Growth kinetics of microalgae in microfluidic static droplet arrays.
ABSTRACT We investigated growth kinetics of microalgae, Chlorella vulgaris, in immobilized arrays of nanoliter-scale microfluidic drops. These static drop arrays enabled simultaneous monitoring of growth of single as well as multiple cells encapsulated in individual droplets. To monitor the growth, individual drop volumes were kept nearly intact for more than a month by controlling the permeation of water in and out of the microfluidic device. The kinetic growth parameters were quantified by counting the increase in the number of cells in each drop over time. In addition to determining the kinetic parameters, the cell-size distribution of the microalgae was correlated with different stages of the growth. The single-cell growth kinetics of C. vulgaris showed significant heterogeneity. The specific growth rate ranged from 0.55 to 1.52 day(-1) for different single cells grown in the same microfluidic device. In comparison, the specific growth rate in bulk-scale experiment was 1.12 day(-1) . It was found that the average cell size changes significantly at different stages of the cell growth. The mean cell-size increased from 5.99 ± 1.08 to 7.33 ± 1.3 µm from exponential to stationary growth phase. In particular, when multiple cells are grown in individual drops, we find that in the stationary growth phase, the cell size increases with the age of cell suggesting enhanced accumulation of fatty acids in older cells. Biotechnol. Bioeng. © 2012 Wiley Periodicals, Inc.
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ABSTRACT: Global warming can be slowed, and perhaps reversed, only when society replaces fossil fuels with renewable, carbon-neutral alternatives. The best option is bioenergy: the sun's energy is captured in biomass and converted to energy forms useful to modern society. To make a dent in global warming, bioenergy must be generated at a very high rate, since the world today uses approximately 10 TW of fossil-fuel energy. And, it must do so without inflicting serious damage on the environment or disrupting our food supply. While most bioenergy options fail on both counts, several microorganism-based options have the potential to produce large amounts of renewable energy without disruptions. In one approach, microbial communities convert the energy value of various biomass residuals to socially useful energy. Biomass residuals come from agricultural, animal, and a variety of industrial operations, as well as from human wastes. Microorganisms can convert almost all of the energy in these wastes to methane, hydrogen, and electricity. In a second approach, photosynthetic microorganisms convert sunlight into biodiesel. Certain algae (eukaryotes) or cyanobacteria (prokaryotes) have high lipid contents. Under proper conditions, these photosynthetic microorganisms can produce lipids for biodiesel with yields per unit area 100 times or more than possible with any plant system. In addition, the non-lipid biomass can be converted to methane, hydrogen, or electricity. Photosynthetic microorganisms do not require arable land, an advantage because our arable land must be used to produce food. Algae or cyanobacteria may be the best option to produce bioenergy at rates high enough to replace a substantial fraction of our society's use of fossil fuels.Biotechnology and Bioengineering 07/2008; 100(2):203-12. · 3.65 Impact Factor
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ABSTRACT: We present a droplet-based microfluidic technology that enables high-throughput screening of single mammalian cells. This integrated platform allows for the encapsulation of single cells and reagents in independent aqueous microdroplets (1 pL to 10 nL volumes) dispersed in an immiscible carrier oil and enables the digital manipulation of these reactors at a very high-throughput. Here, we validate a full droplet screening workflow by conducting a droplet-based cytotoxicity screen. To perform this screen, we first developed a droplet viability assay that permits the quantitative scoring of cell viability and growth within intact droplets. Next, we demonstrated the high viability of encapsulated human monocytic U937 cells over a period of 4 days. Finally, we developed an optically-coded droplet library enabling the identification of the droplets composition during the assay read-out. Using the integrated droplet technology, we screened a drug library for its cytotoxic effect against U937 cells. Taken together our droplet microfluidic platform is modular, robust, uses no moving parts, and has a wide range of potential applications including high-throughput single-cell analyses, combinatorial screening, and facilitating small sample analyses.Proceedings of the National Academy of Sciences 08/2009; 106(34):14195-200. · 9.74 Impact Factor
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ABSTRACT: Poly(dimethylsiloxane) is currently the material of choice for rapidly fabricating microfluidic devices. As the size of these devices decreases, a significant hydrodynamic flow is generated due to permeation of fluid through the channel walls. We develop a theoretical model verified by single bead tracking experiments, which demonstrates that large flow rates (>10 microm/s) can be passively generated in a straight microchannel filled with water. Realizing that this flow may be unwanted in some applications, we present a method to eliminate it by inhibiting mass transfer of water into the poly(dimethylsiloxane) walls. Furthermore, we explore applications to harness this passively generated flow inside a microfluidic device such as bead stacking, chemical concentration, and passive pumping.Proceedings of the National Academy of Sciences 08/2005; 102(31):10813-8. · 9.74 Impact Factor