Application Note...

Series 6000 Digital Pressure Transducers

Application:

Control of liquid droplet size using precise pressure control

Challenge:

Flow Cytometry is the measurement of physical and chemical characteristics of small particles using a flow cytometer. Biological particles of interest, such as tumor cells, are placed in a liquid suspension. A fluorescent dye, selected because it will bind to the particles of interest, is added to the solution. The suspension is made to flow in a stream past a light source, usually a laser beam, one particle at a time. The wavelength of the light is selected such that it causes the dye, which is attached to the desired particles, to fluoresce. A computer counts and/or analyzes the cells or other particles as they pass through the laser beam and fluoresce.

Cells or other particles can also be sorted from the stream and diverted into separate containers by applying a charge to the particles of interest. Some particle characteristics, such as size and shape, do not require the use of dyes. These characteristics are determined by the light dispersion they cause as the particles flow past the laser beam.

A specialized laminar flow element is used to mix the test sample and the liquid suspension together and flow past the laser. The pressure on the backside of the flow element determines the point at which the stream of liquid separates into droplets. The droplets must form prior to being counted by the laser beam.

Solution:

The pressure was measured using one or more Mensor Series 6000 Digital Pressure Transducers in a pressure control loop. Using a known pressure allows for shorter setup times and more consistent results.