission probability and light-stimulated electromagnetic wave collapse. I will conclude by presenting preliminary experimental results testing these effects. These quantum phenomena could lead to new methods for directly determining protein orientation within complexes, complementing the spontaneous emission-based methods.