Shah and sine convolution Fourier transform detection for microchannel electrophoresis with a charge coupled device

This paper describes an improved format for Shah convolution Fourier transform (SCOFT) detection that utilizes the spatial resolution of a charge-coupled device (CCD) rather than a fixed optical mask to perform a Shah or sine convolution over a fluorescence signal. The laser-induced fluorescence from a 9-mm section of microfabricated channel is collected with a CCD at 28 Hz. Each image frame is multiplied by a convolution function to modulate the collected signal through space. Each frame is then summed to generate an intensity-versus-time data set for Fourier analysis. The fluorescence signal oscillates at a frequency dependent upon both the convolution function multiplied across each data frame and the velocity of fluorescent microspheres or a plug of fluorescent dye flowing through the channel. This SCOFT technique affords more flexibility over formats that employ a physical mask and provides data that can be optimized for signal-to-noise (S/N) or resolution information. A 1,000-fold improvement in S/N is demonstrated for a plug of fluorescein dye. Detection of fluorescent beads exhibited frequency signals that were dependent upon the bead size distribution, the electric field, and the electrophoresis buffer concentration. Data are presented demonstrating the quantitation of fluorescent microspheres.