Microfluidic technology for plankton research

Abstract

Plankton produces numerous chemical compounds used in cosmetics and functional foods. They also play a key role in the carbon budget on the Earth. In a context of global change, it becomes important to understand the physiological response of these microorganisms to changing environmental conditions. Their adaptations and the response to specific environmental conditions are often restricted to a few active cells or individuals in large populations. Using analytical capabilities at the subnanoliter scale, microfluidic technology has also demonstrated a high potential in biological assays. Here, we review recent advances in microfluidic technologies to overcome the current challenges in high content analysis both at population and the single cell level.

Figure 1

Droplet trapping using hydrostatic pressure. (a) Schematic of the experimental setup of the hydrostatic pressure head for trapping the droplets, (b) time‐stamped images showing the formation of single algae culture plug (i–iv) and droplet arrays (v–x), and (c) the microchip after trapping 30 droplets. Reproduced, with permission from 11. The high-throughput microfluidic microalgal photobioreactor array. (d) The platform was composed of four layers – a light blocking layer, a microfluidic light–dark cycle control layer, a microfluidic light intensity control layer, and a microalgae culture layer. (e) Enlarged view of a single culture compartment having five single-colony trapping sites. (f) A single-colony trapping site composed of four micropillars. Reproduced, with permission from 16.

Figure 2

(a) 3 spiral rectangular channels (500, 300 and 200 μm high) are cascaded to fractionate a mix of particles with a wide range of diameter (100, 50 and 30μ). Reproduced, with permission from 33. (b) Tiled micrograph images of a portion of a “tertiary series” sampler used for lab testing. Concentrations of Cyclidium sp. become greatly-enriched towards the 5th gallery in the series, in some cases, completely filling the terminal gallery with protists (inset). Reproduced, with permission from 35.

Figure 3

(a) Schematic view of the experimental setup of passive sorting system. (b) Micrographs of the three different species of algae. (c) Examples of images captured at the end of the spiral channel (d) Normalized distributions of the algae across the channel cross section. Reproduced, with permission from 37. (e) Schematic view of a hybrid sorting system; Droplets are generated and focused to the side wall of the microchannel by oil phase flow from inlet 3. Then, single cell encapsulated droplet are separated by magnetic field. The scale bar is 200 μm. Reproduced, with permission from 45.

Figure 4

Sorting C. reinhardtii low-chlorophyll cell-containing droplets from empty droplets. (a) Images taken of droplets before sorting; (b) 91% droplets collected in the “positive” channel contain cells whereas only 6% of negative droplets are occupied, false “negatives”. Scale bar = 100 μm. (c) Images recorded during sorting show that cell-containing droplets are deflected into the “positive” channel (top panel), whereas empty droplets flow into the “negative” channel (bottom panel) 41.

Figure 5

(a–d) Phase contrast microscopy of the four species of phytoplankton. (e) Probability density function of measured swimming speeds for each species. (f) Timeseries of the mean square displacement for each species. The solid line represents a linear fit to the diffusive regime, from which the effective translational diffusivity, D, was obtained. (g) Schematic of the serpentine microfluidic device (left, plan view; right, isometric view, not to scale) showing the imaging plane (light blue) and the flow profile (red) at the channel mid-depth. (h) Flow velocity profiles measured at the mid-depth plane using cells as tracers (blue dots), fitted with a parabolic profile (red line). Error bars correspond to the standard error of the mean [50].

Figure 6

(a) Schematic diagram of the competitive immunoassay in the immune-reaction columns. (b) Illustration of the chip operations to complete the immunoassay. The center circle area of the chip is graphical shown: each process of the reagent loading was controlled by two valves (Valve 1 and Valve 2). Status of the valves is clarified by different colours: red for action; gray for inaction. Reproduced, with permission from 62.

Figure 7

(a) Swimming trajectories of Silicibacter sp. cells across the microfluidic channel following injection of f/2 growth medium as a chemoattractant (control). Each white path is the trajectory of a single bacterium. (b) Swimming trajectories of Silicibacter sp. cells within a band of Synechococcus elongatus extracellular products, demonstrating strong accumulation in the band of chemoattractant. Reproduced, with permission from 68.

Figure 8

Photomicrographs of labeled cells. Green labels show enzyme-labeled fluorescent compounds located at the alkaline phosphatase sites. Red labels are chlorophyll a pigments. (a) Typical fluorescence and bright-field images of four droplets containing single living labeled cells. (b) Difference in labeling between three dead cells with numerous labels at the surface (upper image) and a living cell with a single label located at the bottom of the flagellar apparatus (bottom image). (c) Example of the kinetics of a single living cell labeled in droplet. Reproduced, with permission from 73.

Figure 9

Illustration of the droplet microfluidics based microalgae screening platform for analyzing microalgal growth and oil production. The platform is composed of three functional parts (i) the droplet generation/culturing region for culture and growth monitoring, (ii) the on chip staining region for tagging Nile red fluorescent dye to oil bodies of microalgae, and (iii) the rinsing/analysis region for oil quantification. Reproduced, with permission from 80.