A Twelve-Channel Automatic Device for Continuous Recording of Cell Aggregation by Measurement of Small-Angle Light-Scattering

We describe here a 12-channel aggregometer, evolved from the instrument described by Beug & Gerisch in 1972, which records the course of aggregation or agglutination of cells or other particles by following the changes in light-scattering of the aggregating suspension. The instrument incorporates a simple memory system for condensing the data, introduces an improved cuvette design, and can be adjusted in its responsiveness to light-scattering by particles of different sizes. In our aggregometer, a vertical wheel in an opaque thermostatted chamber accommodates up to 12 cuvettes each containing a cell suspension and an air bubble. The constant rising of the bubble as the wheel rotates causes the stirring action which promotes aggregation. At a certain point in its rotational path, each cuvette is penetrated by a beam of light focused upon an absorbing beam stop centred in front of a photomultiplier tube. Particles suspended in the cuvette scatter a portion of the light beyond the beam stop into the photomultiplier tube to produce an electrical pulse proportional to the photon input. Collection of these pulses with the wheel in continuous motion avoids any disturbance of the course of aggregation. The pulses are routed to memory circuits for summation and eventual recording by a 12-channel printing potentiometer which automatically colour-codes and numbers each curve. The cuvettes consist of 2 glass microscope coverslips affixed with silicone grease over a hole in a thin, stainless steel blank. They are very durable and are easily dismantled and reassembled for cleaning. The coverslips are replaced after each use. The discoid chamber of our cuvette permits uniform circulation of the bubble, which in turn causes gentle stirring of the aggregating suspension at a rate that is a direct and continuous function of rev/min. Measurement of light-scattering at small angles (3-5.5°) provides great sensitivity to the disappearance of single cells and progressively less sensitivity to the coalescence of aggregates of progressively larger size. The signal generated by the photomultiplier tube decreases as aggregation proceeds. At 32 rev/min, one data point per channel, representing the sum (average) of 24 successive measurements, is printed every 458. In the course of a 60-min assay under standard conditions, up to 23040 individual readings can be automatically taken, summed and plotted. In a comparison of 8 identical samples run simultaneously, the printed values after 60 min agreed with a standard deviation of ±2%.