Applications, techniques, and microfluidic interfacing for nanoscale biosensing

Biosensors based on nanotechnology are rapidly developing and are becoming widespread in the biomedical field and analytical chemistry. For these nanobiosensors to reach their potential, they must be integrated with appropriate packaging techniques, which are usually based on nano/microfluidics. In this review we provide a summary of the latest developments in nanobiosensors with a focus on label-based (fluorescence and nanoparticle) and label-free methods (surface plasmon resonance, micro/nanocantilever, nanowires, and nanopores). An overview on how these sensors interface with nano/microfluidics is then presented and the latest papers in the area summarized.     

Dynamic adhesive forces in rough contacting bodies including normal and sliding conditions

Using a high-resolution, high-dynamic bandwidth capacitive force transducer and two piezoelectric actuators, adhesive pull-off forces between nominally flat rough silicon surfaces were measured under various dynamic conditions in normal and tangential directions and environmental humidity levels. The upper specimen approached and retracted with a constant velocity in the vertical (normal) direction, while the lower specimen started moving in the horizontal (tangential) direction during the middle of the contact. The experiments were performed under 35 and 60% relative humidity conditions. It was found that sliding of the contacting surfaces led to a significant reduction in pull-off forces under low-humidity contact conditions, whereas it caused higher pull-off forces under partially wet contact conditions. Comparing the effects of sliding velocity and sliding distance on the measured pull-off force values, it was found that the sliding distance played an important role in the increase in pull-off forces.     

Micrometer‐sized DNA–Single‐Fluorophore–DNA Supramolecule: Synthesis and Single‐Molecule Characterization

The synthesis of single‐fluorophore‐bis(micrometer‐sized DNA) triblock supramolecules and the optical and structural characterization of the construct at the single‐molecule level is reported. A fluorophore‐bis(oligodeoxynucleotide) triblock is synthesized via the amide‐coupling reaction. Subsequent protocols of DNA hybridization/ligation are developed to form the supramolecular triblock structure with λ‐DNA fragments on the micrometer length scale. The successful synthesis of the micrometer‐sized DNA–single‐fluorophore–DNA supramolecule is confirmed by agarose gel electrophoresis with fluorescence imaging under UV excitation. Single triblock structures are directly imaged by combined scanning force microscopy and single‐molecule fluorescence microscopy, and provide unambiguous confirmation of the existence of the single fluorophore inserted in the middle of the long DNA. This type of triblock structure is a step closer to providing a scaffold for single‐molecule electronic devices after metallization of the DNAs.     

Lifting gate polydimethylsiloxane microvalves and pumps for microfluidic control

We describe the development and characterization of pneumatically actuated "lifting gate" microvalves and pumps. A fluidic layer containing the gate structure and a pneumatic layer are fabricated by soft-lithography in PDMS and bonded permanently with an oxygen plasma treatment. The microvalve structures are then reversibly bonded to a featureless glass or plastic substrate to form hybrid glass-PDMS and plastic-PDMS microchannel structures. The break-through pressures of the microvalve increase linearly up to 65 kPa as the closing pressure increases. The pumping capability of these structures ranges from the nanoliter to microliter scale depending on the number of cycles and closing pressure employed. The micropump structures exhibit up to 86.2% pumping efficiency from flow rate measurements. The utility of these structures for integrated sample processing is demonstrated by performing an automated immunoassay. These lifting gate valve and pump structures enable facile integration of complex microfluidic control systems with a wide range of lab-on-a-chip substrates.     

A novel device for in-situ nanomechanics of 1-D nanostructures

This paper reports the development of an in-situ nanotensilometer that enables highly reliable mechanical tensile testing on individual micro-/nanoscale structures. The device features independent measurement of force and displacement histories in the specimen with nanoNewton force and sub-nanometer displacement resolutions, respectively. Moreover, the device is well suited for in-situ testing of free-standing micro/nanostructures within a high resolution scanning electron microscope, which permits continuous high-resolution imaging of the specimen during straining. In order to conduct the nanomechanical tests the ends of the specimen are attached to the probe tips of the device using electron-beam induced deposition. The general capabilities and features of the nanotensilometer are illustrated by presenting results of nanomechanical tensile tests on electrospun polyaniline microfibers.     

Circular braided glass fiber/epoxy composites with helical architecture (coil spring) fabricated by plaster-sacrificial compression molding for structural automotive applications

Various approaches to reduce the weight of electronics and automobile devices have been explored. For instance, an alternative polymer was utilized to replace metals. In the present study, a new circular braided glass fiber/epoxy composite (braid angle: 45°, fiber: 48 vol%) with a helical structure was fabricated as a model coil spring for weight reduction. A plaster-sacrificial compression mold was especially designed to fabricate helical composites without voids. The spring design was validated by the experimental results of torsional tests. Plastic deformations of the epoxy resin were measured using creep tests to eliminate high-temperature plastic deformation (HTPD) of the composites. Pre-strain applied thermal aging was utilized to remove HTPD. Mechanical properties of the composites were also investigated. The mechanism of mechanical failure was found to be the interfacial failure. For preparation of uncured prepreg, resin permeability was measured to a range of 10⁻¹⁰ m². Resin transfer in the glass fiber-braided textiles occurred due to the combination of viscous and diffusional flow mechanisms. Based on the results in this study, the facilely designed coil spring composite can be used for various applications, especially automotive parts.     

Improved Biomolecule microarrays by Printing on Nanoporous Aluminum Oxide Using a Continuous‐Flow Microspotter

Biomolecules, including protein A, albumin, and immunoglobulin G, are spotted on top of a nanoporous substrate by using a continuous‐flow microspotter (CFM) system, which normally produces spots 3 to 4 orders of magnitude more sensitive than conventional biomolecule printing methods. The spots are observed with a fluorescence scanner. By using the CFM to print spots on nanoporous substrates, an additional order of magnitude increase in signal is observed, which leads to high signal‐to‐background ratios, highly saturated spots, and a measurable signal at printing concentrations as low as 1.6 ng mL^?1. This technique produces highly concentrated biomolecular spots from dilute samples and significantly increases the sensitivity of sensing platforms.     

Individuals’ religiosity and emotional coping in response to disasters

Providing information to help individuals cope physically and psychologically with a disaster is critical in crisis communication. However, how individuals cope is relatively understudied. In particular, researchers have examined how people emotionally cope during different types of crises, but not in a natural disaster context and not religiosity. Yet, religiosity can be important during disasters, given that about 89% of adults in the United States believe in God (Pew Research Center, 2014). Through ten focus groups (N = 77) and a survey (N = 1,484), this study examines how residents of the Southeast United States cope in response to tornadoes. Findings indicate that participants experience anxiety and fear during a tornado, but fear and hope trigger physical action taking (e.g., sheltering in place or collecting supplies). Prayer during a tornado does not significantly predict action taking. Religiosity significantly predicts physical action taking.