Microfluidic tools are providing many new insights into the chemical, physical and physicochemical responses of cells. Both suspension-level and single-cell measurements have been studied. We review our studies of these kinds of problems for red blood cells with particular focus on the shapes of individual cells in confined geometries, the development and use of a 'differential manometer' for evaluating the mechanical response of individual cells or other objects flowing in confined geometries, and the cross-streamline drift of cells that pass through a constriction. In particular, we show how fluid mechanical effects on suspended cells can be studied systematically in small devices, and how these features can be exploited to develop methods for characterizing physicochemical responses and possibly for the diagnosis of cellular-scale changes to environmental factors.

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Implementing DNA and protein microarrays into lab-on-a-chip systems can be problematic since these are sensitive to heat and strong chemicals. Here, we describe the functionalization of a microchannel with two types of magnetic beads using hydrodynamic focusing combined with a passive magnetic separator with arrays of soft magnetic elements. The soft magnetic elements placed on both sides of the channel are magnetized by a relatively weak applied external magnetic field (21 mT) and provide magnetic field gradients attracting magnetic beads. Flows with two differently functionalized magnetic beads and a separating barrier flow are introduced simultaneously at the two channel sides and the centre of the microfluidic channel, respectively. On-chip experiments with fluorescence labeled beads demonstrate that the two types of beads are captured at each of the channel sidewalls. On-chip hybridization experiments show that the microfluidic systems can be functionalized with two sets of beads carrying different probes that selectively recognize a single base pair mismatch in target DNA. By switching the places of the two types of beads it is shown that the microsystem can be cleaned and functionalized repeatedly with different beads with no cross-talk between experiments.

In this article, we present a simple and fast optical method based on transmission microscopy to study the stochastic wetting transitions on micro- and nanostructured polymer surfaces immersed in water. We analyze the influence of immersion time and the liquid pressure on the degree of water intrusion in individual microcavities on these surfaces as well as the lifespan of their superhydrophobicity. We show that transitions among the three wetting states (Cassie, Cassie-impregnating, and Wenzel) occur with a certain pressure threshold (300 mbar for a microcavity diameter of 7.5 μm). Below this threshold, the transitions between the Cassie and the Cassie-impregnating states are reversible, whereas above this threshold, irreversible transitions to the Wenzel state start to occur. The transitions between the different wetting states can be explained by taking into account both the Young-Laplace equation for the water menisci in the cavities and the diffusion of dissolved gas molecules in the water. In addition, the wetting transitions had a stochastic nature, which resulted from the short diffusion distance for dissolved gas molecules in the water between neighboring cavities. Furthermore, we compared the contact angle properties of two polymeric materials (COC and PP) with moderate hydrophobicity. We attributed the difference in the water repellency of the two materials to a difference in the wetting of their nanostructures. Our experimental observations thus indicate that both the diffusion of gas molecules in water and the wetting properties of nanostructures are important for understanding the sustainability of superhydrophobicity of surfaces under water and for improving the structural design of superhydrophobic surfaces.

We present the design, fabrication, characterization, and demonstration of a new passive magnetic bead separator. The device operates in an effective state when magnetized by an external magnetic field of only 50mT, which is available from a tabletop electromagnet. We demonstrate the complete capture of 1.0μm fluorescent magnetic beads from a 7.5μL sample volume traveling at an average linear fluid velocity of 5mm∕s.

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Previous attempts to tune the electrical properties of large-scale graphene via nanopatterning have led to serious degradation of the key electrical parameters that make graphene a desirable material for electronic devices. We use thermal nanoimprint lithography to pattern wafer-scale graphene on a 4-in. wafer with prefabricated 25 mm2 devices. The nanopatterning process introduces a modest decrease in carrier mobility and only a minor change in residual doping. Due to the rapid fabrication time of approximately 90 min per wafer, this method has potential for large-scale industrial production. The chemiresistive gas sensing response towards NO2 was assessed in humid synthetic air and dry air, with devices showing a response to 50 ppb of NO2 only when nanopatterned.