Field Testing of a Microfluidic Particle Counter for Oceanographic Applications

We have built and tested a third generation microfluidic device that can be deployed on autonomous platforms for remote detection of medium and large microscopic particles in the ocean. The instrument has no moving parts and does not require sheath fluid, thus allowing for robust operation in oceanographic settings. Sequential along-channel measurements provide quantitative information on particle flow rate, thereby allowing particle concentration to be calculated and removing the need for a metering pump in applications where ambient water is flowing past the device or when the device is installed on a moving platform. Field testing indicates that a 300 x 500 micron cross-sectional area of the flow channel is suitable for detecting individual phytoplankton, diatom chains, and microzooplankton. Particle size is inferred from the relative strength of the voltage signal generated by a detection event and ranges from 10–250 microns with a resolution of approximately 20 microns. During field testing, concentrations derived from the instrument were statistically indistinguishable from a benchtop FlowCAM in nearly all samples tested.