A convenient on-line device for reagent addition, sample mixing, and temperature control of cell suspensions in flow cytometry.

We describe a simple and inexpensive device which permits the addition of up to three different solutions into a cell suspension which is on-line in a flow cytometer. The mixing chamber houses a disposable plastic cuvette stirred with a magnetic stirrer. The sample chamber is attached to a circulating water bath, hence accurate temperature control is achieved. Because the system is prepressurized and the sample line is very short, the delay time-between the point of sample modification and the point of analysis is reduced to a few seconds. Thus reagents may be added rapidly, and kinetic measurements of high temporal resolution are possible. Because the temperature of the sample chamber is regulated, binding can be observed over longer time periods than was previously possible. We demonstrate the usefulness of this device in determining the binding of fluoresceinated hexapeptide to human neutrophils under conditions where the stimulus is infused into the cell suspension while on-line in the cytometer.