Stephen C. Miller, Ph.D.
Illuminating biological processes with chemistry
Our laboratory is primarily focused on the non-invasive optical imaging of the intracellular environment with fluorescence and bioluminescence.
Fluorescent molecules. Study of the intracellular environment using fluorescence is limited by the inherent absorbance of living tissues. Most optical probes in use today absorb and emit light in the visible wavelength region. Absorption of visible wavelength light by cellular components (e.g., flavins, porphyrins) generates excited state molecules that can give rise to background fluorescence and phototoxicity. In animals such as the mouse, absorption of light by the hemoglobin in blood is so great that visible wavelength fluorescence is not viable for imaging.
Living tissue is most transparent to light beyond the visible range, in a spectral region known as the near-IR (650-900 nm). Although this is the ideal spectral window for any optical probe of living cells or organisms, most near-IR fluorophores are unsuitable for use in the intracellular environment because they either lack cell-permeability or give high-background labeling of cellular organelles and membranes. One of our major goals is thus the design and application of new near-IR fluorophores and probes that can freely enter living cells and facilitate studies of specific intracellular events.
Bioluminescent molecules. Luciferase-catalyzed light emission can also be used to report on the intracellular environment, and can be used in live animals. Nonetheless, the properties of luciferase are inherently limited by the ability of the luciferin substrate to access the luciferase, and by its photophysical properties (e.g., emission wavelength). Work in our lab is directed toward the development and optimization of luciferases and luciferins for applications ranging from high-throughput screening to bioluminescence imaging in mice.