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Due to the numerous toxicological effects of lead, its presence in the environment needs to be effectively monitored. Incorporating a biosensing element within a microfluidic platform enables rapid and reliable determinations of lead at trace levels. A microchip-based lead sensor is described here that employs a lead-specific DNAzyme (also called catalytic DNA or deoxyribozyme) as a recognition element that cleaves its complementary substrate DNA strand only in the presence of cationic lead (Pb2+). Fluorescent tags on the DNAzyme translate the cleavage events to measurable, optical signals proportional to Pb2+ concentration. The DNAzyme responds sensitively and selectively to Pb2+, and immobilizing DNAzyme in the sensor permits both sensor regeneration and localization of the detection zone. Here, the DNAzyme has been immobilized on a PMMA surface using the highly specific biotin–streptavidin interaction. The strategy includes using streptavidin physisorbed on a PMMA surface to immobilize DNAzyme both on planar PMMA and on the walls of a PMMA microfluidic device. The immobilized DNAzyme retains its Pb2+ detection activity in the microfluidic device and can be regenerated and reused. The DNAzyme shows no response to other common metal cations and the presence of these contaminants does not interfere with the lead-induced fluorescence signal. While prior work has shown lead-specific catalytic DNA can be used in its solubilized form and while attached to gold substrates to quantitate Pb2+ in solution, this is the first use of the DNAzyme immobilized within a microfluidic platform for real time Pb2+ detection. [ABSTRACT FROM AUTHOR]

We propose a new type of micro/nano fluidic mixer based on non-equilibrium electrokinetics and demonstrate its mixing performance. We fabricate the device with two-step reactive ion etching, one for nanochannels and one for microchannels. Mixing is achieved by strong vortex structures formed near the micro/nano channel interface. We expect the proposed device to be beneficial in the development of micro total analysis systems, since it is simple in its design with minimal fabrication complications. [ABSTRACT FROM AUTHOR]

Dry film photoresists (DF PRs) are widely used to perform photolithography on non-traditional substrates such as printing circuit boards, plastic sheets, or non-planar surfaces. Commercially available DF PRs are usually in a negative tone and rather thick, limiting lithographic resolution and versatility. The relatively large pressure required for lamination also prevents the technology from being used for delicate substrates. Here we present a modified soft-lithographic process, namely photoresist blanket transfer (PR BT), transferring a spin-coated PR film from a flat elastomeric stamp to a substrate. The elastomeric stamp is highly compliant, bringing the PR film into intimate contact with the substrate and eliminating the need for a large lamination pressure. Photolithography on unconventional substrates such as etched, fragile, and porous ones is demonstrated. Single or multiple transfers of PRs by BT are utilized to fabricate multilayer, free-standing, and re-entrant polymeric microstructures. A fragile and porous substrate such as an anodized aluminum oxide membrane can also be patterned using PR BT. Moreover, a reliable method to create metal electrodes and high surface area catalysts inside microchannels is discussed for novel microfluidic applications. [ABSTRACT FROM AUTHOR]

This paper reports a new type of hierarchically structured surface consisting of re-entrant silicon micropillars with silicon nanowires atop for superhydrophobic surface with extremely low hysteresis. Re-entrant microstructures were fabricated on a silicon substrate through a customized one-mask microfabrication process while silicon nanopillars were created on the entire surface of microstructures, including sidewalls, by a metal-assisted-chemical etching process. The strategy of constructing hierarchical surfaces aims to reduce the actual contact area between liquid and top part of solid surface, thereby increasing the contact angle and reducing the sliding angle. The strategy of using re-entrant profile of the microstructure aims to prevent a liquid droplet from falling into cavities of roughened structures and decrease the actual contact area between the liquid droplet and sidewalls of solid structures, therefore reducing adhesion forces acting on the liquid droplet. Our measurement shows that the surface incorporating both hierarchical and re-entrant strategies exhibits a sliding angle as low as 0.5°, much lower than sliding angles of surfaces only incorporating either one of the strategies. [ABSTRACT FROM AUTHOR]

We report the design and fabrication of a microheater unit as a key component of an integrated micro gas preconcentrator that has an ultra-small preconcentrator volume (<0.25 µL) and microvalves for fast injection speeds (<1 ms). Monolithic integration of the microvalves into the microheater of the preconcentrator gives rise to challenges in designing the microheater and implementing thermal isolation for low power and energy consumption. A preconcentrator chamber, 3.5 × 1.5 mm2 in planform area and 40 µm deep, was built in the device layer of a silicon-on-insulator wafer and filled with an array of microposts with a preconcentrator volume of 0.2-0.25 µL. Different generations of the microheaters and their mating dies were fabricated to show the effects of thermal isolation and thermal mass of the system on the performance of the heater. The microheater assembly with the least thermal mass and most thermal isolation can reach 300 °C in 100 ms with 12.3 W of power and is expected to consume less than 2 J during the operation of each preconcentration cycle. [ABSTRACT FROM AUTHOR]