Single-cell genotyping of phytoplankton from ocean water by gel-based cell manipulation

A comprehensive understanding of phytoplankton diversity is valuable for assessing an environment of interest as phytoplankton are primary producers in various aquatic food webs. Microscopic analyses are useful for diversity assessment based on characteristic cell morphologies. However, phylogenetic classification based solely on morphology requires an extremely high level of expertise. The genetic approach is another option for evaluating phytoplankton diversity; however, it cannot reveal morphological information. To integrate these two approaches, we developed an original technology that is referred to as microcavity array (MCA)/gel-based cell manipulation (GCM). The model experiments using monocultures of various phytoplankton indicated that the efficiencies of cell recovery and isolation of single-cell plankton were dependent on cell size and shape. Cells with widths larger than the cavity width showed high level of recovery and isolation efficiency. Subsequent whole-genome amplification (WGA) of isolated single-cell plankton provided a sufficient amount (approximately 30 μg) of WGA products for genetic analyses. Furthermore, we showed that MCA/GCM could directly analyze phytoplankton in ocean water obtained from Suruga Bay, Japan, without any cumbersome pretreatment. These results indicate that MCA/GCM technology is a powerful tool for elucidating the phytoplankton diversity in marine environment. This article is protected by copyright. All rights reserved.

On-demand inkjet-printed microdisk laser with air cladding by liquid flow microetching

We have novelly, to the best of our knowledge, developed the liquid flow microetching method that can treat a single microdisk in a microregion with precise position control for inkjet-printed microdisk lasers. The injection-drain wet etching setup consisted of two microneedles that successfully performed a formation of a fine undercut structure of an inkjet-printed microdisk on a pre-pedestal layer through the individual wet etching process. Then measurement of the undercut structure using scanning electron microscopy and lasing characteristics with whispering gallery modes were carried out to demonstrate performance of the etched microdisks. The measured lasing threshold decreased by half compared with that of the unetched microdisk directly printed on a fluorine-type film. A point to note is that this etching method exhibits an excellent undercut and lasing characteristics even when using a clad pre-pedestal layer having a refractive index higher than that of core microdisks. This technique, combined with inkjet printing, offers a powerful tool for individually designing a microdisk and can help develop novel devices that comprise several inkjet-printed microdisks being evanescently coupled.

Microchip System for Patterning Cells on Different Substrates via Negative Dielectrophoresis

Seeding cells on a planar substrate is the first step to construct artificial tissues in vitro. Cells should be organized into a pattern similar to native tissues and cultured on a favorable substrate to facilitate desirable tissue ingrowth. In this study, a microchip system is designed and fabricated to form cells into a specific pattern on different substrates. The system consists of a microchip with a dot-electrode array for cell trapping and patterning and two motorized platforms for providing relative motions between the microchip and the substrate. AC voltage is supplied to the selected electrodes by using a programmable micro control unit to control relays connected to the dot-electrodes. Nonuniform electric fields for cell manipulation are formed via negative dielectrophoresis (n-DEP). Experiments were conducted to create different patterns by using yeast cells. The effects of different experimental parameters and material properties on the patterning efficiency were evaluated and analyzed. Mechanisms to remove abundant cells surrounding the constructed patterns were also examined. Results show that the microchip system could successfully create cell patterns on different substrates. The use of calcium chloride (CaCl ₂) enhanced the cell adhesiveness on the substrate. The proposed n-DEP patterning technique offers a new method for constructing artificial tissues with high flexibility on cell patterning and selecting substrate to suit application needs.

Microalgae in Microwell Arrays Exhibit Differences with Those in Flasks: Evidence from Growth Rate, Cellular Carotenoid, and Oxygen Production

Microalgae are cultivated in macro-scale reactors traditionally and the relevant knowledge is based on bulk analysis. Whether the knowledge and laws are true for cells under micro-cultivation is still unknown. To better understand microalgal physiology, micro-cultivation of microalgae, and unicellular tracking and analysis of its response in vivo is necessary. In the study, cellular responses of Chlorella vulgaris to micro-cultivation is studied, with cells in flasks as a control. Five different microwell depths ranging from 10 to 200 μm with a fixed diameter of 100 μm, and four diameter levels from 30 to 200 μm with a fixed depth 60 μm were investigated. Unicellular dynamics showed that cell number differences among various types of microwells with different initial cell numbers decreased as cultivation processed. Besides, the specific growth rate of C. vulgaris on microwell arrays was much higher than that in flasks and so cells on microwell arrsys can be much sensitive to pollutants. Thus, the interesting characteristics may be used in cell sensor applications to enhance sensitivity. The specific growth rate of C. vulgaris on microwell arrays decreased gradually as the microwell diameter increased from 30 to 200 μm while presented a unimodal trend as depth decreased from 200 to 10 μm. Furthermore, we used Raman Spectroscopy and Non-invasive Micro-test Technique to analyze cellular responses in microwells for the first time to track the changes in vivo. Results indicated that unicellular carotenoid content increased as microwells became larger and shallower. The flow rate of oxygen rose gradually as the depth increased from 10 to 100 μm, but then decreased rapidly as the depth deepened to 200 μm. In fact, it is a combined result of cell physiology and density. In summary, cells in microwells with the diameter/depth ratio ~1 owned the highest specific growth rates and oxygen flow rates. Simulations also suggested that better mass transfer occurred in microwells with higher diameter-to-depth ratios.

