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Microparticle Flow Sensor

As many as 1,000 microparticles can be identified, tracked, and counted.

The microparticle flow sensor (MFS) is a system for identifying and counting microscopic particles entrained in a flowing liquid. The MFS includes a transparent, optoelectronically instrumented laminar-flow chamber (see figure) and a computer for processing instrument-readout data. The MFS could be used to count microparticles (including micro-organisms) in diverse applications — for example, production of microcapsules, treatment of wastewater, pumping of industrial chemicals, and identification of ownership of liquid products.

In addition to the instrumented chamber and the computer, the system includes a process controller and pumps. The instrumentation on the chamber includes one or more laser(s) and/or lightemitting diode(s) for illuminating the microparticles in the flow path, and a high-resolution digital camera with a magnifying lens for capturing sequential images of the illuminated microparticles as they move across the chamber. The MFS acts partly as a spectrophotometer in that it measures the amount of light reflected or transmitted by each microparticle at the laser wavelength(s).

ImageThe chamber is only 20 µm thick, and the liquid is pumped through it at a rate of about to 200 µL/min, giving rise to a low-shear laminar flow that forces the entrained microparticles to move across the chamber abreast. Hence, no microparticle shadows another microparticle, and as a result, every microparticle can be op-tically observed and analyzed separately from every other microparticle.

Special-purpose software running on a Pentium III 400-MHz computer processes the image data to locate individual microparticles and track their trajectories. If the microparticles of interest have known spectral characteristics (for example, if they have been dyed), then the software can identify the microparticles of interest and/or distinguish them from other microparticles (e.g., sediment) by means of the amounts of light transmitted or reflected by the various microparticles at different wavelengths. Tracking of microparticle trajectories can yield data on sedimentation rates, which are useful for identifying and distinguishing among microparticles of different sizes and compositions. Image data are also analyzed to determine microparticle sizes and shapes, which are also indicative of microparticle identities. The software can count and track more than 1,000 microparticles simultaneously as well as perform statistical analysis of microparticle data. A complete cycle of acquisition and processing of image data is only 5 seconds long.

This work was done by Dennis R. Morrison of Johnson Space Center.

This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, Johnson Space Center, (281) 483-0837. Refer to MSC-23277.