Noncontact manipulation of nano/micromaterials presents a great challenge in fields ranging from biotechnology to nanotechnology. In this study we developed a new strategy for the manipulation of molecules and cells based on diffusiophoresis driven by a concentration gradient of a polymer solute. By using laser focusing in a microfluidic device, we created a sharp concentration gradient of poly(ethylene glycol) (PEG) in a solution of this polymer. Because diffusiophoresis essentially depends on solute gradients alone, PEG solute contrast resulted in trapping of DNA and eukaryotic cells with little material dependence. Furthermore, quantitative analysis revealed that the motility of migrating cells was enhanced with the PEG concentration, consistent with a theoretical model of boosted cell migration. Our results support that a solute contrast of polymer can exert an interfacial force gradient that physically propels objects and may have application for the manipulation of soft materials.

In living tissues, a cell is exposed to chemical substances delivered partially to its surface. Such a heterogeneous chemical environment potentially induces cell polarity. To evaluate this effect, we developed a microfluidic device that realizes spatially confined delivery of chemical substances at subcellular resolution. Our microfluidic device allows simple setup and stable operation for over 4 h to deliver chemicals partially to a single cell. Using the device, we showed that subcellular glucose exposure triggers an intracellular [Ca2+] change in the β-cells. In addition, the imaging of a cell expressing GFP-tagged insulin showed that continuous subcellular exposure to glucose biased the spatial distribution of insulin granules toward the site where the glucose was delivered. Our approach illustrates an experimental technique that will be applicable to many biological experiments for imaging the response to subcellular chemical exposure and will also provide new insights about the development of polarity of β-cells.

We have developed a novel microfluidic device for space-and time-resolved (4D) visualization of intracellular events when a cell surface is partially exposed to external stimuli. The device, fabricated using 3D rotational inclined UV lithography of photoresist SU-8, consists of a cell-containing chamber and a flow channel separated by a thin vertical wall having a lateral micrometer aperture smaller than a cell. A cell is first immobilized on the aperture by suction from the flow channel using a syringe pump, and a chemical stimulant is then fed to the channel so that only the cell surface bounded by the aperture is subjected to the stimulus without leakage to other part of the cell surface. The subsequent lateral signal propagation inside the cell can be visualized using high-speed fluorescence confocal microscopy. As an experimental demonstration of the device, 2-NBDG (fluorescence glucose analog) intake into a mouse insulinoma cell, MIN6m9, was visualized in 4D resolution.

In this paper, we proposed the novel method for manipulating DNA fibers on microbridges fabricated by the single mask UV lithography process. Chromosomes were stretched and immobilized on microbridges by the centrifugal force, and the chromosornes could be individually accessible platforms for DNA fiber applications, It was confirmed the validity of the proposed method by applying suspended chrornosomes to the FISH analysis.

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