Anisotropy upgrade for single photon counting

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Many chemical processes occur on very fast time-scales, from thousands to millions of times faster than humans can blink their eyes. Probe molecules, which light up when irradiated, are used to follow these fast chemical reactions. The change of the probe's fluorescence intensity with time is detected with a technique called single photon counting (spc). This proposal requests funds to enhance the capability of the spc to enable time-resolved fluorescence anisotropy measurements. Anisotropy experiments will provide information on how fast probes tumble. These experiments are essential for the Bohne group to obtain information on the changes in sizes of supramolecular systems. The Moffit group needs anisotropy measurements to characterize quantum dots. The detection of protein-protein interactions is studied in the Hof group on the protein S100A7, which is a key component of a novel breast cancer signaling pathway. Anisotropy experiments use polarizers as requested in this proposal. However, the polarizers will decrease the light intensity of the non-polarized light of our current excitation source (hydrogen flash lamp). For this reason, high intensity pulsed diode lasers (DLs) and pulsed light emitting diodes (LEDs) are also requested.