Digital Microfluidics for Manipulation and Analysis of a Single Cell

The basic structural and functional unit of a living organism is a single cell. To understand the variability and to improve the biomedical requirement of a single cell, its analysis has become a key technique in biological and biomedical research. With a physical boundary of microchannels and microstructures, single cells are efficiently captured and analyzed, whereas electric forces sort and position single cells. Various microfluidic techniques have been exploited to manipulate single cells through hydrodynamic and electric forces. Digital microfluidics (DMF), the manipulation of individual droplets holding minute reagents and cells of interest by electric forces, has received more attention recently. Because of ease of fabrication, compactness and prospective automation, DMF has become a powerful approach for biological application. We review recent developments of various microfluidic chips for analysis of a single cell and for efficient genetic screening. In addition, perspectives to develop analysis of single cells based on DMF and emerging functionality with high throughput are discussed.

Capillarity Guided Patterning of Microliquids

Soft lithography and other techniques have been developed to investigate biological and chemical phenomena as an alternative to photolithography-based patterning methods that have compatibility problems. Here, a simple approach for nonlithographic patterning of liquids and gels inside microchannels is described. Using a design that incorporates strategically placed microstructures inside the channel, microliquids or gels can be spontaneously trapped and patterned when the channel is drained. The ability to form microscale patterns inside microfluidic channels using simple fluid drain motion offers many advantages. This method is geometrically analyzed based on hydrodynamics and verified with simulation and experiments. Various materials (i.e., water, hydrogels, and other liquids) are successfully patterned with complex shapes that are isolated from each other. Multiple cell types are patterned within the gels. Capillarity guided patterning (CGP) is fast, simple, and robust. It is not limited by pattern shape, size, cell type, and material. In a simple three-step process, a 3D cancer model that mimics cell-cell and cell-extracellular matrix interactions is engineered. The simplicity and robustness of the CGP will be attractive for developing novel in vitro models of organ-on-a-chip and other biological experimental platforms amenable to long-term observation of dynamic events using advanced imaging and analytical techniques.

Droplet-based microfluidics for high-throughput screening of a metagenomic library for isolation of microbial enzymes

This paper proposes a high-throughput, function-based screening approach of a metagenomic library for isolating novel microbial enzymes by droplet-based microfluidics. We used gel microdroplets (GMDs) dispersed in oil as picoliter-volume reaction vessels for lipolytic enzyme by encapsulating cells in individual GMDs. Using this approach, we monitored the growth of individual cells encapsulated in GMDs and assessed the enzyme reaction activities at the level of an individual GMD. We then applied this method to screen lipolytic enzyme genes from the metagenomic library constructed from soil collected from a quercus serrate forest of Mount Tsukuba, Ibaraki, Japan. In the workflow presented in this study, metagenomic library clones were encapsulated in 100-pL GMDs with a fluorogenic reporter substrate. A total of 67,000 metagenomic library clones can be screened in only 24 h with reduced consumption of reagents (i.e., <10 μL). As a result, we identified a novel lipolytic enzyme, EstT1, belonging to the EstD2 family of esterases and containing a putative signal peptide, which facilitates enzyme export and catalyzation of substrates in the periplasm. Our study demonstrates the potential of microfluidic GMDs as an efficient tool for metagenomic library screening of industrially relevant enzymes with the potential of significantly reducing the cost and time factors involved in successful practical application of microbial enzymes.

In vivo live cell imaging for the quantitative monitoring of lipids by using Raman microspectroscopy

A straightforward in vivo monitoring technique for biomolecules would be an advantageous approach for understanding their spatiotemporal dynamics in living cells. However, the lack of adequate probes has hampered the quantitative determination of the chemical composition and metabolomics of cellular lipids at single-cell resolution. Here, we describe a method for the rapid, direct, and quantitative determination of lipid molecules from living cells using single-cell Raman imaging. In vivo localization of lipids in the form of triacylglycerol (TAG) within oleaginous microalga and their molecular compositions are monitored with high spatial resolution in a nondestructive and label-free manner. This method can provide quantitative and real-time information on compositions, chain lengths, and degree of unsaturation of fatty acids in living cells for improving the cultivating parameters or for determining the harvest timing during large-scale cultivations for microalgal lipid accumulation toward biodiesel production. Therefore, this technique is a potential tool for in vivo lipidomics for understanding the dynamics of lipid metabolisms in various organisms.