Applications of array biosensor for detection of food allergens

Although food is a necessity, compounds within food products can be dangerous and life-threatening for people with food allergies. These allergy-causing compounds, such as proteins from eggs and milk, must be identified on the labels of commercial products. Unintentional contamination of food with these compounds occurs as a result of storage, manufacturing procedures, or cleaning procedures. A sensitive, specific, and rapid method to identify foods containing allergens is required by the food industry. The array biosensor, a rapid detection system, may provide a solution to this need. The array biosensor performs fluorescent immunoassays on the surface of a planar waveguide by first running samples, then fluorescently labeled antibodies, over a surface patterned with capture antibodies. An optical image is captured by a charged-coupled device camera and converted into fluorescence values. Signal intensity and spot location provide information on the compound and its concentration. The array biosensor has been successfully demonstrated for toxin, bacteria, and virus detection at low levels in under 20 min in food, clinical samples, and environmental matrixes. An assay for detection of ovalbumin as an indicator of egg contamination has been developed with limits of detection of 25 pg/mL in buffer and 1.3 ng/mL (13 ng/g) in non-egg pasta extract (buffer:pasta 10:1, v/w).     

Design and evaluation of a Dean vortex-based micromixer

A mixer, based on the Dean vortex, is fabricated and tested in an on-chip format. When fluid is directed around a curve under pressure driven flow, the high velocity streams in the center of the channel experience a greater centripetal force and so are deflected outward. This creates a pair of counter-rotating vortices moving fluid toward the inner wall at the top and bottom of the channel and toward the outer wall in the center. For the geometries studied, the vortices were first seen at Reynolds numbers between 1 and 10 and became stronger as the flow velocity is increased. Vortex formation was monitored in channels with depth/width ratios of 0.5, 1.0, and 2.0. The lowest aspect ratio strongly suppressed vortex formation. Increasing the aspect ratio above 1 appeared to provide improved mixing. This design has the advantages of easy fabrication and low surface area.     

UV polymerization of hydrodynamically shaped fibers

Most natural and man-made fibers have circular cross-sections; thus the properties of materials composed of non-circular fibers are largely unexplored. We demonstrate the technology for fabricating fibers with predetermined cross-sectional shape. Passive hydrodynamic focusing and UV polymerization of a shaped acrylate stream produced metre-long fibers for structural and mechanical characterization.     

Nanosecond Time‐Resolution Study of Gold Nanorod Rotation at the Liquid–Solid Interface

Early studies showed that the adsorption of nanorods may start from a special “anchored” state, in which the nanorods lose translational motion but retain rotational freedom. Insight into how the anchored nanorods rotate should provide additional dimensions for understanding particle–surface interactions. Based on conventional time‐resolution studies, gold nanorods are thought to continuously rotate following initial interactions with negatively charged glass surfaces. However, this nanosecond time‐resolution study reveals that the apparent continuous rotation actually consists of numerous fast, intermittent rotations or transitions between a small number of weakly immobilized states, with the particle resting in the immobilized states most of the time. The actual rotation from one immobilized state to the other happens on a 1 ms timescale, that is, approximately 50 times slower than in the bulk solution.     

A hard microflow cytometer using groove-generated sheath flow for multiplexed bead and cell assays

With a view toward developing a rugged microflow cytometer, a sheath flow system was micromachined in hard plastic (polymethylmethacrylate) for analysis of particles and cells using optical detection. Six optical fibers were incorporated into the interrogation region of the chip, in which hydrodynamic focusing narrowed the core stream to ∼35 μm × 40 μm. The use of a relatively large channel at the inlet as well as in the interrogation region (375 μm × 125 μm) successfully minimized the risk of clogging. The device could withstand pressures greater than 100 psi without leaking. Assays using both coded microparticles and cells were demonstrated using the microflow cytometer. Multiplexed immunoassays detected nine different bacteria and toxins using a single mixture of coded microspheres. A549 cancer cells processed with locked nucleic acid probes were evaluated using fluorescence in situ hybridization.     

Antimicrobial peptide-based array for Escherichia coli and Salmonella screening

A method based on solid-phase microextraction (SPME) followed by gas chromatography with microwave-induced plasma atomic emission detection for determining 16 pesticides of different chemical families (organochlorines, organophosphorus compounds and pyrethrins) in honey is proposed. Parameters affecting the sample enrichment step, such as sample mass, ionic strength, absorption and desorption times and temperatures, were carefully optimized in the direct immersion mode. Element-specific detection and quantification was carried out by monitoring the chlorine (479 nm), bromine (478 nm) and sulphur (181 nm) emission lines, which provided nearly specific chromatograms. The matrix effect was evaluated for samples of different floral origin, it being concluded that standard addition calibration was required for quantification purposes. The detection limits ranged from 0.02 to 10 ng g⁻¹, depending on the compound and the honey sample under analysis. The method is reliable and can be considered useful for routine monitoring. None of the honey samples analyzed contained the studied compounds at concentrations above the corresponding detection limits.     

Hydrodynamic and electrical considerations in the design of a four-electrode impedance-based microfluidic device

A four-electrode impedance-based microfluidic device has been designed with tunable sensitivity for future applications to the detection of pathogens and functionalized microparticles specifically bound to molecular recognition molecules on the surface of a microfluidic channel. In order to achieve tunable sensitivity, hydrodynamic focusing was employed to confine the electric current by simultaneous introduction of two fluids (high- and low-conductivity solutions) into a microchannel at variable flow-rate ratios. By increasing the volumetric flow rate of the low-conductivity solution (sheath fluid) relative to the high-conductivity solution (sample fluid), increased focusing of the high-conductivity solution over four coplanar electrodes was achieved, thereby confining the current during impedance interrogation. The hydrodynamic and electrical properties of the device were analyzed for optimization and to resolve issues that would impact sensitivity and reproducibility in subsequent biosensor applications. These include variability in the relative flow rates of the sheath and sample fluids, changes in microchannel dimensions, and ionic concentration of the sample fluid. A comparative analysis of impedance measurements using four-electrode versus two-electrode configurations for impedance measurements also highlighted the advantages of using four electrodes for portable sensor applications.

The good,the bad,and the tiny: a review of microflow cytometry

Recent developments in microflow cytometry have concentrated on advancing technology in four main areas: (1) focusing the particles to be analyzed in the microfluidic channel, (2) miniaturization of the fluid-handling components, (3) miniaturization of the optics, and (4) integration and applications development. Strategies for focusing particles in a narrow path as they pass through the detection region include the use of focusing fluids, nozzles, and dielectrophoresis. Strategies for optics range from the use of microscope objectives to polymer waveguides or optical fibers embedded on-chip. While most investigators use off-chip fluidic control, there are a few examples of integrated valves and pumps. To date, demonstrations of applications are primarily used to establish that the microflow systems provide data of the same quality as laboratory systems, but new capabilities-such as automated sample staining-are beginning to emerge. Each of these four areas is discussed in detail in terms of the progress of development, the continuing limitations, and potential future directions for microflow cytometers.     

A portable automated multianalyte biosensor

The array biosensor employs an array of capture molecules on a planar optical waveguide to interrogate multiple samples simultaneously for multiple targets. In assay development and demonstration studies published previously, we have quantified this biosensor's capability for rapid identification of a wide variety of targets in complex sample media. This paper describes the miniaturization and automation of the array biosensor for portability and on-site use. The fluidics have been redesigned and constructed with reliability and commercial production of disposable components in mind. To demonstrate the automated operation, simultaneous assays were automatically conducted on samples containing both ovalbumin and staphylococcal enterotoxin B. Results demonstrate the capability of the biosensor for detection and quantification.