Microfluidic passive samplers for in situ collection of live aquatic protists

Abstract

This paper describes the development of microfluidic passive samplers for the collection of live protists from natural aquatic habitats. Microfluidic passive samplers provide several potential benefits over existing sampling methods. For example, they offer greater versatility, higher throughput, and do not require the disruption of specimens through the use of fixatives, stains, or by extraction. In lab testing, a marine ciliate Cyclidium sp. was concentrated from 600 cells per mL in a laboratory microcosm to above 2 × 10⁸ cells per mL within individual microfluidic observation galleries. In field experiments, live protists and other microorganisms were collected from surface water and sediment in a northeastern Connecticut stream. Protists were accumulated to 1 × 10⁷ cells per mL in individual observation galleries. Concentrating and isolating protists enables high-resolution, long-term observation of live, unstained protists. The compact arrangement of observation galleries facilitates high-throughput analysis. Sampler versions were created that differed in the degree of channel branching, the spatial density of galleries, and the size and shape of gallery entrance constrictions. Lab and field testing illustrated tradeoffs in performance among sampler variations in terms of the fraction of occupied chambers, overall on-chip biomass density, and in the types of protists and in the range of sizes of protists collected. Recommendations are provided to facilitate the adoption of microfluidic passive samplers for environmental characterization, research, and educational purposes.