Fluorescence decay measurement by calculation of inner product

Abstract

An apparatus and its accompanying method measures fluorescence decay, fluorescence amplitude and fluorescence polarization. The instrument includes a light emitting diode or laser diode light source, an amplified photodiode detector, and electronics and software for calculating the phase of the fluorescence from the computed inner product of the scattering and fluorescence signals. The electronics for measuring fluorescence decay includes two signal synthesizers, two downconverters, a simultaneously sampling analog-to-digital converter and means for calculating the inner product of the downconverted waveforms. A signal source, preferably a direct digital synthesizer, is used in combination with a digital-to-analog converter to provide a controllable output signal. That signal drives a modulatable light source, which is a light emitting diode, a laser diode or a combination of the two. Excitation light from the light source excites the sample fluorophore which is immobilized in a solid material. Fluorescence is detected using an amplified photodiode. The received signal is downconverted using a pair of mixers. The downconverted signals are digitized and stored. Preferably, the signals are digitized using a two-channel synchronous analog-to-digital converter controlled by a digital signal processor. Data from each channel are multiplied and summed to provide the inner product.