A new technique for detecting fluorescently labelled cells at very low densities

We have developed a new cytometric method that has the potential for detecting fluorescently labelled cells at very low densities against a high density background of non-fluorescing cells of similar size. The method uses a Waveform Analysis Interface which is an electronic device that is essentially an "add-on" to a flow cytometer. It takes the amplified fluorescence and scatter signals from the flow cytometer and measures their intensities at microsecond intervals. It can be programmed to react only to cells with specific characteristics and ignore all others. In this mode it is possible to detect fluorescently labelled cells at densities down to about 1.mL-1 against a background density of non-fluorescent cells of similar size of more than 1 x 10(7).mL-1. This application may have considerable potential for cancer diagnosis and therapy.