MEASURING CONDITIONS FOR HIGH NUMERICAL APERTURE FLUORESCENCE CORRELATION SPECT

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We have begun prototype development of a new fast and efficient lifetime imaging scheme specifically designed for use with MPM. This novel technique electronically weights the 2PE fluorescent signal by the time of arrival of the fluorescent pulse relative to the excitation pulse by multiplication with a linear ramp. Early arriving photons are weighted proportionally less than late arriving photons to reflect the lifetime of the fluorophore. The ramp acts to provide analog time information to the signal, which is preferable to discrete time binning when low numbers of fluorescent photons are collected. The processing electronics produce an output that will be proportional to the fluorophore lifetime. This technique is similar to that of the fast time gating method, but the sensitivity is potentially much greater for low levels of fluorescence where the statistical fluctuation in the photon arrivals demands narrower binning. Furthermore, integrated electronics to perform the necessary p rocessing are inexpensive and readily available.