Analysis of the intrinsic scatter and fluorescence profiles of marine algae can be used for general classification of
organisms based on cell size and fluorescence properties. We describe the design and fabrication of a Microflow
Cytometer on a chip for characterization of phytoplankton. The Microflow Cytometer measured distinct side-scatter and
fluorescence properties of Synechococcus sp., Nitzschia d., and Thalassiosira p. Measurements were confirmed using
the benchtop Accuri C6 flow cytometer. The Microflow Cytometer proved sensitive enough to detect and characterize
picoplankton with diameter approximately 1 mm and larger phytoplankton of up to 80 mm in length. The wide range in
size discrimination coupled with detection of intrinsic fluorescent pigments suggests that this Microflow Cytometer will
be able to distinguish different populations of phytoplankton on unmanned underwater vehicles. Reversing the
orientation of the grooves in the channel walls returns the sample stream to its original unsheathed position allowing
separation of the sample stream from the sheath streams and the recycling of the sheath fluid.
A rapid, automated, multi-analyte Microflow Cytometer is being developed as a portable, field-deployable sensor for onsite
diagnosis of biothreat agent exposure and environmental monitoring. The technology relies on a unique method for
ensheathing a sample stream in continuous flow past an interrogation region where optical fibers provide excitation and
collect emission. This approach efficiently focuses particles in the interrogation region of the fluidic channel, avoids
clogging and provides for subsequent separation of the core and sheath fluids in order to capture the target for
confirmatory assays and recycling of the sheath fluid. Fluorescently coded microspheres provide the capability for highly
multiplexed assays. Optical analysis at four different wavelengths identified six sets of the coded microspheres
recognizing Escherichia coli, Listeria, and Salmonella as well as cholera toxin, staphylococcal enterotoxin B (SEB), and
ricin, and assay results were compared with those of a commercial Luminex analysis system.
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